bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigations on SnS
Authors: Albers W. , Haas C. , Vink H. J. , Wasscher J. D.
Published: April 2005

The p, T, x diagram of the Sn-S system was determined especially in the region of the compound SnS. The pressure of S2 in equilibrium with SnS and a liquid phase was found to extend over several decades up to 25-mm Hg at the ``Sn-rich'' side, whereas at the ``S-rich'' side the S2 pressures in equilibrium with solid SnS and a liquid phase lie between 25-mm Hg and 100-mm Hg. It was shown that the existence region of solid SnS very probably lies entirely at the excess sulfur side. The hole mobility in a plane perpendicular to the c axis, ≈90 cm2/v sec at room temperature, was proportional to T−2,2 for higher temperatures. The mobility in the direction of the c axis was about five times smaller. Reversible annealing effects were found for temperatures above 200°C which could be explained by assuming association of neutral Sn vacancies. Absorption measurements showed that the edge absorption is due to indirect transitions. The bandgap was 1.08 ev at 300°K and 1.115 ev at 77°K. Interband transitions in the valence band were also found. The effective charge of the atoms (e*=0.7e0) and the effective masses of the holes in the three principal crystal directions (ma*=mb*=0.20m0; mc*≈m0) were determined from reflection measurements in the infrared. From these values and the value for the density of states mass obtained by means of the Seebeck effect (md*≥0.95m0), the number of equivalent maxima of the valence band was found to be at least four.
Electron Spin Resonance in Semiconducting Rutile
Authors: Chester P. F.
Published: April 2005

The ESR spectra of oxygen-deficient and doped rutile have been investigated at liquid helium temperatures. Niobium and tantalum are shown to give rise to the donors Nb4+ and Ta4+ rather than Ti3+. The spectrum of reduced rutile depends on the method of reduction. Reasons for this are discussed. Under certain circumstances, involving hydrogen reduction, a particularly simple spectrum is observed. This degenerates and is replaced by a single line as the temperature is raised. A similar effect is obtained by increasing the concentration of centers. Possible assignments are discussed. Vacuum reduction results in distinctly different spectra which persist to higher temperatures. Resistivity measurements indicate a higher activation energy, by a factor of three, for vacuum-reduced samples.
Optical Properties of Free Electrons in CdS
Authors: Piper W. W. , Marple D. T. F.
Published: April 2005

The contribution of free electrons to the refractive index and extinction coefficient of Ga-doped CdS has been measured in a series of samples with carrier concentrations ranging from about 1017 to 2×1019 electrons/cm3. The effective mass m* for electrons near the bottom of the conduction band was calculated from the free electron contribution to the refractive index and from the carrier concentration as determined from the Hall coefficient. The result, m*=(0.22±0.01)me is in satisfactory agreement with previous studies by other workers. The magnitude and wavelength variation of the absorption coefficient observed with about 1017 carriers/cm3 are in fair agreement with theoretical results calculated for a polar-mode lattice scattering mechanism. Although similar data for 2×1018 carriers/cm3 are in good quantitative agreement with the impurity scattering theory at room temperature, the absorption for high carrier concentration is observed to decrease with temperature, in contradiction with the theory for a nondegenerate population. A theory for the degenerate concentration range is needed. Reflection and transmission of radiation polarized parallel and perpendicular to the crystal C axis were studied for one sample. These data show (m⊥*/m∥*)=1.08±0.05.
Some Properties of HgSe–HgTe Solid Solutions
Authors: Rodot M. , Rodot H. , Triboulet R.
Published: April 2005

HgTe1−xSex solid solutions have been prepared, with x varying from 0 to 1. The samples are n type near x=1 and p type near x=0, but, due to the high electron-to-hole mobility ratio, electronic conudction is dominant in the range 100–400°K in all samples. The concentration of free electrons lies between 5·1016 and 3·1018 cm−3. Measurements of the Hall mobility μH and magnetothermoelectric effect ΔQ show that, for Se-rich samples, lattice scattering is dominant in the range 77–400°K and that, near room temperature, μH ∝ T−2. For Te-rich samples, lattice scattering is dominant in the range 200–400°K and, near room temperature, μH ∝ T−1. Effective masses have been calculated and it is seen that the conduction band is not parabolic. The detailed band structure and the exact value of the mobility seem to depend little upon structural factors. For x=0.5 and x=0.9, the electron mobility can reach 12 000 cm2 v−1 sec−1 at 293°K and 30 000 cm2 v−1 sec−1 at 77°K.
Righi-Leduc Effect in Mercuric Selenide
Authors: Whitsett Charles R.
Published: April 2005

A preliminary study has been made of the Righi-Leduc effect in mercuric selenide (HgSe). The Righi-Leduc magnetothermal effect is the thermal analog of the Hall effect wherein temperature plays the role of voltage and heat flow replaces electric current. The effect is particularly large in HgSe because of the coincidence of large electron mobilities (as high as 1.5 m2/v sec at 300°K) and low lattice thermal conductivity (about 0.02 w/°K cm at 300°K). Results are presented of measurements of the Righi-Leduc coefficient S as a function of temperature, magnetic field strength, and electron concentration. Classically, for a one-carrier material, S≅(κE/κ)μ, where κE is the electronic, κ is the total thermal conductivity, and μ is the electron mobility. This expression is in qualitative accord with the experimental results. At room temperature S ranged between 0.27 and 0.34 m2/v sec for samples that had between 55×1017 and 5.6×1017 electrons/cm3.
Band Structure of HgSe and HgSe–HgTe Alloys
Authors: Harman T. C. , Strauss A. J.
Published: April 2005

