THE hcp-fcc PHASE TRANSITION IN 3He FROM THE TRIPLE POINT TO 6 kbar

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THE hcp-fcc PHASE TRANSITION IN 3He FROM THE TRIPLE POINT TO 6 kbar

M. Ryschkewitsch, J. Franck, B. Duch, W. Daniels

To cite this version:

M. Ryschkewitsch, J. Franck, B. Duch, W. Daniels. THE hcp-fcc PHASE TRANSITION IN 3He

FROM THE TRIPLE POINT TO 6 kbar. Journal de Physique Colloques, 1982, 43 (C4), pp.C4-413-

C4-414. �10.1051/jphyscol:1982462�. �jpa-00222181�

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JOURNAL DE PHYSIQUE

CoZZoque C4, supplgment au n o 12, Tome 4 3 , de'cembre 1982 page C4-413

THE

hcp-fcc

PHASE TRANSITION I N 3 ~ e FROM THE

TRIPLE

POINT TO

6 kbar

M.G. Ryschkewitsch, J.P. Franck*, B.J. Duch and W.B. Daniels

Department of Physics, University of Delaware, Newark, DeZaware 19711, U . S . A.

(Accepted 16 September 1982)

Abstract.-The hcp-fcc transition in 3 ~ e was studied using an optical method from the triple point at 17.65 K and 1560 bar, to about 6 kbar. The temperature hysteresis and transition kinetics are very similar to those of the corresponding transition in 4 ~ e . In one crystal of 3 ~ e heterophase fluctuations preceding the transition were observed.

The hcp-fcc transition in 4 ~ e has recently been intensively investigatedlY2. For the light isotope 3 ~ e , however, the phase line is at present based on only two points close to the triple point with the fluid3. The present work constitutes the first investigation of the phase diagram of 3 ~ e to reasonably high pressures, as well as the first investigation of some aspects of the transition kinetics.

The 3 ~ e crystals were grown in an optical high pressure cell from commercial 3 ~ e gas with a stated impurity content of less than 0.1%. The transition was detected elliptometrically, since hcp 3 ~ e is birefringent

,

^{whereas f}cc 3 ~ e is isotropic. The experimental details of this work have been described in Ref. (2).

In Fig. 1 we are showing the phase diagram obtained so far. As in 4 ~ e , the transition shows temperature hysteresis, as well as a definite transition width. The hysteresis increases from about 160 mK at 1.62 kbar to 1.28 K at 5.60 kbar, the transition width varies between these pressures from 16 mK to 0.9 K. Both heating and cooling transition temperatures lie within experimental error on straight lines with slopes of dP/dT=555?22 bar/K (heating transition), and dP/dT=731+46 bar/K (cooling

transition). These slopes are very near those obtained for the 'He transition. Our best present estimate of the hcp-fcc-fluid triple point is 17.65 K and 1560 bar.

Theoretical predictions4 of this transition find an increasing slope with increasing pressure, leadingeventuallyto negative slope. There is no indication for this behaviour in the experimental results.

It was noted that in almost all crystals investigated, the virgin cooling transition occurred at a considerably lower temperature (up to 1 K ) , than following transitions. The transition temperatures Ms and As of Fig. 1 were therefore obtained only after several transformation passes. Reproducibility of the transition

temperatures after several passes was about 10 mK for As and 50 mK for Ms. On some occasions, for transitions close to the triple point, it was found that the amount transformed became smaller after many passes through the transition, leading eventually to a complete suppression of the cooling transition. Partial melting and recrystal- lization of the crystal restored the transition. It was generally observed that Ms was much more susceptible to thermal history and crystal quality. In one deliberately strained crystal, showing poor light transmission, Ms was 1.9 K lower compared to a good crystal at the same density, whereas As was raised by only 0.1 K. It should be noted that during the rather extensive study of the 4 ~ e transition, no case of the

complete suppression of the transition was ever observed.

On one occasion a severely strained crystal was grown near the triple point pressure. In this crystal the original fcc-hcp transition did not occur during the

*Permanent address : Department of Physics, University of Alberta, Edmonton, Alberta T6G 2J1, Canada

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982462

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JOURNAL DE PHYSIQUE

i n i t i a l cool-down (down t o

-

^{1 0 K).} On s u b s e q u e n t h e a t i n g , t h e t r a n s i t i o n o c c u r r e d a b r u p t l y n e a r Ms, p r e c e d e d by h e t e r o p h a s e o s c i l l a t i o n s , s e e F i g . 2. These o s c i l l a t i o n s were a l s o p r e s e n t m s u b s e q u e n t hcp-fcc t r a n s i t i o n s , a l t h o u g h t h e t r a n s i t i o n s were n o t s o a b r u p t , s e e Fig. 3. The h e t e r o p h a s e o s c i l l a t i o n s had a p e r i o d o f between 15 and 30 s e c , and c o n t i n u e d f o r a b o u t 3 t o 5 mins b e f o r e t h e o n s e t of t h e t r a n s i t i o n . T h i s c r y s t a l i s t h e o n l y one s o f a r which h a s shown t h e s e o s c i l l a t i o n s . No s i m i l a r e f f e c t h a s been observed i n 4 ~ e .

Conclusions: The f i r s t i n v e s t i g a t i o n o f t h e hcp-fcc 3 ~ e t r a n s i t i o n shows t h a t t h e t r a n s i t i o n i n most a s p e c t s i s v e r y s i m i l a r t o t h a t i n t h e heavy i s o t o p e 4 ~ e . The t r a n s i t i o n i s t h e r e f o r e a l s o most l i k e l y of m a r t e n s i t i c t y p e . Some a s p e c t s of t h e t r a n s i t i o n , i n p a r t i c u l a r t h e s e n s i t i v i t y o f t h e Ms t e m p e r a t u r e t o t h e r m a l h i s t o r y and c r y s t a l q u a l i t y , i s more pronounced i n 3 ~ e ; i t may b e connected w i t h t h e l a r g e r m o b i l i t y o f t h e 3 ~ e atom.

T h i s r e s e a r c h was s u p p o r t e d i n p a r t by N a t i o n a l S c i e n c e Foundation Grant No. 9t!R 8100660.

R e f e r e n c e s

1. FRANCK J . P . , Phys. Rev. B

22

(1980) 4315.

2. FRANCK J.P. and DANIELS W.B., Phys. Rev. B (1981) 2456.

3. FRANCK J . P . , Phys. Rev. L e t t e r s

L

(1961) 435.

4. HOLIAN B.L., GWINN W.D., LUNTZ A.C. and ALDER B.J., J. Chem. Phys.

2

(1973) 5444.

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