Irreversible phase transition and compressibility of terbium

Journal of the Less-Common Metals Elsevier Sequoia S.A., Lausanne - Printed

243

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Short Communications Irreversible phase transition and compressibility of terbium* Recently, europium

MONTFORT AND SWENSON~ publishedcompressibilitydataonterbium,

and scandium

which were appreciably

different

from results obtained

by

one of the present authorsa. In an attempt to resolve the differences, Dr. SWENSON very kindly furnished a very pure sample of terbium for additional pressure-volume measurements.

This sample contained

0.02 wt. TJ, interstitials,

predominantly

less than 0.04 wt. ‘$4 metallic

impurities

and

oxygen.

In our first pressure run (at 22°C) with the new material, an irreversible phase transition was observed at about 25 kb. Figure I presents the loading and unloading PV curve for this test. The irreversible loading and unloading

volume change is about 0.6~/~. On subsequent

cycles the discontinuity

in volume was not observed;

however,

there seems to be a kink in the PI/ curve at about 25 kb, or the same pressure at which the irreversible phase transition occurred.

Fig. 1. Pressure-volume curve for terbium first pressure cycle STROMBERG AND STEPHENS~ observed resistance-pressure to the irreversible

an irreversible

cusp in the electrical

curve of terbium at about 27 kb; this effect was undoubtedly transformation observed in the present work.

due

transition.

The difference between the two earlier sets of PV data may be due to this Both investigators used similar modifications of the piston-cylinder

method

described

by BRIDGMAN4, in which the sample

is encased

in a soft, solid

pressure-transmitting medium such as lead or indium. It is usual practice to “season” samples; that is, to pressurize such a sample assembly to the maximum pressure range before taking data. Such a seasoning serves to remove both natural porosity in the sample plus porosity introduced during the assembly of sample, pressure-transmitting medium, and seals. MONTFORT AND SWENSON apparently seasoned their samples to 25 kb, while STEPHENS seasoned to 40 kb. The phase transition was not noticed in the *Work performed under the auspices of the U.S. Atomic Energy Commission. J.Less-Common

Metals, 17 (1969) 243-246

SHORT COMMUNICATIONS

244

4o-kb seasoning. This was perhaps due to the lower purity of STEPHENS’ samples, which may have made the transition very sluggish and spread the transition over a large pressure range. STEPHENS AND LILLEY~ have described a technique whereby PV curves can be obtained for samples without initial pressure seasoning. This technique was used to obtain the data shown in Fig. I. Pressure-volume data for terbium are shown in Table I. It may be seen that terbium in the h.c.p. phase is much more compressible than is transformed terbium. This is shown by the difference in AV/VO in the first cycle compared to succeeding cycles and in the I-atm compressibility data shown in Table II. As may be seen, the data on the first cycle are in fair agreement with those of MONTFORT AND SWENSON. However, data from the second and succeeding cycles are much lower than that of the first pressurization; data from these cycles are closer to the earlier work of Stephens. The latter two sets of data differ by about 4%, with the earlier work lower. This may be due to the relative purity of the samples. TABLE I VOLUME CHANGES P

Av/VoVERSUSPRESSUREFORTERBIUM

AV/Vo

(kb)

0

5 IO

I5 20 25 25 30 35 40 TABLE

MONTFORTAND SWENSON,

This work,

1st cycle,

This work, succeeding cycles, Sm structure

#robably Sm structW%

STEPHENS,

h.c.p. structure

h.c.p. and Sm structure

0 0.0125 0.0250 0.0375 0.0500

0 0.0124 0.0248 0.0366 0.0481 0.0588 0.0645

0 0.0111 0.0221 0.0334 0.0437 0.0542

0 0.0107 0.0211 0.0318 0.0420 0.0518

0.0735 0.0824 o.og12

0.0638 0.0728

0.0609 0.0694

0.0813

0.0777

1

ONE-ATMOSPHERE

COMPRESSIBILITIES

AND

DENSITIES FOR TERBIUM _

Compressibility (mb-1) MONTFORT This work, This work, STEPHENS, Calculated

density density

AND SWENSON, h.c.p. structure: 1st cycle, h.c.p. structure: succeeding cycles,Sm structure: probably Sm structure: from crystallographic data:

2.50 2.48 2.22 2.14

Density (@ma)

8.272 8.345 8.252 (h.c.p.)

Also shown in Table II are experimentally determined densities. The initial of the sample, 8.272 g/cm3, compares reasonably well with the 8.252 g/cm3 obtained from crystallographic data for h.c.p. terbium6. In order to identify the structure of the transformed material, thin wire

J. Less-Common

Metals, 17 (1969) 243-246

SHORTCOMMUNICATIONS samples were subjected the samples. diameter radiation.

