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The excess enthalpies of liquid GaGeTe and GaSnTe alloys
JournaJ of the Less-Common
Metals, 136 (1987)
183
183 - 191
THE EXCESS ENTHALPIES OF LIQUID Ga-Ge-Te ALLOYS
AND Ga-Sn-Te
B. GATHER, E. IRLE and R. BLACHNIK Anorganische
Chemie, Universitiit Osnabriick Postfach 44 69, D-4500 Osnabriick (F.R.G.)
(Received May 15,1987)
The excess enthalpies of the liquid alloys Ga-Ge-Te and Ga-Sn-Te were measured in a heat-flow calorimeter at 1203 K. The enthalpy surface in the ternary space in both systems is characterized by a valley stretching from the exothermic minimum in the Ga-Te system to the minima of the Ge-Te and Sn-Te systems. The minima in the ternary systems were found in this valley, i.e. on the sections Ga,Tes-GeTe and Ga,Tes-SnTe. A comparison of the experimental data with those calculated from the excess enthalpies of the constituent binaries with the aid of the Bonnier model, reveals only small deviations. A preliminary investigation was made into the ternary phase diagram of Ga-Sn-Te. This system contains the two quasibinary sections GazTe,-SnTe, GaTe-SnTe and the ternary compound Ga6SnTe10. The previously reported compounds GazSnTe3 and GaSnTe, do not exist.
1. Introduction Recently, we reported the excess enthalpies (HE) of liquid ternary alloys containing tellurium [l]. These systems were chosen in such a way that two binary tellurium systems with strong exothermic interactions were combined with one system in which the melt is a regular solution. The excess enthalpies of mixing in the metal-tellurium binaries vary as a triangularshaped function of the concentration. This unusual behaviour has been explained by Wagner [2]. He assumed that compounds were formed in the liquid state. The observed excess enthalpies for these ternary systems differ from data which were calculated with the aid of models [3]. We found that in In-Sb-Te the calculated excess enthalpies HE are less exothermic than those observed [ 41, whereas in Ag-Sb-Te the calculated enthalpies are more exothermic than the observed values [5]. In the first case the biggest deviation was found at a concentration which corresponds to the compound In$bTe,. This compound contributes to the excess enthalpy in the liquid *Dedicated to Prof. Dr. A. Rabenau on the occasion of his 65th birthday. OQ22-5088/87/$3.50
@ Elsevier Sequoia/Printed
in The Netherlands
184
state by additional ternary interactions. Though In,SbTez decomposes peritectically, associates of this composition probably exist in the melt. In the case of the system Ag-Sb-Te, the observed effect was related to a tendency of immiscibility around the section Ag,Te-Sb. During the present investigation, the excess enthalpies of the ternaries Ga-Ge-Te and Ga-Sn-Te were measured in the liquid state. More information about ternary interactions should be gained in systems with tellurium as one component. The system Ga-Te contains the compounds GaTe and Ga,Te3 [6, 71 which both melt congruently. The excess enthalpy in the liquid state varies as a triangular-shaped function of the concentration. The position of the minimum (-35.7 kJ mol-‘, 1140 K [8, 91) corresponds to the composition of Ga*Te,. The system Ge-Te [lo] contains the compound GeTe which melts congruently at 1001 K. At lower temperatures a peritectoidal phase was found at 51 mol.