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RESEARCH ON CRYSTAL GROWTH

AND CHARACTERIZATION AT THE

NATIONAL BUREAU OF STANDARDS

JULY TO DECEMBER 1963

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
idards

I 4 1968

1S1GT0
NATIONAL BUREAU OF STANDARDS

tecknical ^ote 236

ISSUED APRIL 6, 1964

RESEARCH ON CRYSTAL GROWTH

AND CHARACTERIZATION AT THE

NATIONAL BUREAU OF STANDARDS

JULY TO DECEMBER 1963

Edited by H. Steffen Peiser National Bureau of Standards

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature.

For sale by the Superintendent of Documents. U.S. Government. Printing Office Washington, D.C., 20402 - Price 40 cents.
Contents

1. Introduction 1

2. Crystal Growth 2 2.1 Growth of Dislocation-Free Metal Crystals from the Melt 2 2.2 Kinetics of Growth of Crystals from the Melt 4

2.3 Thermodynamics of Segregation of Solute Atoms

to Stacking Faults in FCC Binary Alloys 6

2.4 Theory of Dendritic Crystallization 6

2.5 High-Temperature Crystal Growth 7 2.6 Study of Temperature Distribution in the Verneuil Process 7 2.7 Crystal Growth and Structure Studies 7 2.8 Crystal Growth from Solution 8

2.9 Spherulitic Growth in Relatively Pure Systems 9

2.10 Homogeneous-Nucleation Studies 9

2.11 Single Crystals of Long-Chain Hydrocarbons 11

2.12 Crystallization of Polyethylene from the Melt 11

2.13 Theory of Crystallization of Bulk Linear Polymers 11

2.14 Crystallization of Polymers from Solution 12

2.15 Crystallization of Polyethylene Fractions 12

2.16 Electrodeposition of Single Crystals 14

2.17 Crystallographic Characterization of Pseudopentagonal

Twins in Electrodeposited Copper Dendrites 14

2.18 Thermal Etching and Crystal Growth of Methane 14

2.19 Evaporation of Gold onto Cleaved Zinc Surfaces 16

2.20 Studies of Small Crystals of Nickel and Nickel Halides 16

2.21 Kinetics of Whisker Evaporation 18

2.22 Theoretical Studies in Crystal-Whisker Growth 18

2.23 Growth Kinetics of Crystal Whiskers by Field-Emission

Techniques 20

2.24 Field-Emission Studies of the Growth and Oxidation

of Single Crystals 20

2.25 Condensation of Tungsten on a Cold Tungsten Substrate 23

3. Defect Characterization 23

3.1 Magnetic Properties of Salt Single Crystals

at Low Temperatures 23

3.2 Optical Properties of "Pure" and Impure Crystals,

Paramagnetic Centers 24

3.3 Laser Microprobe for Analysis of Very Small Samples 24

3.4 Study of Crystal Defects 25

3.5 Defects in Thin Oxide Films 25

3.6 Effect of Point Defects on the Dynamic Properties

of Crystals 27

3.7 Crystal Symmetry and Crystal Properties 27

3.8 Dislocations in Metals by Electron Microscopy 28

3.9 Growth of Helical Dislocations 28

3.10 Characterization of Electrodeposited Crystals 28

3.11 Second-Order Twinning in Aluminum 31

3.12 Accurate Measurement of Fundamental Electrical

Properties of Semiconductor Crystals 31

3.13 Crystal Characterization of Diffraction Topography 33

3.14 Automation of Single-Crystal X-Ray Diffraction

Intensity Measurements 37

3.15 X-Ray Studies -- — 37

3.16 High-Voltage Laue Photographic Inspection of Large

Single Crystals 37

3.17 Chemical Purity by Dielectric Cryometry 38

3.18 Optical Properties of Cadmium Sulfide and Telluride 38

ii
3.19 Irradiation Studies 38

3.20 Development of Adiabatic Solution Calorimeter 38

4. Crystal Physical Properties 39

4.1 Reference Data on Single-Crystal Elastic Constants 39

4.2 Deformation and Fracture of Ionic Crystals 39

4.3 Studies in Solid-State Theory 39

4.4 Electronic Transport 40

4.5 Hall-Effect Measurements 40

4.6 Dielectric and Mechanical Properties 41

4.7 Dielectric Properties of Semiconductors 41

4.8 Crystals of Organic Molecules 43

4.9 Low-Temperature Thermometry 44

4.10 Oxide Melting-Point Standards 44

4.11 Dilatometric Studies of Polymers 44

4.12 Thermal Conductivity of Paramagnetic Crystals 45

4.13 Magnetic-Resonance Studies - I - 45

4.14 Magnetic-Resonance Studies - II 46

4.15 Nuclear-Magnetic-Resonance Studies in

Yttrium-Iron Garnets 48

4.16 Electron-Spin-Resonance Studies of Transition-Metal

C omp lexes 48

4.17 Low-Temperature Nuclear Orientation 48

4.18 Microwave Measurements on Single-Crystal Ferrimagnetics 49

4.19 Adsorption on Metal Single Crystals 49

4.20 Superconductivity in Niobium 50

4.21 Experimental Determination of Atomic-Scattering Factors 50

4.22 Soft X-Ray Spectroscopy 50

5. Crystal Chemistry

5.1 Crystal-Structure Analysis 51

5.2 Crystal Chemistry of Calcium Phosphates 51

5.3 Standard X-Ray Diffraction Powder Patterns 52

5.4 Crystals with Large Lattice Spacings 52

5.5 Phase Equilibria 52

5.6 Allotropy in Some Rare-Earth Metals at High Pressures 53

5.7 Crystal Chemistry of Silver Iodide 53

5.8 Rapid X-Ray Diffraction Photography of

Polycrystalline Materials 54

5.9 Structure of Silica Whiskers 54

5.10 Structure Models for Amorphous and Crystalline

Phases of Simple Substances 55

5.11 Radial-Distribution Studies of Glasses 55

5.12 High-Resolution Small-Angle X-Ray Camera 55

5.13 Physical Structure of Crystalline Copolymers 56

5.14 High-Pressure Microscopy of Crystal Transformation and

Growth 56

5.15 Optical Observations of Pressure-Induced

Transformation in Polymers 57

5.16 Infrared Spectroscopy of Crystalline Inorganic Borates 57

5.17 Crystal-Field Studies by Matrix Spectroscopy 58

5.18 Spectroscopy of Diatomic Impurities in Rare-Gas

Crystalline Matrices 58

5.19 Molecular Energy Levels 58

6. Partial List of Participants 59

7. Literature References 65

in

RESEARCH ON CRYSTAL GROWTH AND CHARACTERIZATION

AT THE NATIONAL BUREAU OF STANDARDS

JULY TO DECEMBER, 1963

Edited by

H. Steffen Peiser

Abstract

The National Bureau of Standards with partial support from the Advanced Research Projects

Agency is continuing diverse research projects on the growth and characterization of crystals. This

note summarizes the individual NBS activities in

this and closely related fields during July to

December, 1963. Lists of NBS publications appertaining to that period and of participating NBS

scientists are appended.

INTRODUCTION

This is the third biannual collection of brief statements on research

in progress at the National Bureau of Standards on crystal growth and characterization. In the first of these collections (NBS Technical Note 174,

issued on March 15, 1963) the general purpose, background, and program area were described. They still apply, together with a few extensions that are explained in the second NBS Technical Note 197 (issued on September 23, 1963) , The style, format, and principal headings adopted in the second biannual

statment have been found convenient and have been used again in the research

summary now presented for the period July to December, 1963.

Much of the work described is still being carried out with the support

of the Advanced Research Projects Agency which, in anticipation of future

technological demands in crystal science, is encouraging the National Bureau

of Standards to produce pure and perfect reference crystals by newly developed techniques, if necessary, under closely controlled conditions, and to

apply precise measurement techniques to the characterization of such crystals,

The projects thus -undertaken on behalf of ARPA are so closely interwoven with

other projects carried on under the Bureau's own mission, that in a summary

of the technical activities and results as is here presented, distinction

cannot readily be made between the two kinds of projects. The ARPA initiative and support are therefore gratefully acknowledged here, but individual

acknowledgements are not included in the text. Only in the few instances in

which financial support from other agencies contributed to the program is an appropriate acknowledgement given.

Editorial work has been lightened by the efforts of Miss Lois L. Bardeen

and the assistant editors who have represented the Bureau divisions as follows : Electricity

Metrology

Heat

Analytical Chemistry

Mechanics

Polymer

I. L. C^o :er

p. E. Pontius

J. F. Schooley

L. J. Frolen

R. S . Marvin

E. Passaglia
Metallurgy

Inorganic Solids

Atomic Physics

Instrumentation

Physical Chemistry

Cryogenic Engineering

Radio Standards Physics

The NBS "Crystal Group" has continued its lectures, visits, and informal

colloquia. Contacts and collaboration with other research laboratories have

been encouraging, and there have been several exchanges of special crystals.

Harry C. Allen, Jr. is taking over the co-ordination of the NBS/ARPA program.

In relinquishing his duties as co-ordinator , H. Steffen Peiser thanks all the

contributors to this program. Much of its success depends on the quality and

quantity of the research that still lies ahead, but the statements here presented may pave the way for significant contributions to crystal science.

R. L. Parker

F. A. Mauer

H. P. R. Frederikse

J. C. French

D. E. Mann

R. L. Powell

J. L. Da Ike

2. CRYSTAL GROWTH

Contributions to this chapter are concerned

with mechanisms and techniques of crystal

growth and dissolution of single crystals.

2.1 Growth of Dislocation-Free Metal Crystals

from the Melt

R. W. Dickson, Physical Properties Section,

H. C. Vacher, Metallurgy Division,

T. H. Orem, Corrosion Section, and

R. L. Parker, Crystallization of Metals Section

The background of this work is given in NBS Technical Notes 174, Section

4.3, and 197, Section 2.3. A major part of the effort on this project during

the past six months has been spent in setting up the Lang camera on the

Rigaku-Denki microfocus X-ray apparatus, and in learning techniques required

for photographing dislocations with it. This camera, which is on loan from

Rutgers University, was received in August, 1963, in lieu of the new unit to

be delivered by Rigaku-Denki.

Prior to this time, the microfocus unit was employed in divergent-beam

(pseudo-Kossel line) studies of single crystals of aluminum, bismuth, copper,

germanium, lithium fluoride, calcite, and ammonium dihydrogen phosphate, ADP;

135 photographs of these crystals were taken. The method is found to give a good measure of lattice misorientations within a crystal down to about 3 minutes of arc. Although there is insufficient space here to summarize all the

results, it should be mentioned that a number of Al crystals pulled by us from the melt, and several ADP crystals grown by Torgesen et al., Crystal

Chemistry Section (compare Section 2.8) showed no discernible misorientation,

within the above mentioned accuracy.

Since acquiring the Lang camera, we have taken about 160 photographs

with it; these have been made on single crystals of Al, Si, Ge, and LiF . We

first learned how to obtain good photographs of dislocations in Si. Due to

space limitations, we present here only the results on Al crystals pulled

from the melt of 99. 9997c purity. Figure 1 is a photograph of the crystal
Fig.l Crystal Puller

mm

cm

Fig. 2 Optical photograph Al crystal #6

Imm

I 1 Fig. 3 Dislocation

topograph Al crystal #6

Fig. 4 Al crystal #11
puller used in these experiments. Figure 2 is an optical photograph of one of the 12 Al crystals studied so far. It is here about 1.5 mm in diameter;

it was etched down in aqua regia from its 4 mm original diameter. Figure 3

shows a dislocation topograph of a portion of this specimen. Particularly

interesting are the small loops (—50 microns in size) which are seen, some of

these having the form of two arcs of a circle. These loops are very similar

in appearance to loops seen in quenched-aluminum foils by electron-diffraction

contrast, although the latter are much smaller in size. It is possible that

our loops are dislocation loops formed by collapse of vacancy disks which in

turn are formed by the vacancy supersaturation occurring after cooling in the

crystal puller. These loops have not been observed in thinner (~.I mm) Al

crystals (see Fig. 4). In this figure we do see regular bands of impurity

build up near the tip; these correspond with thickening of the crystal at

this point. Their regular separation of 0.86 mm coupled with the pulling

speed of 0.33 mm/min gives a time spacing of 2.7 minutes, which corresponds

with the cycle time of the temperature controller: as is known, impurity

segregation occurs during temperature fluctuations. There is also a twisting effect, which is always of the same sense as the direction of crystal

rotation, and which reverses when the rotation is reversed. Experiments are underway to eliminate this twisting effect, thought to be due to the torque

exerted by an oxide skin on the melt surface. Al crystals grown at the

Battelle Institute, Columbus, Ohio, under conditions similar to ours but

without oxide skin on the melt have been received by us and are being examined.

In December, Dr. U. Bonse visited us and discussed his Cu-crystals work

[Bonse et al., Physica Status Solidi, 3, K 355 (1963)] which shows that dislocation densities of <500/cm2 can be obtained by pulling Cu crystals from

the melt.

2.2 Kinetics of Growth of Crystals from the Melt

J. G. Early and R. L. Parker,

Crystallization of Metals Section

As outlined previously (see NBS Technical Notes 174, Section 4.4 and 197,

Section 2.4) the objective of this project is to investigate the kinetics of

the growth of crystals from the melt and, in particular, to study the role

of interface temperature and orientation.

The experimental technique employed has been described theoretically by

Tiller and Kramer [J. Chem. Phys .

, 37, 841 (1962)]. The technique permits

the determination of the velocity oTT~interface motion as a function of interface supercooling. Tiller and Kramer have successfully carried out several

experiments on high-purity tin based on this method (as yet unpublished)

.

The first three months of this reporting period have been spent in ac- cumulating the necessary equipment. Figures 5 and 6 are photographs showing

the apparatus as used in several early experiments. A bell-jar type vacuum

system has been purchased and installed which allows the experiments to be

carried out at pressures in the range 10~ 6 to 10 7 torr. A motor-driven

Variac provides a periodically varying current to the heater that floats on top of the liquid metal in the crucible. The heater establishes a periodic

temperature wave within the metal in the crucible. A fixture has been as- sembled to fit inside the bell- jar to hold the crucible, measuring thermocouples, and the heater. Amplifying and recording equipment have been set

up to provide the necessary instrumentation.

Periodic temperature waves (having an amplitude of less than 0.001°C

with a period of 30 seconds) have been generated, measured, and recorded.

Several preliminary experiments have been performed with the apparatus on

99.97. pure tin. This was done to check out the operation of the various
Fig. 5 Photograph of apparatus

showing vacuum system with belljar in raised position, motordriven Variac as used in growth

studies

Fig. 6 Close-up showing crucible

with an aluminum radiation

shield, thermocouples and heater

mounted on vacuum-system base

plate
components of the apparatus and to observe the effect on a thermocouple signal of the passage of the solid- liquid interface past the thermocouple. An

attempt was also made to determine the position of the solid-liquid interface

under equilibrium conditions.

Additional experiments are now in progress on single-crystal samples of

99.999 and 99.99997° tin. Later, experiments will be made on lead of 99.999

and 99.99997, purity. At present, a number of seed single crystals of 99.9997,

tin have been grown by an inverted Bridgman technique. These seeds will be

used to grow large single crystals in the measuring crucibles.

2.3 Thermodynamics of Segregation of Solute Atoms

to Stacking Faults in FCC Binary Alloys

R. deWit,

Lattice Defects and Micros tructures Section, and

R. E. Howard,

Metal Physics Section

Instead of assuming with others [Dorn, Acta Met., 11, 218 (1963), and

Suzuki, J. Phys . Soc. Japan, 17, 322 (1962)] that the width of the extended

dislocation remains fixed during segregation, we suppose that the width always has the equilibrium value corresponding to the local concentration at

the fault and thus changes continually. The condition for thermodynamic

equilibrium between the fault and the bulk becomes

AxA

-A^B

- (V/t)(dY/dc £

) = -(dY/dc £ )[(l-c)^iA

+ cAXgD/Y

which differs from the previous work, referred to above, where the right

hand side was equated to zero. Here A and B denote solvent and solute atoms,

respectively, f the faulted region of thickness t, Au. = u, - u. is the difference in chemical potential between the faulted and unfaulted regions, c the concentration of solute atoms, y the stacking fault energy, and V the

molar volume. A consequence is that, unless a miscibility gap exists, y>0

for all concentrations. Hence, contrary to Suzuki, the stacking fault width

can never increase indefinitely. If the y-c curve is known for the unsegregated alloy, we can find the y-c curve for the fully segregated alloy by

numerical solution of our equation. The latter curve always lies below the

former. If the latter curve describes the results of node-analysis experiments and the former those of work- hardening experiments to measure the

stacking- fault energy, then our theory resolves some of the discrepancy that

exists in the literature [Thornton, Mitchell, and Hirsch, Phil. Mag., 1_, 1349 (1962)].

2.4 Theory of Dendritic Crystallization

S. R. Coriell and R. L. Parker,

Crystallization of Metals Section

This project was started on December 18, 1963. Preliminary plans are

to study diffusion-controlled growth of crystals, with particular emphasis

on the conditions necessary for dendritic growth to occur. Our problem of

interest is the solution of the diffusion equation with a time -dependent

boundary condition. Previous work in this area is being studied. Of particular importance is a recent article by Mullins and Sekerka [J. Appl. Phys.,

34, 323 (1963)] in which the stability of the shape of a spherical particle

undergoing diffusion-controlled growth is considered. They show that the

sphere is stable below and unstable above a certain radius. Further work

along these lines appears to be desirable. As a start, the cylindrical

symmetry problem is being worked through.
•k 2.5 High-Temperature Crystal Growth

W. S. Brower and E. N. Farabaugh,

Crystal Chemistry Section

Work described earlier (NBS Technical Notes 174, Section 4.1, and 197,

Section 2.1) has been continued with the purpose of determining the influ- ence of growth parameters on the perfection of refractory-oxide crystals.

Crystals of rutile grown at widely varying rates (0.3-12 cm/hr) were

examined by an etch technique in an effort to determine the effect of growth

rate on crystal perfection (compare Section 2.7). It was found that the

dislocation densities (~5 x 10 B cm~

2

) did not vary significantly from the

slowest to the most rapidly grown crystal. The examination of the series

of samples is being continued to determine if there is any significant variation in the number and size of the sub-grains.

The high-frequency (45 - 90Mc) rf induction heater has been put into

operation and various coil designs have been investigated to obtain the optimum configuration for direct coupling. Slightly reduced rutile has been

successfully melted, with the improved coil designs. The present aim is to use either rutile or another oxide having a rather high electrical conductivity near its melting point in initial attempts at floating-zone crystal

growth of semiconductor materials.

2.6 Study of Temperature Distribution

in the Verneuil Process*

F. Ordway,

Inorganic Solids Division, and

P. R. Miller,

Crystal Chemistry Section

Measurements of temperature in the growing crystal during the flamefusion process have been made with Ir/60% Ir-407o Rh thermocouples. The

measurements indicate that a very high vertical temperature gradient exists

in the portion of the boule near the cap, and this decreases proportionally

with the logarithm of the axial distance to a constant gradient that is very

small by comparison. Existing theories agree with the results only in a rough qualitative manner. The theoretical problem is being studied further,

and attempts are being made to determine the radial temperature gradients

.

