The dissociation pressures and thermodynamic properties of Cu2Te(c), Ag2Te(c), Ag1.9Te(c), and Ag1.64Te(c)

J. Chem.Thermodynamics1972,4,903-913

The dissociation pressures and thermodynamic properties of CuzTe(c), AgJe(c), AgJe(c), and &.Je(c) K. C. MILLS

Division of Chemical Standards, National Physical Laboratory, Teddington, Middlesex, U.K. (Received 10 April 1972) The dissociation pressures of C&Te(c), AgaTe( Agl.eTe@), and AgI.BrTe(c) have been determined using the Knudsen effusion method. Standard enthalpies of formation calculated from these pressures are compared with values reported in the literature.

1. Introduction Copper and silver tellurides occur naturally as the minerals, weissite (Cu,Te), hessite (Ag2Te), and stuetzite (Ag 1.64Te) and also occur as major constituents of the slime produced in the electrolytic rehning of copper.(‘* 2, Recent interest in these materials originates from their potential use in semi-conductor technology. Dissociation pressure measurements for Cu,Te(c) and Ag,Te(c) have been published by Kochnev and Zaidman(3) and by Zhiteneva et al., (4) but no dissociation pressuresare available for Ag,.,Te(c) and Ag ,.,,Te(c). The only reliable thermodynamic data for Cu,Te(c) are heat capacities in the temperature range 298 to 950 K due to Kubaschewski.(‘) Some reliable thermodynamic properties@- 11) for the silver tellurides are available for temperatures below 600 K. Standard thermodynamic properties for copper telhuide and the silver tellurides are calculated from the dissociation pressures measured in this study and are compared with extant values for these thermodynamic properties.

2. Experimental MATERIALS

Copper telluride (Cu,Te) was prepared from weighed amounts of tellurium (purity 99.999 mass per cent) and copper powder (purity 99.9 mass per cent), which was reduced with hydrogen immediately before the preparation of the telluride. Pellets were made from an intimate mixture of the elements and these were enclosed in silica capsules which were evacuated and heated to 1420 K for 2 h. The sample was then annealed at 800 K for 4 d and slowly cooled to room temperature over a period of 3 d. An X-ray analysis of the sample revealed only the presence of Cu,Te(c). The silver tellurides were prepared from tellurium (purity 99.999 mass per cent) and silver grain (purity 99.9 mass per cent). Samples were prepared from weighed

904

K. C. MILLS

amounts of the elements, which were intimately mixed, compressedinto pellets, and enclosed in silica containers which were evacuated and heat treated as described below. Ag,Te(c). After the pellets had been heated for 3 h at 1250 K, the sample was cooled to room temperature over a period of 4 d. An X-ray analysis of the solid showed the presence of the low-temperature form of Ag,Te(c) only. Ag,.,Te(c). After the pellets had been heated for 20 h at 730 K and the sample had been annealed at 500 K for 2 d it was cooled, ground, remixed, and annealed in an evacuated capsule at 500 K until required. No X-ray analyses were carried out on the specimen becauseAg,,gTe(c) decomposesbelow 393 K. Ag,.,,Te(c). After the pellets had been heated at 1070 K for 12 h, the specimen was cooled to 500 K and annealed at this temperature for 3 d. An X-ray analysis of the sample revealed only the presence of the Ag,.,,Te(c) phase. MEASUREMENTS

Dissociation pressures greater than 10-i Pa (w 10e6 atm) were determined by the use of the Knudsen effusion apparatus described previously,(i2) but pressures less than this value were determined in another apparatus by measuring the mass loss of a silica Knudsen cell held at the selectedtemperature for periods of 100 h or more. The mass losseswhich occurred in the initial heating and final cooling periods of the furnace in the experiments were negligible. The pressures calculated from the observations were found to be independent of orifice area, which was within the range 0.49 to 1.58 mm2. Temperatures were measured with a Pt-to-@ + 13 mass per cent of Rh) thermocouple and the values recorded were basedon the International Practical Temperature Scale of 1968. The composition of the effusing gas at the mean temperature of the vaporization studies was determined by a series of experiments in which the effusate was collected on a cold finger placed 1 cm above the effusion orifice of the Knudsen cell. After X-ray analysis of the condensed effusate, the copper or silver content of the effusate sample (3 to 40 mg) was determined calorimetrically with 2,2’-biquinolyl, (C,H,N,),, or p-(diethylamino)-benylidene rhodanine, (C,H,),N. C,H, . CH : C-0, respectively, and the Te content obtained by reducing the solution with SO2 and weighing of the precipitated tellurium. A few experiments were carried out at different temperatures within the temperature span of the vaporization studies and no appreciable change in the chemical composition of the effusate was observed.