% tellurium. In the system Sn-Te only one compound is observed. SnTe melts congruently at 1079 K [ 111. The excess enthalpies in the liquid state of the systems Ge-Te and Sn-Te are similarly shaped functions of the concentration. The position of both minima (-12.00 kJ mol-‘, 1140 K [12], Ge-Te; -23.95 kJ mol-‘, 1140 K [13], Sn-Te) lies close to the compositions GeTe and SnTe respectively. The phase diagrams of Ga-Ge and Ga-Sn are of the eutectic type [ 141. The melts of both systems are regular solutions [15,16]. The phase diagram of the ternary system Ga-Ge-Te was determined by Kra et al. [17, 181. They found the compound GaGeTe which crystallizes in a layer structure, derived from the GaSe type [19]. The compounds GaGeTe, and GazGeTe3, reported by Nasirov et al. [20], do not exist. Kra et al. observed two miscibility gaps in the ternary system. One of these has its origin at the binary Ga-Te and closes in the ternary space at approximately 14 mol.% germanium. The other lies in the ternary space around the centre of the section GazTes-Ge. The phase diagram of the ternary system Ga-Sn-Te is not known. The sections Ga*Te,-SnTe [21] and GaTe-SnTe [22] and the lattice parameters of the compounds GazSnTe3, GaSnTe, [21, 221 and Ga$nTeis [23] have been reported in the literature. 2. Experimental details The ternary excess enthalpies were measured in a heat flow calorimeter under an argon atmosphere. Mixtures with compositions Gao.zGeo.s, Gao.aGeo.s, Ga0.sGeo.4, Ga0.2Ge0.s, Ga0.sSn0.2, Gao.6Sn0.4, Gao.4Sno.6 and Ga,.,Sn,., or pure tellurium were heated to the reaction temperature in the calorimeter cell. In the first case tellurium and in the second case the binary mixtures were added from ambient temperature to the melt. The registration and evaluation of the thermal effects was done with a computer. The signals
185
were recorded on a Commodore 8032~sk and stored on a floppy disc (Commodore SFB 1001). After the measurements, the results were displayed on a plotter (NPR 5500, Neumiiller). The display was used to determine the integrations limits. The integration was performed on the computer by a program developed by the authors. The excess enthalpies of the sections Ga0_4Te,_,-Sn, 5Te,. 5 and Ga0.~Te0.6-Ge0. STe, 5 were measured by mixing the constituent molten compounds in the calorimeter. In both cases the calorimeter was calibrated before and after each mixing experiment by dropping pellets of tin (298 K) into a silica tube standing in the melt. The enthalpy increments H(T - 298 K) of tin and tellurium were taken from the data of Gr@nvold et al. [24, 251. The enthalpy increments of the mixtures were measured in separate experiments. The binary alloys Ga-Ge and Ga-Sn were prepared by reacting gallium (99.99; VAW) with germanium and tin (both with purity 99.999%; Preussag) in sealed evacuated silica ampoules. The reacted products were annealed for 14 days. The purity of the tellurium was 99.995% (Preussag). The samples for the phase diagram investigations were prepared similarly. The samples were annealed for one month at various temperatures.
3. Results The results of a preliminary examination of the phase diagrams GazTe,SnTe and GaTe-SnTe are given in Figs. l(a) and (b). Both sections are quasi-
.?.l!!LL . .. 936
Ga_ie3 (4
2o
LO
mole -%
6o SnTe
8o
SnTe
GaTe
z”
Lo SnTe 6o mole-%
*'
SnTe
@I
Fig. 1. Quasibinary sections in the ternary Ga-Sn-Te (a) the section GazTerSnTe (b) the section GaTeSnTe. 0, annealing temperature of 823 K; x , annealing temperature of 923 K.
Tellurium (mole fraction)
HE (kJ mol-‘) -7.694 -7.966 -12.930 -13.901 -16.737 -16.591 -17.494 -16.808 -16.495 -16.121 -15.569 -15.035 -14.247 -13.590 -12.625 -11.889 -10.574 -9.618 -8.259 -7.021 -5.395 -4.628 -2.506 -2.672
Tellurium (mole fraction)
0.863 0.854 0.750 0.736 0.655 0.652 0.584 0.511 0.496 0.486 0.466 0.455 0.431 0.418 0.391 0.376 0.339 0.319 0.215 0.246 0.189 0.174 0.097 0.094
HE (kJ molwl)
-6.714 -6.365 -6.698 -11.278 -10.855 -12.049 -13.005 -13.816 -13.973 -13.557 -13.640 -13.792 -13.590 -12.760 -12.736 -11.441 -11.874 -9.843 -10.208 -7.914 -8.286 -5.682 -6.026 -3.583 -3.616 -1.694 -1.804
Tellurium (mole fraction)