245

to X-ray

Exposure

analysis

within minutes

of release of pressure from

times were made as short as possible with the use of a small-

camera (d=57.3 mm). Photographs were taken with both Fe and Cu Many patterns showed only the normal h.c.p. Tb, but some clearly showed

that a transformation had occurred. The success in obtaining these latter photographs seemed strongly dependent on the time and manipulation of sample required to take the

photograph.

one-half

When

the

transformed

hour and then photographed,

Tb

was heated

ilz vacua to 500°C

only normal Tb and trace amounts

for

of Tb203

were observed. The powder pattern be interpreted hexagonal

as resulting

of transformed from a Sm-like

Tb is given in Table III.

This pattern

can

phase of Tb plus trace amounts of a double

phase following the arguments used by JAYARAMAN for the Sm-like phase are a=8.83

close packed (d.h.c.p.)

AND SHERWOOD7 in the case of Gd. Cell constants +0.06

_&anda=23.42

c=25.76

10.08

+0.05’

A. These

or, in terms of the hexagonal

constants

were calculated

cell, a=3.58

+O.OI A and

with a least-squares

programs

T.-\BI,EIII X-RAY

DATA

FOR

TRANSFORMED

TERBIUM

d

hkl*

I

d

hkl

I

3.09 3.04 2.86 2.80 2.76

100 II0 333 211 **

4 2 IO 4 2

I-97 1.86 I.79 1.66

433 **

I I 5 3

2.66

221

5

322 332 **

1.38 2.24 L.II

I.03

roi

544 **

I

I

1.58 I.52 I ,485

554 432,LLO 311

2 I

I

I.433

666

7

I

*hkZ for rhombohedralindexing. **denotesd.h.c.p. lines.

using data obtained

from a 57.3-mm-diameter

camera and FeKa

A). The lines in Table III which have been starred tion that orientation,

the d.h.c.p.

phase is also present.

as well as the fact that

radiation

are accounted

Because

of the pronounced

most lines were broad,

(A= 1.937

for by the assump-

we recognize

preferred that

this

interpretation of the powder patterns of transformed Tb cannot be rigorously defended. It is of interest that all our patterns, as well as the one reported by

JAYARAMAN ANDSHERWOOD, show these extra lines. Calculated

volume change for the h.c.p. +

The corresponding

change for the Gd transformation

Sm transformation

of Tb is I.o~/,.

was reported to be 1.3%.

MCWHANANDSTRvRNsgalso reported that Tb transforms

to the Sm structure;

this evidence was based on X-ray measurements under pressure. However, the authors did not resolve all the lines; their conclusions were based on the similarities of the Tb lines to that of Gd under pressure,

using the fact that

JAYARAMANAND

SHERWOOD observed Gd to transform from h.c.p. to the Sm structure. We wish to thank Dr. C. A. SWENSONAND Dr. F. H. SPEDDINGfor providing the high-purity terbium sample. We acknowledge Mr. EBEN LILLEYfor assistance in

J. Less-Commo~z

Metals,

17 (1969) 243-246

246

SHORT COMMUNICL~TIONS

the high pressure setups and Mr. VERNON SILVEIRA for powder photography. We also Dr. C. A. SWENSON and Dr. D. B. MCWHAN for reviewing the manu-

wish to thank script.

Chemistry Department, Lawrence Radiation Laboratory, University of California, Livermore, Calif. 94550 (U.S.A.)

D. R. STEPHENS QUINTIN

JOHNSON

I C.E. MONTFORTANDC.A.SWENSON, J.Phys.Chem.Solids, 26(1965)623. 2 D. R. STEPHENS,J. Phys. Chem. Solids, 25 (1964) 423. 3 H.D. STROMBERGANDD.R.STEPHENS,J. Pkys.Chem.SoZids, 25 (1964) 1015. 4 BRIDGMAN,Collected Experimental Papers, Vol. 6, 1964, zl-50, Paper No. 134. 5 D. R. STEPHENS AND E. M.LILLEY, in B. FRENCH AND N. M. SHORT (eds.), Proc. ConJ Shock Metamorphism. (in press). 6 K. A. GSCHNEIDNER,JR.,Rare Earth Alloys, Van Nostrand, New York, 1961 7 A. JAYARAMANA~D R.C.SHERWOOD, Phys.Rev.Letters, 12 (1964)~~. 8 L.HEATON,J.GVILDYSANDM.MIUELLER, ArgonneNat.Lab.Rept.B-106~1964. g D. B. MCWHANAND A. L. STEVENS,Phys. Rev., 139 (1965) A682.

Received October 3Ist, 1968 J. Less-Common Metals, 17 (1969)243-246