JHPS' - 3/3-6* - dfo+tf

NBSIR 75-754

NASA CR-1 34869

A

Rota, R. 3., Brewer, 3., Parkier, H. 3.,

Minor, D. B., Waring, J. L., Alkali

oxide-tantalum, niobium and antimony oxide

ionic conductors, RASA CR-13^869, 76 pages

(National Technical Information Service,

Springfield, Va . 1975).

ALKALI OXIDE-TANTALUM, NIOBIUM AND ANTIMONY OXIDE IONIC CONDUCTORS

by

R. S. Roth, W. S. Brower. H. S. Parker, D. B. Minor and J. L. Waring

prepared for

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

CONTRACT C-50821-C

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

WASHINGTON, D. C. 20234

TABLE OF CONTENTS

SUMMARY 3

1.0 INTRODUCTION 5 2.0 DISCUSSION OF RESULTS 6

2.1 The System Nb

20

5 -4Rb

20 : llNb^ 6

2.2 The System Ta

20

5-4Rt>

20: llTa^ 6

2.3 The System Sb_0.-NaSbO_ 7

2 4 j

2.3.1 NaSb0

3

. . . 8

2.3.2 Pyrochlore Solid Solution 8

2.3.3 Polymorphism of Sb^ 10

2.4 The System Sb„0,-KSb0 o 11

2 4 3 2.4.1 Hydroxyl Ion Stabilization of Cubic Potassium

Antimonate 11

2.5 The System Sb o0. -NaSbO„-NaF 13

2 4 3

2.5.1 The System NaSbO^NaF 13

2.5.2 The Ternary System 14

2.6 Other Systems 15

2.6.1 Alkali Bismuthates 15

2.6.2 Alkali-Rare Earth Systems 15

2.6.3 Further Studies in the System Nb

2 05

:KNb0

3

16

2.7 Pellet Fabrication 16

2.7.1 41K

20:59Nb20

5

("2:3"*, K

4

Nb

6

0

17 ) 16

2.7.2 4Rb

2 0:llNb2

0

5

(11-layer phase) 18

2.7.3 Large Pellets for Ionic Conductivity Measurements .... 18

2.8 Crystal Growth and Synthesis 20

2.8.1 Crystal Growth by Pulling from the Melt 20

2.8.1.1 Hexagonal Tungsten Bronze in the K O-Ta 0,-WO.

System f . .\\ 20

2.8.1.2 The System KNbO^Nb^ 22

2.8.1.3 The System Rb 0-Nb 9 0. 22

1
2.8.2 Flux Growth 23

2.8.2.1 The System Rb

20-Nb20

5

-MoC>

3

23

2.8.2.2 The System Rb

20-Ta2

0

5

-Mo0

3

24

2.8.2.3 The System Rb

2

0-Ta

20

5

-RbF 24

2.8.2.4 The Systems ASbC^-Sb^-AF (A = Na.K.Rb) 24

2.9 Ion Exchange 26

3.0 RELATION OF STRUCTURAL MECHANISMS OF NON-STOICHIOMETRY TO

IONIC CONDUCTIVITY 27

3.1 Hexagonal Tungsten Bronze-type Phases (HTB) 28

3.2 Pyrochlore Phases 28

3.3 Hexagonal Tungsten Bronze - Pyrochlore Series 31

3.4 Body Centered Cubic Antimonates 32

3.5 The Phase 2Ko 0:3Nb o 0- 35

I I 5

4.0 SUMMARY OF RESULTS 36

5.0 FUTURE WORK 37

REFERENCES 38

FIGURE CAPTIONS 40

TABLES OF EXPERIMENTAL DATA' 50

DISTRIBUTION LIST 69

2
> •

SUMMARY

This report summarizes work carried out between January 1, 1974 and

December 31, 1974 under an agreement with the National Aeronautics and

Space Administration, Lewis Research Center (Interagency Agreement

PR545160) to study the phase equilibria of alkali oxide-tantalum,

niobium and antimony oxide systems and synthesis of phases which might

have interesting ionic conductivity. It also includes work performed

since the last contract (Interagency Order C-29933-C [1]) which ended in

October 1973, as well as that done since the formal ending of the

present contract and the issuance of this summary report.

In addition to the six systems reported in the previous contract

(Interagency Order C-29933-C [1]) the phase equilibrium relations of four

additional systems were investigated in detail. These consisted of

sodium and potassium antimonates with antimony oxide and tantalum and

niobium oxide with rubidium oxide as far as the ratio 4Rb20 : IIB2OC

(B=Nb, Ta) . The ternary system NaSb0

3

~Sb

20^-NaF was also investigated

extensively to determine the actual composition of the body centered cubic

sodium antimonate. In addition, various other binary and ternary oxide

systems involving alkali oxides were examined in lesser detail. The phases

synthesized were screened by ion exchange methods to determine mobility

of the alkali ion within the niobium, tantalum or antimony oxide (fluoride)

structural framework.

Five structure types were found to be of sufficient interest to

warrant further investigation. These structure types are (1) hexagonal

tungsten bronze (HTB) (2) pyrochlore (3) the hybrid HTB-pyrochlore hexagonal ordered phases (4) body centered cubic antimonates and (5)

2K20:3Nb20^. Although all of these phases exhibit good ion exchange

properties only the pyrochlore in the Sb20^-NaSb02 system has so far

been prepared with Na+

ions as an equilibrium phase and as a low porosity

3
ceramic. Unfortunately Sb in the channel apparently Interferes with

ionic conductivity in this case , although relatively good ionic con- ductivity was found for the metastable Na ion exchanged analogs of

RbTa20^F and KTaWO^ pyrochlore phases. Small crystals of the other

phases can generally be prepared by flux techniques and ion exchanged

with Na

+

. However, in the one case where congruency allows large

crystals to be pulled from the melt (41^0: HIM^O^) ion exchange

techniques up to M50°C are not sufficient to accomplish replacement

with Na

+

ions.

4
1.0 INTRODUCTION

The program described in the present report involves the preparation

of single crystals and ceramic specimens of materials which have passed

some preliminary screening tests and appear to be potential candidates as solid ionic conductors. Much of the preliminary screening was done under

previous work order (No. C-29933-C) [1]. Furthermore the phase equilibrium

diagrams have been studied for some systems in which promising candidates

have been discovered but for which no phase data existed.

Crystals and ceramic specimens were prepared or synthesis attempted

for various different structure types and compositions, including the

hexagonal tungsten bronze and pyrochlore phases in the system I^O-Ta^^-WO^

,

the 2K20:3Nb2O^ type phase and the phases in the system Rb20-Nb20^. In

addition specimens of the pyrochlore phase and the body centered cubic phase

of the NaSb0„-Sb o0,-NaF system were examined.

3 2 4

The phase equilibria diagrams of the Rb20-Nb

20^ and Rb20-Ta20,_ systems

were examined as well as those of the Sb o 0.-NaSb0_ and Sb„0.-KSbO„. In

2 4 3 2 4 3

addition the equilibria in the system Sb20^-NaSbO^-NaF were investigated.

Other compositions examined included the alkali rare earth oxide systems

and alkali oxide-bismuth oxide systems although no high temperature

equilibrium phases were found in any of these systems.

The method of flux synthesis was used to prepare small single crystals

for the first time of the pyrochlore phase RbTa20^F and the body centered

cubic phases of F stabilized potassium and sodium antimonates

.

In the following discussion all ratios (1:3, 3:5, etc.) refer to the

alkali/metal ratio rather than to the particular starting material that

may have been used.

5
2.0 DISCUSSION OF RESULTS

2.1 The System Nb

20

5

-4Rb

2

0:llNb

2

0

5

The system RbjO-NbjO^ was Investigated from the region of about

27 mole % RbgO to the Nb^ end member. Ten compositions were prepared

by dry mixing stoichiometric amounts of Rb^O^ and Nb

20^ and calcining

in open Pt crucibles at 500°C and 600°C for extended periods of time

with intermediate grindings. The specimens were heated at higher

temperatures in sealed Pt tubes in resistance wound quench-type furnaces

(Table 1) . The x-ray diffraction patterns of these quenched specimens

were used to establish the phase equilibrium diagram shown in Figure 1.

Single crystals of the eleven layer (11-L) (4Rb

20: llNb

20

5

) , hexagonal

tungsten bronze (HTB) (21.75Rb

2

0:78.25Nb

202) and Gatehouse tungsten bronze

(GTB) (11.5Rb

2

0:88.5Nb

2

0,.) phases (see reference [1] for nomenclature

of phases) were grown from the melt by modified Czochralski techniques.

Single crystal fragments of the 11-L phase were used in ion exchange

experiments but did not provide better results than isostatically pressed

pellets prepared from calcined powder.

Unit cell dimensions for all phases are given in the summary table

of x-ray data at the end of this report (Table 12) . They were determined

from both single crystal precession patterns and x-ray powder diffraction

patterns (CuKa radiation, Ni filtered) with the aid of a computer least

squares program. Only the phase occurring at low temperatures at about

15 mole % Rb

20 has not been indexed, as no single crystals were obtained.

2.2 The System J Ta o 0 c -4Rb o 0:llTao0 c 2 5 2 2 5

The system Rb

20-Ta20

5 was investigated from 26.67 mole % Rb

2

0 to

100 mole % Ta

20^. Eight compositions were prepared and the system was

investigated by conventional quenching methods. The samples were

heated in open Pt trays at 500° and 600°C and then heated in sealed

6
Pt tubes at higher temperatures. The phases were identified by comparison

with known structures in the K20-Ta20,- and Itf^O-I^O^ systems. Equilibria

was assumed to have been established when successive heat treatments

showed no change in the x-ray diffraction patterns. As in the K^O-^^O,.

[1,2] and Itt^O-ltt^O^ systems a layer sequence 9-L, 16-L, 11-L (in order of

increasing alkali content) was found to be present. The HTB and GTB-like

phases [1] were also found to be present. The results of the experiments

are given in Table 2 and the phase equilibrium diagram interpreted from

this data is shown in Figure 2.

2.3 The System Sb^-NaSbC^

The system between the compositional limits of NaSbO^ and Sb20^

has been examined in detail. Thirteen compositions were studied by air

by conventional quenching techniques and the materials were examined by

single crystal, powder, and high temperature x-ray diffraction techniques.

The phase equilibrium diagram, Figure 3, has been constructed from the

data given in Table 3. When Sb20^ is reacted at low temperature 0^750-

1000°C) with alkali carbonate it generally looses the CC^ and picks up

oxygen from the atmosphere to satisfy equilibrium conditions of the

phases formed, which may involve oxidation of the antimony ions. Therefore the antimonate systems reported here are not strictly binary.

The compound NaSbO^ (ilmenite-type) was found in this work to melt

at about 1555±5°C. An intermediate pyrochlore solid solution exists

from about 37.5 mole % Nao 0:62.5 mole % Sb o 0. to 24 mole % Nao 0:76 mole %

2 2 4 2

Sb_0, at 1350°C. The 1:3 composition probably does not really correspond

+3 +5 structurally to [NaSb ]Sb„ 0_ although the 3:5 composition may be

+3 +5 written as [Na. c Sb c ]Sb n 0, c see Section 3.2. The 3Na„0 : 5Sb„0, com1.5 .5 2 6.5 2 2 4

position apparently melts congruently at 1490±5°C. The solidus curve

falls from this temperature to about 1340±5°C at 24 mole % ^£0:76 mole

% Sb20^. A two phase region exists between the pyrochlore solid solution

and Sb20^. An unknown phase was found to occur in the system which could

7
be made approximately single phase by calcining the composition

15 mole % Na

2

0:85 mole % Sb^ at 750°C and reheating in a sealed Pt

tube to 1000°C for 64 hours in the presence of PtC^. This phase has

an as yet unindexed x-ray diffraction pattern with the four strongest

lines occurring at d values equal to 3.283, 2.798, 3.453, 8.23A.-

2.3.1 NaSb0

3

The compound ^20^20^ was first reported to occur by Schrewelius

[4] and to be hexagonal with a=5.316 and 0=15. 95A and an ilmenite structure.

This compound was found in the present work to melt congruently at about

1555±5°C. No other stable polymorphs were encountered.

2.3.2 Pyrochlore Solid Solution

One intermediate phase, a cubic pyrochlore solid solution mentioned by

Stewart and Knop [5], was characterized in the system. The compositional

varies from approximately Na

20:3Sb20^ to 3Na20:5Sb20^ with unit cell

dimensions varying from 10.289 to 10.286A respectively. Since the

pyrochlore is a tunnel structure and since this pyrochlore is the only

one reported that contains sodium that can be formulated by direct

synthesis it was worthy of further study as a possible ionic conductor.

For ionic conductivity measurements dense materials were needed and •

several experiments were conducted with Na20:Sb20^ (1:2) in an effort to

determine its stability under high pressure and temperature. In the first

experiment, 2.25 g of single phase pyrochlore material were prepressed at

2/

10,000 psi,- packed into a Pt cylinder 3/8 O.D. x 1 1/2" long with Pt0

2 and sealed. This sealed crucible was heated to 1000°C and 69,800 psi with

catastrophic results. Apparently this phase is not completely stable in

this. temperature-pressure range and some of the material reacted with

the Pt container resulting in a melting of the Pt. The remaining

— 10A" = 1.0 nanometers

2/ — The use of psi, bar, and kbar follows the current common practice of

workers in the field. Note that 1 bar = 10^ N/m2 (or pascal) = 10^

dyn/cm2 = 0.9869 atm = 14.504 psi. The accepted international standard

(SI) unit of pressure is the pascal or newton per meter squared.

8
specimen, slightly depleted in antimony oxide, was found by x-ray

diffraction to contain a pyrochlore phase plus ilmenite (1:1).

The next experiment was scaled down in amount of material and

pressure. A few milligrams of material were sealed in a 3 mm diameter

Pt tube and heated to 700°C and 4,000 psi for 1 hour in the presence

of Pt02« The material remained 1:2 (pyrochlore) with slight sintering.

A similar experiment was conducted at 1000°C and 4,000 psi for 2 hours.

