Heat capacities of liquid SbSe and BiSe alloys

Journal of Non-Crystalline Solids 117/118 North-Holland

(1990)575-578

575

HEAT CAPACITIES OF LIQUID Sb-Se AND Bi-Se ALLOYS Fujio KAKINUMA, Satoru OHNO and Kenji SUZUKI* Niigata College of Pharmacy, 5-13-2 Kamishin'ei-cho, Niigata 950-21, Japan * I n s t i t u t e for Material Research, Tohoku University, Sendai 950, Japan Measurements of heat capacities for l i q u i d Sb-Se and Bi-Se alloys were carried out up to 800 °C using an adiabatic scanning calorimeter. Anomalous temperature variation of heat capacity was observed for l i q u i d Sbo.45Seo.55, Sbo.5Seo. 5 and Bi2Se3 alloys. Broad maxima were observed in the temperature dependence of t h e i r heat capacities. In contrast, the heat capacity for l i q u i d Sb2Se3 a l l o y shows l i t t l e temperature v a r i a t i o n . In the concentration dependence, the maximum of the heat capacity deviates from the stoichiometric composition of M2Se3 in both a l l o y systems. The c h a r a c t e r i s t i c behaviour of heat capacities for l i q u i d Sb-Se and Bi-Se alloys can be a t t r i b uted to a change in intermediate-range order and in local bonding. I . INTRODUCTION

ing configuration.7)

In the solid state, Sb-Se and Bi-Se a l l o y

In t h i s paper, we report

the results of heat capacity measurements for

systems have intermediate compounds, l ) Sb2Se3

l i q u i d Sb-Se and Bi-Se alloys.

compound has a layered structure 2) and the nature of covalent bond. 3)

The structure of

2. EXPERIMENTAL PROCEDURE

BipSeR~ ~ ~all°y is isotype with that of Sb2Se3 a l l o y . 2'4j However, the composition range of

pressure were made with an adiabatic scanning

the i m m i s c i b i l i t y in the l i q u i d state d i f f e r s

calorimeter.

Measurements of heat capacities at constant The p u r i t i e s of Se, Sb and Bi are

between the Sb-Se and Bi-Se systems, l )"

99.9999%, 99.999% and 99.999%, respectively.

Liquid Sb2Se3 and Bi~Se3 alloys are typical l i q u i d semiconductors. 5" The Sb-Se and Bi-Se

The sample quantity contained in the quartz cell is about 0.15 mol.

The rate of heating was

a l l o y systems e x h i b i t a nonmetal-metal t r a n s i -

about 0.9 °C/min.

tion with the change of composition and temperature. 5)

heat capacity measurements are e s s e n t i a l l y same as described p r e v i o u s l y . 7)

The experimental details of

The enthalpies of mixing for l i q u i d Sb-Se and Bi-Se alloys are most exothermic at a stoichiometric composition of M2Se3.6)

The density

3. RESULTS Figure 1 shows the molar heat capacities Cp

change on melting is very small for these com-

for l i q u i d Sb, Se and Sbl_xSe x alloys with x =

pounds. 3)"

0.5 - 0.7 as a function of temperature.

These results suggest that the chemi-

cal short-range order due to covalent bonds in the solid state is retained a f t e r melting.

The

For

l i q u i d Sb-Se a l l o y s , the heat capacities show a characteristic temperature dependence with

change in the electronic properties f o r these

change in Sb concentration.

l i q u i d systems may be a t t r i b u t e d to the change

concentration, temperature coefficients of C P become smaller up to the composition of Sb2Se3.

in the bonding configuration. I t is interesting to study the structural modifications due to the change of composition and temperature.

The heat capacity gives useful

information of the rearrangement of local bond0022-3093/90/$03.50 ~) Elsevier Science Publishers B.V. (North-Holland)

With increasing Sb

The heat capacity of l i q u i d Sb2Se3 a l l o y shows l i t t l e temperature v a r i a t i o n . The value of Cp for l i q u i d Sb2Se3 a l l o y is 9.4 cal/mol-K just above the melting temperature. I t should be

F. Kakinuma et al./ Heat capacities of liquid Sb-Se and Bi-Se alloys

576

15

15

.o

A

i

,,,r ;.

o 10 E

o

tO

tO

U

U

E 10

Sb

r., u 5

Q.. u

0 400

I 500

I I I 600 ?00 800 TEMPERATURE (°C)

FIGURE 1 molar heat capacities for liquid Sb-Se alloys: I) 50 at%Se, 2) 55 at%Se, 3) Sb2Se3, 4) 70 at%Se

- e - ?00 °C -0-600

15-

Bi 5

m

0 z,00

I I I 600 ?00 800 TEMPERATURE (°C)

I 500

FIGURE 3 Molar heat capacities for liquid Bi-Se alloys: I) 33 at%Se, 2) 50 at%Se, 3) 55 at%Se, 4) Bi2Se 3 5) 65 at%Se

- o - ?50 °C -

15~=~

oo o

o

E 10to u

m

•

OOo

0 Sb

I I I I I I I (15 Sbl-xSex

o 0 o

U

v 0. C~

5

J

m

to

Q.