A detailed analysis of Hall coefficient data obtained at temperatures between 77° and 350°K has been made for HgSe and HgSe0.5Te0.5 samples containing excess donor concentrations up to 1019 cm−3. On the basis of previous magnetoresistance, Seebeck coefficient, and reflectivity data, a spherically symmetric non-quadratic conduction band exhibiting the ε(k) dependence described by Kane was adopted in making the analysis. Calculations based on a conventional two-band model failed to give quantitative agreement with experiment, but good agreement was obtained on the basis of a model in which the conduction band and one valence band overlap in energy. Therefore the materials are semimetals rather than semiconductors. The best fit to the data was obtained with an overlap energy of 0.07 ev for both HgSe and HgSe0.5Te0.5, with hole density-of-states masses of 0.17 m0 and 0.30 m0, respectively. With increasing carrier concentration, the optical absorption edge for heavily doped HgSe exhibits a shift to higher energies which is characteristic of n-type materials with low electron effective masses. Qualitatively, the optical data are consistent with a semimetal band model rather than with a semiconductor model, since the interband absorption edge apparently occurs at photon energies less than the Fermi energy.
Isothermal Crystallization Kinetics of Polyethylene. III. Influence of the Sample Preparation
Authors: Rabesiaka J. , Kovacs A. J.
Published: April 2005

Isothermal crystallization in bulk has been compared dilatometrically with linear polyethylene samples which have been molded in different ways, including melt orientation and sintering of precipitated powders from dilute solutions. These experiments show significant differences in the crystallization kinetics, which in some cases cannot be removed even by prolonged heating of the melt prior to crystallization. The data have been analyzed by an empirical expression in terms of nucleation and growth processes, according to the theoretical approach of Avrami. The results suggest that, in general, the melted polyethylene is not in a true thermodynamic equilibrium and includes some ``quasi-indestructible'' clusters, which act as heterogeneous nuclei in the crystallization process. The nature and the amount of these nuclei depend on the molding, melting, and mechanical history of the sample, so that the semicrystalline material may have a wide variety of structure.
Non-Newtonian Viscosity of Polymers
Authors: Porter Roger S. , Johnson Julian F.
Published: April 2005

The rheology of concentrated and bulk polymer systems has been investigated. Studies have been made on a low molecular weight series of several polymers using capillaries and a high shear concentric cylinder viscometer. The compositional and shear conditions for non-Newtonian flow have been closely defined. Limiting high and low shear viscosities and the path of non-Newtonian flow may be consistently correlated for concentrated systems of linear, flexible polymers. The minimum molecular weight for non-Newtonian flow is related to the transition at low shear in log viscosity vs log molecular weight correlations. For non-Newtonian systems, changes in apparent activation heat for viscous flow are reported as a function of shear. The conditions for laminar flow shear degradation of polymers are also given.
A Graphical Method for Determination of Mobility Ratio in the Semiconductors from Hall Effect Measurements Only
Authors: Pigoń Krzysztof
Published: April 2005

A method is presented for the approximate estimation of mobility ratio b=μn/μp from the Hall constant measurements taken in the vicinity of the intrinsic region and in this region itself. It is based on the discussion of a formula giving the Hall constant of a nondegenerate semiconductor at the exhaustion. Examples of these determinations are given; the results obtained show reasonable agreement with others' estimations.
Effects of Phosphor Powder Dispersion in Electroluminescent Lamps
Authors: Thornton W. A.
Published: April 2005

The statistical distribution of phosphor crystals in the solid dielectric material of a practical electroluminescent lamp influences the observed characteristics of the lamp. Calculation on the basis of a very simple model shows that maximum efficiency is favored by high phosphor concentration, fine particles, and thick phosphor layers; the slope and intercept of the usual brightness voltage plots are affected by the same variables. Measurements on electroluminescent lamps with these variations are in substantial agreement with the predictions.
Theory and Application of a Superposition Model of Internal Friction and Creep
Authors: Macdonald J. Ross
Published: April 2005

Energy dissipation in solids is important in both transient and steady-state measurements. The results of such measurements can be associated with a distribution of relaxation times provided the material is linear. In the present work, general relations are derived for the attenuation factor, phase factor, and specific dissipation function 1/Q pertaining to transmission of small amplitude stress waves in a material describable by a distribution of relaxation times. Next, a specific, physically realizable relaxation time distribution is used to obtain a creep function and to relate transient creep and frequency response measurements. Curves of 1/Q vs frequency are calculated with a digital computer and show a region approximately proportional to frequency at sufficiently low relative frequencies, a region of virtual frequency independence, and a final region proportional to inverse frequency at high relative frequency. The relation of the present work to other treatments of creep and internal friction is discussed, and the applicability is examined of the analytic and numeric results to creep measurements on metals and rocks, to low-frequency wave transmission in the earth, to other damping results for the earth as a whole, and to higher-frequency wave transmission and vibration results for geophysical and other solids. Good agreement between theory and experiment is found for frequency regions where adequate data are available, indicating that all the damping phenomena considered may be well described by a linear theory in the range of very small strain.
X-Ray Measurement of Stacking Fault Widths in fcc Metals
Authors: Warren B. E.
Published: April 2005