0.853 0.841 0.827 0.736 0.724 0.680 0,640 0.624 0.599 0.577 0.547 0.530 0.503 0.499 0.470 0.432 0.430 0.386 0.384 0.330 0.326 0.260 0.254 0.182 0.161 0.090 0.069
0.854 0.738 0.647 0.587 0.538 0.509 0,503 0.499 0.462 0,477 0.453 0.445 0.416 0.409 0.373 0.367 0.319 0.318 0.252 0.242 0.172 0.168 0.091 0.077
Gaa6Geo.4-Te
Gao.4Ww-Te
-10.053 -16.646 -22.054 -22.745 -21.167 -20.340 -19.669 -19.712 -19.384 -18.659 -18.045 -17.226 -16.255 -15.494 -14.094 -13.485 -11.550 -11.232 -8.645 -8,016 -5.447 -4.850 -2.741 -2.291
HE (kJ mol-‘)
for the reaction xGa(l) + yGe(l) f (1 -x
Gao.zGeo.a-Te
Excess molar enthalpies at 1203 R of the system Ga-Ge-Te
TABLE 1
0.883 0.867 0.770 0.751 0.685 0.660 0.604 0.538 0.503 0.500 0.497 0.477 0.471 0.444 0.437 0.404 0.397 0.357 0.344 0.290 0.281 0.204 0.201 0.112 0.111
Tellurium (mole fraction)
GaasGeaz-Te
-7.861 -8.854 -16.913 -17.899 -23.396 -23.770 -27.861 -26.378 -23.734 -23.349 -24.133 -22.210 -21.609 -20.177 -19.412 -17.748 -16.934 -14.850 -13.871 -11.363 -10.540 -7.396 -6.818 -3.797 -3.379
HE (kJ molP1)
- y)TeU) + Ga,GeyTe(l-,-,)~l)
Cz Q,
2
HE (kJ mol-‘)
-9.629 -10.419 -18.477 -19.013 -22.610 -24.552 -25.292 -25.953 -23.278 -24.073 -22.728 -22.587 -21.183 -20.587 -19.483 -17.740 -16.015 -14.055 -13.978 -9.631 -8.378 -4.346 -3.978
0.858 0.844 0.715 0.715 0.640 0.613 0.562 0.540 0.521 0.509 0.506 0.491 0.474 0.454 0.448 0.409 0.396 0.349 0.336 0.262 0.240 0.142 0.135
at 1203
Tellurium (mole fraction)
Excess molar enthalpies
TABLE
0.851 0.835 0.713 0.703 0.605 0.594 0.533 0.516 0.477 0.445 0.400 0.348 0.289 0.220 0.151 0.069
Tellurium (mole fraction)
Ga&Sno.e-Te
K of the system
-11.341 -11.984 -20.556 -21.804 -25.893 -26.076 -26.064 -23.038 -22.704 -20.604 -17.629 -14.425 -11.104 -7.618 -4.439 -1.340
xGa(l)
+ ySn(1)
0.851 0.821 0.731 0.672 0.639 0.583 0.573 0.534 0.530 0.506 0.503 0.496 0.486 0.471 0.468 0.446 0.435 0.405 0.391 0.366 0.340 0.323 0.274 0.262 0.184 0.164 0.125 0.095
Tellun’um (mole fraction)
Gao.6 Sno.4-Te
for the reaction
HE (kJ mol-*)
Ga-Sn-Te
-12.318 -13.626 -21.079 -25.429 -27.026 -28.522 -27.409 -25.784 -26.947 -24.718 -24.755 -23.312 -23.738 -23.093 -22.479 -21.037 -20.275 -18.227 -17.181 -15.636 -13.971 -12.915 -10.190 -9.558 -5.824 -5.073 -3.371 -2.298
HE (kJ mol-I)
+ (1 --x
-
0.846 0.845 0.731 0.727 0.642 0.632 0.542 0.516 0.505 0.491 0.490 0.471 0.456 0.435 0.420 0.395 0.381 0.353 0.349 0.309 0.280 0.252 0.172 0.167 0.095 0.079
Tellurium (mole fraction)
Gao.8Sn~~-Te
-12.196 -12.687 -22.137 -22.867 -27.768 -30.096 -28.960 -27.330 -24.566 -25.510 -25.798 -23.343 -23.540 -21.232 -20.395 -18.514 -17.633 -15.645 -15.465 -12.692 -10.808 -9.393 -5.567 -5.304 -2.131 -1.800
HE (kJ mol-‘)
y)Te(l) + Ga,Sn,Tq-,-,)(I)
188
binary. The ternary phase diagram is divided by these two sections into three subsystems. The section GaTe-SnTe differs considerably from that reported by Dovletov et al. [21] and Rustamov et al. [22]. The compounds Ga$nTes and GaSnTez do not exist. A similar observation was made by Kra et al. [17, 181 in the ternary system Ga-Ge-Te. They were not able to prepare the compounds Ga,GeTe, and GaGeTe, previously described by Nasirov et al. [20]. The excess molar enthalpies HE of the reactions xGa(l) + yGe(l) + (1 -X
-Y)Te(l)
+ Ga,Ge,Ter-,-,(l)
and xGa(l) +ySn(l)
+ (l--r
--y)Te(l)+Ga,Sn,Tel_,-,(l)
were measured at 1203 K. The data are listed in Tables 1 and 2. All values obtained in the experiments were used in a threedimensional fitting procedure. The resulting isoenthalpic lines are presented in Figs. 2 and 3, which are projections of the enthalpy surface on the Gibbs triangle. The enthalpy surfaces of the systems are determined by a valley of minima which were Te
/
Ga
I
A
Fig. 2. Projection ternary.
A
A
20
A
A
40 mole-% Ge
of the isoenthalpic
/\
60
A
n 80
lines onto the Gibbs
\ A
‘Ge
triangle in the Ga-Ge-Te
189
Te
Ga Fig. 3. Projection ternary.