2.7 Crystal Growth and Structure Studies

D . E . Roberts

,

Solid State Physics Section

Cadmium telluride, CdTe, is being prepared by the Bridgman technique as described in the previous report. CdTe is now also obtained by vapor growth

in a closed tube at temperatures from 800 °C to above 1000 °C. The resulting

crystals have the form of needles, platelets, or cubes of a few millimeters

in dimens ion

.

_.This work was partially supported by the Atomic Energy Commission.
Crystals of cadmium sulfide, CdS , have been prepared from the vapor

phase. Growth occurs at temperatures from 900-1100°C in a vacuum or in an atmosphere of hydrogen sulfide, H2 S . Crystals are in the form of needles or platelets of a few millimeters in dimension. The virgin surfaces of" vaporgrown materials are especially valuable for optical measurements.

Rutile, Ti02 , is being grown by the Verneuil technique. The present

emphasis is on the preparation of boules of a larger size and a higher degree

of perfection (compare Sections 2.5 and 3.15).

A number of attempts have been made to diffuse impurities into samples

at high temperatures. Samples include Ti03 , strontium titantate, SrTi03 , magnesium fluoride, MgF8 , and lead fluoride, PbF2

. Success has been very

limited, but further attempts will be made.

2.8 Crystal Growth from Solution

J. L. Torgesen, A. T. Horton, and J. Strassburger

,

Crystal Chemistry Section

Single-crystal growth from aqueous solution by temperature-program

techniques (see NBS Technical Notes 174, Section 4.5, and 197, Section 2.5)

has continued to produce specimens of ammonium dihydrogen phosphate (ADP)

(pure, and containing chromium impurity) and sodium chlorate (pure, and con- taining copper impurity). Crystals of ADP, growing in the presence of chromic ions, show the tapered habit and retention of chromium adjacent to the

tapered vicinal faces. They revert essentially to normal habit on continued

growth after the chromic ion activity is reduced to a low value by the addition of a complexing agent, ethylenediamine tetraacetic acid.

Habit changes in sodium chlorate single crystals grown in the presence

of cupric ions are characterized by greater predominance of {110} and {111}

faces. Spectrographic analysis of sectioned portions of the crystals indicates cupric-ion content in material deposited on the growth surfaces differing for the various faces in the order { 111}>{ 100}>{110}

.

Limited success has been achieved in the growth of potassium and sodium

chloride from pure aqueous solution. Crystal faces are rough and polycrystalline growth is common. Experiments on the effect of pH in the growth of

small seed crystals of sodium chloride indicate that pH range 3 to 5 yields

seed crystals of better quality than_those grown in more acid or neutral so- lutions. Moreover, the danger of OH ion contamination would be expected to

be reduced at lower pH.

An effort to produce (KAP) potassium acid phthalate single crystals of

adequate size and perfection for long-wavelength X-ray spectroscopy is presently being initiated (see Section 3.13 of this Technical Note). The crystals will be grown both by a temperature-programming technique and by an isothermal solvent-evaporation method [Karpenko et al., Sov. Phys . Cryst.,

6, 120 (1961)].

Characterization of ADP crystals by X-ray diffraction topography (see

Section 2.1, and especially 3.13) has shown the specimens to be of high intrinsic quality. Particularly important in these investigations have been

the methods of surface preparation. It has been shown, as was suspected

from earlier work on other materials, that conventional techniques of abrasive-wheel cutting, followed by grinding and polishing, introduce many dislocations. Sectioning of the crystals with a string-saw, using water as the

solvent, followed by etch-polishing with ethyl alcohol-water mixtures, produces specimens in which high intrinsic perfection is retained. Relatively

large areas of the specimens are essentially dislocation free and show strains

only of long-range order. Flat etch-polishing is accomplished by rotating

8
and advancing the crystal specimen closely adjacent to, but not touching, a rotating glass plate over which flows a thin film of the alcohol-water etchant

The growth of single crystals of sparingly soluble salts in silica gel

has continued to be used in the production of a variety of materials. Of

special note are crystals of calcium tartrate (up to 1 cm in longest dimension) possessing well-developed habit and good optical quality, and calcium

carbonate (up to 1 mm in diameter) . Phase changes in the mercuric iodide

system have been observed visually and by time-lapse photography through the

microscope. The change from the first- formed yellow mercuric iodide to the

red form is not a solid-solid transition, but follows a dissolution and re- growth mechanism. However, if the surrounding silica gel is allowed to dry,

a solid-solid transition from the red to the yellow form ensues.

In the lead-iodide system the crystallization of the mono- or di-iodide

is dependent on localized iodide-ion concentration. First-formed di-iodide

changes to the mono-iodide with reduction of iodide concentration by diffusion. The formation of dendritic metallic copper in tetrahedra by reduction

of the cupric ion results from the crystallization of an intermediate oxide

of copper (possibly Cu4 0) in tetrahedral habit, with retention of this habit

as reduction to the metal proceeds. The silica-gel method for growing single

crystals seems most applicable to materials having solubilities of the order

of hundredths of one percent. Little success has been achieved to date with

very slightly soluble salts such as the silver halides and metallic sulfides.

2.9 Spherulitic Growth in Relatively Pure Systems

G. S. Ross and L. J. Frolen,

Analytical Chemistry Division

In some conditions in many materials, the observed mode of crystal

growth is spherulitic. In general, spherulite-forming systems have a high

impurity content, and the spherulites have a small radial growth rate.

Keith and Padden [J. Appl. Phys . , 34, 2409 (1963)] proposed a phenomenological theory explaining spherulitic growth in both polymer systems and others

which are characterized by their high impurity content.

Recently it was observed that diphenylalkanes form spherulites , but in

contrast to the Keith-Padden systems, these materials have a low impurity

content and the radial growth rate is very rapid. In both types of systems,

material is deposited between the spherulitic fibers. In the Keith-Padden

systems, this material is assumed to be impurity and it may or may not crystallize after the initial spherulitic growth. In our systems, the interfibrillar material must be nearly pure diphenylalkane. We postulate that

this material exists in a glassy state during the spherulitic growth but that

it in turn crystallizes as the sample is warmed. Crystallization is observed

after the original spherulitic formation as shown in the series of pictures

(Fig. 7, a-d) . Work on the spherulite-forming diphenylalkanes is being con- tinued. The results obtained are inconsistent with the Keith-Padden theory,

and we feel the theory must be modified if it is to include spherulitic

growth in nearly pure systems.

2.10 Homogeneous-Nucleation Studies

F. Gornick,

Polymers Division, and

G. S. Ross, L. J. Frolen, and D. J. Termini,

Analytical Chemistry Division

Characterization of a group of well purified diphenylalkanes has been

9
f "?'fl7Wff&P" JfUff

'

K

Fig. 7 Spherulites of 1,2-diphenylethane, showing crystallization phenomenon

which occurs at room temperature, (a) Spherulite formed in alcohol bath,

cooled to -75°C; (b) after 1/2 min atm. T (c) after 1 min atm. T

(d) after 6 min atm. T

10
continued (see NBS Technical Note 197, Section 2.8). Dilatometric studies of

several members of the series are being completed to establish the existence

of solid-solid phase transitions. The viscosities of 1,4-diphenylbutane and

2, 2-diphenylbutane have been measured over a 100-degree temperature range including the supercooled liquid region.

A cinephotomicrographic assembly for both time-lapse and variable con- tinuous speed-photography has been ordered and will be received and tested

in January. Development of apparatus and techniques for the study of homogeneous nucleation in both polymeric and non-polymeric systems is being con- tinued.

2.11 Single Crystals of Long-Chain Hydrocarbons

J. M. Crissman and E. Passaglia,

Polymers Physics Section

An attempt is being made to grow large single crystals of the n-alkanes

C 33 H66 and C 94 Hig0 . These crystals, which are model systems for polymer

crystals, are to be used to determine various physical properties of these

materials, in particular, the elastic constants.

The method used is the modification of the Bridgman technique developed by Horton [U. S. Patent No. 2754180, issued July 10, 1956]. So far

only polycrystalline aggregates of both materials have been produced, and

it is speculated that this is caused by insufficient purity of the starting

compounds

.

In C 94 H190 , which has been examined in some detail, the crystals grow

such that the [010] direction is along the temperature gradient. This is

undesirable, since this is the fastest growing direction. Means of inducing

the crystal to grow with [001], the slowest growth direction, along the temperature gradient are being tried.

2.12 Crystallization of Polyethylene from the Melt

J . J . Weeks

,

Dielectrics Section

In a previous publication [Weeks, 1963] the observed increase in the

melting temperature of linear polyethylene with increase of crystallization

time was interpreted to be a result of isothermal thickening of the lamellae.

Direct experimental verification of the thickening by low-angle X-ray diffraction measurements is desirable in assessing the possible importance of

increased crystal perfection as an explanation for the melting behavior.

Since measurements will have to be made at the crystallization temperature,

a hot stage is required. This stage has been constructed and its control

characteristics are being determined.

2.13 Theory of Crystallization of Bulk Linear Polymers

J . D . Hoffman

,

Polymers Division

A review article, "Theoretical Aspects of Polymer Crystallization with

Chain Folds: Bulk Polymers", has been prepared for publication. The theory

of crystallization of bulk linear polymers with chain folding is discussed

in terms of recent developments. Specific topics covered are: (a) rate of

crystal growth and size of folded nuclei; (b) theoretical and experimental

11
estimates of the fold-surface free energy, and estimates of the surface free

energy of "fringed micelle" and "switch-board" type crystals; (c) basic

causes of essentially regular folding in bulk; (d) rejection of short-chain

species during crystallization; (e) melting behavior of thin chain-folded

lamellae; (f) gradual thickening of lamellae on isothermal storage; (g) homogeneous, pseudohomogeneous , and heterogeneous nucleation; (h) voids and included point defects as a part of the concept of the degree of crystallinity;

and (i) phenomena occurring in Stage 1 and Stage 2 of bulk crystallization

isotherms (annealing) . A comparison of theory and experiment is carried out

by means of data, some previously unpublished, on polyethylene and polychlorotrifluoroethylene. The theory with essentially regular folding is found to

be satisfactory.

2.14 Crystallization of Polymers from Solution

F. Khoury,

Polymer Physics Section

Polypropylene crystallizes isothermally at 110 - 115°C from |% solutions

in amyl acetate in the form of aggregates which exhibit an apparent polyhedral habit under the optical microscope. These aggregates, which are square

or slightly rectangular-shaped, of approximately uniform size (sides 4-5p.)

and overall thickness (~2|i.) possess a composite (distinct from single-crystal)

morphology, features of which are specifically related to their habit. Replicas of their largest surfaces (parallel to the square cross-section) re- veal (under the elecrron microscope) an open network consisting, apparently,

of two sets of narrow (~200 A) ribbon- like fibrils oriented with their re- spective lateral edges at ~90° to one another and at -45° to the sides of the

square (or rectangular) shaped periphery (Fig. 8). A narrow fringe of similarly oriented intercrossing fibrils is detected in transmission around the

latter periphery; the aggregates are otherwise essentially opaque to the e- lectron beam (Fig. 9) . Distinctly lamellar structures have also been observed in the peripheral regions of some aggregates. The lattice orientation

in the fibrils and lamellae as well as the origin of the dual morphology and

pseudopolyhedral habit of these aggregates, samples of which exhibit a monoclinic [Natta et al., Atti accad. nazl. Lincei Rend., Classe Sci. Fis. Mat.

e Nat., _21, 363 (1956)] X-ray powder diagram are being investigated. The

elucidation of these features should provide information pertinent to a better understanding of the mechanism of crystallization of polypropylene in

general and spherulitic crystallization in particular, since structures ex- hibiting a similar habit to that described above have been observed (under

the optical microscope) to form during the early stages of development of

polypropylene spherulites

.

2.15 Crystallization of Polyethylene Fractions

R. C. Neuman and J. Powers

,

Macromolecules : Synthesis and Structure Section

The thermal conditions for which linear polyethylene shows a morphological change (from a ringed spherulite to a granulated crystal habit) have

been reported previously (NBS Technical Note 197, Section 2.7). Increases

in low-angle X-ray diffraction spacing, partial melting and recrystallization,

and increases in lamellar thickness have already been reported in the literature for these same thermal conditions. We are testing our postulate, therefore, that the common crystallization mode in polymers (spherulitic nucleation and then growth) is complicated by the existence of lamellar-thickness

changes in the temperature range in which polyethylene spherulites might be

expected to develop slowly.

12
Fig. 8 Carbon replica of the surface of a pseudopolyhedral aggregate of

polypropylene revealing an apparently intermeshed fibrillar structure. The

sides of the aggregate with respect to this electron micrograph coincide in

orientation with those of the aggregate shown in Fig. 9.

Fig. 9 Transmission electron

micrograph of a polypropylene

aggregate exhibiting its pseudopolyhedral habit and fringelike peripheral morphology.

13
2.16 Electrodeposition of Single Crystals

F. Ogburn and J. D. Young,

Electrolysis and Metal Deposition Section

Under suitable conditions copper will grow epitaxially when electrodeposited on a copper single crystal. This seemed to offer a promising method

of growing large single crystals of copper by electrodeposition with a seed

crystal to initiate the process. Initial attempts, however, led to polycrystalline deposits except for the first microns of deposit (Ogburn and Newton,

1963) . Efforts are being continued to develop this technique for growing

massive single-crystal deposits of copper. Some progress has been made in

that single-crystal deposits about 10 mm x 10 mm x 2 mm now have been obtained, but not without polycrystalline material on the sides.

2.17 Crystallographic Characterization of

Pseudopentagonal Twins in Electrodeposited

Copper Dendrites

B. Paretzkin and H. S. Peiser,

Crystal Chemistry Section, and

F. Ogburn,

Electrolysis and Metal Deposition Section

A brief note has been written on the pseudopentagonal twins reported in

NBS Technical Note 197, Section 2.10 (Ogburn, Paretzkin, and Peiser, 1964).

The unusual crystallographic twinning is possible because of the <110>

elongation coupled with the angle lll^lll being 70°32' or nearly 360°/5.

Since there is a twofold axis of symmetry parallel to [110] most features

of the twin can be described equally well in terms of pseudodecagonal symmetry. Figure 10 shows the angular relationships in the [110] zone for the

{111] faces of a crystal A that is twinned by rotation about [111] producing

crystal_B and about [111] producing crystal C. Further twinning of B about

its [111] and C about its [111] introduces only two new crystals having

orientations D and E, respectively. The planes (111) of D and ( 111) of E

[just as ( 111) indicates the position of (111) after twin operation, so ( 111) here indicates the position of (111) after two twin operations, the first

of which left it unchanged] are inclined by 7°20' to each other, this being

five times the difference between 360 °/5 =72° and the above mentioned angle

111^111 = 70°32'. Theoretically only three individuals are needed to show

full pseudodecagonal (or pseudopentagonal) character; A, B, and E; or A, B,

and D; but in practice orientation E can be achieved only through orientation

C, and D only through B; so a minimum of four individuals are really needed

for this pseudosymmetry . It is easily seen how, by repeated twinning, pairs

of {111} faces at 7°20' to each other can be introduced all around the zone. A considerable number of repetitions can produce a twin displaying clear

pseudopentagonal character; but as the number of twin operations becomes large,

angles that are multiples of 7°20' will appear until eventually the twin may

resemble a polycrystalline sample with (110 > fiber orientation.

2.18 Thermal Etching and Crystal Growth of Methane

G. L. Pollack and R. S. Willams

,

Crystal Chemistry Section

The techniques which were previously developed for growing and etching

rare-gas solids are being extended to other molecular crystals and, in particular, have already been used to grow crystals of methane of about

14
001

D

E

ill AC

LL! Bp

Fig. 10 Angular relationships of {111} faces in [110] zone of cubic crystals

twinned repeatedly to produce pseudopentagonal symmetry along the zone axis

A indicates original crystal.

B indicates crystal obtained by twinning A by [111] rotation.

C

" " » " " A " [111] " D

" " " " " b

" [ 111 ] " E

" " ii ii ii c

M [HI] "

15
centimeter dimensions in a polycrystalline block (Williams and Pollack, 1964)

The crystals are thermally etched so that single grains and growth habits may

be visually observed. These habits have been studied as functions of crystal growth rate (0.5 cm/hr - 5 cm/hr), impurity content, initial nucleation

conditions , and other parameters

.

The research is aimed at accomplishing two things, the first of which

is the preparation of large crystals suitable for study of the low-tempera

ture solid-state properties of methane. Ultrasonic-velocity and elasticconstant determinations as well as thermal-conductivity and diffusion measurements can be undertaken most meaningfully on large single crystals. Crystals

have already been grown of sufficiently good quality and size so that measurements of this kind are practical.

The second aim is to study the mechanism of solid-solid phase nucleation.

Methane is the simplest molecular solid with a phase change suitable for such

a study and it is proposed to observe crystal growth and crystal properties

in the region of the change which occurs at about 20 °K. Thus far, observations on suitable crystals have extended from the triple-point temperature

(about 89 °K) down to 77 °K, and the experiments are shortly to be extended

to even lower temperatures. The grain sizes are apparently rather little

changed by these variations in temperature and no unconquerable difficulties

in reaching 20 °K and below are as yet anticipated.

2.19 Evaporation of Gold onto Cleaved Zinc Surfaces

L. K. Ives and A. W. Ruff, Jr.,

Lattice Defects and Microstructures Section

The initial stages of nucleation and growth of gold vacuum deposited

on freshly cleaved {0001} zinc surfaces have been studied by replica electron

microscopy. To assist in interpretation, cleaved rock-salt surfaces were

placed adjacent to each zinc sample prior to evaporation. Evaporation rates

were typically one monolayer /minute in an ambient vacuum of 10~ 5 torr. The

average geld thickness was varied from about one to ten monolayers

.

The results on as -cleaved rock-salt surfaces were in agreement with

those of Bassett. Isolated gold nuclei (diameter 20-50 A) were found at all

coverages. Cleavage steps were visibly decorated down to monatomic heights

(Fig. 11).

As-cleaved zinc surfaces also exhibited isolated gold nuclei, less regular in shape than those on the companion rock-salt surface (Fig. 11) . Long

linear chains of nuclei were observed and interpreted to indicate surface

steps. These decorated steps occurred much less frequently than on rock salt.

A series of zinc samples were deformed and a small fraction of the slip steps

produced showed preferential gold nucleation. It is believed that impurity

contamination of the zinc surfaces strongly affects the nucleation and growth

processes in comparison with the rock-salt results. Current efforts involve

a study of different replication methods and their effect on the observed

distribution of nuclei.

2.20 ^Studies of Small Crystals of Nickel

and Nickel Halides

D. R. Winder,

Radio and Microwave Materials Section

Nickel whiskers, nickel halide whiskers, and platelets have been grown

for studies of dimensionality in magnetism. The conditions for growth of

these crystals have been studied and the growth characteristics of the

16
Fig. 11 Carbon extraction replicas of deposited gold film, average thickness about 3 monolayers; (a) as-cleaved rock-salt substrate illustrating

gold nuclei and step decoration; (b) as-cleaved zinc substrate illustrating

some step decoration and clustering of nuclei.

17
platelet habit investigated. A paper by Winder and Sickafus on the last subject was presented at the Pasadena Meeting of the American Physical Society

in December, 1963. The abstract follows:

"Crystals of NiBr2 and NiCl2 , grown by sublimation, exhibit dendrites

and platelets having circular growth spirals, trigonal symmetry, and deliquescent properties. Fizeau interferograms are utilized to determine step

heights of the spirals. Growth spirals on opposite sides of a platelet are shown to be related. Appearance of isolated concentric spirals, not only

of the expected opposite sense but also of the same sense, and of large step

height indicate that large variations in Burgers vectors occur through the

connecting region. Trigonal symmetry is displayed by the dendritic structure

and polygonal growth structure."