The Pt©2 was decomposed and there was grain growth. The x-ray pattern

was of 1:2 pyrochlore. In the next experiment, two samples in sealed

platinum tubes were heated at 1100°C and 5,000 psi for 3 hours.

Platinum oxide was added to only one of the tubes before sealing. The

specimen without PtO„ was a single phase pyrochlore which appeared

to be a very dense material. The measured density was 5.21 g/cm . The specimen containing Pt02 was not dense.

In the last experiment two 5 mm diameter x 1 1/4" long tubes were

flattened (to a rectangular shaped cross section, 1.5 mm thick) packed

with material, sealed and heated to 1100°C and 4,000 psi. After heating,

this specimen was very thin and brittle and the specimen fragmented when

the Pt was mechanically removed. Again the specimen was quite hard with

3 a measured density of 5.26 to 5.29 g/cm . The average density of four

3 measured fragments was 5.26±.05 g/cm .

For ionic conductivity measurements, pellets of Na20:2Sb20^ (3/4"

in diameter) were placed in sealed platinum foil envelopes and hot

pressed by a commercial company at 1100°C and 5,000 psi. The pellets

were well formed single phase material with a density of 96% theoretical

(See Section on Mechanisms of Non-stoichiometry 3.2). The ionic con- ductivity of these pellets was measured at NASA Lewis Research Center

(LeRC) [6] and they were found to be essentially insulators.

f* "H3 +5 —2

The distribution of the various ions (i.e. Na , Sb , Sb ,0 ) in the Na20:2Sb20^ has not as yet been determined from single crystal

structure analysis. The structure of this material is currently

9
being determined at NBS. Until the results of this analysis are forthcoming it may he assumed that the "lone pair" electrons associated with

+3 +

Sb will not allow the passage of Na through the channels.

3/

2.3.3 Polymorphism of Sb^—

Two stable polymorphs of Sb20^ have been reported in the literature.

They are a-Sb^ which is orthorhombic [7] a=5.436, b=11.76, c=4.810A

and 6-Sb

2

0

4

which is monoclinic [8] a=11.905, b=4.834, c=5.383A and

3=101° 22'. From Table 4(a) it can readily be seen that specimens quenched

from a temperature composition region represented on the phase diagram,

Figure 3, as Sb20^ + pyrochlore may contain either a-Sb20^ and/or 3-Sb20^

when quenched from high temperatures and ambient pressures and examined

at room temperature. From this seemingly inconsistent data it would

appear that the a-Sb20^ form and $-Sb20^ form have a polytypic relationship. To help resolve this problem a high resolution electron microscope

study should be done.

From the date in Table 4(b) it appears that the 3 form is the

equilibrium high pressure form of Sb20^. Insufficient data has been

collected to establish if an equilibrium boundary curve exists, between

a-Sb20^ and 3°-Sb20^ at various temperatures and pressures. When specimens are sealed and heated under pressure in the presence of Pt02 in either Pt

or Au tubes single phase 3-Sb20^ is obtained. However when, heated under

pressure without the Pt02» a two phase specimen results, 3-Sb20^ and the

dense high pressure form of ^2^3 (valentinite) . A similar polytypic

relationship probably exists for the two polymorphs of Sb20g.

Some samples of Sb20^ will be sent out of house for electron diffraction studies in an attempt to establish the polytypic relationship

of a-Sb20^ and 3-Sb20^. Some additional experiments will be conducted

to establish the high pressure boundary curve between a and 3-Sb20^.

3/ — Most of the polymorphism study of Sb

20A was conducted prior to the

issuance of Interagency Agreement PR545160, and is included in this

report for the sake of completeness.

10
2.4 The System Sb^-KSbC^

This system has been examined between the compositional limits of

KSbO^ and Sb

20^. Sixteen compositions were studied by conventional

quenching techniques and the materials were examined by powder and by

single crystal x-ray diffraction techniques. Compositions which were

initially calcined at 500 and 700°C for 60 hrs, were dried at 230°C for

1 hr, sealed in Pt tubes and reheated. The results of the experiments

are given in the data presented in Table 5 from which the subsolidus

relationships have been established as shown in Figure 4. The compound

KSbOg with an ilmenite structure has been previously reported [9], A body

centered cubic solid solution phase originally reported as KSbO^ [9] has

been found to occur metastably at about 47.5% K

2

0. The 3K

2

0:5Sb

2

0,- compound reported previously [10.11] was found in this work to melt

congruently at about 1400°C. The K

2

0:2Sb

2

0,- compound reported previously

[11] was found in this work to have a phase transition at about 1000°C

and to dissociate to pyrochlore plus 3K

20:5Sb2

0

5 at about 1150°C. The

low temperature form of this compound labeled P2^/c represents a monoclinic phase with a=7.178A, b=13.378A, c=11.985A and $=124°10\ Single

crystals of this phase were grown by flux evaporation . from the composition

50K

2

0:5Sb

2

0^:45MoO^. The unit cell and space group were determined from

these crystals and confirmed by least square indexing of the powder diffraction pattern of the low temperature form of the compound K

2

0:2Sb

20^.

The pyrochlore solid solution exists at 1150°C from about 15 mole %

K„0:85 mole % Sb„0. to greater than 30 mole % Ko0:70 mole % Sb„0. . The

2 2 4 ° 2 24

melting characteristics of these phases have been partially determined

and are currently being reported.

2.4.1 Hyroxyl Ion Stabilization of Cubic Potassium Antimonate

The compound KSbO^ was reported previously [12] as being cubic at

ambient conditions when previously subjected to high temperatures and

pressures. In this work two experiments were conducted, heating single

11
phase KSbOj ilmenite in sealed platinum tubes at about 750°C and 88,000

psi, utilizing argon as a pressure medium. The. first of these, a two-hour

run, showed only one small cubic line in the x-ray pattern but the

specimen quickly reacted with atmospheric moisture. This experiment was then repeated for a longer time, 7 hours. In this time the material

apparently reacted with the sealed Ft tube. The specimen was ground,

mixed with petroleum jelly, and subjected to x-ray diffraction analysis

before too much hydration could take place'. The x-ray pattern showed

lines of a material not seen by us previously. It may be concluded

that this is a somewhat reducing environment and some of the material

has transformed to K90 and s b20 3 which in turn melted and reacted with

the Pt container.

The body centered cubic phase was not formed at the above stated

conditions. However, occasionally small amounts of a cubic phase were seen

in the x-ray powder diffraction pattern of KSbO^ ilmenite heated at ambient

pressure. For these reasons specimens of 1:1 and 3:5 mole ratios

K20:Sb20^ were equilibrated in air at 750°C for 60 hours and picked up

oxygen to form the phases KSbO^ and K^Sb^O^g and then were reheated for one hour at 1200°C to drive off all excess moisture. X-ray diffraction

patterns of these specimens showed single phase ilmenite and the

3K20:5Sb20^ compound. Portions of these 1200°C calcines were then

weighed and mixed in acetone in the appropriate ratios to yield com- positions of 46, 47, 47.5, 48 and 49 mole % 1^0. Each of these specimens

was dried at 240°C for one hour and heated in open Pt tubes at 1200°C

for one hour. Only the x-ray pattern of the 46% specimen showed a little

3K20:5Sb20y the others contained only the cubic phase. A new specimen

of 48 mole % K^O was prepared in the same way except the Pt tube was

sealed. After one hour at 1200°C, the x-ray pattern of the specimen

showed only about 50% cubic. A new specimen of 48% was prepared by

weighing the 1:1 and 3:5 phases immediately after removal from the

12
1200°C furnace and sealing the material in a flattened Pt tube within

1-2 minutes. This tube was then inflated at 1200° for a few minutes

and the material mixed by shaking in a "wiggle-bug" . The sealed

specimen was then heated for 64 hours at 1200°C. The resultant specimen

had exceedingly large grain growth indicating considerable solid state

recrystallization but showed no cubic phase. The conclusion is

inescapable that access to atmospheric moisture is probably necessary

for the formation of the cubic phase at atmospheric pressure.

A paper entitled "Flux Synthesis of Cubic Antimonates" was published

by the present authors during the course of this work [13]. In addition

to the discovery that the F ion stabilized the formation of the body

centered cubic phase of potassium antimonate it was disclosed that the cubic

antimonate could also be obtained by reacting KSbO- with a small amount

+3 +4

of other cations with small radii like B , Si , etc. It now appears

obvious that in this reaction the boron or silicon (etc.) actually ties

up some of the K

+

ion in a second phase and allows the K

+

deficient

antimonate to react with atmospheric moisture to form the cubic antimonate

previously thought to be "KSbC>

3

"

.

2.5 The System Sb^-NaSbC^-NaF

2.5.1 The System NaSbC^-NaF

To determine if NaF additions will stabilize the body-centered cubic

phase similar to the 6KSb0

3

:KF-phase, NaF was added to NaSbO^ in the ratio

of 3NaSb0

3

:NaF, 4NaSb0

3

:NaF, 5NaSb0

3

:NaF, and 6NaSb0

3

:NaF. The x-ray

diffraction patterns of these specimens contained varying amounts of

body centered cubic phase, ilmenite, and NaF. After heating at 750°C

and 1000° C in sealed Pt tubes, the x-ray patterns showed only ilmenite

and NaF, however at ^1150° C all the compositions contained some body

centered cubic-type phase. The compositions 3NaSb0

3

:NaF and 4NaSbC>

3

:NaF,

when heated in sealed Pt tubes at M.250°C, did not contain ilmenite and

13
appeared to be the closest to single phase cubic. The small crystals

of 4NaSbO^:NaF prepared by quenching in a small sealed tube appeared

to be well formed truncated octahedrons. However, the room temperature

x-ray diffraction pattern of the material had somewhat diffuse lines . with the exception of the hOO lines which were reasonably sharp, suggesting rhombohedral symmetry. This material was placed on a hot stage

microscope slide and analyzed by x-ray diffraction from room temperature

up to 220°C. At 190°C the material appeared to start to go cubic and

by 220°C a good quality cubic x-ray diffraction pattern was obtained

(a^.SSSA). When the material was cooled to room temperature the symmetry

was again non-cubic. As the hOO lines deteriorate somewhat on cooling,

the true symmetry of the room temperature form is probably no higher

than monoclinic or triclinic rather than rhombohedral. It was therefore

not unreasonable to expect that a body centered cubic phase could be

obtained by direct synthesis with NaF without the necessity for Na

+

ion exchange.

2.5.2 The Ternary System

X-ray diffraction patterns (single crystal and powder) of selected NaFflux synthesized (see Section 2.8.2.4) washed crystals show only a truly

cubic bodyccentered phase (a=9.334A). It must be postulated that the

composition formed by this technique is slightly different from that made

essentially single phase at 4NaSbO^:NaF in a sealed tube. In an attempt

to obtain a fluorine-substituted body centered cubic phase which exists at

room temperature the compositions shown in Table 6 were prepared and show

the reported phases when quenched from 1250°C. Equilibrium was not

obtained in overnight heat treatments at 1200°C. At 1350°C the body

centered cubic phase started to decompose. The composition 68NaSbO,j:4Sb20^:

28NaF (mole percent) was chosen as the best composition for further studies

on ceramic procedures (Section 2.7).

14
The phases found in the specimens heated at ^1250°C are summarized

in "equilibrium" diagrams for the quaternary system NaSbC>2-Sb202-Sb20^-NaF

(Figure 5) and the ternary plane of this system NaSbO^-Sb20^-NaP (Figure 6)

2.6 Other Systems

During the course of this study other alkali-oxide systems were sur- veyed, to decide whether interesting phases existed in these systems.

Among those investigated were sodium and potassium bismuthates and sodium

and potassium with several rare earth oxides, N^O^, Sn^O^, and G^O^

as well as with ^O^.

2.6.1 Alkali Bismuthates

Samples of sodium bismuthates and potassium bismuthates were prepared

from the respective alkali carbonates and ^^O-j anc^ heated in open Pt

tubes at 500°C for various periods of time (Table 7) . X-ray diffraction

patterns showed essentially single phase Bi2("> 3 w^ t ^ several small

unidentified peaks in the Na20-Bi20-2 samples. These peaks did not

correspond with those of commercial NaBiO^ (apparently prepared according

to Scholder and Stobbe [14]), which decomposes to Bi20-2.

2.6.2 Alkali-Rare Earth Systems

Alkali carbonates were dry mixed with the respective rare earth

oxides and heated as shown in Table 8. X-ray diffraction patterns were

recorded with Ni filtered Cu radiation. A "?" indicates an unknown phase

which is present as one or two small peaks in the pattern.

The only significant result of these studies appears to be the

presence of the cubic rare earth structure in Gd20-3 well above its

equilibrium transition. Apparently the alkali ion enters the rare

earth oxide lattice to some extent, altering the polymorphic conditions.

15
2.6.3 Further Studies in the System Nb

2

0

5

:KNbC>

3

During the interim between this contract and the previous one, it

became apparent that the compound 2K

2

0:3Nb

20^ might have interesting ionic

conductivity. However, as the exact ratio 40K

2

0:60Nb

20^ did not yield

a single phase, new compositions were prepared (Table 9) and the com- position AlKgO^tft^O^ was further studied. The conclusion that this is

probably a non-stoichlometric phase led to a revision of the NbgO^-KNbO^

phase diagram (Figure 7)

.

2.7 Pellet Fabrication

2.7.1 AlK

2

0:59Nb

2

0

5

("2:3", K

4

Nb

6

0

1? )

Evaluation by LeRC of the never-hydrated single crystal of K^NbgO^y

supplied by NBS resulted in a request for single phase, polycrystalline,

never-hydrated pellets of this same composition.

The starting material was prepared by dry mixing KNbO^ and Nb

2

0,j

in appropriate amounts, followed by calcining at 800°C for 10 hours

and 1000°C for 30 hours with intermediate grinding. Pellets were pressed

without binder at 10,000 psl in a 5/8 inch diameter steel die. Sintering

was done in air at 1125°C for 18 hours. The pellets were removed from

the sintering furnace at temperature, immediately placed in a silica

*\> -5

glass tube, evacuated to p ^ 2x10 torr and sealed for transmittal.