3. Calculations In all experiments the condensed effusate was found to be predominantly tellurium as can be seen from table 1. For the pressure and temperature ranges employed in this investigation it can be shown from thermodynamic data that the effusing gas in the Ag,.,Te(c) and the Ag 1.64Te(c) studies is Te,(g) but in the Cu,Te(c) and Ag,Te(c) studies the effusing gas is a mixture of Te(g) and Te,(g). It is therefore necessaryto calculate the partial pressures of the Te(g) and Te2(g) speciesfrom the recorded rate of mass loss of the tellurides.

DISSOCIATION

PRESSURES OF TELLURIDES

905

For steady-state effusion the pressure p of a speciesof molar mass A4 is given by the Knudsen equation, p = (l/a)(dw/dt)(2xRT/M)“2, (1) where (dw/dt) is the mass effused per unit time through an orifice of area a, R is the gas constant, and T is the temperature. Thus for reaction (2), A,Te(c) = xA(c) + aTe(g) + (( 1- a)/2}Te,(g), (2) the partial pressuresof Te(g) and Te,(g), denoted by subscripts 1 and 2 respectively, are given by the equations: p1 = (l/a)(dw,/dr)(2~RT/M,)L’2, (3) p2 = (l/a)(dw2/dt)(2xRT/M2)“2 = (l/a)(dw2/dt)(2nRT/2M,)1’2. (4) Rearrangement and addition of equations (3) and (4) yields (dw,/dt)+(dw,/dt) = (dw(total)/dt} = a(Ml/2nR7’)‘~“(pl +21j2p2), (5) where {dw(total)/dt } is the total rate of mass loss due to the effusion of Te(g) and Te2(g). For the reaction: (6) Te2(g) = 2Te(g), the values of p1 and p2 are related by (7)

K" = P3P2P0,

where K” and p” are the standard equilibrium constant? and the standard pressure, here 101 325 Pa (= 1 atm). Thus from equations (5) and (7) (pl +21/2pf/Kop”) = (27cRT/M1)‘~2(l/a)(dw(total)/dt}. (8) As values of K” at various temperatures are available from equation (9),(13)p1 can be obtained for a chosen temperature from a solution of the quadratic equation (8) and p2 can then be obtained from equation (7). log,, K” = -13742(T/K)-‘+4.962+0.232 log&T/K). (9)

4. Results and discussion Throughout this paper R = 8.3143 J K-’ mol- ’ and the standard pressure is 101 325 Pa. The standard states of copper, silver, and tellurium are respectively, cubic copper, cubic silver, and trigonal tellurium at 298.15 K. The following values of molar mass were employed: Cu,Te(c), 0.254 68 kg mol-’ ; Ag,Te(c), 0.343 34 kg mol- ’ ; Ag 1.90Te(c),0.332 553 kg mol-‘; and Ag,.,,Te(c), 0.304 507 kg mol-‘. Since the tellurium content of all the condensed effusateswas greater than 97 mass per cent, as can be seen from the data in table 1, it follows that if the gaseous t The standard equilibrium constant K” is dimensionless and for reaction (6) is defined by the expression : K” = exp I(&

- 2~3lRTl

= f ?lfap”,

where subscripts 1 and 2 represent Te(g) and T%(g) respectively and p” and f denote standard chemical potential and fugacity, respectively, and pa is the standard pressure. Since the partial pressures m and p2 are low, the fugacities can be equated with the partial pressures, so that K” = P:lP2,“.