2.21 Kinetics of Whisker Evaporation

R. L. Parker, S. C. Hardy, R. L. Anderson, and

T. Wagner,

Crystallization of Metals Section

On this project, the reader should refer to NBS Technical Notes 174,

Section 4.16, and 197, Section 2.15. A paper entitled, "Growth and Evaporation Kinetics and Surface Diffusion of K and Hg Crystal Whiskers" , (Parker

,

Anderson, and Hardy, 1963) has been published during this reporting period.

We have continued our study particularly on the growth and evaporation of

Hg whiskers , and have obtained about 700 photographs taken under different

conditions of super-saturation and temperature.

Figure 12 shows a typical growth and evaporation sequence for Hg. There

is some evidence that logX is a linear function of 1/T, T being the absolute

whisker temperature, but the data have considerable scatter. The phenomenon

of snapping or tipping noted earlier for K whiskers [Anderson and Parker,

Bull. Am. Phys . Soc, 8, 393 (1963)] has been observed and studied in Hg

whiskers. Both abrupt and gradual rotations of the whisker about its point

of attachment to the substrate can be observed; these angles varied from

to 90°, in as many as 50% of the whisker population. A complete reversal to

the original position often occurs. The motion, not to be confused with

Brownian motion which is also observed, can sometimes be induced by vibration.

The mechanism of this effect is not known.

A study of the causes underlying stoppage of length growth in Hg whiskers was begun. It is proposed to use our present data on this to compare

and evaluate the four current theories relating to this effect.

2.22 Theoretical Studies in Crystal-Whisker Growth

J. A. Simmons and R. E. Howard,

Metal Physics Section,

R. L. Parker,

Crystallization of Metals Section, and

H. J. Oser,

Computation Section

In NBS Technical Note 197, Section 2.16, the background to this work is

described. The implicit solution for the time-dependent whisker -growth problems has been extended to include the more realistic assumption that the

surface concentration at the tip remains at the equilibrium concentration

with the surrounding vapor.

18
c

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ONo

CO CO

-=1-

— o

a:o c

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ON

OJo

a.o

OJooOi O

0\

cn 3: I o

CO

OJo

COvoI

coCO

CO X.

a,uo

ex

cO>

CO

JJaou

cou$

co •H3anoco

•HU

COo

a,

co>

CO XIc

CO

x.o x e> OJ CN1 • !-( o

II— C>0 OJ -H * fe CL O

~> II oo O

vo a. t— "v. I Q_

II II

cn DC 1o

19
Although the explicit numerical computation for x(t) is not yet available, due in part to programming difficulties, the following asymptotic re- sults have been established:

x(t) = y V DJ when either x(t) » VdT or x(t) » Vd~

1

and

x(t) when x(t) « both VdI and Vd . 7

Here 7 is the growth constant, D is the coefficient of surface diffusion, I

the mean time for an atom on this whisker surface to evaporate, and x(t) is

the position of the whisker tip at time t as measured from the substrate.

From this expression for the limiting linear velocity it is found that

the approximate quasi-steady-state solutions derived by Blakely and Jackson

[J. Chem. Phys., y]_, 428 (1962)] and Dittmar and Neumann [Z. Elektrochem. , 64, 297 (I960)] are correct only in the limit y I « 1, When y 7 » 1, the

"dTscussion of whicker-growth rates by Gomer [J. Chem. Phys., 38, 273 (1963)] seems qualitatively correct.

The equations and limiting linear velocity for growth have also been

found to be valid for the case of whisker evaporation. Further publications

are pending (Simmons, Parker, and Howard, 1964; and Simmons, Howard, and

Parker, 1964).

2.23 Growth Kinetics of Crystal Whiskers by

Field-Emission Techniques

S. C. Hardy and R. L. Parker,

Crystallization of Metals Section

Well developed, symmetric patterns have now been obtained from potassium

whiskers grown from the vapor at a much greater pressure than had been used

previously. This was done by heating a potassium-coated wall opposite the

substrate; allowing the tube to cool in order to reduce the vapor pressure;

and then examining the emission patterns. Figure 13 shows a fie Id- emission

pattern from a [100] oriented whisker. [110] oriented patterns were also

photographed. Patterns of uniform emission are often seen simultaneously

with symmetric patterns. We do not yet understand clearly why structured

patterns are obtained from whiskers grown at these high vapor pressures. It

may be a whisker-size effect since the main difference caused by the higher

vapor pressure should be a different radius and length distribution.

Preliminary experiments studying the heterogeneous nucleation of mercury on tungsten field emitters are in progress. The object of these experiments is to measure the vapor supersaturation required to form a critical

nucleus as a function of substrate temperature.

2.24 Field-Emission Studies of the Growth

and Oxidation of Single Crystals

W. J. Ambs and E. Escalante,

Corrosion Section

Experiments on the growth and oxidation of magnesium films deposited on tungsten are still in process. So far, rates of surface diffusion and desorption have been measured with established field-emission techniques (Ambs

and Escalante in preparation). Multilayer diffusion with a sharp boundary

was observed to take place with the activation energy dependent on the crystal face (see Fig. 14) . Activation energies around 13 kcal/mole were observed. At higher temperatures, desorption occurred in two stages with

20
Fig. 13 (100) K whisker field-emission pattern

21
Fig. 14 a: Mg deposit on the side of W emitter; b,c: Migration of Mg around

(110) takes place as temperature is raised slightly; d,e,f: Beginning of migration around (100) at a higher temperature; g,h,i,j,k,l: Mg closes around

(100)

22
activation energies of ~34 and 94 kcal/mole. A minimum work function of

3.48 volts was observed. At the end of the first desorption stage this rose

to 3.95 volts compared to 4.52 volts for clean tungsten.

2.25 Condensation of Tungsten on a Cold

Tungsten Substrate

R. D. Young

Electron Physics Section

A field-ion microscope was used to study the deposition of tungsten onto

a liquid-hydrogen-cooled tungsten emitter. Tungsten was evaporated onto one- half of the emitter, and then field evaporated from the surface in small

steps. An examination of successive photographs showed that atoms were deposited in a very irregular way, comprising little groups and hills. The

photographic evidence together with Monte-Carlo calculations support the

assumption that the incident atoms are retained in the first potential well

they encounter.

This experiment gives the positions of deposited atoms in atomic detail.

It is hoped that this work will stimulate others to exploit the field-emission microscope for the investigation of condensation processes.

3. DEFECT CHARACTERIZATION

Contributions to this chapter are con- cerned with studies of defect-sensitive

properties of single crystals.

3.1 Magnetic Properties of Salt Single Crystals

at Low Temperatures

B. W. Mangum, #

Cryogenic Physics Section, and

R. P. Hudson,

Heat Division

In addition to the joint effort described below, one of us, B. W. Mangum,

has also been producing some rare-earth trichloride crystals. Anhydrous

single crystals of lanthanum trichloride, each containing either cerium trichloride, praseodymium trichloride, samarium trichloride, neodymium trichlordie, terbium trichloride, holmium trichloride, or erbium trichloride at a concentration of either 0.2, 0.5, or 2.0 mole percent, have been grown from

the melt. The method used was one in which the anhydrous trichloride, sealed off in a quartz tube under one- third atmosphere of helium, was slowly

lowered through a furnace with a high temperature gradient.

As a joint effort some of these crystals are being used in an investigation of the spin-lattice relaxation times of Ce+3

, Nd+3

, Pr+3, Sm+3

, Tb+3

, No+3

, and Er+3 ions. The pulsed microwave method is used for measuring the

relaxation times. The frequency of the microwaves is lOKMc/sec and the

temperatures at which the measurements are made are between 1°K and 4.2°K.

Measurements have been made on Sm+3 but are not yet complete. The relaxation

times for Sm+3 show anisotropy with respect to the field direction at the

lowest temperatures. Further measurements are in progress.

During the period covered by this report, a paper has been published

(Hudson and Mangum, 1963)

.

23
3.2 Optical Properties of "Pure" and Impure Crystals,

Paramagentic Centers

R. F. Blunt,

Solid State Physics Section

Spectra of a number of systems have been recorded, mainly at room temperature, including: spinel (:Mn); strontium titanate, SrTi03 (:Ti); magnesium fluoride, MgF 2 ; with X-ray induced color centers; spinel (:Cr); and

manganese fluoride, MnF3 (:Co). The emphasis has been on the last material.

Besides the "regular" Mn spectrum, the crystals exhibit three broad bands

attributable to cobalt, presumably as substitutional Co 2+

. These bands seen

at 6 900, 13 300, and 19 200 cm-1 are identified, respectively, as arising

from 4 T X (F) —>

4 T2 (F) , 4 AS (F) , and 4 T X (F) transitions. The latter is actually three partially resolved bands at 18 400, 20 200, and -21 000 cm" 1

. The

simple crystal-field theory yields a Dq of ~800 cm-1 and a calculated position of 14 800 cm-1 for the 4 A2 (F) band. Rhombic distortion of the F

- octahedral cation coordination will depress the 4 A3 level since it involves two

anions at greater distance than that of the other four, as well as a splitting of the orbital triplet states.

Color centers have been produced in MgF2 crystals by X- irradiation . So

far bands at 27 000 and 40 000 cm-1 have been observed and both are easily

annealed out at 500 °C

.

3.3 Laser Microprobe for Analysis of Very

Small Samples

B. P. Scribner, M. Margoshes , and S. D. Rasberry,

Spectrochemical Analysis Section

Studies of the laser microprobe, described and illustrated in NBS Technical Note 197, Section 3.10, have continued with particular emphasis on improving the performance of the instrument and in observing the spectra produced by laser excitation of solids. Because of the high energy of the laser

pulse, deterioration of several components of the optical system has occurred,

The affected portions were the cement layer between components of the microscope used to focus the laser beam, an upper lens component of one objective

(cracked) , and an interference filter used as an end plate in the laser crystal system (damaged) . The objective is now assembled without cement and

the manufacturer has replaced the interference filter with a reflector con- sisting of a stacked array of sapphire plates. The possibility of replacing

the glass lens system with a reflecting mirror objective is being considered.

Finally, a Mylar cover assembly has been placed over the objective end piece

to protect the lens from deposits of sample material ejected by the laser

beam.

Observations of the spectra produced by the laser pulse with and without spark cross -excitation have been made by integrating several pulses in

each case. For the vapor jet produced by the laser pulse alone the spectra

are weak and the spectral lines are highly self-absorbed. With the spark

discharge through the jet of vapor produced by the laser pulse, the intensity is increased many times and the spectral lines are reasonably sharp and

show little self-absorption. The sensitivity and reproducibility of the

latter excitation are being studied. Preliminary observations on zinc-base

alloys show that about 0.2 u.g of material is vaporized by each laser pulse.

By integrating 5 pulses, it was possible to detect 10~ 5 M-g of Si, Cu, and Mg

as impurities in the zinc sample. This represents a remarkably sensitive

level of detection in microanalysis. To assist in improving the reproducibility of the source, techniques are being developed to measure independently the reproducibilities of the flash lamp (which supplies energy to the

ruby crystal) and the laser pulse.

24
The laser has been applied in analysis for the identification of a surface film 3 microns thick, and a metallic grain inclusion, 0.01 mm2 overall

area by 5 microns thick.

3.4 Study of Crystal Defects

D.J. Barber and N. J. Tighe,

Physical Properties Section

Studies of dislocations in crystals of artificial sapphire by means of

transmission electron microscopy have been continued. Specimens are thinned

with the aid of a device which produces a hot chemical jet (Tighe, 1964).

Current work is concerned with dislocations in specimens twisted on the basal

plane. A dislocation extending between two etch pits is shown in Figure 15.

A hot stage capable of temperatures up to 2000 °C is now complete; a tilting

hot stage is under consideration.

Crystals of magnesium fluoride, MgF3 , exhibit radiation damage after

electron irradiation which produces dislocation loops. This process is being

studied with the aid of a cold stage.

In collaboration with E. N. Farabaugh (Crystal Chemistry Section) crystals of rutile have also been thinned for transmission work, and the effects

of non-stoichiometry on dislocation behavior will be studied.

3.5 Defects in Thin Oxide Films

J. Kruger, C. L. Foley, and H. T. Yolken,

Corrosion Section

Thin-foil electron microscopy and diffraction were applied to a study

of the films formed on iron during potentiostatic anodic polarization. The

techniques consisted of anodically polarizing thinned iron foils in boric

acid-sodium borate solutions at various passive potentials. By then flooding the surface, while it was at the passive potential, with an inert liquid

it was possible to retain the electrochemically formed films so that they

could be studied in the electron microscope. Selected-area transmission

electron-diffraction studies of these foils offered the advantage that one could study the epitaxial relationship of the oxide with metal substrates

of different orientation on a single polycrystalline specimen.

These studies have thus far revealed that the film formed under the con- ditions described is an oxide with a spinel 'structure (Fe 3 4 or y Fes 3 ) whose lattice parameter is less than those for bulk Fe3 4 or y Fe2 3

. This

indicates a spinel oxide having vacancies, a possibility suggested by one model of the passive film in the literature. The epitaxial relationships

between the oxide and the substrate are now being worked out.

o Studies of the existence of strain in thin (~30 A) oxide films formed

on iron single-crystal surfaces at low oxygen pressures have been started.

These studies measure by ellipsometry the optical constants in the visible

spectrum of the oxide growing on surfaces of different crystallographic

orientations. We hope to detect variations in epitaxially induced strain

on oxides growing on substances of differing orientation by observing the

effects of this strain on the position of the absorption peaks of the oxide.

25
Fig. 15 Electron transmission micrograph of a chemically thinned {0001}

section of artificial ruby. A short dislocation segment is shown terminating at the centers of two etch pits, both on the same surface

26
3.6 Effect of Point Defects on the Dynamic

Properties of Crystals

J. B. Wachtman, Jr., and S. Spinner,

Physical Properties Section

Elastic and electrical properties are being studied as a function of

temperature and frequency, and the results interpreted in terms of chemical

impurities and related point defects

.

Mechanical and electrical relaxation occurring in thoria, Th02 , containing up to 1.5 mole percent calcium oxide, CaO, has been interpreted in terms

of oxygen vacancies trapped by Ca ions (Wachtman, 1963). The investigation

is being extended to cover a wider range of frequency and composition dependence. The model will thus be subjected to more stringent tests after it

has accounted satisfactorily for the previously obtained observations.

The study of Ni-doped rutile has yielded two internal-friction peaks

which may be associated with isolated as well as with paired Ni ions . Earlier work on vacuum-reduced rutile (Wachtman and Doyle, 1964) appears to be

consistent with this interpretation. Further insight into ionic movements

in rutile could be obtained by studying internal friction associated with

oxygen-vacancy motion. Such vacancies should exist in chromium-doped rutile

and suitable specimens are being prepared.

Previous work on relaxation processes by this project has been interpreted in terms of a nearest-neighbor model. A model including neighbors out

to second nearest was published by Franklin (1963). Franklin's approach has

been applied to two types of paired point defects including neighbors out to

third nearest (Franklin, Shorb, and Wachtman, 1964).

3.7 Crystal Symmetry and Crystal Properties

J . B . Wachtman , Jr .

,

Physical Properties Section, and

H. S. Peiser,

Crystal Chemistry Section

The effect of crystal symmetry upon physical properties continues to

be a fruitful field of investigation despite the extensive treatment by Voigt

many years ago. The revived interest stems in part from the discovery of new properties unknown to Voigt and in part from the realization that spacegroup symmetry is important for some properties despite the fact that the

classical treatment deals only with point-group symmetry.

The types of point defects which can cause internal friction and the

type of stress required have been determined for many of the common refractory-oxide structures as reported previously in NBS Technical Note 197, Section 3.5.

A systematic scheme of all possible subgroups reached by the action of

homogeneous stress has been reported for all 230 space groups by Peiser,

Wachtman, and Dickson (1963) . This tabulation is expected to be useful in

studying other properties in addition to internal friction. Possible applications include the splitting of magnetic-resonance spectra under stress and

the classification of symmetry changes associated with solid solution.

A tabulation is being made for the centrosymmetric space groups showing

the mapping of all the special positions of a given group onto the special

positions of each of the space subgroups which can be reached by homogeneous

27
stress. This should be a useful addition to the space-group reduction tables

mentioned above.

3.8 Dislocations in Metals by Electron Microscopy

A. W. Ruff, Jr.,

Lattice Defects and Microstructures Section

A study of dislocations in low stacking-fault energy materials has been

initiated. Transmission electron-microscope observations on extended dislocations should permit the determination of the stacking-fault energy and its

variation with alloy composition. Initial results on extended nodes in 302

stainless-steel foils have been obtained. The rare observation of a singleended Frank-Read source in operation has been made (Fig. 16)

.

3.9 Growth of Helical Dislocations

R. deWit,

Lattice Defects and Microstructures Section

The abstract of a paper published during the reporting period follows

(deWit, 1963):

"Conclusions reached in a paper by Weertman [Trans. Met. Soc. AIME, 227 , 1439 (1963)] are amplified in a mathematical and graphical way. It is shown

that in a stressed crystal, a straight dislocation may be in a position of

unstable equilibrium with respect to helix development, and how a small perturbation may start the dislocation off on its helical path. Helix development occurs by diffusion; bulk diffusion is necessary for development from

a screw, but core diffusion is sufficient for development from an edge dislocation. For a mixed dislocation helix development can take place by core diffusion if the helix also climbs; a diffusion reversal takes place when

the slope of the helix equals the slope of the Burgers vector. The work

done on a crystal by the external forces is graphically shown to be consistent with the direction of motion of the dislocation in helix development.

Finally, a detailed mechanism for tangle formation from helices is presented.

In the course of helix development, a glide situation may be reached where a segment of each helix loop lies in a slip plane in which it can expand by

glide. Thus is it visualized how a helix can deteriorate into a tangle."

3.10 Characterization of Electrodeposited Crystals

F. Ogburn and A. deKoranyi

Electrolysis and Metal Deposition Section

Copper dendrites are easily formed by electrodeposition from cuprous

chloride solutions. These often take the form of flat tree-like structures

with the branches and trunk all in one plane. X-ray diffraction and metallographic examination of a few such dendrites show that a growth twin ex- tends throughout the branches and trunk of these dendrites (Fig. 17) . The

absence of three-dimensional branching is clearly associated with the presence of a growth twin which has a marked influence on the growth of an electrodeposit

.

Examination of electrodeposited lead dendrites, which are also flat,

shows them to contain flat voids or channels, and to be oriented with {111}

planes parallel to the overall dendrite or platelet. At least two orientations of the lead are always present. These sometimes have a normal twin

relationship but may have a rotational relationship other than the 60° of

the twin structure. These dendrites are being investigated further with

28
Fig. 16 Transmission electron micrographs of a single-ended Frank-Read

source (s) in operation. Sample is 302 stainless-steel foil approximately

2000 A thick

29
Fig. 17 Section of copper dendrite showing twin boundary
respect to the angular relationship of the crystals making up the dendrites

and to the crystallographic direction of their growth.

3.11 Second-Order Twinning in Aluminum

T. H. Orem,

Corrosion Section

In a continuing study of the corrosive behavior of aluminum, a number

of instances of twinning have been observed in specimens prepared for this

purpose. An especially noteworthy example, showing incontrovertible evidence of second-order twinning in aluminum, is shown in the accompanying

photograph of a twinned aluminum rod (Fig. 18)

.