The composition 2K

2

0:3Nb

20^ (K^NbgO^) was observed to contain a small

amount of the tetragonal tungsten bronze (TTB) second phase. This second

phase was completely eliminated by using a starting composition of

41K

2

0: 59Nb

20^. A large batch of this 41:59 K/Nb composition was prepared

and successfully exchanged as shown in Table 10. A pellet of the unexchanged

41:59 composition was prepared and sintered at 1100°C for 1 hour and subsequently exchanged. However, the problem of hydration with the 41:59 com- position is much more severe than with the 2:3. It was necessary to maintain

the sample at temperatures ^ 100 - 150 C to obtain a powder diffraction

16
pattern and to our dismay, the exchanged pellet hydrated and decrepitated

while being x-rayed in laboratory air. More elaborate precautions were

necessary to successfully characterize pellets of this composition. It

is not known if the lack of the TTB second phase increased the sus- ceptibility to hydration or if this is due to a slightly higher than

stoichiometric amount of K+

(Na+

in the exchanged material) in the

lattice

.

A series of heating experiments was performed to determine the

optimum sintering conditions for pellets of nominal composition

41K

20:59Nb

2 0 5> At a temperature of 1100°C overfiring of the pellet

was pronounced, as evidenced by the presence of a small amount of a liquid phase and marked reduction of niobium. Attempts to reoxidize

the sample by annealing at lower temperatures were not completely successful. Temperatures of 1000° and 1040° C (the melting point of KNbO^)

did not result in sintering sufficient to develop any mechanical strength.

A temperature of 1050° and 2 hours time was found to result in sound

pellets. X-ray characterization of the material after this heat treatment showed only single phase "2:3".

As stated above, the problem of hydration in this composition is severe at all stages of the fabrication and exchange. The following

schedule was adopted in order to minimize the exposure to laboratory air,

with each subsequent fabrication step performed with a minimum of delay.

Single phase isostatically dry at

41K 0:59Nb 0 * ?nn

PrSSS

"* P ress "* 220° c powder 1 D /UU pS1 20,000 psi 0.5 hr

sinter at place in fused quartz _ 1050°C * tube, evacuate to p<10

2 hrs torr and seal off

A similar procedure was used for the pellets to be exchanged, except that

at the completion of sintering, the pellets were placed individually in

17
NaNO^ and exchanged at 450°C for 64-68 hours. At the completion of the

exchange period, the excess NaNO^ was removed by leaching in methyl

alcohol, the pellets were dried at 200°C for 0.5 hours and then placed

in a fused quartz tube, evacuated and sealed.

During the exchange period, the pellets appeared to suffer no physical degradation and x-ray powder diffraction of a sample obtained

from the center of a test pellet showed that complete exchange to the

Na phase had occurred.

Six pellets of the "2:3" K phase and three pellets of the exchanged

"2:3" Na+

phase have been submitted for evaluation.

2.7.2 4Rb

2

0:llNb

2

0

5

(11-layer phase)

Pellets of the 4:11 composition were prepared by using 1 weight

percent stearic acid as a binder, pressed in steel dies at 10,000 psi

and sintered at 1200°C in air for 56 hours. The pellets were sound

and showed little tendency to spall or disintegrate during exchange in

molten KN0

3

(see Table 10).

2.7.3 Large Pellets for Ionic Conductivity Measurements

As mentioned several times, the problems of hydration and com- positional changes resulting from volatility or change in oxygen content

in the alkali niobates, tantalates and antimonates necessitate the use

of rather extreme measures to produce sound pellets. The complete

encapsulation of the starting composition at the earliest stage possible

in the fabrication process appears to be successful in some cases. In

such cases, the specimen remains encapsulated until ready for evaluation.

Two compositions were prepared for large dense specimens to be sent

to LeRC, 41K

2

0:59Nb

2

0

5

and NaSb0

3 _x

F

x> The NaSb0

3_x

Fx was prepared

by holding 7Sb 90. :93KF at ^1000°C for less than 10 minutes and then

18
separating the fines from the coarser grains by washing, settling, and

centrifuging the insoluble product. The fines were then ion exchanged

two times with NaNO, at 450°C - 2 hrs. The exchanged phase (NaSbO- F ) J X X

gave an x-ray pattern which was single phase cubic. The powders were

pressed into 3/4" diameter pellets which were repressed isostatically

at 20,000 psi. These pellets were placed in platinum envelopes, sealed on three sides and were again isostatically pressed to remove most of

the air from the container. The envelopes were sealed and sent to a commercial company for isostatic hot pressing at M.100°C and 5,000 psi.

The 4IK2O: 59Nb20^ specimen was submitted to LeRC, unopened, in the

platinum envelope. Duplicate specimens were used to determine physical

integrity and phase composition of the pellets. The NaSbO_ F specimen

j —X X was not single phase after hot pressing, apparently as a result of decomposition under pressure. Three phases were evident: a cubic phase, the

pyrochlore solid solution and NaF, It was felt that the exchanged product

had a composition too close to a phase boundary with resultant instability

under pressure. For this reason, it was decided to directly react the

constituents to form the desired sodium containing phase directly and

then hot press the product. A composition of 68NaSb0.j:4Sb

2

0^:28NaF

was chosen.

Attempts to fabricate a large, dense specimen of the composition

68NaSb0.j:4Sb20^:28NaF ware largely unsuccessful. Direct reaction of

the components at 750°C for 60 hours and 1000°C for 1 hour in open

containers, with periodic grindings, resulted in a product containing

NaSbO^ (ilmenite) and a trace of NaF. Calcining temperatures as high

as 1265°C were required to form a single phase material of the desired

cubic structure. A trace of NaF was always present as a second phase.

The use of such high calcining temperatures results in a coarse-grained

product which could not easily be ground fine enough to produce a sinterable powder. Attempts to hot press the specimens in platinum envelopes,

19
using the same technique described above for the 41:59 and KSbCL F

specimens, at a temperature of 1250°C for 10 minutes were unsuccessful.

It is recommended that if these experiments are repeated, only the lower

temperature calcines (at 750° and 1000°C) should be used, and the final

desired phase in the pellet be produced by appropriate choice of time

and temperature of hot pressing.

2.8 Crystal Growth and Synthesis

Many of the phases discovered during the phase equilibria studies

of the alkali tantalate, niobate and antimonate systems have not been

previously reported in the literature. One of the objectives of the

crystal growth portion of the study has been to synthesize and grow

small single crystals for x-ray diffraction studies to provide structural

information on these materials and assist in the interpretation of

x-ray diffraction powder patterns. The second, and equally important

objective, has been to grow single crystals of the potentially useful

K and Rb phases for use in studies of ion exchange behavior for the

purpose of obtaining Na

+

phases. These studies are described in Section

2.9 of this report.

In general the choice of technique was dictated by the characteristics

of the desired phase, i.e. congruent or incongruent melting, volatility

of one or more components of the phase, range of coexistence with liquid,

and desired final size of crystal. Both fluxed melt and Czochralski

techniques were utilized, and in some cases, the flux evaporation technique

was used for the preparation of small crystals.

2.8.1 Crystal Growth by Pulling from the Melt

2..8. 1.1 Hexagonal Tungsten Bronze in the K20-Ta20^-W0.j System

Selective phase equilibria experiments with mixtures of KTaO^ (KT) and

W0

3

in the neighborhood of KT:2W0

3

(K

2

0:Ta

2

0

5

:4W0

3

) during the previous

contract confirmed the existence of a hexagonal tungsten bronze (HTB)

20
structure. Single phase compositions were easily prepared between

the pyrochlore composition, 1^0:13202^02, and a composition KTaO^tSWO^

where a second, unidentified phase appeared. At the same time, exploratory

crystal growth runs at lower T^O^ contents were encouraging and gave

some promise of adaptation to the accelerated crucible rotation technique

(ACRT) for single crystal growth of this bronze structure. However,

considerably more work is required to determine the liquidus surface

and primary field extent before such experiments would be definitive.

A 50 gram batch of 26.6K

2

O:3.3Ta

2

O

5

:70.1WO

3

, prepared from KT,

K^WO^ and W0^ was premelted by induction heating in a platinum crucible.

The crucible was then covered and transferred to a growth furnace.

Following a 10 hour soak at 1200°C, the temperature was lowered at 2.5°C hr~^

to 500°C and the crucible removed from the furnace. Results were essentially

the same as obtained in previously reported work with a cooling rate of

approximately 30° hr~^. Crystals were in general small, the largest

ranging from about 6x6x0.2 mm to 3x3x0.1 mm. The yield, based on visual

estimate, was small.

Because of the small total yield and extensive nucleation and growth

of small platelets, an attempt was made to pull crystals of the HTB from

the fluxed melt. A 250 gram charge of composition 27^0: 5Ta

20^ :68W0^ was placed in a platinum crucible in a growth furnace which was baffled

to provide an essentially isothermal chamber except directly above the

center of the melt where the platinum pull rod was inserted. The charge

was held at 1225° for three hours prior to attempting growth. Although

no evidence of solid was present on the surface of the melt, extensive

freezing of polycrystalline material occurred when the pull rod was

inserted. The temperature was raised in increments and the polycrystalline

mass redissolved. All attempts to achieve growth were unsuccessful at

temperatures up to 1250°

.

21
In the final attempt, at 1265° C, crystallization on the pull rod was

slow enough to allow a 16 hour pull. X-ray diffraction examination of

the results indicated that the crystals obtained were the desired phase.

However, physically, the crystals were in the form of small plates, bound

together by the frozen melt. It appears that a considerable effort would

be required to establish suitable conditions for the growth of larger

single crystals of this HTB. This would probably require a minimum of

1-2 man years.

2.8.1.2 The System KNb0

3

~Nb

2

0

5

Single crystals of K^Nb^O^ have rather easily been grown both at

other laboratories [15] and at NBS. However, the material hydrates

readily in laboratory air with subsequent degradation of the crystalline

perfection, which is not regained by drying. In order to provide LeRC

with a large single crystal which had never been hydrated, a crystal was grown from a melt of the same composition, removed from the puller while

still at a temperature of 300-400°C and immediately placed in a fused

^ 4/ silica ampoule, evacuated to p<2xl0"° — torr and sealed for transmittal.

Later conversations with LeRC indicated that the behavior of this

crystal was indeed different, and as described in the section on pellet

preparation, never hydrated pellets were also supplied for evaluation.

2.8.1.3 The System Rb

2

0-Nb

2

0

5

A 100 gram batch of 29Rb

2

0: 71Nb

2

0

5 was calcined at 400° for 60

hours and used for crystal pulling experiments. Five single and/or polycrystalline boules of the 4:11 (Rb:Nb) (11-layer) hexagonal phase were

pulled from the melt by the top seeded solution method. The crystals

were obtained using both seeded and unseeded pull rods. These crystals

were used as "purified" material for the growth of single crystal 11L

for use as a stable end member of the system and for chemical analysis.

— The use of torr follows the current common practice of workers in

the field. Note that 1 torr = 1.32 x 10^3 atm = 1.34 x 102 N/m2 .

22
The crystals appear to be susceptible to thermal shock and therefore

must be cooled relatively slowly. Self-seeded crystals show a marked

preference for growth perpendicular to the c-axis. At least one excellent

cleavage (basal-plane) is evident.

Crystals of the hexagonal tungsten bronze (HTB) phase in this system

(21.75Rb

20:78.25Nb20^) were grown by pulling from a melt of the same composition (experiments performed by C. Jones while on an American

University Research Participation Program). Large, clear water-white

crystals were easily obtained but all fractured into rather large blocks

upon cooling. All attempts to prevent cracking were unsuccessful and

the cause remains unknown, but may be related to a symmetry change to

orthorhombic on cooling.

Crystals of the Gatehouse tungsten bronze (GTB) (11.5Rb

2

0:88.5Nb

2

0

5

) phase were grown from a melt of composition 16Rb20 : 84Nb

2

0^- (experiments

performed at NBS by D. Klein while on an American University Research

Participation Program) . Small single crystal boules were successfully

grown, but again fractures developed as soon as the boules were removed

from the melt at the completion of the run in spite of all attempts at

slow cooling of the boule.

2.8.2 Flux Growth

2.8.2.1 The System Rb

2

0-Nb

20

5>Mo03

Nine different compositions in this system were prepared (2 gm

batches) and heated by induction to temperatures in the 900°-1100°C

range in small platinum crucibles. Recrystallization and/or volatility

of the MoO^ resulted in the formation of small crystals. Crystals

(2mm+) of the 11 layer hexagonal (4:11) phase were obtained from com- positions of 30Rb

2

0:5Nb

2

0

5

:65Mo0

3

and 30Rb

20:10Nb

2

0

5

:60Mo0

3

. A

27.5Rb 9 0:10Nb 9 0_:62.5MoCL composition yielded small crystals of the GTB

23
phase (Ml. 5 mole % Rb

20) and H-NbgO^ and 28Rb2

0:5Nb

2

e> 5

:67Mo0

3

yielded

small single crystals of the HTB (^21.75 mole % Rb

20) . No crystals of

the unidentified phase occurring at about 15 mole % Rb

2

0 in the binary

system were obtained with any MoO^ flux composition. This is further . reason to believe this phase may not be an equilibrium compound in the

binary system.

2.8.2.2 The System Rb

2

0-Ta

2Q

5

-Mo0

3

Six different compositions were prepared in the ternary system for

flux evaporation crystal growth. Single crystals of the 9 layer phase

(1:3) were grown using compositions of 30Rb

2

0:10Ta

2

C>2:60Mo0

3

and

35Rb

2

0:5Ta

2

0,. :60Mo0

3

. Crystals of the other phases in the binary system

Rb

2

0-Ta

2

0,. could not be obtained using this method, probably because their

primary fields do not extend to such high MoO^ contents, or to the

relatively low temperatures involved.

2.8.2.3 The System Rb^-Ta^-RbF

In view of the success obtained by the flux synthesis route in the

KSbO^-KF system [13] similar attempts were made using RbF and Ta

20^.

A 95RbF:5Ta

20^ composition was completely liquid at about 925°C and on cooling yielded acicular crystals of an unknown phase. A 75RbF: 25Ta

20^

composition was heated to about 1150°C for 30 seconds and quickly cooled.