40 mole-% of the ~oenth~pic
60
80
Sn
Sn lines onto the Gibbs triangle in the Ga-Sn-Te
TABLE 3 Excess molar enthalpies of tbe sections MasTea&IaasTetns in the ternary system C&-MTe (M = Ge, Sn) at 1203 K for the reaction ~M~.~Te~~(I) * (1 -~)Ga~,~Te~~(I) + Gao.4-a4xMo.s~Ted6-atc(l)
S%s Teas-Gao.4Teo.a
Geo.sTeo.s-Gao.4Teo.6 Gea5Teo.s
HE
(mole fraction)
(kJ mol-“)
0.099 0.200 0.401 0.500 0.600 0.699 0.797 0.900
0.91 1.69 2.57 2.71 2.37 1.83 1.27 0.61
SnasTeas
HE
(mole fraction)
(kJ molvl)
0.091 0.211 0.286 0.400 0.501 0.604 0.700 0.900
0.57 1.16 1.42 1.49 1.53 1.40 1.21 0.53
190
found on the sections Ga,Tes-GeTe and Ga,Tes-SnTe. The enthalpies of mixing increase from this valley in the direction of the tellurium comer and in the direction of the Ga-Ge(Sn) binaries. Al’fer et al. [26] (Fig. 4 of that reference) measured the excess enthalpies of the system Ga-Ge-Te by quantitative differential thermal analysis. The data lead to an enthalpy surface similar to that found in this investigation. However, the absolute values of the enthalpy data differ considerably. In addition, the excess enthalpies of the ternary mixtures were calculated from the thermodynamic data of the constituent binaries, using the models of Kohler [27], Bonnier [3] and our own improvement of the Bonnier model [28]. The best agreement was achieved with the latter method. In the system Ga-Sn-Te no deviation was found between calculated and observed data within the experimental error. In the Ga-Ge-Te system the calculated data are less exothermic than the observed data. This deviation was found in the subsystem GaTe-GeTe-Ge-Ga with maximum deviations of about -1 kJ mall’. Acknowledgment We wish to express our gratitude to the Stiftung Volkswagenwerk the Fonds der Chemischen Industrie for their support of this work.
and
Keferences 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
B. Gather and R. Blachnik, 2. Metollkd., 74 (1983) 212. C. Wagner, Thermodynamics of Alloys, Addison-Wesley, Reading, MA, 1952. E. Bonnier and R. Caboz, C. R. Acad. Sci., 250 (1967) 527. B. Gather, B. Legendre and R. Blachnik, J. Less-Common Met., 77 (1981) 71. B. Gather and R. Blachnik, 2. Metallkd., 73 (1982) 245. R. Blachnik and E. Irle, J. Less-Common Met., 113 (1985) 21. F. Alapini, J. Flahaut, M. Guittard, S. Jaulmes and M. Julien-Pouzol, J. Solid State Chem., 28 (1979) 309. R. Blachnik and E. Irle, unpublished work, 1985. H. Said and R. Castanet, J. Less-Common Met. 68 (1979) 213. B. Legendre and C. Souleau, C. R. Acad. Sci., Ser. C, 284 (1977) 315. S. Kurosawa, Y. Nakamura and M. Shimoji, J. Less-Common Met., 70 (1980) 119. C. Bergman and R. Castanet, Ber. Bunsenges. Phys. Chem., 80 (1976) 774. R. Blachnik and B. Gather, 2. Metallkd., 74 (1983) 172. M. Hansen and K. Anderko, Constitution of Binary Alloys, McGraw-Hill, New York, 1958. B. Predel and D. W. Stein, 2. Metallkd., 62 (1971) 499. J. P. Bros, R. Castanet and M. Lafitte, C. R. Acad. Sci., Ser. C, 264 (1967) 1804. G. Kra, R. Eholie and J. Flahaut, Ann. Chim. (Paris), (1978) 257. G. Kra, R. Ebolie and J. Flahaut, C. R. Acad. Sci., Ser. C, 284 (1977) 889. D. Fenske and H. G. v. Schnering, Angew. Chem., 95 (1983) 420. Ya. N. Nasirov, M. I. Zargarova, R. S. Gamidov and M. M. Aksperov, Zzu. Akad. Nauk SSSR, Neorg. Mater., 6 (1970) 990. K. Dovletov, Kh. Emiyazov and A. S. Malkova, Zzu. Akad. Nauk SSSR, Neorg. Mater., 12 (1976) 1964.
191 22 P. G. Rustamov, B. B. Kuliev, M. A. Aliyanov and E. M. Kuliev, Phys. Status Solidi, A, 3 (1970) K 139. 23 M. Guittard, F. Alapini, S. Jaulmes, M. Julien-Pouzol and J. Flahaut, Mater. Res. Bull., 13 (1978) 1157. 24 F. GrOnvold, Rev. Chim. Miner., 11 (1974) 568. 25 F. Grdnvold, J. Drowart and E. F. Westrum, Jr., The Chemical Thermodynamics of Actinide Elements and Compounds, Part 4 (The Actinide Chalcogenides), International Atomic Energy Agency, Vienna, 1984. 26 S. A. Al’fer, L. A. Mechkovskii and A. A. Vecher, Zh. Fiz. Khim., 57 (1983) 1528. 27 F. Kohler, Monatsh. Chem., 91 (1960) 738. 38 B. Gather, Program and abstract, Colphad, 12 (1983).