The two grains immediately within the elliptically shaped boundary are twinned with respect to that part of the rod outside this boundary. The

two grains are thus first-order twins with respect to the latter. The wedgeshaped grain is twinned with respect to the above two grains at both the

straight and jagged boundaries of the wedge. Thus the wedge-shaped grain

bears a second-order twin relationship with that part of the crystal outside

the elliptical boundary.

3.12 Accurate Measurement of the Fundamental Electrical

Properties of Semiconductor Crystals

J. C. French, L. J. Swartzendruber , G. G. Harman, and

H. A. Schafft,

Electron Devices Section

Extensive calculations were completed which were related to the solution of a number of electrical potential problems arising from two- and fourpoint probe measurements on a variety of single-crystal sample shapes. Nonuniformity of resistivity and errors in probe placement or sample size were

considered.

Although generally conceded to be less accurate than the two-point

probe method outlined in Section 3.6 of NBS Technical Note 197, the fourpoint probe is by far the most widely used device for the measurement of re- sistivity of semiconductor single crystals. It provides a simple, non-destructive test and is therefore of great industrial and scientific importance.

A significant industrial concern over the use of four-point probes to determine the uniformity of resistivity of silicon wafers, together with the desire to use this simple technique to screen s'amples for the more accurate but

more time consuming two-point probe measurements in the work of this project,

led to the current emphasis on these calculations.

The results have been the determination of the correction factors for

four-point probes on rectangular parallelepiped samples with plated ends

(permitting the comparison of two- and four-point probe measurements for

calibration purposes) the correction factors for four-point probe measurements as a function of position on thin circular wafers, the disclosure of

the limits of the ability of the four-point probe to detect regions of non- uniform resistivity, and the relation of the measured non-uniformity to that

actually present (Swartzendruber, 1963). Tables of the numerical values re- quired in each case have been prepared through use of the 7090 computer, and

publication of the results is proceeding. A few samples are shown in Figure

19.

The four-point probe can be used to eliminate grossly non-uniform

samples, but in order to measure the variation in resistivity with greater

31
Fig. 18 Al twin

„

5-0.

tro

§

° 6 '

0* o /

.2 0.1- / / o

° 0.2 / /

( P

iROBE

4SPL ace

sME

1 1.0

•

/ / / (\ pi / / \ / / 0. y

1 /' /

/ /

u

/ /

•

/

PROBE DISPLACEMENT, A

c°ll 3< 0.6 H

Du 0.<

cro

<-> 0.! ^1

U

ai

] cp Roe E D ISP

( -AC

.6 EMEC NT,11A

l

(a) In-line array displaced along a radius(b) In-line array displaced perpendicularly

to a radius

(c) Displaced square

array

Fig. 19 Correction factors for three arrangements of four-point probes on thin circular semiconductor single-crystal samples plotted against probe

displacement. The correction factor, T) .relates the apparent resistivity , p (calculated from the usual expressions appropriate to the in-line or square

array) to the true resistivity of the sample p, in the expressions:

p = p /a+V

32
linear resolution, and yet rapidly, a machine for photovoltaic probing has

been completed and is awaiting evaluation. It will scan a sample at rates

up to about one centimeter per minute to yield a meter reading or, upon calibration, a plot of resistivity vs. length on an x-y recorder. Sample preparation techniques, though not fully developed, have already advanced to a point which makes the high-resolution scanning possible. The samples so far

measured by manual probing have shown that non-uniformity of resistivity will

be of major concern in this work.

The work on second breakdown in transistors mentioned in Section 3.6 of

NBS Technical Note 197 (project leader H. A. Schafft) has continued with the

application of temperature-sensitive phosphors to detect the location of the

breakdown site before excessive damage to the transistor has occurred. It

has been possible to show that structural irregularities are important to the

development of second breakdown (Schafft and French, 1963) . Work concerned

with the identification and role of crystal defects in producing these structural irregularities as well as influencing the development of second breakdown will now begin.*

The continuing investigations of electroluminescence (project leader

G. G. Harman) have been concerned primarily with the spectral emission characteristics of materials such as ZnS and CdS with various impurity levels

and under such excitation as ultra-violet light and electron bombardment.

The effects of the ambient atmosphere on electroluminescence have also been

studied empirically, with polycrystalline powders being used to increase the

surface to volume ratio. Most of this work was done at the University of

Reading in England under an NBS training program.

There have recently been published some additional results from the now

concluded studies of muscovite mica (Ruthberg, 1963) .**

The solid-state technology project (J. C. French, project leader) has

devoted a major part of its effort to work on silicon single-crystal nuclearparticle detectors, devices which have had a major impact on high-energy particle studies because of their excellent energy resolution and convenient

size and operating characteristics.

3.13 Crystal Characterization

by Diffraction Topography

R. D. Deslattes,

Crystal Chemistry Section

The double-crystal diffraction apparatus, plans for which were discussed

in NBS Technical Note 197, Section 3.7, was completed and placed in operation

in September. Its precision has proved equal to the expectations indicated

in the former report. A considerable amount of exploratory work has been

carried out, and the following results are noted.

The first investigation concerned questions of method. Previous doublecrystal work has been restricted to the case of symmetrical reflection from

pairs of identical crystals in dispersive (+,+) and non-dispersive (+,-)

configurations. The former case is limited in sensitivity by the large na- tural width associated with characteristic X-ray lines. The latter configuration gives rise to multiple and/or diffuse images (owing to the inevitable lack of spectral purity in the source) unless slits and large diffraction

This work was supported in part by the Rome Air Development Center.

**

This work was supported in part by the General Services Administration.

33
Fig. 20 Double-crystal diffraction topograph from a pair_of natural quartz

specimens. The samples were cut parallel to a set of {1120} planes, ground,

polished, and etched for 20 minutes in 357o HF

Fig. 21 Double-crystal diffraction topograph of sample of KAP analyser crystal. The reference crystal was ADP (101) and the spectrometer configuration (2,-5)

34
I0

C

Fig. 22 Rocking curve

(2,-5) for the pair of

crystals used in obtaining

Fig. 21. The logarithmic

intensity scale allows

study of the remote tail

regions

-12 -8-4 4 8 ROCKING ANGLE (SECONDS OF ARC)

Fig. 23 Diffraction

topographs from a pair

of ADP (101) crystals.

These had been string

sawed and chemically

polished. The image

doubling is due to un- dispersed alpha doublet. Although the significant long-range

strain appears, there

are some regions free

of the small images

which are tentatively

identified as emergent

dislocations

-12 -8 -4048

ROCKING ANGLE (SECONDS OF ARC)

16

Fig. 24 Rocking curve

(2,-2) for the pair

of crystals used in

obtaining Fig. 23

35
angles are employed. In this case, only a small part of the crystal can be

explored without scanning, and one of the more attractive features of the

double-crystal arrangement is eliminated.

In an attempt to avoid these difficulties, the negative orders of double

diffraction from crystals having almost equal interplanar spacings have been

especially investigated. The total dispersion in this case is the difference of the dispersions for the two crystals. If this difference is sufficiently large so that the a-doublet separation exceeds the combined Darwin

widths for the two crystals, the doublet is resolved and no restriction of

horizontal divergence is required to secure unique imaging. This result re- quires only that the lattice constants differ by more than a few parts in

ten- thousand — a condition which obtains rather often for crystals of different species. On the other hand, if a match within about 10% is obtained,

then the contribution of spectral-line width to the rocking curve does not

exceed that due to the diffraction process itself. Hence, a sensitivity

within a factor of two of the maximum attainable is realized. There is, of

course, a considerable and desirable gain of intensity in the (+,-) configuration relative to that in the (+,+) configuration. Double-crystal diffraction topographs taken from calcite crystals with copper, K , and tungsten, L , radiation in the above configurations confirm these elementary

expectations

.

In addition to the above investigation of method, several groups of

crystals were studied. These included specimens of natural quartz and calcite, specimens of solution -grown ammonium dihydrogen phosphate, ADP, and

potassium acid phthalate, KAP, and specimens of melt-grown germanium and

silicon

.

Natural quartz specimens of high spectroscopic quality were obtained

commercially. In addition to defect images which appeared similar to those

reported by other -investigators , several specimens exhibited topographs re- sembling a class of visual aurora as shown in Figure 20. In the case of one

pair, etching for 20 min . in 35% HF did not alter the image. The effect is

not understood at present; however, it may be conjectured to be analogous to

the well known strain effects of segregated point defects. These have been,

in the case of synthetic crystals, associated with irregularities in growth

conditions. In the case of the natural-quartz crystals, the analogous irregularities may be associated with geological epochs. Somewhat similar

effects have been observed in specimens of natural New Mexican calcite.

The synthetic crystals investigated were solution grown by temperatureprogram techniques. One family consisted of KAP crystals obtained commercially. The object in this case was to find crystals suitable for longwavelength X-ray spectroscopy. The results, as typified in Figure 21, indicate that spectra recorded by such crystals would be of dubious validity at

best. The crystals exhibit both local defects, presumably dislocations, and

long-range strain fields which together result in less than one tenth of the

crystal reflecting at any one angle. As shown in Figure 22, the corresponding rocking curves [versus a relatively perfect ADP (101) reference] also

indicate the futility of attempting to apply such crystals to problems in

precise spectroscopy.

The second family of synthetic crystals consisted principally in (101)

cuts of ADP (see NBS Technical Note 197, Section 2.5). The major part of

this investigation was found to be concerned with techniques of surface preparation (see Section 2.8 of this Technical Note). Results obtained after

moderate improvement in preparation technique are indicated by the topograph

in Figure 23. The corresponding rocking curves appear in Figure 24. These

suggested the possible utility of suitably prepared ADP specimens for longwavelength X-ray spectroscopy. Results obtained at 8.3 A are given elsewhere in this report (see Section 3.18).

36
3.14 Automation of Single-Crystal X-Ray

Diffraction Intensity Measurements

F . A . Mauer

,

Crystallography Section

The importance of automatic equipment in obtaining accurate measurements of single-crystal diffraction intensities for studies of crystal perfection and for structural analysis was pointed out in NBS Technical Note

197, Section 3.13. Current plans call for the automation of an existing

X-ray diffractometer and single-crystal orienter to be carried out by a commercial firm in two steps. The first step (to be completed by July, 1964)

involves fitting the three shafts of the manual device with shaft encoders

and motors so that the shaft positions can be read and set with an accuracy

of ± 0.01° by an operator at a remote console. On a command from the operator, the final setting of each shaft is to be recorded on punched-paper tape

and on a printer. Likewise, the number of counts registered by the scaler

in measuring background and peak intensities is to be recorded.

The second step (to be completed later) involves the addition of a programmer, a block- tape reader, and a comparator so that the machine will be

capable of reading commands from a punched-paper tape, making the necessary

settings, and recording the data, all without human intervention.

3.15 X-Ray Studies

M. I. Cohen,

Solid State Physics Section

The crystals now being studied include those mentioned in Technical

Note 197, Section 2.2, and in addition sodium azide, NaN3 ; potassium azide,

KN3 ; and cadmium sulfide, CdS . A survey of the major misorientations present in a Verneuil-technique-grown crystal of rutile, Ti03 , is under way

(compare Section 2.7). The crystal was grown at a rate of approximately

1 cm per hour. Incomplete results indicate an average sub-grain size of a- bout 2 mm. The "c"-axis deviation between grains is about ± 1°, and the ro3.16 High-Voltage Laue Photographic Inspection

of Large Single Crystals

B. Paretzkin and H. S. Peiser,

Crystal Chemistry Section

This method (see NBS Technical Notes 174, Section 5.13, and 197, Section 3.14) has been shown to be suitable for revealing misorientations and

strain in thick crystals, even while they are enclosed in a vacuum system or

a furnace (Paretzkin and Peiser, in preparation). The authors are ready to

collaborate with anyone wishing to characterize crystals under such conditions . The most interesting aspect for further work is the coherence observable over cyrstal distances of the order of 1 cm. In this respect the method is very sensitive to regional crystal misalignments of only a few seconds

of arc.

37
3.17 Chemical Purity by Dielectric Cryometry

G. S. Ross and L. J. Frolen,

Analytical Chemistry Division

In Section 5.18 of NBS Technical Note 174, a new method was described

in which the dielectric constant was measured in conjunction with the change

in temperature as the sample melted. From the data obtained the chemical

purity can be calculated with high precision. These studies have been com- pleted (Ross and Frolen, 1963).

3.18 Optical Properties of Cadmium Sulfide

and Telluride*

L. H. Grabner and R. C. Keezer,

Solid State Physics Section

Irradiation of undoped cadmium sulfide, CdS , platelets just to the longwavelength side of the absorption edge produces a decrease of the photocurrent (quenching) due to radiation on the short wavelength side. Noteworthy

characteristics are: (1) Quenching spectra, measured hitherto at the temperatures 293°K, 205°K, and 94 °K, duplicate the spectra of the blue-edge

photoluminescence [Pedrotti and Reynolds, Phys . Rev., 120 , 1664 (I960)] (except for luminescence due to the simultaneous emission of a photon and a phonon, the analog of which is absent in the quenching spectra). The quenching spectra are sensitive to radiation polarized parallel or perpendicular

to the c-axis in the same manner as the luminescence is polarized. (2) When

the sample is irradiated with constant intrinsic light, photocurrent versus

voltage shows an ohmic region followed by a saturation range. This presumably is due to hole injection [Lampert, Phys. Rev., 125 , 126 (1962)]. Quenching is observed only in the saturation region and its magnitude is a function of the voltage. Contacts are of melted indium.

3.19 Irradiation Studies

M. I. Cohen,

Solid State Physics Section

Crystals of magnesium fluoride, MgF 2 , have been irradiated by X-rays in

connection with a study of color centers (see report by Blunt, Section 3.2).

Accelerating potentials of 50, 140, and 250 kV were used. Analysis of the

optical absorption spectra showed that centers had been produced and that

the 50 kV radiation was slightly more efficient in the production of these

centers. Total dosage per sample was on the order of 50,000 roentgens.

A specimen of MgF2 was irradiated by 100 kV electrons in an electron

microscope. Examination with an optical microscope showed an area of < 1mm2 colored yellow-green. Optical absorption data could not be obtained due to

the small size of the spot.

3.20 Development of an Adiabatic Solution Calorimeter

D . D . Wagman

,

Thermochemistry Section

An adiabatic high- temperature solution calorimeter (see NBS Technical

J-This work was supported by the Office of Naval Research

38
Note 174, Section 5.4) has been completed and assembled. Preliminary trials

to test the vacuum tightness of the assembly and to determine the efficiency

of the stirring and of the sample-holding mechanisms are under way. After

this the thermocouple leads that operate the shield controls will be installed, at which time the apparatus will be ready for adiabatic operation.

It is anticipated that for maximum attainable precision, an additional

control system to regulate the temperature at the top of the shield will have

to be installed, but the purchase of the necessary electronic equipment has

been temporarily postponed.

4. CRYSTAL PHYSICAL PROPERTIES

Contributions to this chapter are concerned

with the physical properties of crystals

which do not depend primarily upon the degree

of crystal perfection or whose dependence on that perfection is not the principal aim of

the investigation.

4.1 Reference Data on Single-Crystal Elastic Constants

J. B. Wachtman, Jr., S. Spinner, and

R. W. Jackson,

Physical Properties Section

Elastic constants of inorganic single crystals are being determined as

a basic physical property when suitable crystals become available. The e- lastic constants of uranium dioxide, U02 , at 25°C were determined by

Wachtman, Wheat, Anderson, and Bates (1964). Work is now under way on a determination of the temperature dependence of the elastic constants of rutile

over the range 25°C to 600°C. A crystal of thoria, Th02 , has been obtained

and collaboration with P. M. Macdeo of the Glass Section is planned to determine the elastic constants by an ultrasonic technique.

Experimental capabilities are being enlarged by the construction of a Schaefer-Bergmann apparatus for the measurement of elastic constants . In

this apparatus, ultrasonic standing waves are used as a diffraction grating

for monochromatic light.

4.2 Deformation and Fracture of Ionic Crystals

S. M. Wiederhorn,

Physical Properties Section

The surface energy of solids is an important factor which influences

the breaking strength; yet surface energy is difficult to determine, particularly for surfaces which are not cleavage planes . A technique for making

such determinations by use of a modified Gilman-Westwood method is being

investigated with glass for the exploratory measurements. In this technique,

a crack is propagated in stages; the plane of propagation is controlled by

a scratch inscribed before the test. Early results on glass give reasonable

values of the surface energy.

4.3 Studies in S olid-State Theory

A. H. Kahn,

Solid State Physics Section

39
A tight-binding calculation of the electronic energy bands of strontium

titanate, SrTi03 , has been completed. The over-all picture is that of a con- duction band derived from Ti-3d states spread to a width of ~4 eV by a-bonding with the 0-2p states, and with smaller splittings by cubic crystalline

fields and rr-bonds . Similarly, the valence bands are derived from 0-2p

states spread by a large a p-d bond, a smaller tt p-d bond, and smaller splittings by axial crystalline fields and a and n bonds between the oxygen ions.

The over-all valence bandwidth is -4 eV.

The calculated band structure is in satisfactory agreement with experiments relating to conductivity, Hall effect, thermoelectric power, and X-ray

emission. The experimental and theoretical results were reported at the

Buhl Conference in Pittsburgh (Kahn, Frederikse, and Becker, 1963). The theoretical analysis, together with a qualitative discussion of a similar calculation for rutile, Ti02 , will be submitted to the Physical Review.

4.4 Electronic Transport

H. P. R. Frederikse, J. H. Becker,

W. R. Hosier, and W. R. Thurber,

Solid State Physics Section

Investigation of the lower-lying conduction bands in rutile by measurements of the Hall coefficient and electrical conductivity is nearing completion. It has been established that for temperatures above 40 °K appreciable

conduction in more than one band takes place. Analysis in terms of two bands

leads to an energy separation of the band minima of approximately 0.05 eV.

Work is in progress to determine parameters describing these bands (effective

masses, location of the minima, etc.) and scattering mechanisms (mobility,

i.e. electron-phonon and electron-impurity interactions). From the work one may also conclude that reduction of rutile leads to several types of lattice

defects

.

A method was developed to obtain low resistance metal-semiconductor contacts by use of localized pulsed heating, with best results achieved with a ruby-laser beam.

The conductivity and the Hall and Seebeck coefficients of reduced and

doped strontium titanate, SrTi03 , were measured over the temperature range

4. 2-300 °K. An average effective mass of (6-16) m was deduced from these

experiments. This value agrees well with the results of a recent energyband calculation for SrTi03 based on a tight-binding approximation (see

A. H. Kahn, Section 4.3). One can also conclude that the original impurity

level of the SrTi03 crystals is of the order of (1-2) x 10 l8 cm~ 3

. Introduction of donors (Ti3+

, Nb4+, etc.) below this level gives rise to strong com- pensation .

4.5 Hall-Effect Measurements

S. Rubin,

Engineering Electronics Section

The initial objectives of this project were the establishment of standardized terminology and measuring methods for Hall-effect generators and re- lated devices. The objectives have now been expanded to include magnetores is t ive dev ices.

