PRESSURE-INDUCED SEMICONDUCTOR-TO-METAL TRANSITION IN LIQUID Te-Se MIXTURES

HAL Id: jpa-00220191

https://hal.archives-ouvertes.fr/jpa-00220191

Submitted on 1 Jan 1980

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

PRESSURE-INDUCED

SEMICONDUCTOR-TO-METAL TRANSITION IN LIQUID Te-Se MIXTURES

M. Yao, K. Suzuki, H. Hoshino, H. Endo

To cite this version:

M. Yao, K. Suzuki, H. Hoshino, H. Endo. PRESSURE-INDUCED SEMICONDUCTOR-TO-METAL

TRANSITION IN LIQUID Te-Se MIXTURES. Journal de Physique Colloques, 1980, 41 (C8), pp.C8-

28-C8-31. �10.1051/jphyscol:1980807�. �jpa-00220191�

JOURNAL DE PHYSIQUE

CoZZoque C8, suppZ6mennt au n08, Tome

4 1 ,

aoQt 1980, page C8-28

PRESSURE-INDUCED SEMICONDUCTOR-TO-METAL TRANSITION IN LIQUID Te-Se MIXTURES

M. Yao, K. ~uzuki*, H. ~oshino*' and H. Endo

Department o f Physics, Faculty o f Science, Kyoto University, Kyoto

6 0 6 ,

Japan.

*co21ege of Genera2 Education, University o f Tokyo, Tokyo

253,

Japan.

z * ~ a c u ~ t y o f Education, Hirosaki University, Hirosaki

036,

Japan.

Abstract.- The electrical conductivity 0 , the thermoelectric power S and the sound velocity C have been measured for liquid Te-Se mixtures in a wide temperature and pressure range. Substantial changes in 0 and S from semiconducting to metallic values are induced by a slight application of pressure.

The region where such changes occur is determined on the concentration-temperature plane and in that region the prominent maxima in the temperature variations of compressibility appear. It is suggested that the observed semiconductor-to-metal transition is originated from the structural change.

INTRODUCTION--

A

number o f experiments have demonstrated that the electronic properties of liquid Te-Se mixtures change substantially w i t h temperature and concen- tration. The mixtures w i t h Se-rich concen- tration exhibit semiconducting behaviour at L o w temperatures. With increasing T e concentration o r increasing temperature the serniconduc ting nature changes towards metallic. Liquid Se is

known to

contain chain molecules derived from two- fold covalently bonded atoms together with dangling-bond atoms, and the character o f bonding among these chain molecules i s v a n d e r Waals type. By addition o f T e atoms, the concentration o f threefold bonded atoms increases and when i t becomes a suf- ficient amount the metallic character ap- pears. Since such chain structure w i t h an-

isotropic bonds i s expected to be trans- formed to the structure w i t h more isotrop- i c bonds by changing pressure and tempera- ture, i t i s interesting to study the eleca tronic and thermodynamic properties of the liquid Te-Se mixtures a t various pressures

and temperatures. In this paper, w e report the results o f the electrical conductivity

o , the thermoelectric power S and the

sound velocity C o f liquid Te-Se mixtures

weer

high pressures.

EXPERIMENTAL PROCEDURES-- T h e electrical conductivity o f liquid Te-Se mixtures h a s b e e n measured i n the pressure range 2-25 k b a r b y using the piston cylinder method u p to

6 5 0 ~ ~

and i n the pressure range 0-1 k b a r b y u s i n g a n internally heated auto-

clave u p to

1 6 0 0 ~ ~ .

T h e thermoelectric power S h a s been measured simultaneously w i t h

a

a t the lower pressures (0-1 kbar).

T h e sound velocity i n liquid Te-Se mix- tures h a s been measured b y the ultrasonic pulse transmission/echo technique n e a r the atomospheric pressure u p to 800 C and the 0

adiabatic compressibility

PS

h a s been es- timated b y using density data[l]

.