Metals, 136 (1987)
183
183 - 191
THE EXCESS ENTHALPIES OF LIQUID Ga-Ge-Te ALLOYS
AND Ga-Sn-Te
B. GATHER, E. IRLE and R. BLACHNIK Anorganische
Chemie, Universitiit Osnabriick Postfach 44 69, D-4500 Osnabriick (F.R.G.)
(Received May 15,1987)
The excess enthalpies of the liquid alloys Ga-Ge-Te and Ga-Sn-Te were measured in a heat-flow calorimeter at 1203 K. The enthalpy surface in the ternary space in both systems is characterized by a valley stretching from the exothermic minimum in the Ga-Te system to the minima of the Ge-Te and Sn-Te systems. The minima in the ternary systems were found in this valley, i.e. on the sections Ga,Tes-GeTe and Ga,Tes-SnTe. A comparison of the experimental data with those calculated from the excess enthalpies of the constituent binaries with the aid of the Bonnier model, reveals only small deviations. A preliminary investigation was made into the ternary phase diagram of Ga-Sn-Te. This system contains the two quasibinary sections GazTe,-SnTe, GaTe-SnTe and the ternary compound Ga6SnTe10. The previously reported compounds GazSnTe3 and GaSnTe, do not exist.
1. Introduction Recently, we reported the excess enthalpies (HE) of liquid ternary alloys containing tellurium [l]. These systems were chosen in such a way that two binary tellurium systems with strong exothermic interactions were combined with one system in which the melt is a regular solution. The excess enthalpies of mixing in the metal-tellurium binaries vary as a triangularshaped function of the concentration. This unusual behaviour has been explained by Wagner [2]. He assumed that compounds were formed in the liquid state. The observed excess enthalpies for these ternary systems differ from data which were calculated with the aid of models [3]. We found that in In-Sb-Te the calculated excess enthalpies HE are less exothermic than those observed [ 41, whereas in Ag-Sb-Te the calculated enthalpies are more exothermic than the observed values [5]. In the first case the biggest deviation was found at a concentration which corresponds to the compound In$bTe,. This compound contributes to the excess enthalpy in the liquid *Dedicated to Prof. Dr. A. Rabenau on the occasion of his 65th birthday. OQ22-5088/87/$3.50
@ Elsevier Sequoia/Printed
in The Netherlands
184
state by additional ternary interactions. Though In,SbTez decomposes peritectically, associates of this composition probably exist in the melt. In the case of the system Ag-Sb-Te, the observed effect was related to a tendency of immiscibility around the section Ag,Te-Sb. During the present investigation, the excess enthalpies of the ternaries Ga-Ge-Te and Ga-Sn-Te were measured in the liquid state. More information about ternary interactions should be gained in systems with tellurium as one component. The system Ga-Te contains the compounds GaTe and Ga,Te3 [6, 71 which both melt congruently. The excess enthalpy in the liquid state varies as a triangular-shaped function of the concentration. The position of the minimum (-35.7 kJ mol-‘, 1140 K [8, 91) corresponds to the composition of Ga*Te,. The system Ge-Te [lo] contains the compound GeTe which melts congruently at 1001 K. At lower temperatures a peritectoidal phase was found at 51 mol.% tellurium. In the system Sn-Te only one compound is observed. SnTe melts congruently at 1079 K [ 111. The excess enthalpies in the liquid state of the systems Ge-Te and Sn-Te are similarly shaped functions of the concentration. The position of both minima (-12.00 kJ mol-‘, 1140 K [12], Ge-Te; -23.95 kJ mol-‘, 1140 K [13], Sn-Te) lies close to the compositions GeTe and SnTe respectively. The phase diagrams of Ga-Ge and Ga-Sn are of the eutectic type [ 141. The melts of both systems are regular solutions [15,16]. The phase diagram of the ternary system Ga-Ge-Te was determined by Kra et al. [17, 181. They found the compound GaGeTe which crystallizes in a layer structure, derived from the GaSe type [19]. The compounds GaGeTe, and GazGeTe3, reported by Nasirov et al. [20], do not exist. Kra et al. observed two miscibility gaps in the ternary system. One of these has its origin at the binary Ga-Te and closes in the ternary space at approximately 14 mol.