This work was supported by the Bureau of Naval Weapons

40
Two new sensitivity indices for Hall generators, one a function of control current alone and the other a function of magnetic induction alone, have

been proposed and are included in the Hall-generator standard referred to in

Section 4.3 of NBS Technical Note 197. The new indices are useful for small

signal as well as static applications of Hall generators.

Work was begun on a standard of definitions, terminology, letter and

graphic symbols for magnetoresistive devices. Initial contact has been made

with manufacturers of magnetoresistive devices, and a first draft of proposed standards in this area will be circulated in the early part of 1964.

Work in the area of instrumentation for electron paramagnetic-resonance

magnetic-induction measurements was suspended for most of this period, but

will be resumed in the early part of 1964.

4.6 Dielectric and Mechanical Properties

J. H. Wasilik,

Solid State Physics Section

As a continuation of our investigations of the lattice properties of

single-crystal lead fluoride, PbF 3 (cubic, CaF3 structure), we are measuring

the room- temperature elastic constants of this material using a pulse-echo

technique. This work is being done in collaboration with the Physical Properties Section of the Inorganic Solids Division. Present results are

t ll = 8.88 ± .1, C 44 = 2.45 ± .03, and C l2 = 4.72 ± .11, all x 10 11 dynes/cm2

, A recent report indicated phase changes in NaN3 at 19 °C . This conclusion resulted from analysis of electron paramagnetic resonance and X-ray

spectra [Miller and King, J. Chem. Phys . , ^39, 2779 (1963)].

In collaboration with R. Forman of the Section, we have looked for

anomalies in the dielectric properties (dielectric constant and dielectric

loss) of single-crystal sodium azide, between room temperature (25 °C) and

-10°C; we have concluded that anomalies of ~37o or greater do not exist in

this temperature region when the measuring electric field is in the c direction . We did discern that the capacitance and loss of NaN3 were quite sensitive to humidity variations, exhibiting responses to humidity increases with

response times of the order of seconds. Further investigations of these properties are planned.

4.7 Dielectric Properties of Semiconductors

E. C. Bamberger and J. L. Dalke,

Radio and Microwave Materials Section

As described in Section 5.7, Bienenstock and Bur ley (1963) have found

that the thermal expansion of a phase of silver iodide, Agl, with a zincblende structure is negative to approximately 80 °K, positive in the range of

80° to 110°K, and then attains a constant negative high- temperature value.

This apparently unique and primarily negative thermal expansion in the large

temperature range from 4.2° to 300 °K for cubic Agl was determined from lattice-constant measurements by means of X-ray diffraction techniques.

This work was supported by the Atomic Energy Commission

41
Agl 10 kc/s

10,000

1,000 -

100

Fig. 25a Dielectric

constant of silver

iodide plotted a- gainst temperature

at 10 kc/s

-200 -160 -120 -80 -40

TEMPERATURE, °C

Fig. 25b Dielectric

constant of silver

iodide plotted a- gainst temperature

at 1 Mc

19

1 MC

1

1 1 1 1 1 1 1 /

'

1 /

17 e!—

.

/ —

15 ' —

13

II

Q i . J . 1 t —T^l 1 1 1

€ tan 8 - 2

-

-200 -160 -120 -80 -40

TEMPERATURE, °C

o 40

42
The expansion is explained in terms of a model which shows the dependence of thermal expansion on structure and bonds. The authors discuss the

primary role of covalency and its contribution to the low- temperature con- traction. The particular form of the interatomic interaction appears to con- tribute primarily to the balance between optical and acoustical modes. In

the case of Agl it is the large n in the nearest-neighbor repulsive interaction, r , which accounts for the negative high- temperature limit. The positive thermal expansion at intermediate temperatures is the result of transverse optical modes with frequencies lower than the frequencies of the transverse acoustical modes.

The purpose of the present investigation is to determine the dielectric

relaxation spectrum of Agl and to see if there is any correlation with the

thermal-expansion observations. Measurements of the complex dielectric con- stant show an inflection point in the dielectric-constant versus temperature

curve in the same range where the thermal expansion becomes positive (see

Fig. 25, a and b) . Rather large dielectric-constant values were observed.

These have not yet been explained. Cubic Agl is not available in singlecrystal form. It is thus possible that these large values may come about

from interfacial polarization in the polycrystalline specimens. However, it

is also possible that the mobile Ag ions encounter a potential-well structure which is not yet understood.

4.8 Crystals of Organic Molecules

R. A. Keller and D. E. Breen,

Physical Chemistry Division

The objectives of this new project are to study the properties of the

triplet state and the weak intermolecular interactions in crystals of organic molecules

.

The process of transfer of electronic excitation from one state to an- other is important in the fields of biological activity, electrical conductivity, photosynthesis, and laser technology. In both biological activity

and photosynthesis, the system absorbs energy in one place and transfers this

energy to another form in another place. Information is needed on the basic

mechanisms of such transformations. The interest in the use of organic molecules in lasers and photoconductors is the result of the ease of changing

the physical properties of these molecules by chemical substitution. The

weak interactions between molecular units are in contrast to most of the previous work in solid-state physics which was concerned with systems with

strong interactions between their fundamental units. In molecular systems,

good approximation to the initial and final states of the system undergoing

energy migration are the zero-order states of the isolated molecular unit.

These states are connected by small perturbations either inherent in the

isolated molecule and modified by the solid environment or caused entirely

by the solid environment. We will study these states and the nature of the

small perturbations

.

In particular, we are interested in the intermolecular and intramolecular properties of the triplet state. Triplet states are populated by radiationless transitions from optically excited molecular singlet states. We

will study triplet-state properties such as its lifetime, rise time, temperature effects, solvent effects, polarization, quantum yield, and extinction

coefficient. From these properties, we can derive information on the perturbations which connect the spin-orthogonal triplet and singlet systems.

Triplet excitations have been shown to migrate from molecule to molecule.

This process gives rise to impurity trapping of excitation and to a phenomenon called delayed fluorescence (the process of two excited molecules interacting) which results in bimolecular quenching of the triplet state and in

the production of molecules (in excited singlet states) which then fluoresce.

43
The rate constants and the mechanisms of these migrations and bimolecular

processes are not known. We will attempt to measure these rate constants

and to determine the effect of environment on them.

We will investigate rigid glass or oriented crystal solutions of organic molecules in inert or partially inert solvents. [For example: naphalene

dissolved in naphthalene-d8 , biphenyl, durene, and E.P.A. (a mixture of ethyl

ether, ethyl alcohol, and isopentane) ] . The accessibility of the solvents'

electron states decreases as we proceed down this series.

Some of the experiments mentioned above had been initiated prior to the

start of this project. Measurements of the quantum yields of fluorescence

and phosphorescence of naphthalene and a series of halo-naphthalenes have

been completed and will be submitted for publication. Preliminary experiments on the determination of the extinction coefficient for triplet-triplet

transitions have been completed, but the work will have to be refined before

publication. Apparatus is being constructed for the measurement of phosphorescent rise times. Preliminary investigations on the properties and

mechanisms of delayed fluorescence are under way.

4.9 Low-Temperature Thermometry

H. H. Plumb, G. Cataland, and M. E. Edlow,

Cryogenics Physics Section

A portion of the National Bureau of Standard's effort in low- temperature thermometry is concerned with the resistance of impurity- doped germanium crystals as a sensitive function of temperature below 20°K. Recently,

progress has been made in empirically fitting curves relating resistance and

temperature. The results will be published within the next year.

4.10 Oxide Melting-Point Standards

S. J. Schneider,

Crystallography Section

A compilation of the melting points of 70 metal oxides has been published (Schneider, 1963a). Both the original melting point and equivalent

value based on the International Practical Temperature Scale of 1948 are

presented. Another paper (Schneider, 1963b) clarifies certain misapprehensions about the accepted melting points of corundum, A1S 3 ; magnesium oxide,

MgO; calcium oxide, CaO; and chromium sesqui-oxide, Cr2 3 . Equipment has been constructed which will permit the heating of samples

to 3000 °C in a vacuum or inert atmosphere and to 2400 °C in an oxidizing en- vironment. Design and testing of black-body enclosures have been adjusted

to the aim of achieving the highest attainable accuracy of temperature mea- surement .

In addition, research is now being conducted on possible reactions between oxides and various container materials such as Ir, Pt, and W. Preliminary information indicates that Ir, in an air environment at 1000 °C,

oxidizes to Ir03 , which in turn reacts with the various oxides to form binary compounds, At higher temperatures, the compounds dissociate to Ir metal

and the original oxide.

4.11 Dilatometric Studies of Polymers

F. A. Quinn, Jr. and J. Powers,

Macromolecules : Synthesis and Structure Section

44
a) Polybutene-1 undergoes a spontaneous crystal-phase transformation

from an initially formed phase with a tetragonal unit cell to a denser rhombohedral one. The crystallization process occurs over the period of a week with

a minimum rate at 20°C at atmospheric pressure. Transformation isotherms,

over a temperature range of 0°C to 55 °C and a pressure range of 1 to 800 kg/

cm2

, were measured for polybutene-1 samples in a dilatometry apparatus described by Martin and Mandelkern [J. Appl. Phys . , 34, 2312 (1963)].

The transformation rate increases and the temperature at which the maximum rate occurs shifts upward with increasing pressure. In the lower portion

of the temperature range, proximity to the glass transition temperature

(~ -24°C) undoubtedly influences the transformation process. The presence of

a maximum in the rate and its upward shift with temperature (of the same or- der of magnitude as that of the melting point with pressure) indicate that

polybutene-1 recrystallizes through nucleation and growth steps.

b) Polypentene-1 forms at least two polymorphs, a 3 X and a 4 X helix,

similar to polybutene-1 (NBS Technical Note 174, Section 5.21). The melting

point of the 4, -helical structures is lower (80°C) than that of the 3 X modification (>100 C) . No evidence has been found as yet that the 4 X helix transforms directly to the 3 X form as in polybutene-1. Instead, transformation

from one to the other seems to require an intervening melt phase. The optimum temperature for this transformation is in the vicinity of 80 °C.

4.12 Thermal Conductivity of Paramagnetic Crystals

J. F. Schooley,

Cryogenic Physics Section

During the latter half of 1963, some experimental work has been done on the measurement of the thermal conductivity of neodymium ethylsulfate by the

method mentioned in Section 4.9 of NBS Technical Note 197.

-7

Preliminary results indicate a thermal conductivity of the order of 10

watt (cm deg) -1 at 0.04°K, and a variation very nearly as the square of temperature between 0.02°K and 0.05°K.

Measurements on other crystals of neodymium ethylsulfate are contemplated as checks on both the absolute magnitude and the variation with temperature of the conductivity.

4.13 Magnetic -Resonance Studies - I

T. Chang, R. A. Forman, and

R. E. Payne,

Solid State Physics Section

a) Nuclear Resonance

The nuclear resonance of N

14 in potassium azide, KN3 , has been observed.

Information has been obtained on the structure of the N3 ~ group and some information on the chemical bonding. Further work is in progress.

Nuclear-resonance experiments on the antiferromagnetic compound RbMnF 3 have been completed. Besides a frequency shift of the F resonance similar

to that observed in KMnF 3 [Shulman and Knox, Phys. Rev., 119 , 94 (I960)]

shifts of the Rb lines have also been observed. Information on the crystal

structure after the phase transition and on the p-d and s-d bonding orbitals

have been obtained.

Further studies are in progress on transition-metal oxides and on some

45
nitrogen compounds which are known to undergo phase transitions.

b) Electron-Spin Resonance

The work on molybdenum-doped rutile, Ti03 , has been completed. The

super -hyperfine structure observed in the Mo spectrum indicates fhat the e- lectron-wave function of Mo spreads out rather far (more than 3 A) in the

host lattice of Ti02

. The behavior of other ions in Ti02 is being investigated. Among these

is tungsten which shows signs of superhyperfine structure. It is believed

that this is the first time that tungsten ESR has ever been observed. . Niobium in strontium titanate, SrTi03 , was examined also. The niobium

is probably present in very low concentration and the signal seems to indicate strong saturation.

4.14 Magnetic-Resonance Studies - II

L. M. Matarrese, J. S. Wells, R. L. Peterson,

R. J. Mahler, and A. R. Cook,

Radio and Microwave Materials Section

A yellow-brown specimen of iron-doped synthetic quartz single crystal

has been found to give a well-behaved EPR spectrum of ferric ion (Fig. 26)

without the extraneous, variable- intensity lines characteristic of the green

specimens studied earlier (see NBS Technical Note 197, Section 4.17). So

far, our experiments have been carried out only at room temperature in a K-band spectrometer.

Three sets of five lines each are observed, spread out from 4 to 11 kG.

The behavior of the sets as the magnet is rotated with respect to the crystal

suggests that the ferric ions are distributed amoung three sites differing

only in the orientation of their principal axes which are 120° apart in the

plane perpendicular to the optic axis (Fig. 27) . When the magnetic field is

parallel to the optic axis, all three sites give identical spectra which are superposed to give the five lines shown in Figure 26.

From the measurements of line positions as a function of angle of rotation of the magnetic field in the XZ plane of the quartz, we have determined

the following values for the spin Hamiltonian: g )( (along X-axis) = 2.0036,

gj. (along optic axis) = 2.0031, D (axial field parameter, assumed positive) = 734.8 G, |E| (rhombic field) = 327.4 G, a (a measure of the cubic field) = 37.7 G. We cannot yet say whether the ferric-ion site is substitutional or interstitial, nor do we yet know how the charge is compensated. Further ex- periments, including rotations in other planes, are in progress to try to

answer these questions and to check the parameters.

A marginal oscillator for the 300 Mc range and associated transmission

lines have been built for Electron Nucleus Double Resonance (ENDOR) experiments on single crystals of calcite containing manganese.

The anharmonic creation of nuclear-transition-frequency phonons was observed in sodium chlorate, NaCl03 , and reported at the American Physical

Society meeting in Edmonton.

We also attempted to observe a nuclear double-spin flip transition between the gallium and arsenic nuclei in single crystals of GaAs but the interaction proved to be too small to be observable.

We have succeeded in producing nuclear-spin transitions of fluorine

nuclei via ultrasonic modulation of the magnetic interaction in KMnF 3 in the

46
©

X —*y^v^*V^

=>/2

Z*«p~***H/WoJ .^w.,»w,<^v^vyi

'/2

-y^^^^^v^v*- >f*^*w!W^H^ifc^lW< r

°'2

3+ Fig. 26 EPR spectrum of Fe in quartz (synthetic) at K-band and room temperature. Field increases non-linear ly from left to right, from about 4500

to 11,300 G. The numbers below the lines indicate the value of M in the

transition M<—M-l, assuming a positive value for D, the axial field-splitting parameter. The lower trace is the H parallel to the Z axis (optic

axis) of the quartz. In this orientation, the spectra of all three sites

coincide. When the field is parallel to one of the quartz X axes, it is

thereby parallel to the principal axis of one of the three sites; the spectrum of this site is labeled by the circled l's. At the same time, the

field makes equal angles (60°) with the axes of the other two sites, whose

spectra coincide to give the other five lines observable at this orientation. The origin of the weak lines which can also be seen in these traces

is as yet unknown.

Fig. 27 A model of optically

right-handed a-quartz. The

optic axis is vertical and is

the same as the axis of the

left-handed spiral in the

model. The three inequivalent

substitutional sites are shown near the top of the model and

can be identified by the knobby

sticks attached to them. Site 1 is labeled; the other two sites are in the layers below it.

47
antiferromagnetic state. This work is being submitted to Physical Review

Letters. At present, we are attempting to observe the ultrasonically modulated

magnetic interaction between the aluminum nuclei and the paramagnetic chromium ion in ruby. Success in this experiment will enable us to investigate

the nuclear-paramagnetic relaxation process.

4.15 Nuclear-Magnetic-Resonanance Studies

in Yttrium-Iron Garnets

R. L. Streever,

Magnetic Measurements Section

The nuclear resonance of Fe57 in mixed yttrium-gallium- iron garnets has

been studied. Thus far, the resonance has been observed in concentrations

where up to forty percent of the iron atoms have been replaced with gallium

atoms. These measurements are particularly interesting because nuclear reson- ance frequency is a measure of the magnetizations on the individual sublattices . The concentration in which this magnetization begins to fall rapidly to zero is of importance in studies of dilute ferromagnetism. It will also be possible to determine the ratio of gallium atoms substituting for iron

atoms on "a" and "d" sites. The structure of these crystals, as well as their

magnetic properties, is thereby precisely characterized.

4.16 Electron-Spin-Resonance Studies of

Transition-Metal Complexes

H. C. Allen and G. F. Kokoszka,

Inorganic Solids Division

The EPR spectrum of the tris-coordination compound of Cu+2 with 1-10

phenothroline and 2-2' dipyridine diluted in the matrix of the corresponding

zinc compound has been examined as a function of temperature. At high temperatures, a single absorption is observed in each compound indicating an isotropic g-value. At liquid-nitrogen temperature, each compound exhibits an absorption pattern corresponding to an anisotropic g-tensor with two principal

values. These spectra have been interpreted as arising from a Jahn-Teller

distortion, frozen in at the lower temperatures as described by the theoretical treatment of Liehr and Ballhousen [Ann. Phys . , _3, 304 (1958)]. A report

on the spectrum of the polycrystalline material was presented at the 144th

meeting of the American Chemical Society and has been submitted for publication. Since then, it has been possible to grow some single crystals and

work is progressing on these samples.

Crystals of zinc-doped copper acetate monohydrate are being studied by

EPR techniques. In the normal crystal the copper ions occur in pairs with

an internuclear separation of about 2.6 A. [for reference see Bowers and

Owen, Repts . Progr. in Phys., 18, 304 (1955)]. A relatively strong exchange

coupling has been observed, ancFthe EPR spectrum is characteristic of a species with a spin of one. By substituting zinc ions into the crystal structure, the behavior of a single copper ion may be studied. The results of

this investigation should be submitted for publication early in 1964.

4.17 Low-Temperature Nuclear Orientation

H. Marshak, R. B. Dove, and

R. S. Kaeser,

Cryogenic Physics Section

Helium-3 refrigeration in conjunction with a superconducting split solenoid has been used to obtain a high degree of polarization of a Ho lB sample

48
in the form of a single metal crystal. This target, along with a beam of 350

keV polarized neutrons produced by the Li(p,n) reaction with the Oak Ridge

National Laboratory 3MV pulsed Van de Graaff, has enabled us to investigate

whether or not a spin-spin interaction exists in the optical model potential.

Results of these measurements indicate that the spin-spin interaction, for

this particular case, is lower by approximately two orders of magnitude than

the spin-orbit interaction. Measurements of the change in total neutron cross- section for an oriented and unoriented deformed nucleus have been made.

4.18 Microwave Measurements on Single-Crystal Ferrimagnetics

A. S. Risley and H. E. Bussey,

Radio and Microwave Materials Section

Small quantities of high-purity single-crystal manganese ferrite and

single-crystal yttrium iron garnet were acquired in the past six months. No

measurements were made on these materials during this period. Theoretical

work coupled with experimental results on ferrimagnetic polycrystals has increased our interest in single-crystal materials. Experimentation on single

crystals is planned for the present six-month period.