After leaching with water, a sizeable yield of clear, well-formed,

octahedral crystals of the RbTa^^F pyrochlore phase was obtained.

2.8.2.4 The Systems ASbC^-Sb^-AF (A = Na,K,Rb)

The techniques for synthesis and growth of small crystals of

KSb0

3 _x

Fx

by reaction between KF and Sb

20

5

at temperatures in the 1000°C

range, developed during this contract, have been described [13].

Attempts were made to melt the flux-synthesized KSbO^

x

Fx

in air

with the thought it might be possible to pull crystals directly from

24
a melt of that particular composition. The material decomposed as the

melting point was reached, indicating that pulling in air would not be

feasible. A large batch of ^50 grams was prepared with a composition

of 70KF:30Sb2O, and heated in an effort to obtain a melt- (single phase

liquid) suitable for crystal pulling. At all temperatures below which

there was excessive volatilization a solid phase remained. It seems obvious now that we have to go much higher in KF concentration to obtain

a composition which may be suitable for crystal growth.

Quenching experiments indicated that mostly ilmenite was formed at

temperatures up to M.200°C in the system NaF-NaSbO^. We decided to

attempt a direct synthesis of the sodium cubic phase in the same manner

as for the KSbO- F but at a higher temperature. A 3 gram batch of

.3 TMX X

NaF-Sb20^ (molar ratio 93:7) was heated in a platinum crucible to 1250°C

and the NaF allowed to evaporate for 35 minutes. After leaching the

residue in water we obtained essentially single phase NaSbO- F . j "X X

The largest crystals were of the order of 1 mm. Some flat hexagonal

plates of ilmenite are formed at the lip of the crucible, probably during

volatilization of the sodium antimony fluor-oxide, however these can easily be separated mechanically from the cubic phase.

X-ray diffraction patterns (single crystal and powder) of selected

washed crystals show only a truly cubic body centered phase (a=9.334A).

It must be postulated that the composition formed by this techique is

slightly different from that made essentially single phase at 4NaSbO^:NaF

in a sealed tube.

Exploratory flux evaporation heatings were made in the

KSb0

3

~Sb

20^-KF and RbSbC^-Sb^-RbF systems as a preliminary step

in the determination of suitable starting compositions for flux crystal

growth of the desired ASbO^ F phases. The results are summarized

25
in Table 11. None of the reported compositions would appear to be

suitable for top-seeded solution growth both from the standpoint of

the excessive volatility of the alkali fluoride at the temperatures

involved and the presence of a solid phase. The presence of a solid

phase at such high concentrations of flux (alkali fluoride) indicates

that either a gradient transfer technique in sealed crucibles must be

adopted or the suitability of other flux systems investigated.

An attempt was made to synthesize "RbSbO^" in the cubic polymorph

by direct flux synthesis from the composition 95RbF:5Sb20^ heated for one hour at about 900-1000° C in an open Pt crucible. Well developed

psuedo-octahedral crystals were formed and easily isolated although

their exact composition is unknown. However single crystal x-ray diffraction patterns indicated that these crystals were probably triclinic,

although the observed unit cell was C-centered.

2.9 Ion Exchange

One of the the best screening tests for ionic conductivity of a solid phase is to determine whether or not the alkali ion in the

structure can be exchanged with an alkali ion of a different species.

This may be tested by heating in a large excess of a molten salt (or

solution) containing the second ion. A large number of experiments

of this type were performed on many different compounds found in this

and the previous year's [1] study. The results of these tests are found

in Table 10(a)

.

Most of the exchange experiments have been performed on powdered

materials. In those cases where single crystals could be grown either

by flux techniques or melt techniques (see Section 2.8), attempts were

also made to ion exchange the single crystals.

In general, the results of ion exchange experiments on single crystals

were disappointing in that either disruption of the single crystal

26
occurred or exchange proceeded at extremely low rates. Thus it appears

that a study of technique development for ion exchange of single crystals

would be appropriate if these are to be useful in device applications.

Consideration should be given to the use of an electric field or other

technique in order to obtain a greater driving force for exchange.

Ion exchange experiments were conducted in the I^O-Itt^O^ system

with particular emphasis on the 11-layer compound occurring at or about

4Rb20: llltt^O^ (26.67 mole % Itt^O) . Ion exchange experiments were con- ducted on both single crystal fragments obtained from crystals grown

from the melt and low temperature calcines of 4:11 powders. The single

crystals underwent K

+

exchange in molten KNO, but disintegrated during

Na exchange in NaNO^ during various temperature and time combinations.

Pellets of the 11-L phase were pressed both uniaxially and isostatically

with and without polyvinyl alcohol binder. Pellets were fired and x-ray

patterns made before any attempt was made to induce ion exchange. Generally

the K+exchange occurred without too much degradation of the specimen

but the pellets disintegrated to a fine powder during Na+exchange.

Results of these exchange experiments are also presented in Table 10 (b)

.

The unit cell dimensions for complete ion exchange were developed from

ion exchange in molten salts from very small single crystal fragments.

3.0 RELATION OF STRUCTURAL MECHANISMS OF NON-STOICHIOMETRY TO

IONIC CONDUCTIVITY

It is probably generally accepted that a phase which exhibits

unusual ionic conductivity must necessarily be structurally nonstoichiometric . Unfortunately the opposite is not necessarily true.

Nevertheless a crystallographic understanding of non-stoichiometric

phases is an obvious necessity to the tailoring of new fast-ion conductors.

For this reason it is worthwhile to discuss the nature of the non-stoichiometry which has been observed in this study for those phases which seem

to be of interest.

27
3.1 Hexagonal Tungsten Bronze-type Phases (HTB)

It has already been mentioned in the previous summary report [1]

that the hexagonal tungsten bronze-type phase (HTB) found in binary

alkali niobate and tantalate systems has alkali ions in non-stoichio-

+5 +5 metric positions and excess Nb or Ta ions. These excess pentavalent

ions may well block the alkali ion conductivity as these hexagonal

bronzes cannot be ion exchanged. There are two mechanisms that have

proved effective in altering the ion exchange characteristics of the

hexagonal tungsten bronze-type structures. One is to change the total

alkali: other cation valence ratio by substituting for Ta

+^, for

instance in the system KTaO.,-W0

3

. In this case the HTB phase occurs + +

at about the 1:2 ratio and the K ion can be replaced with Na by

heating in a large excess of NaNO^ . Unfortunately the Na-tantaluratungstate is not stable above about 450°C and therefore cannot be

formed into low porosity ceramics by conventional techniques. The single

crystals of HTB grown with the potassium tungstate flux (Section 2.8.2.1)

need some greater driving force then temperature (<450°) to obtain complet

exchange with Na

+

ions. The alternate to replacing Ta

+^ ions with

ions is to change the structure enough to allow ion exchange (See

Section 3.3)

.

3.2 Pyrochlore Phases

In the KTaO^-WOg system a pyrochlore phase also occurs at about

the 1:1 ratio or Q[TaW]0^. Unfortunately the pyrochlore in this

system transforms to a tetragonal tungsten bronze (TTB) at high temperatur +

Although it can be ion exchanged with Na , this pyrochlore phase also is

not stable above about 450°C. The only stable Na

+

containing pyrochlore i

the one in the Sb20^-NaSbO^, system and apparently this one is not a good

ionic conductor.

28
+ +3 +5 -2

The distribution of Na , Sb , Sb and 0 ions in a pyrochlore

single crystal is currently under evaluation by the Crystallography

Section at NBS. However, certain assumptions can be made which may

enable us to postulate the approximate distribution. The formula

for the compositions observed to result in a pyrochlore structure

+3 might be postulated to be [NaSb ]Sb

2 0

7 for the Na/Sb ratio of

1:3, [Na

2 ^Sb^] Sb^ _ 6?

for 1:2, and [Naj 1/2

Sb i/2 ] Sb 2°6 .

5

for 3:5. However, these compositions do not illustrate the structural

nature of pyrochlore nor account for the observation that the "lone

+3 —2

pair" electrons associated with Sb will not allow 0 " ions to

completely coordinate the antimony and result in apparent vacancies.

The structural formula of pyrochlore should be written as [A_X] [B 0 X,]

L t 0 to emphasize the fact that the octahedral network of B 0X, is required

to be complete if the structure i? to be stable. The A^X ions fill

the intersecting channels in this B„X, framework. In our material

2 6 +5-2 the B.X, framework must be represented as [Sb 0 0,1 and must be

6 + -2 6 +3

stoichiometric. All remaining Na and 0 ions, as well as Sb , must

+2 +5 be in the [A.X] portion of the formula. All Sb must be in

+3

B-X, and only Sb in A„X. Furthermore the maximum number of the

+1 +3 -2 —2 sum of Na , Sb excess 0 (beyond 0^ ) and "lone pair" electrons

cannot exceed three. One can then write the general formula as

[A

20]

+2

[Sb

2 0

6 ]" 2 with [A2 0]

+2 equal to

N4/k + K

1 + Sb

tx

+ °'y 2 + ^kx^ 3

where k equals the ratio Sb/Na. Using the ionic valences and the sum

of the ions equal to three, maximum densities can be calculated and

compared with the observed to test the structural hypothesis. The maximum

density for the Na/Sb ratio of 1:3 represented by the formula

+1 +3 -2 I—I +2 +5 -2

[Na^

g^y

Sb

q 75°Q 533! Iq 75] t Sb 2 is calculated t0 be 5.469 units.

29
For the Na/Sb ratio of 3:5 with the formula

+1 „, «-2 ,+2 rn1. „ n -2

[Na, c Sb n c 0 ft J L c ] [Sb„0,] the density is calculated as 5.406.

1 . j U . j (J . _> U._> Z 0

For the intermediate composition with the Na/Sb ratio of 1:2 and a formula of [Na+^^SbJ^ggO-^^D^ 588 ] +2 [Sb^] -2

the maximum

density is found to be 5.481. The density found for our isostatically

hot pressed specimens is 96.0% of the maximum theoretical density.

It should be remembered however that the true theoretical density

of any given Sb/Na ratio will decrease with decrease in temperature.

Thus the densities obtained on our hot pressed specimens are, in all

probability, greater than 96% of theoretical in view of the expected increased oxidation of the Sb at the relatively low temperatures involved.

As stated above, the pyrochlore structural formula should be

written as [AgX] [BgXg], The RM^O^ is apparently equivalent to

the formula

[2

Rb'

+1 tW"1

as shown by Hong's structural study [16] of single crystals prepared

by the flux synthesis method described by NBS [17] . The Rb

+

ion is

apparently too large for the A sites and it is this preference for the

larger anion site that makes this compound stable. During ion exchange

in KNO_ the K

+

ion apparently enters the A site and, upon exposure to

atmospheric moisture, an HJD molecule occupies the site formerly con- taining Rb . The formula is then

Ok H„01 +1 [Ta^O.F]"1 [LJK H

20r [Ta2

0

5

F]

During sodium exchange it is apparently possible to obtain a non-stoichiometric amount of Na in this lattice. The formula for this phase can probably be written as

30
The product obtained by acid leaching of this pyrochlore is apparently

[2H

30]

+1

[Ta

20

5

F]" 1

.

Although infra-red analysis of the Na+

exchange product does not

indicate (0H)~ [18] it would probably be worthwhile to examine this product

with NMR for hydrogen resonance, a much more sensitive method than infrared adsorption.

3.3 Hexagonal Tungsten Bronze - Pyrochlore Series

The [B

2Xg] framework of the pyrochlore structure can be described

as being made up of alternating layers of the hexagonal tungsten bronze

structure separated by layers of isolated octahedra sharing only two corners with the adjacent HTB layers. If this structure is modified

by increasing the sequence number of either of these types of layers

from ABAB to AABAAB or AAABAAAB etc., a sequence of hexagonal phases

would be formed having the same axis as the HTB structure and with

varying but integral multiplicities of the c_ axis dimension. Such

phases are actually encountered in the K

2

0-Ta

2

0j. [1,2] Rb

20-Nb

20^ and

Rb

20-Ta

20^ systems and have been estimated by us to represent 9-layer,

16-layer and 11- layer sequences. All of the phases can be ion exchanged

for Na+

unlike the HTB in the same systems. The reason for this appears

to be that a rotation or translation of a portion of the layer sequence

allows the isolated vertical channels found in the HTB structure to be

changed to intersecting channels as in the cubic pyrochlore structure.

The exact crystallographic nature of these compounds is currently under

investigation by Dr. B. T. Gatehouse at Monash University, Melbourne,

Australia. Unfortunately, however, the Na+ion exchanged products

are again not stable above about A50°C.

As is the case with the pyrochlore compounds the K

20 containing

phases have unit cell dimensions very similar to or even larger than

the corresponding Rb„0 containing phases. For instance the c-axis for

31
the 11-layer phase in the K^O-Ta^ system is 43.512A while that in the

Rb

2

0-Nb

20

5

system is 43.18A and in the Rb

2

0-Ta

2

0

5

43.19A. This may be

due to a real difference in total alkali content. It may also be due

to hydration of the K

20 phases. No high temperature x-ray data is

available to check this hypothesis but small single crystals of the 2:5

K

2

0:Ta

20^ phase have been noted to crack, spall and jump on exposure

to air.

3.4 Body Centered Cubic Antimonates

A successful method of synthesizing cubic potassium antimonate by

heating in molten KF was published by the present authors during this

contractural period [13]. The major reason for the success in obtaining

completely single phase fluorine stabilized cubic potassium antimonate

is that the potassium ilmenite is H

2

0 soluble and may be easily separated from the cubic material.

An examination of the structural model of the octahedral framework

of the body centered cubic antimonate phase suggests that this structure

must always have some anion (X) occupancy in the 000, 1/2 1/2 1/2 position,

+12 -12

The structural formula thus appears to be [A-^X^

^ sb

i2°36^

with the

alkali ion in position (A) located at (or just off) the juncture of the

open cages. However, it seems very likely from both structural reasons

(bond lengths, etc.) and valency considerations that either or both of

the non-framework positions will be nonstoichiometric . Valency considerations

require that at least two out of 16 alkali ions must be missing and the

+12 -12

structural formula then be [I—

J

2

A^X

2 ] [Sb^O^g] . This formula

corresponds to the composition reported by the Lincoln Laboratory report

[19] for the single crystal x-ray diffraction analyses of the phase

synthesized with KF according to the NBS method [13]:

K

12Sb 12

0

36

.2KF or [ D^f/12 [Sb^]"12

.