A generalized derivation of the broadening of powder pattern lines by stacking faults has been carried through allowing for fault planes of arbitrary dimensions. A minimum dimension for the fault plane Tmin is obtained from the measurable effective particle sizes De(111) and De(200). Values of Tmin of the order of 200 A are obtained for samples of filings of copper, α brass, and silver. The results suggest that, in the drastic cold work involved in filings, the stacking faults tend to extend over rather large distances comparable to the coherent domain dimensions.
(110) Nickel Surface
Authors: Germer L. H. , MacRae A. U. , Hartman C. D.
Published: April 2005

Nickel (110) surfaces, in clean and nearly clean conditions, have been studied by low-energy electron diffraction. When free from foreign atoms, the surface (110) plane of atoms has the normal arrangement expected for such a plane. Very slight contamination by oxygen (and perhaps other atoms) results, in some cases, in an arrangement of the topmost layer of atoms in which nickel and oxygen (or another atom) alternate along each [100] line and also along each [110] line. Study of such a surface has shown that the superficial half-layer of nickel atoms is displaced toward the bulk of the crystal by about 0.10 A.
Production of High Ion Densities in Helium by Means of High Explosives
Authors: Seay G. E. , Seely L. B. , Fowler R. G.
Published: April 2005

Temperatures of about 20 000°K with ion densities ranging from 1017 to 1018 cm−3 have been produced in helium by means of explosive-driven shocks. Helium was used because of its relatively simple structure, but this choice eliminated usual shock methods because of the high sound speed and high ionization potential. Shock waves having sufficient strength and planarity were obtained by reflecting against a glass plate initially strong shock waves produced by high explosives. Equilibrium calculations based on smear camera velocities of accurately plane shocks were used to determine the state of the gas behind the reflected shock wave.

The light emitted consisted of a continuum on which were superimposed shifted and broadened lines of the normal helium spectrum and forbidden lines as well. Time-resolved spectrograms showed evidence of a measurable relaxation time at the shock front but no evidence of significant radiative cooling of the gas behind the shock.

Under the conditions of these experiments, it was demonstrated that a quantitative prediction of the behavior of the helium states with principal quantum numbers 2, 3, and 4 requires consideration of the effects of electrons as well as ions.
Study of Impact Cratering in Sand
Authors: Culp F. L. , Hooper H. L.
Published: April 2005

An investigation of cratering in dry sand using 22-caliber long rifle bullets was carried out. Measurements of craters formed by bullets moving at velocities of 50 to 550 m/sec showed crater volume to vary directly with the square of the bullet velocity at the low end of this range and to approach a linear dependence on bullet velocity at the high end. An equation relating the crater volume to the bullet velocity was developed from a model which assumed hydrodynamic-like flow behind the induced shock wave and was found to provide an excellent fit to the experimental data. It was further found that for velocities below 245 m/sec bullet deformation is small and increases rather slowly with increase in velocity. At 245 m/sec, however, an abrupt transition occurs, and the deformation increases very rapidly. Above 245 m/sec the deformation appears to become constant. This transition velocity is believed to be related to the appropriate velocity of sound in sand.
Band Theory, Valence Bond, and Tight-Binding Calculations
Authors: Löwdin Per-Olov
Published: April 2005

In the theory of the electronic structure of crystals, the fundamental features of the band theory, the valence bond method, and the tight-binding approximation are reviewed. The band theory is studied on the basis of the Hartree-Fock scheme, and the Bloch functions are formed by a projection technique. The main methods for calculating Hartree-Fock functions in a solid are briefly discussed. The advantages and disadvantages of the band theory and the valence bond method are emphasized, and special attention is paid to the correlation error.

In connection with the tight-binding approximation, the importance of the continuum part and of the approximate linear dependencies is stressed. It is shown that a complete orthonormal set of translationally connected atomic orbitals may be constructed as a convenient basis for this approach. The implication of the virial theorem in interpreting the cohesive properties of the ionic crystals is further emphasized.

Some recent refinements of band theory are then discussed. It is shown that a large part of the correlation error can be removed by permitting ``different orbitals for different spins.'' This leads to a scheme intermediate between band theory and valence bond method and, by means of a single parameter, one can obtain an essential lowering of the energy curve and the correct asymptotic behavior for separated atoms or constituents. This approach may be generalized to an extension of the Hartree-Fock scheme, where the total wave function is defined as a projection of a Slater determinant.