0

E 10

5

o

o

o

-

0 1.0 Se

o

0 Bi

I I I t l l l l l 0.5 Bil-xSex

1D Se

FIGURE 2 Concentration dependence of molar heat capacities for liquid Sb-Se alloys

FIGURE 4 Concentration dependence of molar heat capacities for liquid Bi-Se alloys

noticed that the heat capacity of l i q u i d Sbo.45 Seo.55 alloy shows the increase of Cp with in-

liquid Sb-Se alloys as a function of concentration. The values of Cp increase with increasing Sb concentration. In the concentration range of 0.7 < x < 1.0, the change of Cp is r e l a t i v e l y

creasing temperature. For liquid Sbo.5Seo. 5 alloy, a broad maximum is observed in the temperature dependence of Cp and the maximum value of Cp at about 650 °C is 11.2 cal/mol K. Figure 2 shows the molar heat capacities for

small. Abrupt increases of Cp are observed around the composition of Sb2Se3o I t should be noticed that the maximum of Cp in the Cp vs x

577

F. Kakinuma et al. / Heat capacities of liquid Sb-Se and Bi-Se alloys plane deviates from that of the stoichiometric composition of Sb2Se3. Figure 3 shows the molar heat capacities for

• o

A

Sb-Se Bi-Se-

liquid Bi-Se alloys as a function of temperature The heat capacity for liquid Bi2Se3 alloy shows a large temperature variation. For other alloys,

O0

,.3

O0

m

o

the heat capacities have small temperature coefficients.

As shown in Fig.4, the values of Cp

000"

.1,.

<3

increase gradually with increasing Se concentra-

I

-

tion and then abruptly increase around a compo0

sition of x = 0.5. The maximumof Cp in the Cp ichiometric composition of Bi2Se3.

In contrast

tion of this deviation is in the opposite sense. 4. DISCUSSION

i

Sb Bi

vs x plane exhibits the deviation from the stowith the case of liquid Sb-Se system, the direc-

i

I i

i

i

0.5

f I

i

Se

FIGURE 5 Enthalpies of melting for Sb-Se and Bi-Se alloys heat capacity of liquid Sb2Se3 alloy can be attributed to the break in the Sb-Se bonds. Liq-

The electrical conductivities ~ at their melting temperatures d i f f e r considerably between

uid Se-rich Sb-Se alloys consist of Se-like

Sb2Se3 and Bi2Se3 alloys inspite~of the isotype structure in the solid state. 4'5j I t may be

chain structure.

related to the structural modification of these

Se-Se bond breaking. The difference among

compounds on melting.

excess heat capacities with Se concentration

Figure 5 shows the en-

Relatively small excess heat

capacities for these liquid alloys are due to

may be related to the mechanism of the rear-

thalpies of melting AHmelt obtained from the heat capacity data for Sb-Se and Bi-Se alloy

rangement of bonds. For liquid Bi-Se alloy system, the excess

systems. The value of AHmelt for Sb2Se3 alloy is close to that interpolated linearly from the

heat capacities exhibit a strong deviation from

values of Sb and Se.

the Neumann-Kopp rule in the concentration

In contrast, the value of

AHmelt for Bi2Se3 alloy is considerably larger than that interpolated linearly from the values

range 0.5 < x < 0.65. For liquid Bil.xSex alloys with x < 0.4, the heat capacities obey

of Bi and Se.

the Neumann-Kopp rule. This suggeststhat the

I t suggests that the structure of

Sb2Se3 alloy change l i t t l e on melting.

The

structure of Bi2Se3 alloy may be modified during

chemical short-range order of Bi2Se3 may be retained in the concentration range of 0.4 < x

the melting.

< 0.65.

The excess heat capacity ACp is given by ACp = Cp(alloy) + {(l-X)Cp(M) + XCp(Se)} where M denotes Sb and Bi.