32
It seems quite likely, however, that this general formula does not

completely account for all of the preparations which have been observed

to form this structure, whether body centered or primitive. The

observation that a primitive phase can be formed, in air, by reaction

with atmospheric moisture at a 48:52 ratio suggests that this phase

may well have considerably less than 14 alkali ions per unit cell.

The formula must be compensated, in this case, by a substitution of

a monovalent anion (OH, F) in the octahedral framework . The general

formula then becomes O2+x

A

14-xX

2

]+(12~X) [Sb 12°36-xX

x

3 " (12~X)

'

The composition found at ^48:52 in the potassium antimonate system

can be written (assuming a ratio of 11:12 K/Sb or 47.826% K^O)

K

22

Sb 24°71+5H2° "* K

22Sb 24°66 (OH) 10 or [n 5K

11

(OH)

2

] +9 [Sb 120

33

(OH)

3

]" 9

which also can be described as 6K?bO :3Sb 90,.:5K0H (see Figure 8). The +

general formula describing the K containing compositions is then

[., Kiy Xl] + (12"x) [Sb^O_ X']- 2+x 14-x 2 12 36-x x

The above formula contains only pentavalent antimony and apparently

does not completely explain the compositions which form a 'stable' body

centered cubic phase in the system NaSb0

3

:Sb20^

+x

:NaF. The only

formula which does not involve the loss or gain of 0

2

(or F ) when

the Sb

20^ is added in a sealed tube corresponds to:

[CLNa^Fj [Sb

+3

Sbt^ 0_, _ F„ ] 2 14 2 y 12-y 36-2y 2y

which is represented by the join 6:1 — 3:7 on Figures 5 and 6. There

+3

+3

is really no place in the framework structure for Sb and it is

difficult to believe that octahedrally coordinated antimony can be Sb

The lone pair electrons can be attached to the sodium ions instead of

the antimony or just in the vacancies. However, for convenience, the

33
+3

formulas can be written involving Sb . The new formula would then have

two variables:

[ ^2-hcA

14-xX2

] [Sb

y

3sb 12-y°36-(x+2y) X

'(x+2y) ]

represented by the plane in the quaternary system NaSbO^Sb20^5 NaF

bounded by the 6:1 — 3:4 and 6:1 — 3:7 joins of Figures 5 and 6.

However the single phase region in this system actually appears to

contain more NaF than described by this general formula. Apparently

-2

some 0 is evolved in the sealed Pt tubes, the amount depending

on uncontrolled variables such as the amount of free volume in the tube

and on changes from the original composition during treatment. The absolut

maximum amount of NaF which can be accommodated structurally by the body

centered cubic phase can be described by the formula

[Na

16

F

2

] +14

[Sb

+3

2.x

Sb10_x034_2xF2+2x

]-W

which represents a line in the system shown by the join 3:1 — 3:8 in Figur

6 and involves the evolution of one molecule of gas (C^) per formula unit.

The results of our investigations so far suggest that the body centered

phase approaches this formula as a limit. The composition of the cubic

phase in equilibrium with excess Sb20^ and molten NaF actually appears

to touch this line at approximately 10NaSbO.j :Sb20^:6NaF or

[Na

16

F

2 ] [Sb+3Sb;5

0

32

F

4

] + 0

2

.

The single phase distorted cubic material on the binary join NaSbO^NaF

appears to have a composition between 6:1 and 5:1 or approximately

HNaSb0

3

:2NaF or

[Na14.18F

2

] t Sb 12°35.818F

0 W+ - 0909 °2

34
The compositions in the quaternary system thus probably lie on a join

between these two end members.

A large number of experiments were performed in an attempt to

synthesize ceramic products of single phase body centered cubic sodium

antimonate "stabilized" with F

+

. Although we have not yet succeeded

in preparing such a ceramic all indications point to a short time heat

treatment with specific specimen preparation techniques. These almost

unique conditions indicate that the body centered cubic phase is not

really stable under the conditions at which it is formed. Thus either

its true stability field may lie at some higher or lower partial pressure

of O2 (or OH) or it may always be metastable under any conditions.

3.5 The Phase 2K

20:3Nb

2

0

5

In the previous contract summary report [1] it was reported that

the compound occurring at about 2^0:3^20^ had the unit cell dimensions

a=7.822, b=33.019, c=6.481A when not hydrated. Only the b_ axis expanded

upon exposure to moisture as previously mentioned by Nassau [15] . From

these unit cell dimensions several postulations can be made. The a. direction corresponds to 2x3.911 or two O-Nb-0 distances and probably

represents two Nb-octahedra sharing oxygen at their corners. The c_ direction corresponds to 2x3.2405 or two times the 0-0 distance cor- responding to edge sharing of the Nb-octahedra. The b_ direction is

^10 times the value for edge sharing. It may be assumed that the

structure is made up of layers or slabs perpendicular to b, composed

of octahedra edge-shared in the £ direction and corner shared in the

a_ direction. These slabs must be separated by layers of K

+

ions and

the K+ions should then be rather mobile. That this is actually the case is demonstrated by our reported ion exchange with Na

+

where the

b_ axis changes to 30.78A and the conductivity measurements made by LeRC

[20] . The actual crystal structure of this phase is currently under

investigation by Dr. N.C. Stephenson of the New South Wales Institute

of Technology, Sydney, Australia.

35
Although no ionic-conductivity or even ion exchange studies have

been performed on the compound B^OiSNbgO^ it is sufficiently similar to

the 2:3 phase to warrant some additional study.

4.0 SUMMARY OF RESULTS

1. Single crystals of hexagonal tungsten bronze (HTB) were synthesized

in the system KTaO^-WQ^-I^WO^ by the flux technique. No crystals

large enough to measure conductivity by the presently utilized

techniques were successfully obtained.

2. The phase equilibria up to and including the liquidus of portions of

the systems Rb 20-^205 and Rb20-Ta20^ have been studied and phase

diagrams have been constructed most consistent with the experimental

data. Single crystals were grown of most of the compounds in the

niobate system and the phases were investigated for ion exchange

properties. Single crystal and polycrystalline specimens were

submitted to the sponsor for evaluation.

3. The phase equilibria up to and including the liquidus of the systems

S

^2°A""^a^^3 an(* ^^O^-KSbO^ ^ave b een studied and a phase diagram

has been constructed most consistent with the experimental data.

Polycrystalline ceramic specimens of the pyrochlore phase were prepared and submitted to the sponsor for evaluation.

4. The stabilization of cubic antimonates by addition of F

+

was studied

in an attempt to provide a low porosity Na

+

ion ceramic specimen for

evaluation. Although small single crystals were easily synthesized

by the alkali fluoride flux technique, no crystals larger than

^1-2 mm were obtained.

5. Many other alkali-oxide rare earth oxide and l^O^ systems were examined

but no new interesting phases identified.

6. The phase occurring at about 2K20:3Nb202 was found to have interesting

ion exchange and ionic conductivity properties.

36
5.0 FUTURE WORK

1. Develop techniques to grow large crystals from a flux. Such techniques

have only been reported for a very few phases and generally involve an

inordinate amount of man hours to produce results.

2. Develop techniques to ion exchange large crystals, perhaps by utilizing

an electronic current with a hot alkali salt or solution.

3. Investigate and develop improved fabrication techniques to produce

dense, sound pellets of the 68NaSb02:4Sb20^:28NaF composition in a size suitable for definitive ionic conductivity measurements and

examine the effect of varying composition on conductivity.

4. Obtain crystallographic structure analyses on 2^0: 31^0 ,j and on 4Rb«0:llNb 0 0. (now being conducted by N.C. Stephenson and B. Gatehouse).

37
References

1. R.S. Roth, H.S. Parker, W.S. Brower and D. Minor, Alkali OxideTantalum Oxide and Alkali Oxide-Niobium Oxide Ionic Conductors,

NASA Report No. CR-134599, April 1974.

2. R.S. Roth, H.S. Parker, W.S. Brower and J.L. Waring, "Fast Ion

Transport in Solids, Solid State Batteries and Devices", Ed.

W. vanGool. Proceedings of the NATO sponsored Advanced Study

Institute, Belgirate, Italy, Sept. 1972, North Holland Publishing

Company, Amsterdam (1973) pp. 217-232.

3. B.M. Gatehouse, D.J. Lloyd and B.K. Mishkin, "Solid State Chemistry"

Proceedings 5th Materials Research Symposium, NBS Special Publication

364 (1972) 15.

4. N. Schrewelius, Diss. Stockholm (1943) pp. 144.

5. D.J. Stewart and 0. Knop, Canadian J. of Chemistry 4J3 (1970) 1323.

6. J. Singer, NASA Lewis Research Center, Cleveland, Ohio, (personal

communication).

7. K. Dihlstrom, Z. Ariorg. Allgem Chem. 239 (1938) 57.

8. D. Rogers and A.C. Skapski, Proc. Chem. Soc. (1964) 400.

9. P. Spiegelberg, Ark. f . Kemi Min. och Geol. 14 [5] (1940) 1.

.10. B. Aurivillius, Ark. f. Kemi 25 (1964) 505.

11. H. Y-P. Hong, Preprint from Lincoln Lab., MIT, sponsored in part

by NASA Contract C-43205-C (1974)

.

12. J. A. Kafalas, "Solid State Chemistry", Proceedings 5th Materials

Research Symposium, NBS Special Publication 364 (1972) 287.

13. W.S. Brower, D.B. Minor, H.S. Parker, R.S. Roth and J.L. Waring,

Matl. Res. Bull. 9_ (1974) 1045.

14. R. Scholder and H. Stobbe, Zeit. f. an. u. all. Chemie 247 (1941)

392.

15. K. Nassau, J.W. Shiever and J.L. Bernstein, Jr. Electrochem. Soc.

116 (1969) 348.

16. J.B. Goodenough, H. Y-P. Hong and J. A. Kafalas, Twelfth Monthly

Report - NASA Contract C-43205-C (Aug. 1974).

38
17. R.S. Roth, H.S. Parker, W.S. Brower, J.L. Waring and D.B. Minor,

February and March Monthly Letter Progress Reports, NASA Interagency

Order C-50821-C (1974)

.

18. J.B. Goodenough, K. Dwlght, H. Y-P. Hong and J.A. Kafalas,

Fifteenth Monthly Report - NASA Contract C-43205-C (Nov. 1974).

19. J.B. Goodenough, H. Y-P. Hong and J.A. Kafalas, Ninth Monthly

Report - NASA Contract C-43205-C (May 1974)

.

20. J. Singer, W. L. Fielder, H.E. Kautz and J.S. Fordyce, Bull. Am.

Ceram. Soc. 54 (1975) 454.

39
Figure Captions

Figure 1. Phase equilibrium diagram for the system Nb20,.--4Rb20: lll^O^

• - liquidus values from reference [21] o - completely melted

e - partially melted

x - no melting

Figure 2. Phase equilibrium diagram for the system Ta202-4Rg

20;llTa20j

© - partially melted

• - no melting

Figure 3. Phase equilibrium

Not necessarily a

S = solid, V = vapor)

• - melting

x - no melting

diagram for the system Sb20 , -NaSbO^

.

true binary system. (L = liquid,

Figure 4. Phase equilibrium diagram for the system Sb20^-KSbO^.

Not necessarily a true binary system.

• - melting

x - no melting

ss - solid solution

1:2 - K 0:2Sh 90,

3:5 - 3K

2

O:5SB

2

0

5 P2^/c - low temperature form of K20:2Sb20^

Figure 5. Phase relations in the quaternary system NaSb0.j-Sb20.j-Sb20,j-NaF.

The join 6:1—3:4 represents the. formula

it-WWil [Sbl2°36-xF

x'

The join 6:1—3:7 represents the formula

+5,

Figure

[LJ 0Na iy F 0 ] [Sb+3

2 14 2

Sbt5 O-j. VF, ' J

y 12-y 36-(x+2y) (x+2y) J

6. Phase relations in the ternary system NaSbO,j-Sb20^-NaF

The join 6:1—3:4 represents the formula

[a 2+xNa14-xF 2l £Sb^0

36_x

Fx

]

40
The join 6:1—3:7 represents the formula

(^.ltF

2 ] [Sb;3 Sb$3M^

2y)

F

( ^

2y)

l

The join 3:1 —3:8 represents the formula

[Na16F

2 ] [Sb^Sb^.x

0

34. 2x

F2+2x] + Oj

Figure 7» Phase equilibrium diagram for the system Nb20,--KNb02

x - liquidus values from reference [22]

o - completely melted

e - partially melted

• - no melting

Figure 8. Representation of the ternary system KSb02~Sb20^-KOH illustrating

the hydration of the 11:12 mixture to form the single phase

cubic compound when heated in air,

41
42
1900k1800

1700

1600

1500

1400

1300

LU

ocS 1200

<

S 1100

s

"

iooo

900

800

700

uo

9 L~*

600

500

Xs \

> /fv

GTB

«—

!

HTB

16 L

11 L

() A

• • • • • • •

• • • <

Ta

2 0

5

10 15 20

Mole % Rb 2 0

A3

25 30
44
1500

10 20 30 40 50

Sb

2

0 4

mole % K

2 0 KSbO

3

43
46
Sb 2 0 4

bcc - phase

47
0 5

Nb205

20 25 30 35

mol% K 20

40 45 50

KNb03

48
49
Table 1. Experimental Date for the System NbjOj-ARbjOt'llNbjOj.

Composition Previous Heat Treatment

Temp. Time

*C hr

500

500

600

500

500 600

120

12090

120 120

90

11.5Rb,0:88.5Nb,0.