The band theory can be further refined and connected to the exact solution of the many-electron Schrödinger equation of the crystal by means of an extension of the self-consistent-field scheme, utilizing the so-called reaction operator here exactly defined by means of a simple partitioning technique. The various types of self-consistent field theories are finally compared.
On the Description of Covalent Bonds in Diamond Lattice Structures by a Simplified Tight-Binding Approximation
Authors: Leman G. , Friedel J.
Published: April 2005

The simplest possible tight-binding approximation, using sp hybridized bonds and nearest neighbors overlaps, is used to describe the band structure of diamond, silicon, and germanium. This crude approximation has the great advantage of giving explicit and simple formulas for the Bloch functions and E(k) curves in the whole reciprocal space, as a function of two parameters: an overlap integral λ and an sp promotion energy ε. The general band structure is discussed as a function of ε/λ. The influence of sp hybridization on the band structure, covalent character of the valence electrons, optical and x-ray spectra are discussed. It is shown how the energy gap should be related to cohesive energy and pressure. The reasonable agreement with experiment of these various predictions shows the usefulness of the method to understand in a rough and somewhat qualitative way general properties of covalent bonds in crystals.
Recent Progress of Crystal Field Theory
Authors: Sugano Satoru
Published: April 2005

A brief account is given concerning the theoretical framework of the molecular orbital treatment of crystal field theory. Indirect and direct experimental evidences of electron delocalization are summarized. A historical survey is given of the theoretical treatment of cubic crystal field splitting. Finally, a molecular orbital treatment of the cubic field splitting is presented, emphasizing the importance of π-electron bonding and itinerancy of electrons between a metal ion and ligands.
Symmetry of Transition Metal Impurity Sites in Crystals as Inferred from Optical Spectra
Authors: Weakliem H. A. , McClure D. S.
Published: April 2005

The polarized optical spectra of several transition metal ion impurities in crystals with the wurtzite structure; Cs2ZnX4 (where X−=Cl− or Br−); and Al2O3 have been measured at temperatures ranging from that of liquid helium to room temperature. In all these cases the transition metal ion substitutes for a cation of pure compound. The gross features of the spectra are explained by crystal field theory for the impurity ions in a potential field arising from the nearest-neighbor ligands in their undistorted configuration. The finer details of the spectra and the polarization effects which are observed are used to infer the actual site symmetry of the impurity ion. The trigonal field splitting compared to the calculated value indicates that certain ions in Al2O3 are displaced from the aluminum site along the threefold axis. The breadth of certain bands, and in some cases the lattice vibration progressions which are observed, have been interpreted as being due to a reduction in the symmetry of the electronically exicted ion and its ligand environment from that of the ground-state configuration. In the case of Mn3+ in corundum there is very good evidence for a highly distorted site, presumably due to the Jahn-Teller effect.
Modification of Lattice Vibrations by an Imperfection
Authors: McCombie C. W. , Matthew J. A. D. , Murray A. M.
Published: April 2005

The optical absorption or emission by an electron localized at a point imperfection in a crystal is broadened by lattice vibrations. In a fundamental discussion the normal modes of vibration of the whole crystal must be considered. The effect of a mode depends on the displacements it produces in ions near the imperfection. The presence of the imperfection will modify the modes, and, in particular, change the displacements of ions near the imperfection even when the modes do not become localized at the imperfection. In the case of the F center the temperature dependence of the breadth of the F band suggests that this effect must enhance the broadening produced by low-frequency modes (which will certainly not be localized). That this is to be expected from the dynamical theory of normal modes will be shown by discussing: (1) the vibrations of a one-dimensional chain of particles with two adjacent weakened links, (2) the spherical vibrations of an elastic continuum with a spherical cavity, (3) the vibrations with cubic symmetry round the F center in NaCl if only the first eleven shells of ions round the center are allowed to vibrate. Results obtained with this last model will be compared with experimental results for the breadth of the F band in NaCl as a function of temperature.
Studies on the Substructure of Real Crystals by Optical and Magnetic Resonance Methods
Authors: Bansigir K. G. , Schneider E. E.
Published: April 2005

Direct ultramicroscopic studies and measurements of the optical scattering spectrum of ``pure'' and doped alkali halide crystals are described showing the existence of elementary scattering centers and of assemblies of such centers. The elementary scatterers are established to be impurity precipitates of dimensions not exceeding a few hundred angstroms. The assemblies lead to characteristic ultra-microscopically visible diffraction images representing decorations of branch points of a semi-organized network of dislocations which reflect the state of strain and deformation in the subgrains of the mosaic structure of the single crystals. With increasing temperature the number of elementary scatterers decreases as impurities enter the host lattice into true solid solution, and the size of the assemblies diminishes.