The temperature dependence of heat capacity (1)

As shown in Fig.2,

reflects the change in local atomic structures during the heating of alloys.

The increase of

the heat capacities for liquid Sb-Se alloy sys-

electrical conductivity for liquid semiconduc-

tem exhibit a positive deviation from the Neumann-Kopp rule. The values of ACp for liquid

density caused by the rearrangement of bonding.

Sbl_xSex alloys with x = 0.5 - 0.6 are considerably large. Liquid Sb2Se3 alloy has a covalently-bonded network structure. The large excess

tors are mainly due to an increase of carrier Figure 6 shows the molar heat capacities as a function of electrical conductivity. The maxima of Cp for liquid Sbo.5Seo.5 and In2Te3 alloys

F. Kakinuma et al. / Heat capacities of liquid Sb-Se and Bi-Se alloys

578

In 2Te3

17

Sb.sSe.5\

15~IJ v

13

Sb2Se3

Q.

(.J 11

_

97 5 i 1002

Bi2Sel

T(2Te i 5

I

m

101 2

l

I

I

5 102 2

A structural study of liquid Sb2Se3 alloy indicates that a prepeak is found in the structure factor S(Q) at Q = 1.2 A-I and S(Q) curves seem to be temperature insensitive within the measured temperature range ( ~ 700 °C ) except for a slight difference in the height of the f i r s t peak maximum,lO) It is inferred that the intermediate-range order exsists in Sb2Se3

I

I

I

5 103 2

O" (ohm cm)-t

liquid alloy consisting of large structural units (Sb2Se3)n. The excess heat capacity of liquid Sb2Se3 alloy may be attributed to the destruction of large structural units to

FIGURE 6 Molar heat capacities as a function of electrical conductivity are located at the conductivity range lO0 < ~ < 300 ohm-lcm-l where nonmetal-metal transition occurs.

This indicates that the rearrangement

of bonding is most active in this conductivity range. The correlation between Cp and o for liquid Bi2Se3 alloy is similar to that for liquid In 2 Te3 alloy. The large value of Cp for liquid In 2 Te3 alloy can be attributed to the dissociation of In2Te3-type chemical unit. 8) The excess heat capacity for liquid Bi2Se3 alloy may be also attributed to the dissociation of Bi2Se3-type unit. I t is noticed that the magnitude of Cp for liquid Sbo.sSeo.5 alloy is considerably smaller than that for liquid In2Te3 alloy. This sug-

smaller ones. For liquid Sbo.5Seo.5 alloy, the mechanism of bonding rearrangement may be similar to that of liquid Sb2Se3 alloy.

REFERENCES I. M. Hansen and K. Anderko, Constitution of Binary Alloya (McGraw H i l l , New York, 1958). 2. G.P. Voutsas, A.G. Papazoglou, P.J. Rentzeperis and D. Siapkas, Z. Kristallogr. 171 (1985) 261. 3. M.P. Vukalovich, A.A. Aleksandrov and V.S. Okhotin, Fluid Mechanics 2 (1973) ll8. 4. V.M. Glazov, S.N. Chizhevskaya and N.N. Glagoleva, Liquid Semiconductors (Plenum Press, New York, 1969). 5. T. Satow, O. Uemura, K. Matsumoto and S. Okumura, Phys. Stat. Sol.(b) 140 (1987) 233. 6. T. Maekawa, T. Yokoyama and K. Niwa, J. Chem. Thermodynamics 4 (1972) 873.

gests that the mechanism of bonding rearrange-

7. F. Kakinuma and S. Ohno, J. Phys. Soc. Jpn. 56 (1987) 619.

ment for liquid Sbo.5Seo.5 alloy differs from that for liquid In2Te3 alloy. The temperature variation of Cp for liquid

8. S. Takeda, H. Okazaki and S. Tamaki, J. Phys. C 15 (1982) 5203.

Sb2Se3 alloy is almost negligible as shown in Fig.l. The results of viscosity measurement for

9. T.N. Andrianova, A.A. Aleksandrov, L.A. Razumeichenko and V.S. Okhotin, High temp. 8 (1970) I l l 9 .

liquid Sb2Se3 alloy suggest that the chemical compound Sb~Se3 is preserved up to a temperature of 927 oC. 9, The dissociation of compound Sb2Se3

I0) T. Satow, O. Uemura, S. Akaike and S. Tamaki , J. Non-Cryst. Solids 29 (1978) 215.

may be small and make the minor contribution to the excess heat capacity of liquid Sb2Se3 alloy.