4.19 Adsorption on Metal Single Crystals

R. Klein,

Surface Chemistry Section

The chemisorption of carbon monoxide on tungsten, observed with a fieldemission microscope, showed that the adsorption was non-dissociative. Surface

migration and desorption were observed at several temperatures and the activation energies associated with these processes were derived. The specificity

of the- metal surface is being considered through the study of carbon monoxide

adsorption on a variety of metals. Tantalum, for example, shows behavior

similar to tungsten in its interaction with carbon monoxide. There are differences in detail related, it may be postulated, to the electronic rather

than the geometric structure of the metal. Niobium, as would be expected,

is more closely related to tantalum than to tungsten in adsorption of carbon

monoxide, CO. It is interesting that the field-emission pattern of tungsten

shows the {Oil}, {001}, and {121} planes as dark areas in the field-emission

patterns. These are the areas having relatively high work functions. With

tantalum and niobium only the {011} and {001} planes appear as areas of low

emission

.

The experiments with niobium were done with the field-emission tube immersed ,in liquid helium. Since the superconducting transition for niobium is

9.2°K, a comparison of patterns and work functions of CO-covered surfaces below and above the transition point was possible. (Temperatures above ambient

were achieved by heating a loop wo which the emitter was attached.) No differences could be detected.

It was found for CO on niobium that there are at least three states of

adsorption. There is a weakly bound state, present at high coverage, which

is desorbed in the 100-200 °K range; an intermediate state can be desorbed at

700°K; and the most strongly adsorbed state, present only in a small fraction

(perhaps 10" 2

) of a monolayer, which is desorbed above 1000 °K with indication

of decomposition of the CO.

The general conclusion is that the chemisorption of CO on clean metalcrystal surfaces is a complex process. No simple model can satisfactorily

represent the experimental facts

.

49
4.20 Superconductivity in Niobium

V. D. Arp,

Cryogenic Properties of Solids Section

Superconducting properties of metals depend strongly on the electronic

configuration within the metal, and only weakly on the crystalline structure

of the metal. An exception to this general rule is that as dislocations are added to the crystal structure, diamagnetism becomes strongly irreversible

with applied field. Sensitivity to dislocation content is large in those

metals whose Fermi-surface properties give rise to a short electronic-coherence length. Empirical evidence indicates that this coherence length is un- usually short in niobium. We have found that available superconductivity

theory can predict certain features of the irreversible-magnetization curve

of heavily cold-worked niobium (containing perhaps 10 10 dislocation per cm2 ),

but that current-carrying capacity in a high field is inconsistent with the

theory in this case.

4.21 Experimental Determination of Atomic-Scattering Factors

G. Bur ley,

Crystallography Section

As the initial step in a program of determining experimental values of

the atomic-scattering factors, the determination of an accuracte value for

the Debye-Waller temperature exponent for magnesium oxide, MgO, has been un- dertaken . Accurate X-ray diffraction patterns have been obtained for several different specimens of polycrystalline MgO, with both copper and molybdenum

radiations. The total integrated intensity for each reflection at room temperature has been measured by the pulse-count technique at intervals of 0.05°

(26). Patterns have also been made with a high-temperature attachment for

the dif fractometer at 100 °C intervals to 400 °C . Data reduction is now in

progress

.

4.22 Soft X-Ray Spectroscopy

R. D. Deslattes,

Crystal Chemistry Section

The vacuum two-crystal spectrometer discussed in NBS Technical Note 197,

Section 3.7, was completed by addition of source and detector. It will be

described in detail elsewhere. In anticipation of the first planned experiments in the K series of neon and NaF , it was equipped with potassium acid

phthalate, KAP, crystals obtained commercially. With these, some exploratory measurements revealed that the KAP crystals exhibited resolving power

that was too low to permit serious study of the neon spectrum. It was subsequently demonstrated by means of diffraction topography (see Section 3.13)

that the broad rocking curves resulted largely from high dislocation density

and severe long-range strain in the samples at hand. Subsequent topographic

studies of "specially selected" samples from the commercial source revealed

even more strain, larger dislocation density, and bifurcation of the crystal

plates. These results have halted the program initially planned. Efforts

to produce KAP crystals of adequate perfection for spectroscopy have been

initiated by Torgesen, Horton, and Strassburger (see Section 2.8). Seed

crystals have been prepared and placed in two baths, one isothermal, and the

other temperature programmed. If either or both of these are successful in

producing the large specimens required for spectroscopy, then samples should

be available for evaluation in the next report period.

50
Should these exhibit substantially superior characteristics to the samples

tested so far, the program can return to its original plan.

In the meanwhile, good specimens of ammonium dihydrogen phosphate, ADP,

cut for 101 reflection (2d = 10.6 A) have been obtained (see Sections 2.1 and

2.8). Preliminary spectroscopic results at 8.32 A indicate a resolving power

of 10,000. It is planned, therefore, to replace the original program by one involving use of these ADP crystals to study the valence-emission-band structure of some III - V compounds and, where possible, their group IV analogs.

These include, in particular, the K spectrum of phosphorus in GaP and the K

spectrum of silicon. Also, it is planned to examine in the L series, the

valence-emission spectra of germanium, gallium, and arsenic in GaAs

.

Completion of these rather extensive plans is dependent on the automation

of data acquisition. Components are either on hand or have been ordered at

this time.

5. CRYSTAL CHEMISTRY

Contributions to this chapter are concerned with

studies of individual crystal phases involving

crystal structure, transformations, or chemical

properties not sensitively dependnet upon crystal

perfection

.

5.1 Crystal-Structure Analysis

S. Block, H. M. Ondik, and

A. Perloff,

Crystallography Section

The program of crystal-structure analysis has several facets, including:

(a) evaluation of methods of structure analysis, (b) determination of structural principles of inorganic compounds such as borates and phosphates, and

(c) compilation of single-crystal data. In recent work certain formulae

were tested for applicability and limitations by using them in determining

the structure of sodium tetrahydroxyl borate dihydrate, NaB(0H) 4 .2HS (Block

and Perloff, 1963) . Other structures determined include 1-ethyldecaborane

(Perloff, 1964), sodium trimetaphosphate, Na 3 P3 9 , and its hydrate,

Na 3 P 3 9 .H2 (Ondik, submitted to Acta Cryst.), and BaB4 7 (Block and Perloff,

in preparation)

.

Structural relationships of the low and high temperature forms of lithium phosphate, Li3 P04 , have been investigated by X-ray powder diffraction and

differential thermal analysis (Keffer and Block, in preparation)

.

5.2 Crystal Chemistry of Calcium Phosphates

W. E. Brown and E. C. Moreno,

Dental Research Section

The sparingly soluble calcium orthophosphates , CaHP04 , CaHP04 .2H3 0,

Caa H3 (P04 ) 6 .5H2 0, a-Ca3 (P04 ) 2 , p.Ca3 (P04 ) 2 , and Ca5 0H(P04 ) 3 , comprise a group

of compounds of considerable commercial and biological importance. Their

solubilities in aqueous systems are being measured to gain information that

can be used to predict their relative stabilities under the various conditions where they are encountered.

Of these compounds, Ca 5 0H(P04 ) 3 is of particular significance because

it is the prototype for the crystallites in bone and tooth. It bears a 51
unique structural relationship to the salt Ca8 Hs (P04 ) s .5H2 0, and of major

interest is an understanding of how this relationship influences the chemical

and crystallographic properties of the two salts. Particular attention is

being given to the manner in which Ca 5 OH(P04 ) 3 may enter into growth mechanisms, solubilities, reaction with fluoride, and incorporation of impurities

by the crystallites.

The structure of a-Ca3 (P04 ) 2 is being determined from single-crystal

X-ray data.

5.3 Standard X-Ray Diffraction Powder Patterns

H. E. Swans on,

Crystallography Section

Patterns of pure and well characterized inorganic solids are being produced as comparison standards that are used in identifying crystalline materials of unknown composition. These patterns have been published in twelve

volumes. A thirteenth (Swanson et al., 1964) includes patterns for 51 substances, thirty of which were not previously included in the X-ray Powder

Data File issued by the Joint Committee on Chemical Analysis by X-Ray Diffraction. Twenty-one are to replace earlier and less reliable patterns based

on various sources . A computer is being used to calculate powder-pattern intensities and

spacings from single-crystal data in the case of materials for which observed

data are difficult to obtain.

5.4 Crystals with Large Lattice Spacings

H. E. Swanson,

Crystallography Section

In a search for crystals with large-lattice spacings suitable for use

in long wavelength X-ray spectroscopy, X-ray powder diffraction patterns for

eighteen organic samples (supplied by Leo A. Wall, Polymer Chemistry Section)

and for a number of metal biphthalates prepared in this laboratory were ex- amined. In each group, one or more compounds were found that have strong

reflections at low angles and are worthy of further consideration.

5.5 Phase Equilibria

E. M. Levin and R. S. Roth,

Crystallography Section

Phase-equilibria research is conducted in three areas: (a) glass -forming

systems containing silica, germania, and boric oxide; (b) systems of interest

in electronic research, such as those containing niobia, tantala, and zirconia

and (c) refractory oxide systems, in particular, those containing rare-earth

oxides

.

This work is partially supported by the Joint Committee on Chemical Analysis

by X-Ray Diffraction under the auspices of the American Society for Testing

and Materials, the American Crystallographic Association, the British Institute of Physics, and the National Association of Corrosion Engineers.

52
In a two-part paper on the polymorphism of bismuth sesquioxide, Bis 3 , (Levin and Roth, 1963) discrepancies in the literature have been resolved and,

in addition, the effects of oxide additions on the polymorphism of this com- pound have been reported for 33 selected oxides

.

The solid solution reported to occur in niobia for small cation additions

has been shown actually to consist of discrete phases, apparently isostructural with the mixed tantalum niobium oxide of formula Ta s 05.2Nbs 5 (Waring and

Roth, 1963) . The crystal structures of members of this series are being studied by Roth in collaboration with A. D. Wads ley in Australia.

Results of a study of the stability of bismuth- and stibio-tantalites

have been reported (Roth and Waring, 1963)

.

5.6 Allotropy in Some Rare-Earth Metals

at High Pressures

G. J. Piermarini and C. E. Weir,

Crystallography Section

Work on the lattice parameters and energies of the high-pressure polymorphs of some alkali halides (NBS Technical Note 197, Section 5.6) has been

completed (Weir and Piermarini, 1964a)

.

Most of the rare-earth metals have been obtained and are now being studied. Using an X-ray diffraction camera which incorporates a diamond-anvil

high-pressure cell, studies have been completed on lanthanum, cerium, praseodymium, and neodymium up to 60 kilobars (Piermarini and Weir, 1964b) . These

studies show that for each of these metals a high-pressure modification exists which has a face-centered cubic structure. Cerium was observed to undergo an electronic transition from an fee to a "collapsed" fee structure, cor- roborating previously published results. Apparently, the structural nature

of the transitions "in lanthanum, praseodymium, and neodymium (hep to fee) has never been reported.

* 5.7 Crystal Chemistry of Silver Iodide

G. Burley,

Crystallography Section

The general survey of solid-state properties of silver iodide has been

continued (compare NBS Technical Note 197, Section 5.11). The Debye temperature, strain distribution, and atomic arrangements near the p-a transition

temperature have been studied and some paramagnetic -resonance data from the

literature have been evaluated in terms of other behavior. The Debye temperature was evaluated both from the change of integrated intensities of a single

X-ray reflection over the range from 20° to 120°K for the cubic phase, and

from the variation of intensities with Bragg angle at room temperature for a single crystal of the hexagonal phase. These techniques gave values of 116°

and 119 °K, respectively, compared with 116 °K from heat-capacity data and

107 °K from elastic-moduli determined at room temperature.

Line-broadening analysis of finely ground polycrystalline silver iodide

compared with carefully annealed specimens indicated that the entire contribution to the difference of intrinsic breadth was due to strain and,

T<

" Research supported by the Atmospheric Sciences Program, National Science

Foundation.

53
essentially, not to the effects of small domain size. The strain is nearly

isotropic, with an average value of Ad/d = 4.4 x 10~ 3 and the calculated

stored elastic energy is 0.66 cal g

-1

. Because of the absence of higherorder reflections, analytical methods rather than the more precise Fourier

analysis of peak shapes had to be used.

The previous observation that ice crystals nucleated by freshly prepared

silver iodide smoke had a hexagonal habit, while those formed after exposing

the nuclei to strong light had a rectangular habit has been tentatively ex- plained. The change appears due to the differential rates of photolytic disordering on the prism and basal surfaces of silver iodide. The rate of ice

nucleation has been postulated elsewhere [Mason, Phil. Mag., 8, 505 (1963)]

to depend on the migration distance of surface atoms, so that growth is slowest on those surfaces allowing maximum movement. The preferential destruction of trapping sites on the prism faces during the initial stages of irradiation is then postulated to account for the observed change of habit.

A radial-distribution analysis of X-ray powder-diffraction patterns from

the low-cubic and hexagonal phases just above the transition of both to the

high-cubic phase has revealed substantial differences in bonding. An analysis of these in terms of specific-site occupation statistics is now in progress . Studies of polymorphism (Burley, 1963a) and of primary X-ray extinction

of polycrystalline samples exposed to light (Burley, 1963b) as well as latticemode analysis of the thermal-expansion behavior (Bienenstock and Burley, 1963)

have now been published.

5.8 Rapid X-Ray Diffraction Photography

of Polycrystalline Materials

R. E. LaVilla,

Crystal Chemistry Section

A miniature focusing camera has been fabricated and tested in conjunction

with a microfocus X-ray generator. From a 0.005 in. -thick copper shim-stock

specimen, a good powder pattern was obtained on X-ray film, with an exposure

(at 50 kV and 2.5 mA) of about 0.2 seconds and with unfiltered copper radiation from a 100-micron spot.

Present plans are to complete the installation of an electronic image

intensifier and to investigate the possibility of controlling the exposure

time by electronically pulsing the grid of an X-ray cathode gun. The possible

fabrication of a very high intensity pulsed X-ray tube with a disposable

target is also under study.

5.9 Structure of Silica Whiskers

H. C. Duecker and W. K. Haller,

Glass Section

The silica whiskers previously described (NBS Technical Note 197, Section 5.13) can be grown in a manner which yields a modification of silica un- like any known previously. The monochromatic X-ray diffraction pattern obtained from the finely ground whiskers is similar to that reported for vitreous silica except that several additional humps appear in the curve. The

radial-distribution curve calculated with the Debye scattering equation and

the method of Warren indicates interatomic distances corresponding to those

found in a pentagonal (Si-0) 5 ring. The calculated X-ray diffraction curve

for this ring model in turn has maxima corresponding to the humps found in

54
the experimental X-ray diffraction curve. Since the whiskers used in the

X-ray studies were known to be homogeneous (on the basis of refractive index

and density) the whiskers may be looked upon as partially ordered vitreous

silica.

5.10 Structure Models for Amorphous and Crystalline

Phases of Simple Substances

F . Ordway

,

Inorganic Solids Division

A random network of 300 tetrahedral units has been constructed and measurements have been made for the determination of all coordinates . A ringcounting routine has been written for the IBM 7090 computer and used with

the topological data for the model to tabulate the distribution of ring sizes.

Routines for processing the geometrical data are being prepared. A paper on

this work was presented at the Sixth Congress of the International Union of

Crystallography in Rome, September, 1963.

5.11 Radial-Distribution Studies of Glasses

S. Block and G. J. Piermarini,

Crystallography Section

In connection with a study of immiscibility , models were proposed for

the cation-modifier distribution in borate and silicate glasses. On the basis

of these models certain interatomic vectors are expected. X-ray diffraction

studies have been used to obtain independent information about these interatomic vectors. In the past several months, radial-distribution studies of

strontium borate glasses, in conjunction with previous studies on bariumand cadmium-containing glasses (Block, Molin, and Piermarini, 1963) have indicated a similarity of cation distribution in all these systems. This shortrange order is similar to that found in crystalline barium diborate, Ba0.2Ba 3 whose structure has been determined in this laboratory. Future work is planned to explore the limitations of the similarity of cation distribution in

the vitreous and crystalline states.

5.12 High-Resolution Small-Angle X-Ray Camera

H. Brumberger,

Crystal Cehmistry Section

A small-angle scattering camera, employing the Borrmann effect in germanium for collimation (see NBS Technical Note 197, Section 5.5) was assembled.

Test exposures gf the scattering from carbon indicate that spacings as large as about 2000 A are resolved.

A brief note giving details regarding the instrument has been prepared

and will be submitted for publication.

55
5.13 Physical Structure of Crystalline Copolymers

R. K. Eby,

Polymer Physics Section, and

L. H. Bolz,

Physical Properties Section

Electron microscopy and small-angle X-ray diffraction show copolymers

of tetrafluoroethylene and hexaf luoropropylene to be lamellar. Consideration

of lamellar thickness (typically 200 to 500 A) together with the concentration of perf luoromethyl groups indicates that the groups are incorporated in

the crystalline lamellae and therefore occur as point defects in the lattice

(Eby, 1963 and 1964) . The increase of lattice parameters which should ac- company the presence of these point defects has been observed in diffraction

patterns obtained with a powder camera at 23°C (Eby, 1964). However, this

result is subject to some question because the weak diffraction at large

angles makes correction for film shrinkage difficult. There is also another

question arising from the fact that polytetrafluoroethylene undergoes firstorder transitions at about 290 and 305°K. These transitions, at which both

the lattice parameters and the thermal coefficients of expansion increase, occur at lower temperatures in the copolymers [McCrum, Makromol. Chemie, 34 , 50 (1959)]. Thus, it can be asked whether the lattice of the copolymer is

larger than that of polytetraf luoroethylene at 23 °C, merely "because the co- polymer is at a higher temperature with respect to the phase transitions.

For these reasons, more accurate measurements have been made over a lower

temperature range with a diffractometer , a cold cell (Block et al., 1958)

and an "internal" standard of silicon. A thin layer of the standard was placed on the front surface of the samples and used, together with previous

measurements of silicon (Mauer and Bolz 1955) and [Novika and Strelkov,

Soviet Phys., Solid State, 1, 1687 (I960)] to keep the diffractometer adjusted. The data show the lattice of the copolymer to be larger than that of

polytetrafluoroethylene , even below the transition temperature, which is neai

225 °K for a copolymer with about six perf luoromethyl groups per hundred mainchain carbon atoms

.

5.14 High-Pressure Microscopy of Crystal

Transformation and Growth

A. Van Valkenberg,

Crystallography Section

Earlier work on the high-pressure microscopy of the silver and cuprous

halides (NBS Technical Note 197, Section 5.9) has been published

(Van Valkenburg, 1964).

The triple point of ice VI, ice VII, and liquid water has been observed

under the microscope at a pressure of 22.4 kilobars and a temperature of 80°

C. At the triple point, skeletal crystals of ice VI and VII can be observed

forming and melting in the liquid phase with considerable activity. The

triple point has been approached by three independent routes following the

boundary lines between (1) ice VI and liquid, (2) ice VI and ice VII, and

(3) ice VII and liquid. It was observed that the birefringence of ice VI

decreases as the triple point is approached. It was also observed that the

refractive indices of ice VI approached that of the liquid phase as the

triple point is approached. The sensitivity of this triple point to slight

changes of pressure or temperature is very high and it should make a good

reference point.

Using a gasketing technique with the diamond cell, we observed optical

changes in single crystals or crystal fragments (.2 mm in length) at hydrostatic pressures up to 30 kilobars and a temperature of 150 °C. Kerosene is

56
one of the liquids used to obtain hydrostatic conditions at a pressure of approximately 15-20 kilobars . It was observed that kerosene changes to a mush

of crystallites and liquid above 10 kilobars. The crystallites appear to

have a low birefringence and the liquid is somewhat viscous.