Electron spin resonance experiments on doped alkali halides are discussed which provide direct information on the process of dissolution and reprecipitation of impurity ions. Results on strong exchange effects in the electron spin resonance of the systems MnCl2–NaCl and MnCl2–KCl are presented which are explained in terms of the substructure of very small impurity precipitates deduced from the optical investigations.
Fine-Line Spectra of Chromium Ions in Crystals
Authors: Schawlow A. L.
Published: April 2005

The sharp lines of the optical spectrum of trivalent chromium in oxides can be used to determine the position and splitting of the 2E state. They can be calibrated by stress experiments on an ion which is initially in a purely cubic field, and can then be used to study the surroundings of ions in noncubic fields. Further information can be obtained from ground-state splittings, which depend in a different way on the symmetry of the surroundings. The method is used to investigate deformed cubic sites in magnesium oxide and aluminum oxide. In aluminum oxide, chromium lines as narrow as 0.10 cm−1 have been observed at low temperatures, and show a fine structure attributed to the chromium isotopes. Some progress has been made in understanding the chromium pair spectra observed at higher concentrations.
Equilibration of Lattice Defects in Real Crystals
Authors: Mitchell J. W.
Published: April 2005

This paper describes several mechanisms for the equilibration of lattice defects in a number of crystalline solids in which the state of equilibrium has been disturbed by changes of temperature, diffusion processes, and phase changes, including precipitation from solid solution and internal chemical reactions.
Reactions among Point Defects in Alkali Halides
Authors: Lidiard A. B.
Published: April 2005

Existing knowledge of point defects and their interactions in uncolored alkali halide crystals is briefly reviewed. Attention is drawn to recent experimental and theoretical work which indicates that vacancy pairs are not highly mobile defects. This has important implications for some hypotheses on the kinetics of color center reactions at low temperatures.

This knowledge of defects in uncolored crystals is then applied to a discussion of the reactions which may take place between F centers and impurity ions in additively-colored doped crystals and the theoretical possibilities are compared with experimental information on Z centers. Consideration of the thermodynamic equilibria in these reactions seems to eliminate the Z1 and Z2 centers of Pick as possible causes of either of the Z1 and Z2 absorption bands in KCl. (The Z2 model of Pick is identical with the Z1 model of Seitz and is a divalent impurity cation which has trapped an electron.) Two possible centers for the Z2 band presen tthemselves; (a) an associate of an F center with a divalent cation and (b) an associate of an F center with an impurity-vacancy pair (the Z2 model of Seitz). The structure of the Z1 center is not resolved by these considerations. Attention is drawn to some paradoxical experimental results on Z1 and Z2 centers and further experiments to resolve outstanding questions are suggested.
Kinetics and Equilibria Involving Copper and Oxygen in Germanium
Authors: Fuller C. S. , Wolfstrin K. B.
Published: April 2005

Germanium solutions supersaturated with respect to both oxygen and copper have been investigated in the range 300–500°C by means of conductivity and Hall effect measurements. Kinetics results indicate that the initial rates of disappearance of holes is second order in both the Cu and the O concentrations. The failure of the hole mobility to increase with degree of reaction suggests the formation of an ion cluster. Determinations of ionization energy during reaction show changes in the level scheme of Cu to occur and confirm previous work on the ionization properties of donors produced by oxygen. A tentative model is proposed consisting of an initial cluster of two Cu and four O atoms on which further oxygen reactions take place. The diffusion of oxygen is found to be accelerated by the presence of Cu.
Defects in Mixed Crystals of KCl–KBr
Authors: Smakula A. , Maynard N. , Repucci A.
Published: April 2005

Mixed crystals of potassium chloride and bromide show strong internal strain evidenced by cracking. The minimum of the melting point occurs between 63 and 65 mole % KBr. The microhardness between 25 and 65 mole % KBr is more than twice that of either component. The lattice constant changes linearly with composition. The macrodensity deviates by several percent, indicating a high concentration of defects. The intensity of coloration by electrons shows that defects are not mainly due to vacancies but presumably to larger aggregates of submicroscopic size or interstitials. The broadening of exciton bands, as measured by shifts of the ultraviolet absorption edge, is greatest at a 2:1 KCl–KBr ratio. This may indicate a certain short-range order in KCl–KBr mixed crystals.
Energy and Entropy of Formation and Motion of Vacancies in NaCl and KCl Crystals
Authors: Dreyfus R. W. , Nowick A. S.
Published: April 2005

Recent experiments on the dc ionic conductivity of NaCl crystals doped with divalent cation impurities led to a re-evaluation of some of the basic constants for defect formation and motion in these crystals. The key parameter is the energy of motion εm of a cation vacancy. This parameter has been determined from the temperature dependence of the conductivity under conditions where the concentration of cation vacancies remains fixed. Such conditions apply (1) in the range just below the intrinsic region, and (2) in samples rapidly cooled to below 0°C such as to prevent the attainment of an equilibrium degree of association. From the present work combined with previous data, the jump rate of the isolated positive-ion vacancy in NaCl is ν=12ν0 exp(−εm/kT) with ν0=1014.1±0.3 sec−1 and εm=0.80±0.02 ev. With the aid of earlier measurements in the intrinsic range it is concluded that the energy of formation of a Schottky defect in an NaCl crystal is 2.12±0.06 ev, while the entropy of formation is 6.2±1.8 (in units of k). Very similar results, although of somewhat lower precision, apply to KCl. Finally, a comparison is made between these values and the predictions of existing theories.
Correlation Effects for Diffusion in Ionic Crystals
Authors: Friauf Robert J.
Published: April 2005