^{T h e}

measurement o f C under high pressures h a s b e e n done b y u s i n g the piston cylinder ap- paratus u p to 10 k b a r and u p to 6 0 0 ~ ~ . Further experimental details are described eleswhere [ 2 , 3 ] .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980807

F i g . 1. P r e s s u r e v a r i a t i o n o f 0 f o r l i q u i d Te-Se m i x t u r e s a t 4 6 0 ~ ~ . RESULTS AND DISCUSSION-- F i g u r e 1 shows t h e p r e s s u r e v a r i a t i o n s o f 0 f o r l i q u i d Te-Se m i x t u r e s a t 4 6 0 ~ ~ . The p r e s s u r e v a r - i a t i o n o f 0 f o r l i q u i d p u r e Te i s s m a l l . F o r l i q u i d Te 60S_e40 and TemSe50 m i x t u r e s , o ineneases r a p i d l y w i t h p r e s s u r e i n a r e l a - t i v e l y 1 orr o r e s s u r e r e g i o n (

<

⁵ k b a r ) and reaches nearly metallic values ( 300 ohm-' cm-')

a t h i g h p r e s s u r e s . The r a t e o f i n c r e a s e i n o i s reduced by f u r t h e r a d d i t i o n o f Se.

F i g u r e 2 shows t h e v a l u e s o f ( a l n

o / i 3 ~ ) ~

and ( 3 l n s / ~ P ) ~ for a Liquid Te gOSe50 mix- t u r e a t 100 b a r a s a function of tempera- t u r e . Broad maxima a r e s e e n around 6 0 0 ~ ~ i n b o t h ( a l n O / ~ P ) ~ vs T and

- ( a h s / ~ P ) ~

v s T c u r v e s . These maxima s h i f t towards

F i g . 2 , The p r e s s u r e c o e f f i c i e n t of 0 , ( a l n o / ~ p ) , ( o ) , and t h a t o f S,

( a l n

s / ~ P ) ~

( 0 )

,

a s a function o f temper- a t u r e f o r l i q u i d Te50Se50 m i x t u r e s.

F i g . 3. ( a ) Contour o f c o n s t a n t ( a l n o/a P ) T on t h e X-T p l a n e . Numbers d e n o t e ( a l n O / ~ P ) ~ i n k b a r - 1

.

( b ) Contour o f c o n s t a n t 0 on t h e X-T p l a n e . Numbers d e n o t e o i n ~hrn-~cm".

h i g h e r t e m p e r a t u r e s w i t h Se c o n c e n t r a t i o n . I n F i g .

3

( a ) , t h e c o n t o u r s of c o n s t a n t ( a l n o / a ~ ) ~ a r e shown on t h e c o n c e n t r a t i o n X

-

t e m p e r a t u r e T p l a n e . The b o l d l i n e de- n o t e s t h e r e g i o n where ( a l n

o / ~ P ) ~

h a s t h e maximum v a l u e . The l o c u s o f t h e maximum of - ( a l n s / ~ P ) ~ a l s o f a l l s n e a r l y on t h e b o l d l i n e i n F i g . 3 ( a ) . F i g u r e 3 ( b ) shows t h e c o n t o u r s o f c o n s t a n t 0 on t h e X-T p l a n e a t 100 b a r , t o g e t h e r w i t h t h e same b o l d l i n e a s i n F i g .

3

^(a).

A new r e s u l t o f S f o r l i q u i d p u r e Se i s

-

- +;- 3:

7 -

1500'' +1600,

pure Se

1

Fig. 4. I s o t h e r m s o f S f o r l i q u i d SE.

assa function of P r e s s u r e .

C8-30

^JOURNAL DE PHYSIQUE

p r e s e n t e d i n F i g . 4 a s a f u n c t i o n of p r e s - s u r e . The p r e s s u r e and temperature v a r i a - t i o n s of S o b t a i n e d by u s show n e a r l y t h e same t r e n d a s t h o s e by F i s c h e r and Schmutz- l e r [ 4 3 , though t h e a b s o l u t e v a l u e s of S by us a r e about 30

%

s m a l l e r t h a n t h o s e by them. The p r e s s u r e c o e f f i c i e n t of S i s l a r g e around 1200 0 C, t o which one a t t a i n s when t h e bold l i n e i n F i g . 3 i s e x t r a p o l a t - ed t o 100

%

Se.