Calcium carbonate has two reversible transitions, one at 14 kilobars and

the other at 17 kilobars at room temperature. These two transitions were observed in single-crystal fragments under hydrostatic conditions with temperature changes of up to 100 °C. The transition at 14 kilobars was observed as

a barely perceptible wave crossing the crystal fragment. This transition is

interpreted as being a slight change in the symmetry of the crystal similar

to the a-p transition in quartz. The second transition at 17 kilobars has a volume change of 2 . 77o according to Bridgman and this transition can readily

be observed as a sluggish wave front passing from one end of the crystal to

the other. The crystal changes from one having a uniform birefringence to one of distorted birefringence, suggesting a change from an ordered to a disordered structure. When pressure is released there is a reverse transition

and the birefringence becomes uniform.

5.15 Optical Observations of Pressure-Induced

Transformation in Polymers

J . Powers

,

Macromolecules: Synthesis and Structure Section

Light- transmission measurements previously reported (NBS Technical Note

197, Section 5.8) were continued. The transmission of the diamond anvils

with no sample between them has been measured. The transmission of natural

rubber has been determined. The resulting curve does not show the abrupt

transmission increase over a narrow pressure range exhibited by Teflon and

several other semi-crystalline polymers. Ancillary studies using densitygradient tubes on the effect of compression upon polymer density have been

started.

5.16 Infrared Spectroscopy of Crystalline

Inorganic Borates

C. E. Weir and R. A. Schroeder,

Crystallography Section

Plans for this work were announced in NBS Technical Note 197, Section

5.7. Infrared spectra have been obtained on a large number of crystalline

inorganic borates at room temperature. The data have been compiled and the

results are being prepared for publication.

At the present time, it can be concluded that the spectra of most orthoborates and pyroborates can be interpreted in terms of vibrations of the B0 3 and Bs 5 groups, respectively, and consistent assignments of the observed

bands can be made. For some metaborates a satisfactory assignment of the

spectra can also be given, but the borates having anions with ring structures

generally show spectra of such complexity that even a superficial interpretation is not possible. From correlations between spectra and structure it is

believed that both 3-fold and 4-fold coordinated boron can be identified with

reasonable assurance on the basis of the infrared-absorption spectrum alone.

Very good correlations between structure and spectra have been observed in

many instances

.

57
5.17 Crystal-Field Studies by Matrix Spectroscopy

D . E . Mann , Molecular Spectroscopy Section

The investigation of crystal-field effects through their influence on the infrared spectra of hydrogen and deuterium-halide molecules isolated in

argon and other matrices at low temperatures has been carried to an advanced

stage. The vibration-rotation spectrum of HC1 in argon in the range 4-20°K

has served as the basis of a theoretical analysis recently published by

Flygare [J. Chem. Phys .

, 39, 2263 (1963)] in which it is shown that for an octahedral site the major effect is that due to the interaction of a permanent molecular hexadecapole charge distribution with the fourth gradient

of the electric potential at the molecular center of mass. The results for

DC1 however, indicate that the theory does not yet adequately account for

the interaction of the center of mass motion with molecular rotation, and

remains to be further developed. However, the main features of the HC1 spectra are accounted for.

The non-rotating features in the spectra have been subjected to very

intensive investigation during the past year. In particular, the widths and

positions of the so-called Q lines for HC1 in argon and krypton have been

measured with very high resolving power over a considerable temperature

range — up to 51°K in krypton. It was found that the lines are remarkably

narrow, their width being of the order of 0.15 - 0.25 cm

-1

, and that both

the widths and line positions show a small but definite temperature dependence. Moreover, it was discovered after a long series of careful measurements that initial conditions — deposition rate, concentration, substrate,

and impurities — have a pronounced effect on the proportion of rotating to

non-rotating features in the spectra. Now that these factors have been sorted out, the influence of the nature of the site, the phase, and indeed the

crystallization process itself can come under detailed study with the assiS'

tance of the molecular spectrum as an indicator.

5.18 Spectroscopy of Diatomic Impurities

in Rare-Gas Crystalline Matrices

G. L. Pollack,

Crystal Chemistry Section

The effect of impurities on crystal growth and the mechanism of zone re- fining for molecular crystals at low temperatures have been studied by ex- amining absorption spectra of diatomic species in argon and krypton (Pollack,

1964). The experiments are also of spectroscopic interest. Some transitions

have been observed which may be due to charge exchange in the solution lattices, or to perturbation of energy levels in otherwise forbidden transitions

so that they are allowed.

5.19 Molecular Energy Levels

S . Abramowitz

,

Heat Division

A study of the infrared absorption spectra of carbon monoxide, CO, and

methane, CH4 , in condensed phases of oxygen, nitrogen, and argon has been

made

.

The v 3 fundamental of CH4 was found at 3017 cm

-1 in an oxygen solution

with a half width of 18cm" 1

. The position and half width in liquid oxygen

were the same at 90°, 78°, and 55 °K. In liquid nitrogen at 78 °K, the v 3 vibration was located at 3016 cm

-1

, and in liquid argon at about 80°K at

58
3018 cm

-1

, with half widths of 17 and 23cm-1

, respectively. In a clear crystalline argon solid the peak was located at 3023 cm

-1 with a half width of

25cm_1. This was the only system in which a blue shift relative to the Q

branch maximum vapor frequency of 3019 cm-1 was observed.

Infrared absorption spectra of CO in the region of the first overtone

have been observed in dilute (approximately 1 to 10 parts in 1000) liquid

solutions of oxygen, nitrogen, and argon, and clear crystalline nitrogen and

argon matrices. The overtone band was found at 4249.0, 4252.4, and 4252.0

cm

-1 with half widths of 18.4, 17.8, and 13.7cm" 1 in liquid oxygen, nitrogen,

and argon solutions at 82 °K and 78 °K, respectively. The half width in liquid

oxygen varied from 18.4 to 10.0cm-1 in the temperature range 82°K to 57°K.

The band position was the same but its width was smaller in the crystalline

nitrogen matrix. Two bands were observed in the clear crystalline argon solid at 4245 and 4256 cm

-1

. The solution results cannot be interpreted with

the recent theory of Buckingham, nor can the temperature dependence of the

half width observed in liquid oxygen be explained with existing models.

The work on methane has been published by Abramowitz and Broida (1963)

.

6. PARTIAL LIST OF PARTICIPANTS

There follows a partial list of scientists engaged

in activities described in this note, with indications

of their research fields and organizational location within the National Bureau of Standards. The latter may be

helpful in making contact with individuals for the purpose

of obtaining reprints or further technical information.

Participants at the Washington Laboratories : Abramowitz. Stanley : Ph.D. Polytechnic Institute of Brooklyn, 1963; infrared molecular spectra; Heat Division. Author: 5.19

Allen. Harry C., Jr. : Ph.D. University of Washington, 1951; electron-spinresonance studies; Chief, Inorganic Solids Division. Author: 4.16

Ambler, Ernest : Ph.D. Oxford University England, 1953; nuclear reactions,

low- temperature magnetism; Chief, Cryogenic Physics Section, Heat Division.

Anderson, Richard L. : Growth and evaporation of whiskers; Cryogenic Physics

Section, Heat Division. Author: 2.21

Barber , David J

.

: Ph.D. University of Bristol, England, 1959; growth perfection of crystals; Physical Properties Section, Inorganic Solids Division.

Author: 3.4

Bass , Arnold M. : Ph.D. Duke University, 1949; molecular spectroscopy; Heat

Division

.

Becker, James H. : Ph.D. Cornell University, 1957; optical and transport properties of semiconductors; Solid State Physics Section, Atomic Physics Division. Author: 4.4

Block, Stanley : Ph.D. Johns Hopkins University, 1955; X-ray crystallography;

Crystallography Section, Inorganic Solids Division. Author: 5.1; 5. 11

Blunt, Robert F

.

: Ph.D. Rice University, 1949; optical properties of solids;

Solid State Physics Section, Atomic Physics Division. Author: 3.2

Bolz, Leonard H. : Crystal perfection by electron microscopy; Physical Properties Section, Inorganic Solids Division. Author: 5.13

Bowman , Horace A

.

: Cartesian diver; Mass and Volume Section, Metrology Division

.

Breen, David E

.

: Inter- and intramolecular properties of organic molecules,

crystals, and rigid glasses; Physical Chemistry Division. Author: 4.8

Brower, William S. : Crystal growth by Verneuil process and floating-zone

technique; Crystal Chemistry Section, Inorganic Solids Division.

Author: 2.5

Brown. Walter E. : Ph.D. Harvard University, 1949; solubility and crystallography of calcium phosphate; Dental Research Section, Polymers Division.

Author: 5.2

59
Brumberger, Harry : Ph.D. Brooklyn Polytechnic Institute, 1955; low-angle Xray scattering, critical phenomena, and structure of liquids; present address:

Chemistry Dept., Syracuse University. Author: 5.12

Bur ley, Gordon : Ph.D. Georgetown University, 1962; crystallography of silver

iodide; Crystallography Section, Inorganic Solids Division. Author: 4. 21; 5.

Calvert, Joan P. : Growth of oxide films; Corrosion Section, Metallurgy Division

.

Cataland. George : Low-temperature thermometry; Cryogenic Physics Section,

Heat Division. Author: 4.9

Chang Te-Tse : Ph.D. University of Colorado, 1962; magnetic resonance; Solid

State Physics Section, Atomic Physics Division. Author: 4.13

Cohen, Martin I. : X-ray Diffraction studies of crystals grown at high temperatures^ Solid State Physics Section, Atomic Physics Division.

Author: 3. 15; 3. 19

Cook Richard K. : Ph.D. University of Illinois, 1935; acoustics and solid

state physics; Chief, Sound Section, Mechanics Division.

Cooter, Irvin L. : Nuclear magnetic resonance in garnets; Chief, Magnetic Measurement Section, Electricity Division.

Coriell, Sam R. : Ph.D. Ohio State University, 1961; mathematical physics;

Cyrstallization of Metals Section, Metallurgy Division. Author: 2.4

Crissman, John M. : Ph.D. Pennsylvania State University, 1963; polymer physics;

Postdoctoral Fellow, Polymer Physics Section, Polymers Division.

Author: 2.11

deKoranyi, Alexandra : Crystal growth by electrodeposition, Electrolysis and

Metal Deposition Section, Metallurgy Division. Author: 3.10

Deslattes, Richard D

.

: Ph.D. Johns Hopkins University, 1959; X-ray spectroscopy; Crystal Chemistry Section, Inorganic Solids Division. Author: 3. 13; 4. 22

deWit, Roland : Ph.D. University of Illinois, 1959; dislocation theory;

Lattice Defects and Micros tructures Section, Metallurgy Division.

Author: 2.3; 3.9

Dickson, Robert W. : Homogeneous stress on oxide structures; dislocation studies by X-ray methods; Physical Properties Section, Inorganic Solids Division.

Author: 2.1; 4.1

Dove, Robert B. : Nuclear magnetism; Cryogenic Physics Section, Heat Division.

Author: 4. 17

Duecker, Heyman C : Physical chemistry of glasses; Glass Section, Inorganic

Solids Division. Author: 5.9

Early, James G. : Ph.D. Rennsalaer Polytechnic Institute, 1963; kinetics of

crystallization; Crystallization of Metals Section, Metallurgy Division.

Author: 2.2

Eby, Ronald K. : Ph.D. Brown University, 1958; acoustics, polymer physics;

Polymer Physics Section, Polymers Division. Author: 5.13

Edlow Martin E

.

: Low- temperature thermometry; Cryogenic Physics Section,

Heat Division. Author: 4.9

Eisenstein, Julian C : Ph.D. Harvard University, 1948; low- temperature

magnetism; Cryogenic Physics Section, Heat Division.

Escalante, Edward : Field emission; Corrosion Section, Metallurgy Division.

Author: 2.24

Evans, Eloise H. : Physical chemistry, X-ray diffraction; Crystallography

Section, Inorganic Solids Division, A.S.T.M. Fellowship supported.

Farabaugh, Edward N. : Etch-pits crystal orientation; Crystal Chemistry Section, Inorganic Solids Division. Author: 2.5

Foley, Carol L. : Growth of oxide films; Corrosion Section, Metallurgy Division. Author: 3.5

Forman, Richard A. : Nuclear and quadrupole resonance; Solid State Physics

Section, Atomic Physics Division. Author: 4.13

Franklin, Alan P. : Ph.D. Princeton University, 1949; properties of point

defects in crystals; c/o Inorganic Solids Division.

Frederikse, Hans p R. : Ph.D. Leiden University, the Netherlands, 1950;

semiconductors at low temperatures; Chief, Solid State Physics Section,

Atomic Physics Division. Author: 4.4

French, Judson C : Solid state divices and materials; Electron Devices

Section, Instrumentation Division. Author: 3.12

60
Frolen, Lois J. : Ph.D. Pennsylvania State University, 1963; spectroscopy,

crystallography, microscopy; Analytical Chemistry Division.

Author: 2 .9,2 . 10; 3. 17

Glasgow, Augustus R. : D. Sc. University of Brussels, 1957; preparation and

purification of polymeric forms, phase equilibria, purity determinations at

high pressures; Analytical and Purification Section, Analytical Chemistry

Division

.

Gqrnick Fred: Ph.D. University of Pennsylvania, 1959; physical chemistry

of high polymers; Polymers Division. Author: 2.10

Grabner , Ludwig H

.

: Ph.D. Columbia University, 1950; semiconductors, photoconductivity ,

; Solid State Physics Section, Atomic Physics Division.

Author: 3.18

Greenspan , Martin : Ultrasonics, mechanics; Sound Section, Mechanics Division.

Haller Wolfgang K. : Ph.D. University of Vienna, 1950; physical chemistry

of glasses; Glass Section, Inorganic Solids Division. Author: 5.9

Hardy Stephen C : Vapor growth of metal crystals; Crystallization of Metals

Section, Metallurgy Division. Author: 2.21; 2.23

Harman . George G. : Solid state physics, surface phenomena and electroluminescence; Electron Devices Section, Instrumentation Division. Author: 3.12

Hoffman, John P. : Ph.D. Princeton University, 1949; dielectrics, nucleation

rate of polymer crystals; Chief, Polymers Division. Author: 2.13

Horton, Avery T. : Crystal growth, impurity retention; Crystal Chemistry

Section, Inorganic Solids Division. Author: 2.8

Hosier, William R. : Electronic transport phenomena; Solid State Physics

Section, Atomic Physics Division. Author: 4.4

Howard, Robert E. : Ph.D. Oxford University, England, 1957; theoretical

physics; Chief, Metal Physics Section, Metallurgy Division. Author: 2.3; 2.22

Hudson, Ralph P. : Ph.D. Oxford University, England, 1949; low- temperature

magnetism; Chief, Heat Division. Author: 3.1

Ives, Lewis K. : Electron microscopy; Lattice Defects and Micros true tures

Section, Metallurgy Division. Author: 2.19

Kaeser, Robert S. : Low -temperature magnetism, cryogenics; Cryogenic Physics

Section, Heat Division. Author: 4.17

Kahn . Arnold H. : Ph.D. University of California, 1955; band structure of

rutile crystals, paramagnetic impurities in rutile crystals; Solid State

Physics Section, Atomic Physics Division. Author: 4.3

Keezer . Richard C

.

: Optical properties and physical chemistry of semiconductors; Solid State Physics Section, Atomic Physics Division.

Author: 3.18

Keller, Richard A. : Ph.D. University of California, 1961; inter- and intramolecular properties of organic molecules, crystals, and rigid glasses;

Physical Chemistry Division. Author: 4.8

Khoury, Fred : Ph.D. Leeds University, 1956; morphology and crystallization

of polymers; Polymer Physics Section, Polymers Division. Author: 2.14

Klein. Ralph : Ph.D. University of Pittsburg, 1950; field-emission and lowtemperature chemistry; Chief, Surface Chemistry Section, Physical Chemistry

Division. Author: 4.19

Kokoszka, Gerald F. : Electron-spin-resonance studies; Inorganic Solids

Division. Author: 4.16

Kruger , Jerome : Ph.D. University of Virginia, 1953; corrosion reactions at

metal surfaces; Corrosion Section, Metallurgy Division. Author: 3.5

LaVilla, Robert E. : Ph.D. Cornell University, 1960; study of transient

phenomena by diffraction techniques; Crystal Chemistry Section, Inorganic

Solids Division. Author: 5.8

Levin, Ernest M. : Phase equilibria of oxide systems; Crystallography Section,

Inorganic Solids Division. Author: 5.5

Lippincott, Ellis R. : Ph.D. Johns Hopkins University, 1947; infrared spectroscopy; Crystallography Section, Inorganic Solids Division.

Mangum, Billy W. : Ph.D. University of Chicago, 1961; low-temperature magnetism; Cryogenic Physics Section, Heat Division. Author: 3.1

Mann, David E

.

: Ph.D. University of Chicago, 1948; spectroscopy; Chief,

Molecular Spectroscopy Section, Physical Chemistry Division. Author: 5.17

61
Margoshes , Marvin : Ph.D. Iowa State University, 1953; spectrographic analysis; Spectrochemical Analysis Section, Analytical Chemistry Division.

Author: 3.3

Marshak, Harvey: Ph.D. Duke University, 1955; nuclear reactions, cryogenics;

Cryogenic Physics Section, Heat Division. Author: 4.17

Marvin Robert S

.

: Ph.D. University of Wisconsin, 1949; rheology and polymer physics; Chief, Rheology Section, Mechanics Division.

Mauer, Floyd A. : Instrumentation for crystallography; Crystallography Section,

Inorganic Solids Division. Author: 3.14

McMurdie , Howard F

.

: Crystallography and chemical phase studies; Chief,

Crys ta llography Section, Inorganic Solids Division.

McNish, Alvin G. : Precise density determinations for solid materials; Chief,

Metrology Division

.

Miller, Paul R. : High- temperature crystal growth, crystal orientation; Crystal Chemistry Section, Inorganic Solids Division. Author: 2.6

Milligan , Dolphus E. : Ph.D. University of California, 1958; molecular spectroscopy; Molecular Spectroscopy Section, Physical Chemistry Division.

Moreno, Edgard C : Ph.D. University of California, 1957; physical chemistry;

Dental Research Section, Polymers Division. Author: 5.2

Morris , Marlene C

.

: Physical chemistry, X-ray diffraction; Crystallography

Section, Inorganic Solids Division, A.S.T.M. Fellowship supported.

Ogburn , Fielding : Electrochemistry, electrodeposition; Electrolysis and

Metal Deposition Section, Metallurgy Division. Author: 2 . 16; 2 . 17;3 . 10

Ondik, Helen M. : Ph.D. Johns Hopkins University, 1957; crystallography,

inorganic chemistry; Crystallography Section, Inorganic Solids Division.

Author: 5.1

Ordway, Fred : Ph.D. California Institute of Technology, 1949; X-ray crystallography; Inorganic Solids Division. Author: 2. 6; 5. 10

Orem, Theodore H.: Mechanisms of corrosion processes; Corrosion Section,

Metallurgy Division. Author: 2.1; 3. 11

Oser , Hans J. : Ph.D. University of Freiburg, 1957; boundary value problems;

Applied Mathematics Division. Author: 2.22

Paretzkin, Boris : Study of perfection of single crystlas by X-ray diffraction; Crystal Chemistry Section, Inorganic Solids Division.

Author: 2. 17; 3. 16

Parker, Robert L. : Ph.D. University of Maryland, 1960; growth of crystals;

Chief, Crystallization of Metals Section, Metallurgy Division.