Observations of the motion of ions by means of both diffusion and electrical conductivity measurements usually show deviations from the normal Einstein relation. The interpretation of these deviations often leads to a fairly detailed picture of the types of defects present and the mechanisms of their motion. A correction must always be considered because of the fact that successive jumps of a tracer atom are correlated, as first discussed by Bardeen and Herring, and the origin of this effect is shown by treating diffusion as a random walk problem. For the interstitialcy mechanism a second correction is required because the effective displacement is larger for conductivity than diffusion, and this effect is illustrated with results on AgCl and AgBr. Possible mechanisms for ionic motion in crystals with the CsCl structure are described, and the present interpretation of results for CsBr, CsI, and TlCl is discussed. It appears that vacancy pairs may make an appreciable contribution to the diffusion. Experiments for observing diffusion with an applied electric field are discussed, and an analysis is given of the problem of determining the internal electric field in such situations. If certain experimental difficulties can be overcome, this last technique should provide a powerful extension of methods of investigating the motion of ions in crystals.
Absorption Edge in Degenerate p-Type GaAs
Authors: Kudman I. , Seidel T.
Published: April 2005

Infrared absorption for p-type degenerate GaAs is studied at room temperature for various hole concentrations. At high absorption coefficients, a Burstein-like shift is observed for samples doped above 1019/cm3; this shift is interpreted as a decrease in the valence band electron population. A direct transition analysis was made on 1017/cm3 material, yielding an energy gap of 1.39±0.02 ev. The free carrier absorption was extrapolated to shorter wavelengths and subtracted from the data. The resulting absorption edges extend to energies beyond the fundamental edge and reveal the presence of an added absorption mechanism.
X-Ray Diffraction Studies in the 100 Kilobar Pressure Range
Authors: Jamieson John C. , Lawson A. W.
Published: April 2005

A new technique using ``amorphous'' boron as a pressure vessel yields satisfactory Debye—Scherrer patterns for substances subjected to quasi-hydrostatic pressures ranging up to at least 150 kbar. The pressure attained depends on sample size and its compressibility. In general, the pressure attained is higher for the more incompressible substances. The following substances have been used to test the apparatus: Fe, NaCl, KCl, AgCl, CaCO3, and NaNO3. Evidence for polymorphic transitions was found for all substances except NaCl. The changes in lattice spacings and the observed transformations are consistent with the transition pressures and volume decrements determined by Bridgman or by shock-wave experiments in the case of Fe. The high-pressure structures are tentatively identified.
An Extension of a Theory of Mechanical Damping Due to Dislocations
Authors: Rogers D. H.
Published: April 2005

The theory of damping due to dislocations developed by Granato and Lücke concerning a model of a dislocation line pinned by major (unbreakable) and minor (breakable) pins, the latter distributed at random along its length, is extended in two ways: the hysteretic breakaway loss is calculated for higher amplitudes; and the frequency dependent or dynamic loss is shown to be, also, amplitude dependent. The presence in a crystal of two dislocation systems of different average loop lengths is considered as an explanation of the discrepancy between some of the experimental results and the G and L theory. The configuration of the combined dynamic and breakaway loss for the long loop system for various LN/Lc ratios and LN values is described, where LN, Lc are the average loop lengths between major and minor pins, respectively. An interesting feature is the prediction of a low amplitude maximum in the decrement. The theory does not extend to the high frequency region and like the G and L theory is unreliable for LN/Lc less than 5.
Kinetic Theory of Dislocation Climb. II. Steady State Edge Dislocation Climb
Authors: Balluffi R. W. , Thomson R. M.
Published: April 2005

Quantitative expressions for the steady state climb rate of a straight unconstrained edge dislocation are obtained. The results represent specific solutions to a general kinetic model of climb developed in preceding work (Part I). Solutions are obtained for the case where interstitials in the lattice can be neglected compared to vacancies, where the dominant point defects responsible for fast diffusion along dislocation cores are vacancies, and where unlike jogs attract one another. No a priori assumptions are made about the ability of the dislocation or its jogs to maintain local point defect equilibrium. A wide range of conditions is treated including positive and negative climb where the vacancy concentrations may be either near or far from equilibrium. Positive and negative climb are shown to be inherently different processes, and it is found that dislocations tend to get joggy in crystals far from equilibrium. Several brief applications to problems of current interest are given. A need for critical experiments is emphasized.
Alumina Whisker Growth on a Single-Crystal Alumina Substrate
Authors: Edwards P. L. , Happel R. J.
Published: April 2005

Alumina whiskers have been grown on single-crystal alumina substrates by heating aluminum filings, located near the crystals, to 1400°C in a stream of wet hydrogen. The whiskers grew crystallographically coherent with the substrate, and had their axes either parallel to the c axis or in one of 12 equally spaced directions in the basal plane. These 12 directions divide into two distinct sets, a 〈112̄0〉 set and a 〈11̄00〉 set, each having sixfold symmetry, and with the directions of one set midway between the directions of the other. These growth directions are the screw-dislocation directions in alumina, hence it seems plausible that the whiskers grew coherently with the substrate at the site of emergent screw dislocations.
Giant Optical Pulsations from Ruby
Authors: McClung F. J. , Hellwarth R. W.
Published: April 2005