F i g u r e 5 shows t h e r e s u l t s of

PS

f o r l i q - uid Te-Se m i x t u r e s a: a function of tempera- t u r e , t o g e t h e r w i t h

PS

f o r l i q u i d pure Te

153 and Se [6]

.

A t low t e m p e r a t u r e s t h e

P

-T S curves f o r t h e m i x t u r e s show almost t h e same t r e n d a s t h ~ : "3 ' pure Se

.

With r a l s - i n g temperature Bs-values of the mixtures increase more r a p i d l y than those of Se and they have

t h e maximum v a l u e s a t 4 4 0 ~ ~ f o r l i q u i d Te70Se30, a t 610 O C f o r Te50Se50 and a t 750°c f o r Te 30Se70. A t h i g h e r temperatures

Ps

of t h e m i x t u r e s d e c r e a s e s w i t h i n c r e a s i n g temperature, which i s t h e same behaviour a s t h a t of l i q u i d p u r e Te. It i s n o t i c e d t h a t t h e r e g i o n a t which t h e maximum a p p e a r s i n

Ps

c o i n c i d e s approximately w i t h t h e bold l i n e on t h e X-T p l a n e i n F i g . 3, where t h e semiconductor-to-metal t r a n s i t i o n a r e i n - duced by a s l i g h t a p p l i c a t i o n o f p r e s s u r e .

F i g u r e 6 shows t h e t e m p e r a t u r e v a r i a t i o n of C f o r l i q u i d Te50Se50 m i x t u r e . The sound v e l o c i t y i n c r e a s e s c o n s i d e r a b l y w i t h i n c r e a s i n g p r e s s u r e and t h e t e m p e r a t u r e a t which C shows a minimum s h i f t s towards lower t e m p e r a t u r e s w i t h i n c r e a s i n g p r e s - s u r e . T h i s s u g g e s t s t h a t t h e temperature of t h e semicond~tctor-to-metal t r a n s i t i o n d e c r e a s e s w i t h i n c r e a s i n g p r e s s u r e , which h a s been confirmed by t h e c o n d u c t i v i t y measurement under p r e s s u r e s .

As s e e n i n F i g . 5, t h e l a r g e compressi- b i l i t y i n d i c a t e s t h a t t h e r e e x i s t l a r g e d e n s i t y f l u c t u a t i o n s n e a r t h e t r a n s i t i o n r e g i o n . Near t h e r e g i o n , t h e r e a p p e a r s t h e anomaly i n t h e molar volume Vm v s tempera- t u r e c u r v e s ( s e e F i g .

7

(a)), t h a t i s , t h e thermal expansion c o e f f i c i e n t ap changes from p o s i t i v e t o n e g a t i v e

[I].

Furthermore t h e c o n c e n t r a t i o n v a r i a t i o n s o f o t h e r p r o p e r t i e s such a s t h e Knight s h i f

t[7]

and

F i g . 5. Temperature v a r i a t i o n s o f

P

_S Fig.

6.

Temperature v a r i a t i o n s o f t h e f o r l i q u i d Te-Se m i x t u r e s t o g e t h e r w i t h sound v e l o c i t y f o r l i q u i d Te

5oSe50

p

_S f o r l i q u i d pure Te 5 and Se

6 .

a t v a r i o u s p r e s s u r e s .

t h e a v e r a g e c o o r d i n a t i o n number[8,9] e x h i b i t anomalous b e h a v i o u r s i n t h e same r e g i o n .

The f a c t t h a t t h e maximum i n compressi- b i l i t y a p p e a r s n e a r t h e r e g i o n where

ap

changes from p o s i t i v e t o n e g a t i v e can b e i n t e r p r e t e d by t h e s k e t c h e s shown i n F i g s . 7 ( a ) and (b). These f i g u r e s show t h e thermodynamic a s p e c t s o f t h e s t r u c t u r a l t r a n s i t i o n from S e - l i k e l o o s e l y packed atoms w i t h twofold c o o r d i n a t i o n t o a T e - l i k e dense-

l y packed structure w i t h h i g h l y c o o r d i n a t e d atoms i n t h e m i x t u r e s . The s h a r p s t r u c t u r - a l t r a n s i t i o n , which i s i n d i c a t e d by t h e dashed l i n e s i n F i g s . 7 ( a ) and ( b ) , i s

smeared o u t owing t o t h e t h e r m a l a g i t a - t i o n .