500

500

600

500

600 1000

120

12090

12090

111

Final HeatTreatment

Temp. Time

500 600

800 900

1000

1000 1200

500 600

800

900

1000 1000

1075

1200

500

600

800 900

1000

1000

arS.1

6640

80 1US

60

40

80 ,

60

88

90^

Results of Physical ObservationResults of X-ray Diffraction Analysis

H-Nb.O. + 2i3 H-Nb^ + 3:17

H-Nb 0, + 3:17 H-Nb,0^ + 3:17

H-Nb 2°5 + 3:17

H-Nb

20

5 + GTB

H-Nb 0 + 2:3 H-NbjOj + 2:3

3:17 + H-Nb,0_

3:17 + H-Nb,oj? 3:17 + GTB 4 H-Nb.O.

GTB + 3:17 + H-Nb,0,

GTB + H-Nb 0.

5 GTB + H-Nbpj

H-Nb,0, + 2:3

2:3

3:17 + H-Nb,0_

3:17 + H-Nb,0,

GTB + 3:17

i 3

1148 16 GTB

1200 88 GTB 1280 40 GTB

1340 1 .5 Not melted

1349 23 GTS

1352 ,25 Not melted

1355 .33 Not melted

1361 1 Not melted

1369 .5 Not melted

1375 1 .5 Partial melted GTB

1380 2 Completed melted

20Rb.O:80Nb,O c

500 500

600

500 600

1000

500. 600 1000

1200

500 500

600

J 500

500

600

120 120

90

12090 111

120

90 11116.5

120

12090

120

12090

500 600

750

750

800 900

1000 1000

1075

1200

1156

1177 1180

1183

1226 1262

1349

1153

1153

500

600

800 900 1000

1000

1200

500

600

800 900

1000

1000

10*75 1200

1241

1250

1280

1300

12C£'

90^'

US!

66

40

80

111- 60

16.5

24

2364

18

18

23

84^'

onS.'

66

40

80

c 88

nfe/

6640

80 , Ill-'

60

88

18

16

?16.5

H-Nb 20 5 +2:3

H-Nb^Oj +2:3

11-L + H-Nb,0.

3:17

1 3 3:17

3:17

3:17 3:17

3:17 GTB + HTB

3:17 3:17 + GTB

3:17 + GTB HTB + GTB HTB + GTB

HTB + GTB

GTB + 3:17 GTB + 3:17

H-Nb.O,. + 2:3 H-Nblo' +2:3

3:17 + 11-L

3:17 + 11-L

3:17 + 11-L

9L + GTB + HTB

3:17 + 11-L

3:17 + 9-L + 11-L

3:17 + 9-L

9-L + GTB HTB + 9-L

HTB + 9-L HTB + 9-L HTB + 11-L + 16-L

50
500 120 600 90

1000 111

23.19Rb

20:76.81*!b

20

51000

500 120

500 120

600 90

1149 23 9-L + 3:17 1169 18 9-L + 3:17 1181 89 9-L + GTB

1184 3.5 HTB + 9-L

1313 64 HTB + 11-L

1315 0.5 Not melted

1320 0.5 Partially melted HTB + 11-L 1320 22 Completely melted HTB + 11-L

1328 1.5 Completely melted

1347 16.5 Completely melted

Qy—T X LTT n L T HIS

1200 21^ a7—L,t ±T urn HID 1255 1 R Q_T 7"L -LT UTtt HID

1290 18 .5 9~L HTB

1306 22 HTR + 1 1 —T

500

K / x$

Nb,0, +2:3

600 Nb^Oj +2:3

800 66 11-L +3:17

900 40

1000 80 . 11-L + 9-L

1000 111^

1200 88 9-L 1280 ? 9-L + HTB 1300 40 9-L 500 120 600 90 1000 111

500 63 600 24s-' 500 63

600 24

1290 18.5 1300 16.5 11-L + HTB

500 6#

1000 69^ 9-L + 11-L

1249 22 9-L

1258 67 9-L + 16-L

1262 16 9-L + 16-L

1265 17 9-L + 16-L

1275 117 16-L + ?tr 1284 41 16-L + ?tr 1285 18 16-L + 11-L

1287 67 16-L + 11-L 1291 21 16-L + 11-L

1294 16 16-L + 11-L

1297 22 16-L + 11-L

26.67Rb,0:73.33Nb,0. 500 12o£' H-Nb 0, + 2:3

5500 120 600 902-' H-Nb,0^ + 2:3 500 120 600 90

500 120 500 90 1000 111

25

750 60 11-L

800 66 11-L

900 40 11-L

1000 80 . 11-L

1000 111-' 11-L

1075 60 11-L

1200 88 11-L 1241 18 11-L

1280 40 11-L

1300 40 H-L

1290 18 .5 11-L

1306 22 11-L

1316 0 .5 Not melted

1316 16 Partially melted

1320 0,.5 Partially melted

1330 1 .5 Completely melted

-r Except as indicated by a footnote the samples were quenched into water from the temperature indicated. —^The samples were calcined in open Pt crucibles and pulled from the furnaces at the temperatures

indicated, Rb.O may have been volatilized during these calcines thereby changing the composition to one

greater in mole percent Nb,0 5

. c/ — The sample was a large sealed Pt tube and pulled from the furnace at the temperature and cooled rapidly

on a chill block, —^The sample was removed from the furnace at the temperature indicated and immediately dunked into a beaker

of water. 51
Tabie 2. Experimental Data for the System Ta

20

5-4Rb20:llTa

205

.

Composition Initial Heat Treatment

Temp . Time

°C hr

Final Heat^

Treatment

Temp. Time

°C hr

Results of Physical Observation

Results of X-ray Diffraction Analysis

5Rb

20:95Ta

205

10Rb

2O:90Ta

2O

5

500 500

600

500

500

600

120

120

110

120

120

90

500

600

1340

1500

500 600

800

900 1366 1500

1700

120^

HOP/

120

144 120^

HO?-'

8060 120

120

1

L-Ta

20

5

L-Ta.O. + GTB

H-Ta

20j + GTB

L-Ta

20

5

L-Ta.O. + 9L L-Ta

20f + 9L GTB 4 E-Ta,0.

GTB + H-Ta,o|! (tr) GTB * 3

11.5Rb

20:88.5Ta

20

5 500

500 600

1200

15Rb

2

0: 85Ta

20

5

1330

1340

1277

500

500

600

20Rb

2O:80Ta

2O

5

1200

500 500

600

120

120

110

150

500 600

115

72

136

120

120

110

150

120 120

110

1098 136 1255 27 1318 16 1340 120 1500 144 1603 24

1296 91 1297 117 1307 64 1317 67 1327 18 1330 115 1332 16 1340 72 1704 O.S 1709 0.5

1714 .25 1721 2 1722 1

1317 67

1277 136 1297 117

1331 115

500 120^

600 110^'

800 80 900 60 1000 40 1098 136 1360 120 1473 65 1500 17.5 1500 18 1500 144 1700 2

1707 0.5 1711 0.5

1714 0.5

1715 0.5

500 12<>|' 600 110*-'

not melted

not melted

not melted

partially melted

completely melted

not melted

not melted

completely melted

completely melted

L-Ta.O. + 9L

9L +

zL-Ta,0

9L + L-Ta,0< GTB * ' GTB

GTB

L-Ta,0. + 9L +

GTB 4 f-Ta o0, GTB

GTB

GTB + L-Ta! GTB

GTB GTB

2 5 + L-Ta;o; + L-Ta,0^

'2°5 + L-Ta*0' + L-Ta

20^

GTB

GTB

GTB

GTB

GTB

L-Ta,0 +

L-Ta,0^ +

L-Ta,0^ +

L-Ta,0, +

GTB i 9L GTB + 9L GTB + HTB GTB + HTB GTB + HTB

GTB + HTB

GTB (tr)

1340 120 9L + GTB

52
21.7SRb

2O:78.25Ta

205500

500 600

120 120

110

150

500 500

600

120 120

110

1200 150

26.7Rb

20:73.3Ta2O

5 500

500 600

120 120

110

1200

500

600

1000

1100

1344 1498

1675 1700

1700

1715

1600

1621

1624 1641

1659

1663

1677

1682 1722

1725

500 600

120g/

800 80 9L + L-Ta,0

900 60 9L + L-Ta,0

1000 40 9L + L-Ta,0?

1100 138 9L + L-Ta?0^

1360 120 9L + GTB

1473 65 9L + GTB

1500 18 9L + GTB

1643 24 HTB + 9L (tr) 1700 2 HTB

1700 1 HTB

1706 1 HTB

1474 67 9L + GTB

1477 23 91 + GTB

1477 18 9L + GTB

1479 17 9L + GTB

1479 18 9L + GTB

1480 17 9L + GTB

1482 18 9L + HTB (?) 1482 45 9L + GTB

1484 20 9L + GTB

1486 41 9L + GTB

1488 16 91 + HTB

1488 16 9L + HTB

1498 21 9L + HTB

1706 1 not melted

1716 1 not melted HTB

1717 0.5 partially melted

1721 2 partially melted HTB

500 L-Ta.O,

110-'

40 138

120

144

18

1

1

1

20

317

2119

67

29

18

1616

not melted

partially melted

partially melted

9L + L-Ta,0,

9L

3 9L

9L + ? (tr) 16L + HTB

16L + HTB

16L + HTB

9L

9L

9L9L

9L

9L + HTB (tr) 9L + HTB + 16L

16L + HTB

(tr)

16L HTB

800 80 11L + 2:3 900 60 11L + 2:3 1000 40 11L + 2:3 1098 136 111 + 2:3 1360 120 16L + 1U. 1500 120 16L + 111 1596 24 16L + 111 1625 16 16L + lit 1640 2 161 + 11L 1647 1 16L + 11L 1700 1 11L 1710 1 not melted

1283 72 16L + 11L 1672 1 11L 1719 1 not melted

1725 0.5 11L 1726 16 111

— Except as indicated by b/ the samples were quenched into water from the temperature

indicated.

'— The samples were heated at the temperatures indicated in open Ft crucibles. Due to the volatility of Rb

20 the bulk composition may have shifted to one higher in mole percent Ta,0

s

.

53
Table 3. Experimental Data for Compositions In the System Sodium Antimonate-Antimony Tetroxlde.

a/ Composition Heat TreatmentNa.O Sb2°4 Temp Time Results . mole% mole% "C hr Physical Observation . X-ray Diffraction Analysis—

50 SO

40

37.5

55

60

62.5 (3:5)

33.33 66.67 (1:2)

25 75 (1:3)

23 77

1213 not melted

1264 3 " " 1435 1 1484 1

ii 1502 .08 ii ii 1542 .08 ii n 1569 .08 melted

1602 .08 "

1000 48 not melted

1100 48 "

" 1473 .25 ii ii 1488 .08 partially melted

1495 .08 completely melted

1102 20 not melted

1305 19 n ii 1430 .08 "

Jj 1470 .08 1488 .08 1495 .03 completely melted

1100 48 not melted

1192 ]_ IJUO 1 o ii ii 1326 20 ii ii 1351 j_

ii ii 1373 2 r>nt mot fail / rahaaf n £ 11^^•A^ 1391 2 not melted

1392 .16 1412 .16 n ii 1447 16 ii ii 1454 .33 „ „ 1458 .08 ii ii 1464 .08 ii ii 14/0 no ii ii 1487 • 08 ii it 1490 no .Uo melted

iooo£/ g not melted

1009^' 168 U00

e/

3

ii » 1103^' 91 it ii 1287 2

n n 1292 1.5 ii ii 1306 24 it ii 1307 19 ii it 1316 .5

ii ti 1317 3.5 n n 1354 .75 ii ii 1360 24 n ii 1376 .5

it n 1378 .5 n ii 1411 19 n it 1418 .02 ti ii 1437 24 partially melted

1475 .02 completely melted

750 60 not melted

800 60

800 60 •i it 800 336 1098 16 it n 1192 1

ii 1200 24 1220 2

it ii 1277 2

ii n 1306 24 n ti 1307 iP

ii ti XJi/ lo

it ii 1325 i 1339 .08 1345 .25 1346 .08 1358 .08 1377 .02 partially melted

1427 .02

1200 24 not melted

1266 4 1267 19 1299 .08 1304 .08 1313 .08 1322 .08 1332 .08 1338 .08

NaSbO.

it J

NaSbOj + pyrochlore ss

pyrochlore ss + NaSbO^

Pyrochlore ss

pyrochlore ss

pyrochlore ss

pyrochlore ss

it

pyrochlore ss

pyrochlore ss

pyrochlore as + unknown-y pyrochlore ss + unknown?-, pyrochlore ss + unknown—

pyrochlore ss + unknown pyrochlore ss

pyrochlore ss

pyrochlore ss

pyrochlore ss + NaSbO^

pyrochlore ss + B-Sb,0, pyrochlore + a + Bi' pyrochlore ss^-

pyrochlore s

54
20 80

15 85

10 90

95

1099 672 not melted

1107 144 1200 24 not melted

1220 2.5

1234 2 .

5

it n 1277 16 •i ii 1301 .5 not melted

1305 19 1306 24 „ 1314 .08 1318 .08 1335 .08 1339 .2

ii ii 1340 .08 1345 .2 partially melted

1362 .5

800 74 not melted

800 60

1000 64 1000 64 1007 48 not melted

1107 144 1200 24 ii i» 1200 60

1337 . 2

it n 1340 .2 ii ii 1348 .2 partially melted

800 74 not melted

1007 48 n ii 1107 144 it ii 1234 2 1281 .33 ii ii 1290 .33 „ 1300 .33 1311 ,2 1319 .33 n ii 1334 .33 1337 .2 1351 1 partially melted

1007 48 not melted

1107 144

1234 3.5

k/ pyrochlore as—

pyrochlore ss + a pyrochlore as + a-Sb20

4 pyrochlore ss + B-Sb^O^

NaSbO y

pyrochlore ss + U-Sb^O^ pyrochlore ss + a-Sb^O^

unknown + pyrochlore as + al^} 2(3 t,^J~

a + pyrochlore ss + unknown—

unknown + tr a-Sb,0, (dried 240)^'

unknown + tr o-Sbfo^^' - , pyrochlore + a-Sb-0, + unknown—

pyrochlore ss + a-S6

20

4 + B-SbjO^

pyrochlore ss + a-SbjO^

1/

1/ a-Sb,,0

4 + B-SbjO^ + pyrochlore si

a-SbjO^ + pyrochlore ss

a-Sb^O^ + pyrochlore ss

a-Sb^O^ + pyrochlore ss , a + pyrochlore ss + quenched liquid—

B-Sb.O, + a-Sb-O, + pyrochlore ss^

a-Sb-O, + pyrochlore ss + trace B-Sb.oi'

I 6i

b 2°4-„

a/— All specimens were preheated to 750°C for 60 hours and 1200 C for 19 hours unless otherwise footnoted. Rate of heating and cooling was approximately 3°/mln. For higher heat treatments, speciments were

heated in sealed Pt tubes and quenched from temperatures Indicated. —' The phases identified are given in the order of the amount present (greatest amount first) at room

temperature. These phases are not necessarily those present at the temperature to which the specimen

was heated.