Author: 2 . 1 ; 2 . 2 ; 2 .4; 2 . 21; 2 . 22 ; 2 . 23

Passaglia, Elio : Ph.D. University of Pennsylvania, 1955; mechanical relaxation processes in polymers; Polymer Physics Division. Author: 2.11

Payne, Richard E. : Nuclear resonance; Solid State Physics Section, Atomic

Physics Division. Author: 4.13

Peiser, H. Steffen : Crystallography and crystal chemistry; Chief, Crystal

Chemistry Section, Inorganic Solids Division. Author: 2 . 17; 3 .7; 3. 16

Perloff, Alvin : Structure analysis; Crystallography Section, Inorganic

Solids Division. Author: 5.1

Pfeiffer, Earl R. : Crystal growth from solution; Cryogenic Physics Section,

Heat Division.

Piermarini, Gasper J. : Radial-distribution studies; high-pressure X-ray

diffraction studies; Crystallography Section, Inorganic Solids Division.

Author: 5. 6; 5. 11

Plumb, Harmon H. : Ph.D. Northwestern University, 1954; low-temperature

thermometry; Cryogenic Physics Section, Heat Division. Author: 4.9

Pollack, Gerald L. : Ph.D. California Institute of Technology, 1962; lowtemperature physics; Crystal Chemistry Section, Inorganic Solids Division.

Author: 2. 18; 5. 18

Pontius Paul E

.

: Accurate measurements of mass, volume, and density; Chief,

Mass and Volume Section, Metrology Division.

Powers , Joseph : Ph.D. University of Massachusetts, 1961; kinetics, morphology , and mechanism of crystallization of polymers; Macromolecules : Synthesis and Structure Section, Polymers Division. Author: 2 . 15; 4. 11; 5 . 15

Proctor, Thomas M .: Solid state physics; Sound Section, Mechanics Division.

62
Quinn, Fred A. : Crystallization rate of high polymers; Macromolecules: Synthesis and Structure Section, Polymers Division. Author: 4.11

Rasberry , S tan ley D

.

: Spectrographic analysis; Spectrochemical Analysis Section, Analytical Chemistry Division. Author: 3.3

Read, Susan F.J. : Ph.D. Oxford University, England, 1963; solid state physics:

Temperature Physics Section, Heat Division.

Robbins , Carl R. : Phase-rule equilibria of inorganic systems; Crystallography Section, Inorganic Solids Division.

Roberts, D. Ellis : Crystal growth; Solid State Physics Section, Atomic Physics Division. Author: 2.7

Robinson, Henry E. : Thermal conductivity measurement on solids at high and

low temperatures; Chief, Heat Transfer Section, Building Research Division.

Ross, GayIon S

.

: Nucleation, crystal growth; Analytical Chemistry Division.

Author: 2 .9; 2 . 10; 3 . 17

Roth, Robert S

.

: Ph.D. University of Illinois, 1951; X-ray diffraction studies, phase equilibria; Crystallography Section, Inorganic Solids Division.

Author: 5.5

Rubin, Robert J. : Ph.D. Cornell University, 1951; theoretical chemical physics; Heat Division.

Rubin, Sherwin : Electronic engineering; Engineering Electronics Section, Instrumentation Division. Author: 4.5

Ruff, Arthur W. : Ph.D. University of Maryland, 1963; dislocations and etch

pits; Chief, Lattice Defects and Micros tructures Section, Metallurgy Division.

Author: 2. 19; 3.

8

Ruthberg, Stanley : Materials and physics of vacuum devices; Electron Devices

Section, Instrumentation Division.

Saylor, Charles P. : Ph.D. Cornell University, 1928; precise characteristics

of compounds, accurate microscopic measurements of optical properties; Analytical Chemistry Division.

Schafft, Harry A. : Semiconductor devices and breakdown phenomena; Electron

Devices Section, Instrumentation Division. Author: 3.12

Schneider, Samuel J. : Phase equilibria of oxide systems and melting-point

standards; Crystallography Section, Inorganic Solids Division. Author: 4.10

Schooley, James F. : Ph.D. University of California, 1961; crystal growth for

low- temperature paramagnetic studies; Cryogenic Physics Section, Heat Division. Author: 4.12

Schoonover, Irl C : Ph.D. Princeton University, 1933; research administration, NBS Deputy Director.

Schroeder, Rudolph A. : Ph.D. University of Maryland, 1957; infrared spectroscopy; Crystallography Section, Inorganic Solids Division. Author: 5.16

Scribner, Bourdon F. : Analytical applications of optical and X-ray spectroscopy; Chief, Spectrochemical Analysis Section, Analytical Chemistry Division.

Author: 3.3

Simmons, John A. : Ph.D. University of California, 1961; mathematical physics;

Metal Physics Section, Metallurgy Division. Author: 2.22

Spinner, Sam: Elastic properties of inorganic solids; Physical Properties

Section, Inorganic Solids Division. ' Author: 3.6;4.1

Streever, Ralph L. : Ph.D. Rutgers University, 1960; nuclear magnetic resonance; Magnetic Measurements Section, Electricity Division. Author: 4.15

Swanson, Howard E. : Physical chemistry, X-ray diffraction; Crystallography

Section, Inorganic Solids Division. Author: 5.3;5.4

Swartzendruber , Lydon J. : Solid state physics; Electron Devices Section,

Instrumentation Division. Author: 3.12

Termini, Dominic J. : Nucleation and crystal growth; Analytical Chemistry

Division. Author: 2.10

Thurber, Willis R. : Thermoelectricity; Solid State Physics Section, Atomic

Physics Division. Author: 4.4

Tighe, Nancy J

.

: Defect studies by electron microscopy of non-metallic crystals; Physical Properties Section, Inorganic Solids Division. Author: 3.4

Torgesen, John L. : Ph.D. Columbia University, 1942; crystal growth from

solutions, impurity retentions, crystal properties; Crystal Chemistry Section,

Inorganic Solids Division. Author: 2.8

63
Vacher , Herbert C

.

: X-ray diffraction; Metallurgy Division. Author: 2.1

Van Valkenburg, Alvin : High-pressure transitions; Crystallography Section,

Inorganic Solids Division. Author: 5.14

Wachtman , John B., Jr. : Ph.D. University of Maryland, 1961; mechanical and

electrical properties of crystals; Chief, Physical Properties Section, Inorganic Solids Division. Author: 3.6;.3.7;4.1

Wagman , Donald D

.

: Thermochemistry and chemical thermodynamics; Chief,

Thermochemistry Section, Physical Chemistry Division. Author: 3.20

Wagner, Timothy : Growth and evaporation of whiskers; Crystallization of

Metals Section , Metallurgy Division. Author: 2.21

Wasilik, John H. : Ph.D. Catholic University, 1956; dielectric constant and

losses, ultrasonics; Solid State Physics Section, Atomic Physics Division.

Author: 4.6

Weeks, James J. : Measurements of dielectric properties of polymers, crystallization arid melting of polymers; Dielectric Section, Electricity Division.

Author: 2.12

Weir, Charles E. : Infrared spectroscopy and high-pressure physics; Crystallography Section, Inorganic Solids Division. Author: 5. 6; 5. 16

Wiederhorn, Sheldon M. : Ph.D. University of Illinois, 1960; optical properties of high pressure, fracture of solids; Physical Properties Section, Inorganic Solids Division. Author: 4.2

Will, Richard S. : Electron-field emission; Electron Physics Section, Atomic

Physics Division.

Yolken, Howard T. : Growth of oxide films; Corrosion Section, Metallurgy

Division. Author: 3.5

Young, John D. : Crystal growth by electrodeposition; Electrolysis and Metal

Deposition Section, Metallurgy Division. Author: 2.16

Young, Russell P. : Ph.D. Pennsylvania State University, 1959; surface physics , particularly with the field-emission microscope; Electron Physics Section, Atomic Physics Division. Author: 2.25

Participants at the Boulder Laboratories

Arp, Vincent D

.

: Ph.D. University of California, 1959; superconductivity;

Cryogenic Properties of Solids Section, Cryogenic Engineering Laboratory.

Author: 4.20

Bamberger, Edwin C : Dielectric measurements; Radio and Microwave Materials

Section, Radio Standards Physics Division. Author: 4.7

Bussey, Howard E. : Ph.D. University of Colorado, 1964; magnetism and ferrites; Radio and Microwave Materials Section, Author: 4.18

Cook, Alan R. : Physical instrumentation; Radio and Microwave Materials Section, Radio Standards Physics Division. Author: 4.14

Da Ike, John L. : Characterization of materials at radio frequencies; Chief,

Radio and Microwave Materials Section, Radio Standards Physics Division.

Author: 4.7

Gruzensky, Paul M. : Ph.D. Oregon State College, 1959; physical chemistry

and high-purity materials; Radio and Microwave Materials Section, Radio

Standards Physics Division.

Guntner, Charles S. : Imperfections, flow and fracture, phase transformations;

Properties of Materials Section, Cryogenics Engineering Laboratories.

Jefferson, Clinton F. : Ph.D. University of Michigan, 1959; solid solution

for ferrimagnetic characteristics; Radio and Microwave Materials Section,

Radio Standards Physics Division.

Mahler, Robert J. : Ph.D. University of Colorado, 1963; solid state physics;

Radio and Microwave Materials Section, Radio Standards Physics Division.

Author: 4.14

Matarrese, Lawrence M. : Ph.D. University of Chicago, 1954; solid state physics, EPR resonance spectroscopy related to solid state mechanisms; Radio and

Microwave Materials Section, Radio Standards Physics Division .Author: 4.14

Peterson, Robert L. : Ph.D. Lehigh University, 1959; theoretical physics;

Radio and Microwave Materials Section, Radio Standards Physics Division.

Author: 4.14

64
Powell, Robert L. : Thermal and electrical conduction of metals at low-temperatures; Properties of Materials Section, Cryogenic Engineering Laboratory.

Reed, Richard P. : Imperfections, flow and fracture, phase transformations;

Properties of Materials Section, Cryogenic Engineering Laboratory.

Risley. Alan S. : Magnetism and ferrites; Radio and Microwave Materials Section, Radio Standards Physics Division. Author: 4.18

Wells , Joseph S

.

: Ph.D. University of Colorado, 1964; microwave physics,

solid state physics relating to ENDOR and NMR; Radio and Microwave Materials

Section, Radio Standards Physics Division. Author: 4.14

Winder, Dale R. : Ph.D. Case Institute of Technology, 1957; solid state physics ; Radio and Microwave Materials Section, Radio Standards Physics Division.

Author: 2.20

7. LITERATURE REFERENCES

S. Abramowitz and H. P. Broida (1963): Vibration of Methane in Condensed

Oxygen, Nitrogen, and Argon; J. Chem. Phys . , 39_, 2383.

A. Bienenstock and G. Burley (1963): Thermal Expansion of Silver Iodide; J.

Phys. Chem. Solids, 24, 1271.

I. A. Black, L. H. Bolz, F. P. Brooks, F. A. Mauer, and H. S. Peiser (1958):

A Liquid-Helium Cold Cell for the Use with an X-Ray Diffractometer; J. Res.

Nat'l. Bur. Standards, 61, 367.

S. Block, J. Molin, and G. Piermarini (1963): X-Ray Study of a Cadmium Borate Glass; J. Am. Ceram. Soc, 46, (11), 557.

S. Block and A. Perloff (1963): The Direct Determination of the Crystal

Structure of NaB(OH)

4

.2H

2 0; Acta Cryst., J16, 1233.

G. Burley (1963a): Polymorphism of Silver Iodide; Am. Mineral., 48, 1266.

G. Burley (1963b): Photolytic Behavior of Silver Iodide; J. Res. Nat'l. Bur.

Standards, 67A, 301.

R. deWit (1963): On the Growth of Helical Dislocations; Trans. AIME, 227,

1443.

R. K. Eby (1963): First Order Transition Temperature in Crystalline Polymers; J. Appl. Phys., 34, 2442.

R. K. Eby (1964): An Example of a Lamellar Copolymer; J. Res. Nat'l. Bur.

Standards, ^8A, (3) . R. A. Forman (1963): Nitrogen NMR Chemical Shifts in the Azide Ion; J. Chem.

Phys. . 39, 2393.

R. A. Forman and D. R. Like, Jr. (1963): Quadrupole Coupling Constants from

the Microwave Spectrum of Hydrazoic Acid; J. Chem. Phys., 39/, 1133.

A. D. Franklin (1963): Relaxation Modes for Trapped Crystal Point Defects;

J. Res. Nat'l. Bur. Standards, 67A , 291.

A. D. Franklin, A. Shorb, and J. B. Wachtman , Jr. (1964): Relaxation Modes

of Trapped Crystal Point Defects; a lecture to Brit. Ceram. Soc, Oct., 1963;

for future publication in Trans. Brit. Ceram. Soc.

H. P. R. Frederikse, W. R. Thurber, and W. R. Hosier: Electronic Transport

in Strontium Titanate; Phys. Rev., (accepted).

W. C. Hernandez, Jr. and A. H. Kahn (1963): A Note on the Ga Ivan omagnetic

and Thermoelectric Coefficients of Tetragonal Crystalline Materials; J. Res.

Nat'l Bur. Standards, 67A, 293.

R. P. Hudson and B. W. Mangum (1963): Audio Frequency Dispersion Effects in

Lanthanide Salts at Low Temperatures, in Magnetic and Electric Resonance and

Relaxation ; Wiley & Sons, Inc., J. Smidt, Tech. Univ. Delft, the Netherlands.

E. M. Levin and R. S. Roth (1964): Polymorphism of Bismuth Sesquioxide - I. Pure Bi3 3 . II. Effect of Oxide Additions on the Polymorphism of Bi2 0,;

J. Res. Nat'l. Bur. Standards, 68A, (2).

65
F. A. Mauer and L. H. Bolz (1955): Measurement of Thermal Expansion of Cermet Components by High-Temperature X-Ray Diffraction; W A D C Technical Report,

55-474, 18.

F. Ogburn and C. Newton (1963): Relation of Partial (110) Pole Figures to

Thickness and Microstructure of Electrodeposited Copper; J. Electrochem. Soc,

110 1148.

F. Ogburn, B. Paretzkin , and H. S. Peiser (1964): Pseudopentagonal Twins in

Electrodeposited Copper Dendrites; Acta Cryst., 17 , (accepted).

R. L. Parker, R. L. Anderson, and S.C. Hardy (1963): Growth and Evaporation

Kinetics and Surface Diffusion of K and Hg Crystal Whiskers; Appl. Phys. Lett.,

3, 93.

R. L. Parker and A. Krinsky (1963): Electrical Resistance-Strain Characteristics of Thin Evaporated Metal Films; J. Appl. Phys., J34, 2700.

H. S. Peiser, J. B. Wachtman , Jr., and R. W. Dickson (1963): Reduction of

Space Groups to Subgroups by Homogeneous Strain; J. Res. Nat'l. Bur. Standards, _67A, 395.

A Perloff (1964): The Crystal Structure of 1-Ethyldecaborane; Acta Cryst.,

(accepted)

.

G. L. Pollack (1964): Absorption Spectra of Diatomic Molecules in Liquid

and Crystalline Rare Gases; Advances in Applied Spectroscopy , Plenum Press,

New York, (accepted)

.

F. A. Quinn, Jr. and J. Powers (1963): Measurements of a Maximum in the

Isothermal Crystallization Rate Temperature Curve for Polypentene-1; J.

Polymer Sci. , Part B., 1, 341.

G. S. Ross and L. J. Frolen (1963): Chemical Purity by Dielectric Cryometry;

J. Res. Nat'l. Bur. Standards, 67A , 607.

R. S. Roth and J. L. Waring (1963): Synthesis and Stability of Bismutotantalite, Stibotantalite, and Chemically Similar ABO/ Compounds; Am. Mineral.,

48, (11 & 12) 1348. *

S. Ruthberg (1963): Thermal Behavior of Muscovite Sheet Mica; J. Res. Nat'l.

Bur. Standards, 67A, 585.

S. Ruthberg, M. W. Barnes, and R. H. Noyce (1963): Correlation of Muscovite

Sheet Mica on the Basis of Color, Apparent Optic Angle and Absorption Spectrum; J. Res. Nat'l. Bur. Standards, 67A , 309.

H. A. Schafft and J. C. French (1963): Second Breakdown; Effects of Base

Drive and Structural Defects; a talk presented at the Electron Devices Meeting in Washington, D. C. Oct. 31, and printed as NBS Report No. 8122, Nov. 6.

S. J. Schneider (1963a): Compilation of the Melting Points of the Metal

Ozides; Nat'l Bur. Standards Monograph, 68 . S. J. Schneider (1963b): Discrepancy in the Conversion of Early Melting

Point Temperatures; J. Am. Ceram. Soc, 46, 354.

J. Simmons, R. W. Howard, and R. L. Parker (1964): Theory of Whisker Growth

and Evaporation; J. Appl. Phys., (accepted).

J. Simmons R. L. Parker, and R. W. Howard (1964): Kinetics of Growth and

Evaporation of Metal Whiskers; Bull. Am. Phys. Soc. (Philadelphia Meeting).

H. E. Swanson, E. H. Evans, and M. C. Morris (1964): Standard X-Ray Diffraction Powder Patterns; Nat'l. Bur. Standards Monograph, 2_5, Section 3.

L. J. Swartzendruber (1963): Four-Point Probe Measurement of Non -Uniformities

in Semiconductor Sheet Resistivity; NBS Report No. 8066, Aug. 16. (To be published in more extensive form in NBS Tech. Note 199.)

N. J. Tighe (1964): Jet Thinning Device for Preparation of A^O^ Electron

Microscope Specimens; Rev. Sci. Instr., 35 .

66
A. Van Valkenburg (1964): High-Pressure Microscopy of the Silver and Cuprous

Halides; J. Res. Nat'l. Bur. Standards, 68A , 97.

J. B. Wachtman, Jr. (1963): Mechanical and Electrical Relaxation in ThO? Containing CaO; Phys . Rev., 131 , 517. L

J. B. Wachtman, Jr. and L. R. Doyle (1964): Internal Friction in Rutile

Containing Point Defects; submitted to Phys. Rev.

J. B. Wachtman, Jr., M. L. Wheat, H. J. Anderson, and J. L. Bates (1964):

Elastic Constants of Single Crystal U0

2 at 25°C; Submitted to J. Nuclear Materials . J. Waring and R. S. Roth (1964): 10Me 2 Ov . 90Me 2

O,- Tetragonal Phases Apparently Isostructural with Ta

2

0,- .2Nb

2

0,-; Acta CrystT (accepted).

J. J. Weeks (1963): Melting Temperature and Change of the Lamellar Thickness

with Time for Bulk Polyethylene; J. Res. Nat'l. Bur. Standards, 67A , 441.

C. E. Weir and G. J. Piermarini (1964a): Lattice Parameters and Lattice Energies of High-Pressure Polymorphs of Some Aldali Halides; J. Res. Nat'l.

Bur. Standards, 68A , 105.

C. E. Weir and G. J. Piermarini (1964b): Allotropy in Some Rare-Earth Metals

at High Pressures; Science (USA) (accepted).

R. S. Williams and G. L. Pollack (1964): Crystal Growth and Etching of Methane; Bull. Am. Phys. Soc, 9.

TM ' "U.S. GOVERNMENT PRINTING OFFICE : 1964 —725-531


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