% germanium. The other lies in the ternary space around the centre of the section GazTes-Ge. The phase diagram of the ternary system Ga-Sn-Te is not known. The sections Ga*Te,-SnTe [21] and GaTe-SnTe [22] and the lattice parameters of the compounds GazSnTe3, GaSnTe, [21, 221 and Ga$nTeis [23] have been reported in the literature. 2. Experimental details The ternary excess enthalpies were measured in a heat flow calorimeter under an argon atmosphere. Mixtures with compositions Gao.zGeo.s, Gao.aGeo.s, Ga0.sGeo.4, Ga0.2Ge0.s, Ga0.sSn0.2, Gao.6Sn0.4, Gao.4Sno.6 and Ga,.,Sn,., or pure tellurium were heated to the reaction temperature in the calorimeter cell. In the first case tellurium and in the second case the binary mixtures were added from ambient temperature to the melt. The registration and evaluation of the thermal effects was done with a computer. The signals
185
were recorded on a Commodore 8032~sk and stored on a floppy disc (Commodore SFB 1001). After the measurements, the results were displayed on a plotter (NPR 5500, Neumiiller). The display was used to determine the integrations limits. The integration was performed on the computer by a program developed by the authors. The excess enthalpies of the sections Ga0_4Te,_,-Sn, 5Te,. 5 and Ga0.~Te0.6-Ge0. STe, 5 were measured by mixing the constituent molten compounds in the calorimeter. In both cases the calorimeter was calibrated before and after each mixing experiment by dropping pellets of tin (298 K) into a silica tube standing in the melt. The enthalpy increments H(T - 298 K) of tin and tellurium were taken from the data of Gr@nvold et al. [24, 251. The enthalpy increments of the mixtures were measured in separate experiments. The binary alloys Ga-Ge and Ga-Sn were prepared by reacting gallium (99.99; VAW) with germanium and tin (both with purity 99.999%; Preussag) in sealed evacuated silica ampoules. The reacted products were annealed for 14 days. The purity of the tellurium was 99.995% (Preussag). The samples for the phase diagram investigations were prepared similarly. The samples were annealed for one month at various temperatures.
3. Results The results of a preliminary examination of the phase diagrams GazTe,SnTe and GaTe-SnTe are given in Figs. l(a) and (b). Both sections are quasi-
.?.l!!LL . .. 936
Ga_ie3 (4
2o
LO
mole -%
6o SnTe
8o
SnTe
GaTe
z”
Lo SnTe 6o mole-%
*'
SnTe
@I
Fig. 1. Quasibinary sections in the ternary Ga-Sn-Te (a) the section GazTerSnTe (b) the section GaTeSnTe. 0, annealing temperature of 823 K; x , annealing temperature of 923 K.
Tellurium (mole fraction)
HE (kJ mol-‘) -7.694 -7.966 -12.930 -13.901 -16.737 -16.591 -17.494 -16.808 -16.495 -16.121 -15.569 -15.035 -14.247 -13.590 -12.625 -11.889 -10.574 -9.618 -8.259 -7.021 -5.395 -4.628 -2.506 -2.672
Tellurium (mole fraction)
0.863 0.854 0.750 0.736 0.655 0.652 0.584 0.511 0.496 0.486 0.466 0.455 0.431 0.418 0.391 0.376 0.339 0.319 0.215 0.246 0.189 0.174 0.097 0.094
HE (kJ molwl)
-6.714 -6.365 -6.698 -11.278 -10.855 -12.049 -13.005 -13.816 -13.973 -13.557 -13.640 -13.792 -13.590 -12.760 -12.736 -11.441 -11.874 -9.843 -10.208 -7.914 -8.286 -5.682 -6.026 -3.583 -3.616 -1.694 -1.804
Tellurium (mole fraction)
0.853 0.841 0.827 0.736 0.724 0.680 0,640 0.624 0.599 0.577 0.547 0.530 0.503 0.499 0.470 0.432 0.430 0.386 0.384 0.330 0.326 0.260 0.254 0.182 0.161 0.090 0.069