A s a f i n a l remark, we r e f e r t o t h e r e - s u l t s o f r e c e n t d e n s i t y and NMR measure- ments f o r - l i q u i d p u r e Se [10,11]

.

^{I t was}

found t h a t t h e i s o c h o r e s on t h e P-T p l a n e have afl i n f l e c t i o n a t h i g h t e m p e r a t u r e s and t h a t t h e p r e s s u r e v a r i a t i o n o f t h e r e - sonance s h i f t due t o t h e p a r a m a g n e t i c dan- g l i n g bonds shows anomalous b e h a v i o u r s a t h i g h t e m p e r a t u r e s . These e v i d e n c e s may

F i g . 7. ( a ) The s o l i d l i n e i n d i c a t e s t h e t e m p e r a t u r e v a r i a t i o n o f m o l a r volume a t c o n s t a n t p r e s s u r e . ( b ) The s o l i d l i n e i n d i c a t e s t h e p r e s s u r e v a r i - a t i o n o f m o l a r volume a t c o n s t a n t tem- p e r a t u r e . The dashed l i n e s i n d i c a t e t y p i c a l v a r i a t i o n s o f V i n t h e c a s e

m

o f t h e f i r s t o r d e r phase t r a n s i t i o n .

s u g g e s t t h a t a s t r u c t u r a l t r a n s i t i o n s i m i - l a r t o t h a t i n l i q u i d Te-Se, m i x t u r e s o c c u r s even i n l i q u i d p u r e Se.

ACKNOWLEDGEMENTS-- The a u t h o r s w i s h $0 e x p r e s s t h e i r t h a n k s t o D r . K. Tamura, M r . M . Misonou and M r . M. Mushiage f o r v a l u a b l e

d i s c u s s i o n s .

REFERENCES

1. Thurn,H and R u s k a , J . , J . Non-Cryst.

S o l i d s

G, 331

( 1 9 7 6 ) .

2 . Yao,M., Misonou,M., Tamura,K., I s h i d a , K.

,

^{Tsu j i}

,

^K. and Endo, H.

,

J

.

^Phys

.

^Soc

.

J a p a n

48,

109 ( 1 9 8 0 ) -

3. Yao,M., Suzuki,X. and Endo,H., S o l i d S t a t e Commun.

3,

187 ( 1 9 8 0 ) .

4.

F i s c h e r , R . and Schmutzler,R.W., The P h y s i c s o f Selenium and T e l l u r i u m , ed.

G e r l a c h , E. and G r o s s , P . , 1979 ( s p r i n - g e r , New ~ o r k ) P. 225.

5. Gitis,M.B. and M i k h a i l o v , I . G . , Sov.

P ~ Y S . A C O U S ~ . 12,

1 4

( 1 9 6 6 ) .

6. Gitis,M.B. and M i k h a i l o v , f . G . , Sov.

Phys. Acoust.

13,

251 ( 1 9 6 7 ) .

7 .

Seymour,E.F. and Brown,D., Proc. I n t . Conf. L i q u i d M e t a l s , ed. T a k e u c h i , S . , 1972 ( ~ a y l o r and F r a n c i s ) P. 399.

8. Hoyer,W., Thomas,E. and Wobst,M., Z.

N a t u r f o r s c h u n g ,

z,

1633 ( 1 9 7 5 ) . 9 . B e l l i s s e n t , R . and Tourand,G., J .

,Nan-

C r y s t . S o l i d s

2

and

%,

1 2 2 1 ( 1 9 8 0 ) . 1 0 . F i s c h e r , R . , Schmutzler,R.W. and H e n s e l ,

F., J . Non-Cryst. S o l i d s

35

^and

3,

1 2 9 5 ( 1 9 8 0 ) .

11. Warren, J r . , W.W. and Duree, R . , t o be p u b l i s h e d .