Giant pulses of optical maser radiation have been produced which are several orders of magnitude larger than the commonly observed spontaneous pulses. The pulses were produced by varying the effective reflectivity of the reflecting surfaces at the ends of the ruby rod through a Kerr-cell switching technique. The measured pulse characteristics are found to be in agreement with theoretical predictions.
Piezoelectric and Dielectric Properties of Lead Titanate Zirconate Ceramics at Low Temperatures
Authors: Gerson Robert
Published: April 2005

The piezoelectric and dielectric properties of polarized lead titanate zirconate ceramics were measured between 4° and 77°K. The materials were found to retain strong piezoelectric activity at the lower temperature. For one type of ceramic the planar piezoelectric coupling in liquid helium was about 80% of its room temperature value. Its free relative dielectric constant, measured at 1 kc, rose almost linearly from 380 at 4°K to 1300 at room temperature. The mechanical losses decreased sharply at low temperatures, suggesting a reduction in domain wall mobility.
Low-Noise Beams from Tunnel Cathodes
Authors: Wade G. , Briggs R. J. , Lesensky L.
Published: April 2005

The tunnel cathode consists of a metal-insulator-metal sandwich in which the electrons tunnel through the insulator material. This paper presents an analysis of the noise associated with the space-charge waves of a beam emitted from such a cathode. The beam noise temperature for a refrigerated tunnel cathode is shown to be 2730 δ, where δ is the value in volts of a built-in energy window for the emitted electrons. The value of δ is adjustable by means of a dc potential. Assuming a beam noise temperature of 30°K, the current density is calculated for a variety of cathode parameters. A discussion is presented of the significance of the parameters and of the difficulties which would be encountered in constructing such cathodes for low noise.
Thermoelectric Properties of Some Cerium Sulfide Semiconductors from 4° to 1300°K
Authors: Ryan F. M. , Greenberg I. N. , Carter F. L. , Miller R. C.
Published: April 2005

The thermal conductivity, Seebeck coefficient, and resistivity were measured for a series of sintered cerium sulfide compounds of the thorium phosphide structure. The compounds were in the composition range CeSx (1.33 ≤ x ≤ 1.5) and were prepared with and without strontium sulfide doping. The electrical resistivity and Seebeck coefficient increased with temperature for all samples, similar in appearance to the temperature dependency of a metal. The addition of strontium sulfide to compositions for (x > 1.33) usually led to a decrease in the resistivity and Seebeck coefficient while maintaining the same temperature dependence. The thermoelectric ``figure of merit'' is given for one of the samples and some remarks are made on the conduction mechanism in the system.
An Explanation of the dc Sumoto Effect
Authors: Pickard William F.
Published: April 2005

The dc Sumoto effect is explained in terms of an abnormal fall of potential near one of the electrodes. Experimental evidence is cited to support this theory.
On the Yield Stress of Copper Crystals
Authors: Young, F. W.
Published: April 2005

99.999% copper crystals were deformed in tension using an Instron tensile tester, and the dislocation density and arrangement in the crystals were determined before, during, and after the deformations using an etch pit technique. For crystals of low initial dislocation density, it was found that a large amount of dislocation multiplication occurred prior to yielding. Experimental relationships of dislocation density versus applied stress and versus shear strain were determined. It was found that the yield stress was not related to the initial dislocation density or arrangement. The yield stress was postulated to be determined by the stress necessary to break the gliding dislocations through impurity atom barriers in the crystal.
Growth and Photomicrographical Observation of Argon Crystals
Authors: Beltrami M.
Published: April 2005

Argon crystals are grown with Bridgman's method, and the free surface of the crystal is observed with a microscope in reflected light. In order to observe the crystal at various depths, pumping and sublimation operations are effected until the entire crystal sublimates layer after layer. All the crystals obtained showed many coherent and noncoherent twin boundaries; some of them did not show any grain boundary.
Filamentary Impact Ionization in Compensated Germanium at 4.2°K
Authors: Melngailis I. , Milnes A. G.
Published: April 2005

An experimental study is made of filamentary impact ionization breakdown observed in germanium doped with both group III and group V elements at liquid helium temperature.

The approximate size of the filament at various current values after ionization is estimated from the measurement of voltage-current characteristics of small cross section bars with high current pulses. Measurements are also made with cylindrical ``tecnetron'' structures in which the conduction channel can be reduced to very small areas by reverse bias of a ring-shaped p-n junction alloyed around a small cylindrical bar. Results of the two experiments are consistent. Near the lowest current value at which ionization can be sustained (about 40 μa), the approximate filament diameter is 10−3 cm.
Shock-Induced Electrical Polarization of Alkali Halides
Authors: Linde Ronald K. , Murri William J. , Doran Donald G.
Published: April 2005

Electrical signals attributed to polarization of NaCl, KI, KCl, and CsI crystals shocked in the 10- to 40- kbar and 90- to 220- kbar ranges are described. The signals observed cannot be explained by the simplified models found in the literature, nor has correlation been established between the magnitude or polarity of the polarization signal and the crystal structure or the cation-to-anion mass ratio. There is some correlation with shock pressure for NaCl below 40 kbar. The signal shape is significantly different for shock compression along different crystallographic directions.
Computation of Electrostatic and Rapidly Pulsed Magnetic Fields
Authors: Lewis H. R.
Published: April 2005