0.854 0.738 0.647 0.587 0.538 0.509 0,503 0.499 0.462 0,477 0.453 0.445 0.416 0.409 0.373 0.367 0.319 0.318 0.252 0.242 0.172 0.168 0.091 0.077
Gaa6Geo.4-Te
Gao.4Ww-Te
-10.053 -16.646 -22.054 -22.745 -21.167 -20.340 -19.669 -19.712 -19.384 -18.659 -18.045 -17.226 -16.255 -15.494 -14.094 -13.485 -11.550 -11.232 -8.645 -8,016 -5.447 -4.850 -2.741 -2.291
HE (kJ mol-‘)
for the reaction xGa(l) + yGe(l) f (1 -x
Gao.zGeo.a-Te
Excess molar enthalpies at 1203 R of the system Ga-Ge-Te
TABLE 1
0.883 0.867 0.770 0.751 0.685 0.660 0.604 0.538 0.503 0.500 0.497 0.477 0.471 0.444 0.437 0.404 0.397 0.357 0.344 0.290 0.281 0.204 0.201 0.112 0.111
Tellurium (mole fraction)
GaasGeaz-Te
-7.861 -8.854 -16.913 -17.899 -23.396 -23.770 -27.861 -26.378 -23.734 -23.349 -24.133 -22.210 -21.609 -20.177 -19.412 -17.748 -16.934 -14.850 -13.871 -11.363 -10.540 -7.396 -6.818 -3.797 -3.379
HE (kJ molP1)
- y)TeU) + Ga,GeyTe(l-,-,)~l)
Cz Q,
2
HE (kJ mol-‘)
-9.629 -10.419 -18.477 -19.013 -22.610 -24.552 -25.292 -25.953 -23.278 -24.073 -22.728 -22.587 -21.183 -20.587 -19.483 -17.740 -16.015 -14.055 -13.978 -9.631 -8.378 -4.346 -3.978
0.858 0.844 0.715 0.715 0.640 0.613 0.562 0.540 0.521 0.509 0.506 0.491 0.474 0.454 0.448 0.409 0.396 0.349 0.336 0.262 0.240 0.142 0.135
at 1203
Tellurium (mole fraction)
Excess molar enthalpies
TABLE
0.851 0.835 0.713 0.703 0.605 0.594 0.533 0.516 0.477 0.445 0.400 0.348 0.289 0.220 0.151 0.069
Tellurium (mole fraction)
Ga&Sno.e-Te
K of the system
-11.341 -11.984 -20.556 -21.804 -25.893 -26.076 -26.064 -23.038 -22.704 -20.604 -17.629 -14.425 -11.104 -7.618 -4.439 -1.340
xGa(l)
+ ySn(1)
0.851 0.821 0.731 0.672 0.639 0.583 0.573 0.534 0.530 0.506 0.503 0.496 0.486 0.471 0.468 0.446 0.435 0.405 0.391 0.366 0.340 0.323 0.274 0.262 0.184 0.164 0.125 0.095
Tellun’um (mole fraction)
Gao.6 Sno.4-Te
for the reaction
HE (kJ mol-*)
Ga-Sn-Te
-12.318 -13.626 -21.079 -25.429 -27.026 -28.522 -27.409 -25.784 -26.947 -24.718 -24.755 -23.312 -23.738 -23.093 -22.479 -21.037 -20.275 -18.227 -17.181 -15.636 -13.971 -12.915 -10.190 -9.558 -5.824 -5.073 -3.371 -2.298
HE (kJ mol-I)
+ (1 --x
-
0.846 0.845 0.731 0.727 0.642 0.632 0.542 0.516 0.505 0.491 0.490 0.471 0.456 0.435 0.420 0.395 0.381 0.353 0.349 0.309 0.280 0.252 0.172 0.167 0.095 0.079
Tellurium (mole fraction)
Gao.8Sn~~-Te
-12.196 -12.687 -22.137 -22.867 -27.768 -30.096 -28.960 -27.330 -24.566 -25.510 -25.798 -23.343 -23.540 -21.232 -20.395 -18.514 -17.633 -15.645 -15.465 -12.692 -10.808 -9.393 -5.567 -5.304 -2.131 -1.800
HE (kJ mol-‘)
y)Te(l) + Ga,Sn,Tq-,-,)(I)
188
binary. The ternary phase diagram is divided by these two sections into three subsystems. The section GaTe-SnTe differs considerably from that reported by Dovletov et al. [21] and Rustamov et al. [22]. The compounds Ga$nTes and GaSnTez do not exist. A similar observation was made by Kra et al. [17, 181 in the ternary system Ga-Ge-Te. They were not able to prepare the compounds Ga,GeTe, and GaGeTe, previously described by Nasirov et al. [20]. The excess molar enthalpies HE of the reactions xGa(l) + yGe(l) + (1 -X
-Y)Te(l)
+ Ga,Ge,Ter-,-,(l)
and xGa(l) +ySn(l)
+ (l--r
--y)Te(l)+Ga,Sn,Tel_,-,(l)
were measured at 1203 K. The data are listed in Tables 1 and 2. All values obtained in the experiments were used in a threedimensional fitting procedure. The resulting isoenthalpic lines are presented in Figs. 2 and 3, which are projections of the enthalpy surface on the Gibbs triangle. The enthalpy surfaces of the systems are determined by a valley of minima which were Te
/
Ga
I
A
Fig. 2. Projection ternary.
A
A
20
A
A
40 mole-% Ge
of the isoenthalpic
/\
60
A
n 80
lines onto the Gibbs
\ A
‘Ge
triangle in the Ga-Ge-Te
189
Te
Ga Fig. 3. Projection ternary.