SJ

— Specimen heated in sealed Ft tube at 5,000 psi.

e/ — Specimen previously heated at 1292°C for 1.5 hours.

— Specimen heated in sealed Pt tube in presence of water. The unknown phase formed is probably a hydrate.

Specimen heated in sealed Pt tube in PtO^.

—^•Specimen heated in presence of 5:95 Na^OiSbjO^, which served aa a buffer. — In spite of extensive x-ray study it haa not been determined which of the polymorphic forms of Sb20

4 is the stable form. * s*> 2°ii Ptobably soaked into Pt container and the composition changed to pyrochlore ss. w— Platinum tube leaked. —^ Unknown phase, d-spacing of major lines given in text. This phase is probably a hydrated phase which

exists in the presence of moisture and/or PtO, and can be eliminated by an additional calcining of 1200°C for several hours. Once eliminated this phase does not appear to reform at lower temperatures

in laboratory time. — Specimen contained non-equilibrium material derived from a liquid when quenched from above the liquidus

and examined at room temperature.

55
Table Aa. Experimental Data for Polymorphism in Antimony Tetroxide

Composition Heat Treatment Results

Starting Material Temp . Time Environment Physical Observation X-ray Diffraction

°C hr Analysis^'

a-Sb 90,

3-Sb

20

A Mb204

a-Sb.o.

0-Sb^oJ

a-Sb,0,

e-sb^oj

a-Sb.O.

2 A a-Sb„0,

e-Sb^O*

6-Sb

2o4 a-Sb

20^

6-Sb

20

4

a-Sb

20

4-/

a-Sb.O/^

ii 2 A

1223 .5 sealed Pt tube not melted a + tr 8

ii ii unsealed Pt tube ti ii a

1223 .5 sealed Pt tube not melted B + tr a

unsealed Pt tube volatilised

1223 2 •tied Pt tube net melted $ + tr a

sealed Pt tube ii ii a + Sb 2°: 1303 19 sealed Pt tube not melted 6 + a

n n ii n n ii n 3

1327 .08 sealed Pt tube not melted a + 8

n ii ii ii ii n ii 6 + a

1330 .25 sealed Pt tube not melted e + a

1339 .08 sealed Pt tube not melted a + 8

ii ii ii n it n n 8 + a

13A5 .08 sealed Pt tube not melted 0 + a

1350 .08 sealed Pt tube melted (vapor

soaked into Pt)

1350 .08 sealed Pt tube melted ?

1200

750 800

900

950

large tabular vapor

grown crystals

2A

high temperature

x-ray

open tray

a (starting material

remained a up to 1200°C)

a

iia + 8

a/ — The phases identified are given in the order of the amount present (greatest amount first) at room

temperature. These phases are not necessarily those present at the temperature to which the specimen

was heated, a refers to a-Sb20^ polymorph and 8 to the 8-Sb

20^ polymorph. —^ Material placed on platinum slide and heated and examined by x-ray diffraction at various temperatures. — Poorly crystalline as received SbjO, was heated 750°C - 24 hours and the same specimen which was never

ground was reheated at 800°C - 2A hours, then 900°C - 6A hours and finally 950°C - 24 hours.

56
Table 4b. Experimental High Pressure Data for Polymorphism in Antimflny-Tetroxide

.

Composition

Starting Material

Heat Treatment

Temp Time Pressure Result b/

°c hrs Environment psi X-ray Diffraction Analysis

700 24 Sealed Au tube 88,000 + sb

2o3^

750 48 it ii ii 59,680 II II II

750 96 ii ii ii 73,200 II It II

750 16 ii it ii 89,400 6 + trace ^2°3

751 116 ii ii ii 109,000 8 + Sb 2°3

760 96 Sealed Au tube with Pt0

2 80,000 6 766 96 Sealed Au tube 88,000 6 + Sb

203 775 115 " Pt " 47,500 a + Sb 2°3

775 48 Au " 54,760 6 + sb

2o3 775 48 " Pt " 66,500 II II II

800 24 " Au " 93,000 M II II

800 24 Sealed Au tube with Pt0

2 105,000 6 . 850 16 Sealed Au tube 82,500 6 + sb

2o3 900 72 Sealed Pt tube with Pt0

2 104,000 6

900 72 it n ii ii ii 104,000 6

a- Sb 2°4-

6-Sb

20

4 a/— a-SbjO^ prepared by the oxidation of Sb at 530°C on Pt tray. This material was reheated at 800°C - 60 hrs. —^ The phases identified are given in the order of the amount present (greatest amount first) at room

temperature. These phases are not necessarily those present at the temperatures to which the specimen was heated.

6 form of Sb o 0.

.

2 4 — High pressure form of Sb

203 (valentinite)

.

57
Table 5. Experimental Data for Compositions in the System Potassium Ant toonate-Antimony Tetroxide.

a/ Composition Heat Treatment— Results

K„0 Sb

9

°y. TemP Time Physical Observation X-ray Diffraction Analysis^-

Mole% MoIe% °C hr

5

10

95

90

950

1168

950

1168

60

48

6048

not melted

not melted

pyrochlore ss + a-Sb.O, + 3^Sb-0, , a-Sb

204 + 6-Sb204

4- pyrochlore ss -

c/ pyrochlore ss + a-Sb,0. + 3-Sb.O.—

15

20

25

30

33.33

85

80

75

70

66.67

853 950

966 1168

9SQ

1168

950

1179 1361

1375

1385 1403

950 1178

1366 1380

1382

1399

950

950

998 1050 , 1050s' 1102

1106

f 11064',

1179

12 ifiJ 1214

24

60

4 48

19

6048

6048

.08

.08 .08

.08

60

48

.08 .08

.08 .08

60

64

70 168

168

164

64

1 48

1

2

not melted

not melted

ii ii

not melted

n ii M ii partially melted

ii it completely melted

not melted

ii ii

ti ii partially melted

ii ii completely melted

not melted

pyrochlore ss

pyreehler© @@ + a-Sb,0,

pyreehlere m + a-Sb^O^ g-SbgO^

pyrochlore ss

it

P2

1 /c-/' + pyrochlore ss pyrochlore ss

pyrochlore ss

P2j^/c—^ + pyrochlore ss 1:2 + pyrochlore ss

pyrochlore ss + 3:5

3:5 + P2

1

/>

P2

1/c*/

1/

1:2 s/ + 3:5 + pyrochlore ss + P2

1 /c 1:2-' + 3:5 + pyrochlore x 1:2 + 3:5

3:5 + pyrochlore ss 1:2 + 3:5 + pyrochlore ss 3:5 + pyrochlore ss

35

37.5

65

62.5

950 1178

1380

1397 1409

950 1174

1195 1208 , 950s' 1310

1352

1379

1399 1416

6048

.08

.08

.08

60

88

19

16445

.08

.08

.08

.08

not melted

it ii partially melted

ii ii completely melted

not melted

pyrochlore + 3:5 + pyrochlore ss 1:2 + 3:5

3:5 + pyrochlore

3:5

3:5 + trace cubic

3:5 + trace

completely melted

40 60 950 1174

1208 , 1295s

) 1362s'. 1375s'

60

88

1 20

.5.08

not melted

partially melted

3:5 + cubic

II II 3:5 + 1:1

58
A5

46

47

47.5

55

54

53

52.5

950

X174 1208

1311-e/

1200^

1194^

1200

1212£/

1218^' .

60

88

11

31

88

1745

not melted

ii ii u M

ii ii

not melted

not melted

1 1 ii

not melted

1:1 + cubic + P2,/c

cubic +3:5

3:5 + cubic

3:5 + 1:1

cubic +3:5

cubic + trace 3:5 cubic

cubic +3:5+1:1

cubic + 1:1 + 3:5

1:1

48 52

49

50

51

50

1198 1200

1200^' 1308 . 1103?.

1103^'

1200

750 800

921

946

950 1103

1104

1150

1174

1194 1202

1214 1298

1363

1403 1421 1426

3

1 1;5

.5

1

3

7024

12160

1 22

1 88

11

1

.5

.5.08

.08

.08

not melted

not melted

not melted

cubic

ii cubic +3:5 ilmenite

1:1 cubic + ilmenite + pyrochlore

ilmenite + pyrochlore

cubic

ilmenite

melted

— All specimens were preheated to 500 and 700°C for 60 hours unless otherwise footnoted. Rate of heating and cooling were approximately 3°/min, Specimens were heated in sealed Pt tubes and quenched from temperatures

indicated

.

—^ The phases identified are given in order of the amount present (greatest amount first) at room temperature.

These phases are not necessarily those present at the temperature to which the specimen was heated.

1:2 - K 0.2Sb

205

; 3:5 - 3K

20-5Sb

205 and 1:1 - KSb0

3 - ilmenite structure.

c/ — Non-equilibrium mixture - see Discussion in text. — The phase was indexed from single crystal x-ray precession data which has shown the compound is monoclinic

space group P2

1 /c a=7.178, b=13.378, c=11.985, 8=124°10\ — This specimen was previously heated to 500°, 700° and 1200°C - 19 hours in a sealed Pt tube. — Specimen heated in open Pt tube.

Specimen leaked and changed composition. —^ Composition prepared from a mixture 1:1 and 3:5 - see text for explanation. — Specimen calcined and examined by x-ray diffraction while in form of pellet.

59
Table 6. Experimental Data for the Ternary System NaSbO_-Sb_0.-NaF.

3 2 4

Composition Mole %

Heat

Temp

°C

a/ TreatmentTime

hr X-ray Analysis

NaSbO_

Sb 0

J NaF

4

75.08

3.15

21.77

1250 19 single phase distorted cubic

NaSbONaF

*

67.79

6.25

25.96

1250 19 body centered cubic +

pyrochlore + ilmenite

NaSbO,

Sb 0 NaF

H

53.50

12.34

34.16

1250 19 body centered cubic +

pyrochlore + sodium fluoride

NaSbOSb 0

J NaF

*

39.59

18.27

42.14

1250 19 body centered cubic +

pyrochlore + sodium fluoride

NaSbO„

Sb 0

J NaF

H

69.05

2.90

28.05

1250 19 body centered cubic +

trace sodium fluoride

NaSbO.

Sb 0

J NaF *

49.28

11.37

39.35

1250 19 pyrochlore + body centered

cubic + sodium fluoride

NaSbO.

Sb 0

J NaF

31.20

28.87

39.93

1250 19 pyrochlore + sodium fluoride

NaSbO.

Sb 0

J NaF

84.62

15.38

1268 19 ilmenite + cubic

NaSbO.

Sb 0

J NaF

74.42

2.32

23.26

1261

1268

1 19 distorted cubic + ilmenite

distorted cubic + NaF

NaSbO.

Sb 0

J NaF

70.00

3.33

26.67

1264 1 cubic + ilmenite

NaSbO.

Sb 0

J NaF

65.96

4.26

29.78

1266

1267

119 cubic + ilmenite

cubic + NaF

NaSbO

Sb 0 NaF H

62.96

4.94

32.10

1266

1267

119 cubic + NaF

cubic + NaF

NaSbO.

Sb 0

J NaF

58.82

5.89

35.29

1267 19 cubic + NaF

NaSbONaF

q

68.00

4.00

28.00

1000

1252

1265

1265

1265

116

.1 1.5

72

ilmenite + trace NaF

cubic + trace ilmenite

cubic + NaF

cubic + NaF

cubic + NaF

a/ — Preheated at 750°C for 60 hours open. 60
Table 7. Experimental Data for Alkali Bismuth Oxide Systems.

Composition Temp. Time

°C hr

Results of X-ray

Diffraction Analysis

Na

2

0:Bi

2

0

3

500

500

96

120

^2^3 + tr un^nown

Bi

2

0

3

K

2

0:Bi

2

0

3

500

500

66

120

B *2°3

K

2

0:3Bi

2

0

3

500 66 Bi

2

0

3

61
Table 8. Experimental Data for Alkali-Rare Earth Systems.

Composition Temp Time Results of X-ray

°C hr Diffraction Analysis

Na

2

0:Nd

2

0

3

800 23 a-Nd^

K

2

0:Nd

2

0

3

950 66 a-Nd

2

0

3

+ ?

K

2

0:3Nd

2

0

3

950 66 oi^Nd^ + ?

3K90:Y90. 600 20 Y90- + K9C0,

700 20 " J " 800 20 " " 950 66 Y

2

0

3

K

2

0:Y

2

0

3

500 24 Y

2

0

3

Na90:Sm,0o 800 23 Sm90~

950 1.5 M

Na9 0:3Sm9 0 7 800 23 Sm90,

950 1.5 2, ' J

89.6Na

2

O:10.4Sm

2

O

3

^1350 1-^ Sm

2

0

3

Ko0:3Sm,,0 223Q 800 23 SmJD,,

950 1.5 2m3

K9 0:Sm90, 800 23 Sm90, Z Z

. 950 1.5.,

1250 16 .5^ Sm,0^ + ? 1350 17. 5^' Smfo.

2

V

3

K 0:Gd90 750 90

5 1000 92 . 1365 67^ B-Gd90, + C-Gd 90.

1370 " "

a/ — The sample was heated in an open Pt crucible in an induction heater

and the temperature recorded via an optical pyrometer.

b/— Quenched from temperature indicated.

62
Table 9. Further Experimental Data for the System Nb

2

0

5

-KNb0

3

.