It is often required, for example, in the design of some pulsed controlled-thermonuclear-fusion experiments, to calculate electrostatic fields and to calculate magnetic fields in the approximation that flux does not penetrate metal boundaries of the experimental volume. Computation of such magnetic and electric fields by means of the standard relaxation methods is often difficult and very costly, even with high-speed computers. This is because the boundaries of the region of experimental interest are rather arbitrary and because there are generally current- or charge-carrying conductors within the region that make it nonsimply connected. An alternative method of solving the boundary value problems that determine these electric and magnetic fields, which does not involve a difference approximation to the differential equations, has been developed. With this method, an exact analytic solution of the appropriate differential equation is obtained in the region of interest, and this solution is made to approximate the boundary conditions. The method and its application are described in detail. Examples of the application of the method to some controlled-thermonuclear-fusion experiments are given.
The Laser as a Light Source for Ultramicroscopy and Light Scattering by Imperfections in Crystals. Investigation of Imperfections in LiF, MgO, and Ruby
Authors: Vand V. , Vedam K. , Stein R.
Published: April 2005

A cw 1-mW He–Ne laser was used for the study of 90° light scattering in crystals in the arrangement of an ultramicroscope. Motorized translation of the illuminating objective allowed us to take photographs of extended sections through the crystal. When the laser was compared with light-scattering performance of an unfiltered unpolarized 100-W mercury arc lamp it appeared to be appreciably more intense. On calibration, 880-Å latex particles suspended in water were easily visible by eye, and 3570-Å particles were photographed at 132-sec exposure. It is estimated that 1-h exposures would make visible particles of some 300 Å e.l.d. (equivalent latex diameter) and with more powerful lasers, particles of about 100 Å e.l.d. could be theoretically reached. Lithium fluoride crystals of high purity show scattering defects concentrated at small-angle boundaries. Magnesium oxide crystals of lesser purity show many imperfections. Ruby laser crystals show imperfections at small-angle boundaries and also along lines perpendicular to the boundaries.
Anomalous Attenuation of Piezoelectrically Active Ultrasonic Waves in Photoexcited Cadmium Sulfide
Authors: Harnik E.
Published: April 2005

The structure-sensitive anomaly in the attenuation characteristics of ultrasonic waves in photoconducting single crystals of CdS illuminated with monochromatic light, reported earlier, has been further investigated. The attenuation and amplification characteristics, corresponding to various wavelengths of illumination, have been measured at room temperature and reduced temperatures in a number of samples, and in the same sample submitted to heat treatments in different ambients. The results obtained cannot be explained satisfactorily on the basis of existing theories, and the operation of an additional photosensitive loss mechanism, involving the piezoelectric field which accompanies the ultrasonic wave, has to be invoked. The possibility is examined that this extraneous attenuation arises as a result of photodielectric losses incurred by the piezoelectric field.
Controlled Domain Tip Propagation. Part I
Authors: Spain R. J.
Published: April 2005

Magnetization reversal by the growth of domains at the domain tips is discussed in the light of device applications that such a mode of switching has for the performance of thin-film all-magnetic logic. The propagation of domain tips through a pattern of low coercive force channels built into a magnetic film element of high coercivity makes it possible to control the direction of tip growth and the mutual interaction between domain tips brought into proximity. The dependence of the direction of domain tip growth upon the direction of the applied field, the forces of interaction between domain tips, and the speed of domain tip propagation are shown to provide a new technique for the construction of a variety of magnetic thin-film devices.
Statistical Theory of Electron Transport in the Smooth-Bore Magnetron
Authors: Mouthaan Koenraad , Süsskind Charles
Published: April 2005

Electron transport across the magnetic field in the cutoff smooth-bore magnetron is described on the basis of random fluctuations in the fields. The theory is formulated in terms of the slipping-stream instability, so that a definite mechanism behind the fluctuations in the fields is established. The transport equation appropriate to the analysis is shown to be the diffusion equation; the diffusion tensor follows from the characteristics of the slipping-stream instability. Application of the theory is made to find the cutoff characteristics of the smooth-bore magnetron. Expressions for the electric field, the space-charge distribution, the anode current, and the circulating current are obtained; the results are compared with available experimental results. The agreement between theoretical and experimental results is good, particularly for the anode current. The new theory thus provides, for the first time, an acceptable theoretical explanation of the cutoff characteristics of the smooth-bore magnetron.
Surface Spikes: A Perturbation of Growth Steps
Authors: Sickafus Edward N.
Published: April 2005

During the growth of NiBr2 crystals by sublimation, it has been observed that in addition to the mechanism of growth spirals a secondary mode of nucleation can occur. This is an accelerated growth which appears in the form of surface spikes on growth steps. The surface spikes may move as much as 50 times faster than the unperturbed growth steps. The mechanism of formation is believed to begin with the nucleation of a liquid droplet which wets the growth step and produces the accelerated growth from the liquid phase. The growth occurs at 500°C below the melting point of NiBr2. It is believed that the nucleation of the liquid phase at these temperatures is impurity controlled.