40 mole-% of the ~oenth~pic
60
80
Sn
Sn lines onto the Gibbs triangle in the Ga-Sn-Te
TABLE 3 Excess molar enthalpies of tbe sections MasTea&IaasTetns in the ternary system C&-MTe (M = Ge, Sn) at 1203 K for the reaction ~M~.~Te~~(I) * (1 -~)Ga~,~Te~~(I) + Gao.4-a4xMo.s~Ted6-atc(l)
S%s Teas-Gao.4Teo.a
Geo.sTeo.s-Gao.4Teo.6 Gea5Teo.s
HE
(mole fraction)
(kJ mol-“)
0.099 0.200 0.401 0.500 0.600 0.699 0.797 0.900
0.91 1.69 2.57 2.71 2.37 1.83 1.27 0.61
SnasTeas
HE
(mole fraction)
(kJ molvl)
0.091 0.211 0.286 0.400 0.501 0.604 0.700 0.900
0.57 1.16 1.42 1.49 1.53 1.40 1.21 0.53
190
found on the sections Ga,Tes-GeTe and Ga,Tes-SnTe. The enthalpies of mixing increase from this valley in the direction of the tellurium comer and in the direction of the Ga-Ge(Sn) binaries. Al’fer et al. [26] (Fig. 4 of that reference) measured the excess enthalpies of the system Ga-Ge-Te by quantitative differential thermal analysis. The data lead to an enthalpy surface similar to that found in this investigation. However, the absolute values of the enthalpy data differ considerably. In addition, the excess enthalpies of the ternary mixtures were calculated from the thermodynamic data of the constituent binaries, using the models of Kohler [27], Bonnier [3] and our own improvement of the Bonnier model [28]. The best agreement was achieved with the latter method. In the system Ga-Sn-Te no deviation was found between calculated and observed data within the experimental error. In the Ga-Ge-Te system the calculated data are less exothermic than the observed data. This deviation was found in the subsystem GaTe-GeTe-Ge-Ga with maximum deviations of about -1 kJ mall’. Acknowledgment We wish to express our gratitude to the Stiftung Volkswagenwerk the Fonds der Chemischen Industrie for their support of this work.
and
Keferences 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
B. Gather and R. Blachnik, 2. Metollkd., 74 (1983) 212. C. Wagner, Thermodynamics of Alloys, Addison-Wesley, Reading, MA, 1952. E. Bonnier and R. Caboz, C. R. Acad. Sci., 250 (1967) 527. B. Gather, B. Legendre and R. Blachnik, J. Less-Common Met., 77 (1981) 71. B. Gather and R. Blachnik, 2. Metallkd., 73 (1982) 245. R. Blachnik and E. Irle, J. Less-Common Met., 113 (1985) 21. F. Alapini, J. Flahaut, M. Guittard, S. Jaulmes and M. Julien-Pouzol, J. Solid State Chem., 28 (1979) 309. R. Blachnik and E. Irle, unpublished work, 1985. H. Said and R. Castanet, J. Less-Common Met. 68 (1979) 213. B. Legendre and C. Souleau, C. R. Acad. Sci., Ser. C, 284 (1977) 315. S. Kurosawa, Y. Nakamura and M. Shimoji, J. Less-Common Met., 70 (1980) 119. C. Bergman and R. Castanet, Ber. Bunsenges. Phys. Chem., 80 (1976) 774. R. Blachnik and B. Gather, 2. Metallkd., 74 (1983) 172. M. Hansen and K. Anderko, Constitution of Binary Alloys, McGraw-Hill, New York, 1958. B. Predel and D. W. Stein, 2. Metallkd., 62 (1971) 499. J. P. Bros, R. Castanet and M. Lafitte, C. R. Acad. Sci., Ser. C, 264 (1967) 1804. G. Kra, R. Eholie and J. Flahaut, Ann. Chim. (Paris), (1978) 257. G. Kra, R. Ebolie and J. Flahaut, C. R. Acad. Sci., Ser. C, 284 (1977) 889. D. Fenske and H. G. v. Schnering, Angew. Chem., 95 (1983) 420. Ya. N. Nasirov, M. I. Zargarova, R. S. Gamidov and M. M. Aksperov, Zzu. Akad. Nauk SSSR, Neorg. Mater., 6 (1970) 990. K. Dovletov, Kh. Emiyazov and A. S. Malkova, Zzu. Akad. Nauk SSSR, Neorg. Mater., 12 (1976) 1964.
191 22 P. G. Rustamov, B. B. Kuliev, M. A. Aliyanov and E. M. Kuliev, Phys. Status Solidi, A, 3 (1970) K 139. 23 M. Guittard, F. Alapini, S. Jaulmes, M. Julien-Pouzol and J. Flahaut, Mater. Res. Bull., 13 (1978) 1157. 24 F. GrOnvold, Rev. Chim. Miner., 11 (1974) 568. 25 F. Grdnvold, J. Drowart and E. F. Westrum, Jr., The Chemical Thermodynamics of Actinide Elements and Compounds, Part 4 (The Actinide Chalcogenides), International Atomic Energy Agency, Vienna, 1984. 26 S. A. Al’fer, L. A. Mechkovskii and A. A. Vecher, Zh. Fiz. Khim., 57 (1983) 1528. 27 F. Kohler, Monatsh. Chem., 91 (1960) 738. 38 B. Gather, Program and abstract, Colphad, 12 (1983).