Composition Temp

°C

Time

hr

Results of X-ray

Diffraction Analysis

40.5K

2

O:59.5Nb

2

O

5

600

750

1000

1000

40

84

48 . 48^2:3 hydrate + TTB

2:3 anhydrous + TTB

41K

2

0:59Nb

2

0

5

600

700

750

800

1000

1000

1000

1000

48

85

60

90 , 48^

48 ,

60*-'

2:3 anhydrous

2:3 hydrate

2:3 anhydrous

- Slide heated @ 220° for 96 hours.

- Slide heated > 125°C. - Slide heated to 110°C.

63
Tabla iob. Sunary of Ion Exchange Experiment*

EXCHANGE MEDIUM TEMP TIME

7K

20:13Nbj °5 NaNOj 340" 2 hr

3NaN0

2 :2NaN0

3 244° 24 hr 24V 72 hr

NaN0

3 (aq)S./ 104' 2 hr

19.75K

2Oi81,25Nb

20

5 NaN0

3 ^500° 2 hr

330* 2 hr

ll.SKjOteS.SNbjOj

100* 2 hr

2K

20t3m>2

C'3

NaN0

3

-\-500° 2 hr

340° 1 hr

NaN0

3 (aq)-' 100° 2 hr

25° 72 hr

25* 4 hr

NaOH(aq)-1' 25° 18 hr

HjO (deionlzed) 25" 18 hr

NaX (ac)-^ 25' 18 hr

41K

20tS9Nb

205 Aa prepared hydrated

mm Aa prepared anhydroui

N«N0

3 4S0 3.3 500 1 450 4

KTaWOg

NaN0

3

-v-SOO" 2 hr

315* 2 hr

MaN0

3 (aq)i' 105* 1 hr

RbH0

3 («,)«/ 105* 1 hr

H jO (deionlzed) 100" 1 hr

*.3T*.3U .7C'3

NaN0

3 -V500" 2 hr

340' 2 hr

K

2O:2Ta

20

5

NaNOj ^500° 2 hr

4^20511^205e/

Single Exchange

DJ0

3 400' 3 hr

400' 16 hr

KN0

3 400' 16 hr

450' 36

NaNQ

3 500 1 hr 450 64 hr

414 17 hr 400 16 hr

RESULTS

Decomposed to KNbO, +

KNb

308 + H-Nt>205 Unchanged 7:13(TTB)+Na-TTB(?) Unchanged

No change

NaNbO,

H-Nb

28 5 + residual TTB

S

Decomposed to H-Nb

20j + TTB

g

NaNbO, perovakita

Decomposed to KNbjOg + KNb0

3 Decomposed to NaNbO. . higher hydrate (b-42.2) + TTB^' higher hydrate (b-42.2) + TTBS-'

higher hydrate + TTB^

No change

Unchanged 2i3 + TTB + higher hydrate (acetonate?)!'

Hydrated "2:3" Single phase "2:3"

Complete exchange Complete exchange

Pellets hydrated and decrepitated while being x-rayed

NaTaO,

two phases: KTaWOg + NaTaWOg

RbTaWO, (a.10.352) +

unknown phase

KTaWOg

NaTaOj + HTB

No change

No change using either 900°

(rhomb) or 1300° (TTB) calcined starting material

K exch. 11 L phase a-7.554 c-43.398

K exch. 11 L phase

K exch. 11 L phaae

K exch. 11 L phase

Partially exch. a-7.4 c-43.6 Partially decomposed Partially exch. a-7.458 c-43.19 Partially exch. a-7.472 c-43.23

64
Double Exchange

KNO /400°/3 hr -» NaN0,/400°/l . 5 hr a-7.458 c=43.398 + NaNOj/400°/16 hr a=7.368 c=43.869

KNO

3 /400°/16 hr + NaNO3 /450°/66 hr a-7.366 c=43.898

KNO./400°/16 hr * NaNO,/450°/98 hr a=7.332 c=43.997

KNO,

Rb

2 0:3Nb20

5 450° 3 hr K exch. 9 L phase

a=7.56 c=36.52

21 . 75Rb

20 : 78 . 25Nb

20

5^/

S ingle Exchange

KN0

3

NaNO,

450°

450°

450°

18 hr

99 hr

99 hr

No exchange (?)

Partial exchange, increase in

'c' and partial decomposition

KNO

3 /450°/18 hr

KNO.

Double Exchange

NaNO

3 /450°/23 hr

RbTa

20,F (a=7.519 c=

Single Exchange

340° 2.5

340° 450°

15

16

Partial exchange

=3.888)

Partial exch. (?) a=7.512 c=3.879

NaNO (aq. 20 w %) NaN0

3 340° 3.5

Double Exchange

KN0

3 /450°/16 hr + NaN03 /340°/2 hr

No exchange

No exchange

No exchange

KNO

3 /450°/16 hr * NaNO

3 /450° /44 . 5 hr Some decomposition + partial

exchange a=7.51 c=3.814

NaNO,

3NaN0

2 :2NaN0

3 KNO.

^500°

330°

240°

^500°

2 hr

2 hr

22 hr

2 hr

Unchanged HTB + Na.Nb -XL , (tr) + NaNb0

3 (tr) No change

No change

KNb0

3 + unchanged HTB

a/ — 20 percent by weight of nitrate in deionized water —^ 20 percent by weight of hydroxide in deionized water

c/ — 10 percent by weight salt in acetone — when dried at 220°C this "higher hydrate" or "acetonate" changes to a 2:3 type structure with a_ and the same as original but with a very

small b axis of 30.78A by comparison with the original b=33.019A.

e/— single crystal fragments

65
Table 10b. Summary of Ion Exchange Experiments with 4Rb

20: llNbjOj Pellets.

Starting Pressing Firing K+

Exchange Na+

Exchange Remarks Material History History History History

10000 psi a/

500 "C-90 hr c/ 20000 psi b/

4Rb

20:llNb

20

5 1200 -7 hr

KNO

3-20hr

(3 400° partial

exchange BJ

Pellets cracked during firing

a - 7.522

c - 43.180

Pellet fragment disintegrated

a - 7.128, c - 43.469

t 15°/hr

1200 °-7 hr KNO, -16 hr

<§ 400° partial ex- change

NaNO -18 hr @400J °C partial ex- change

Pellet fragment did not disintegrate

K a - 7.575, c - 43.469 Na+ a - 7.390, c - 43.663

+5° /minute 1200°-lhr

+5° /minute

KNO -1 hr @400° complete

exchange

pellet did not disintegrate K+ a - 7.545, c - 43.332

+3° /minute 1200-1 hr

+3° minute

KNO -19 hr

@400° complete

exchange

pellet displayed some spalling K+ a = 7.555

c 43.428

500-120 hr 600-90 hr d/ 10000 psi a/ HQ0o C- 1 hr KN0--16 hr @40o* complete

exchange

NaN0,-21 hr

"IT K a - 7.551, c - 43.401

Na+ cells not calculated due

to broadness of lines

in diffraction

1100°C-1.5 hr KNO, 16 hr @400 partial

exchange

NaN0,-41 hr

@4 00 partial

exchange

Na exchanged pellet decomposed K+ a - 7.547, c - 43.428

N&+ a - 7.404, c - 43.332

11006 C-1 hr KNO,-7 2 hr

@400° complete

exchange

NaNO,-32 hr @300J

° partial

exchange

K a - 7.557, c - 43.442

Na+ a - 7.484, c - 43.482

10000 psi a/ 1100-lhr

20000 psi b/ 1200-1 hr ~ 1100 - 16 hr 1200 -2 hr

KNO,- 16 hr @400 0 complete ex- change

Pellet cracked during final 1200 8 firing K+ a - 7.557

c - 43.442

500-90 +5" /minute

1200-5 hr

+5* minute

a/= hydraulic

pressure

b/= Isostatlc pressure

c/= Without PVA binder

d/= with PVA

binder

e/= Complete

exchange

RbNb - KNb NaNb -

KNO -2 hr 400°C complete

exchange

KN0

3 -18hr - NaNOj-18 hr

@400" complete @40

°, . exchange complete exchange

a b 7.522A

1 43.180A

7.554A 43.398A

7.368A 43.869A

powder fired in open

tube

K*" a - 7.549, c - 43.387

K+ a - 7.553

c - 43.387

Na+

a 7.375

c - 43.830

66
Table 11. Alkali Fluoride - Sb 0 0, : Flux Evaporation

Composition Temp /Time Results

98KF:2Sb o 0.

2 4

1100°-1200°C

6 hrs

Solid + liquid

x-ray shows KSb0 o F

3—x x small crystals formed

88.0KF:7.2KSbO,:4.8Sb„O. 1100° - 1 hr

3 2 4

Solid + liquid

small crystals formed

90KF:2Sb o 0, :8B o 0 o 2 t 2 3

1100° - 2 hr, slow

cool to 1000°

Solid + liquid

small crystals formed

95RbF:5Sb o 0.

2 4

900° - 1000°C

1 hr

Solid + liquid

small crystals formed

67
Table 12. Summary of X-ray Data.

Composition

System Designation

Alkali OxideHetal

Oxide Symmetry

a

Unit Cell Dimensions

b c 6

Limiting

Possible Reflections

Mole* MoleJ X A A

RbjO-NbjOj il-L

16-L

9-L HTB

26.67 25.5

2521.75

73.33

74.5

7578.25

Hexagonal

Hexagonal

Hexagonal Orthorhonblc

7.522

7,514 7.518 12.991 7.550

43.18 65.12

36.353

7.796

hk£:-h+k+i-3n

hh«:i-2n hhla-2n

hkO:h+k-2n hOl:e-2n

GTB U.5 88.5 Tetragonal 27.484 3.9757 hOO:h-2n

RbjO-TfljOj 11-L

9-L HTB GTB

26.67

21.75

11.5

73.33

78.25

88.5

Hexagonal Hexagonal

Hexagonal

Tetragonal

7.506

7.508

7.531 27.573

43.19

36.41

3.907 3.9018

hU:-h+k+l-3n

hht:l«2n

none h00:h"2n

K

20-Sb2 04 pyrochlore SB

1:2 P2i/c

(variable]

153033.33

33.33

857066.67

66.67

Cubic Cubic Monocllnlc

Monocllnlc

10.331

10.381

19.473 7.178

7.452 13.3787.198 11.985

94'34.4'

124, 10'

hki:h+k,k+«.-2n 0ki:k+4-4n

hkl:h+k-2n hk&mo conditions

hOU: Wn

0kO:k-2n

3:5 37.5 62.5 Orthorhombic 24.274 7.157 7.334 hk£:no conditions 0k«ik-2n

h0iih-2n hkOmo conditions OOtmo conditions

Ns

20-Sb

2 0

4 pyrochlore aa (variable)

2537.5

7562.5 Cubic Cubic

10.289

10.286 hkt;h+k,k+l-2n

0k£:k+£»4n

Probable

Space Group

R3,R3,R32,R3m,R3m

P63mc ,P|2c ,P63mmc P63mc,P62c,P63mmc

Pmcn

R3,R3,R32,R3in,R3m

P6^nc , P32 c , P6 3inmc

P42

1 ,2,PZ2

1m

C2/m (11) P2,/c

Pbsm (11)

Fd3m

68
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USCOMM-NBS-DC 75
1. Report No. 2. Government Accession (Mo. CR-134869 NBSIR 75-754

i 11

3. Recipient's Catalog No.

4. Title and Subtitle ALKALI OXIDE-TANTALUM , NIOBIUM AND ANTIMONY OXIDE IONIC CONDUCTORS

5. Report Date April 1975

6. Performing Organization Code

7. Author(s) R.S. Roth, W.S. Brower, H.S. Parker, D .B . Minor and J.L. Waring

8. Performing Organization Report No. NBSIR 75-754

10. Work Unit No.

9. Performing Organization Name and Address

National Bureau of Standards » Department of Commerce

Washington, D.C. 20234

11. Contract or Grant No. C-50821-C

13. Type of Report and Period Covered Final Report

January 1, 1974-December 31,1974

12. Sponsoring Agency Name and Address National Aeronautics and Space Administration

Lewis Research Center

21000 Brookpark Road

Cleveland, Ohio 44135

14. Sponsoring Agency Code

15. Supplementary Notes

16. Abstract The phase equilibrium relations of four systems were investigated in detail. These consisted of sodium and potassium antimonates with antimony oxide and tantalum and niobium oxide with rubidium

oxide as far as the ratio 4Rb

20:llB,0 (B-Nb, Ta) . The ternary system NaSbO,-Sb,0.-NaF was also

investigated extensively to determine the actual composition of the body centere! cubic sodium

antimonate. In addition, various other binary and ternary oxide systems involving alkali oxides were examined in lesser detail; The phases synthesized were screened by ion exchange methods to determine mobility of the alkali ion within the niobium, tantalum or antimony oxide (fluoride) structural framework. Five structure types were found to be of sufficient interest to warrant

further investigation. These structure types are (1) hexagonal tungsten bronze (HTB) , (2) pyrochlore,

(3) the hybrid HTB-pyrochlore hexagonal ordered phases, (4) body centered cubic antimonates and

(5) 2K20:3Nb„0

5

. Although all of these phases exhibit good ion exchange properties only the

pyrochlore his so far been+

nrepared with Na ions as an equilibrium phase and as a low porosity

ceramic. Unfortunately Sb in the channel apparently interferes with ionic conductivity in this case, although relatively good ionic conductivity was found for the metastable Na ion exchanged

analogs of RbTa„0^F and KTaWOg pyrochlore phases. Small crystals of the other phases can generally

be prepared by flux techniques and ion exchanged with Na . However, in the one case where

congruency allows large crystals to be pulled from the melt (4Rb«0:llNb,0_) ion' exchange techniques

up to ^450°C are not sufficient to accomplish complete replacement with Na ions.

17. Key Words (Suggested by Author(s)) Ionic conductivity; non-stoichiometry; potassium

antimonate; rubidium niobate; rubidium tantalate;

sodium antimonate; sodium antimonate fluoride

18. Distribution Statement

Unclassified - Unlimited

19. Security Classif. (of this report) Unclassified

20. Security Classif. (of this page) Unclassified

21. No. of Pages 7622. Price* $4.75

* For sale by the National Technical Information Service, Springfield, Virginia 22151-

NASA-C-168 (Rev. 6-71)