K. C. MILLS

906 TABLE

Compound Cu,Te(c) Ag3’Wc) Agl.6Te(c) Ag1.64Te(c)

1. Chemical and X-ray analyses of the condensed effusate Chemical analyses of et&sates mass per cent mass per cent of Te of metal 97 99.5 99.7 100

3 0.5 0.3 None detected

X-ray analysis of effusates Te Te Te Te

only only only only

molecules CuTe(g) and AgTe(g) do occur in the effusing gas, these metallic tellurides can be only minor constituents of the vapour. Cu,Te(c) Decomposition of Cu,Te(c) can be considered to occur by the equation: Cu,Te(c) = 2Cu(c) + tire(g) + (( I- a)/2}Te,(g), (10) (where c1is the degree of dissociation of tellurium vapour). The values of logp t 1% p2, and log ptotal calculated from mass losses are listed in table 2 and their temperature dependencesare shown in figure 1 and are given by the equations: logldpl/atm) = - 12475(T/K)-’ +4.424. (11) log,,,(p2/atm) = - 10346(T/K)-1 +2.495. (12) log1 o(Ptot611atm) = -11909(T/K)-‘+4.168. (13) The values of - {G”(T)- H”(298.15 K)}/T for Cu,Te(c) listed in table 3 were calculated from an estimated value for S” (298 K, Cu,Te(c)} of 134.7J K-l mol- ‘(13) and the heat capacities listed by Kubaschewski”’ and by Mills and Richardson.(‘4) The values of - {G”(T) - H”(298.15 K)}/T were those listed for Cu(c) by Hultgren” ‘) and for Te(c), Te(g), and Te,(g) by Mills. (13) The values of AH,(298.15 K) for reaction (10) and for AHF(298.15 K, Cu,Te(c)) obtained by the third-law method are listed in table 2. A mean value, AHi(298.15 K, Cu,Te(c)} = - (42.0 + 9) kJ mol- ’ was obtained.? In 1888 Fabre(‘@ reported a value, AH,“{298 K, Cu2Te(c)} = - 59.8 kJ mol-’ from solution calorimetry experiments but Fabre’s measurements of AH,“{298 K, Cu,Se(c)} are 22 kJ mol-’ more negative than the value obtained from recent calorimetric and Gibbs energy data,(r3) which casts doubt on the accuracy of his measurementsfor Cu,Te(c). Dissociation pressuresof Cu,Te(c) have beenmeasuredby Kochnev and Zaidman,(3) who have reported pressures almost 100 times greater than those recorded in this investigation. The value AHfb(298.15K, Cu,Te(c)) = - 16.68kJ mol-r was calculated from a third-law evaluation of these pressure measurementswhen the auxiliary data listed in table 3 were employed. It has been proposed”3) that the values of AHi(298.15 K) for sulphides, selenides, and tellurides are generally in the ratios 1, (0.72 rf: O.l), (0.52 + O.l), respectively. Using the values, AHF(298.15 K, Cu2S(s)} = -79.9 kJ mol-’ and AHP(298.15 K, Cu,Se(c)} = -65.3 kJ mol-‘, values for t The quoted uncertainty is the standard deviation computed from the uncertainties ascribed to the various measured and estimated thermodynamic properties employed in the calculation of the enthalpy of formation.

T

6.530 6.379 6.334 6.318 6.157 6.064 5.895 5.584 5.847 5.700 5.525 5.373 5.235 5.238 5.296 5.153 5.092

--logdpllatm)

6.444 6.372 6.484 6.635 6.250 6.314 6.129 5.700 6.234 5.944 5.347 5.583 5.434 5.664 5.594 5.445 5.410

___.

0 --logd~~latm)

6.283 6.075 6.102 6.147 5.942 5.871 5.696 5.338 5.698 5.504 5.321 5.165 5.023 5.036 5.119 4.975 4.922

a --h30(~~,~.~/atm)

a

0.394 0.330 0.414 0.508 0.439 0.470 0.461 0.396 0.550 0.466 0.454 0.447 0.441 0.457 0.500 0.494 0.510

a

4,523 4.240 4.523 4.842 4.456 4.523 4.369 3.933 4.619 4.243 3.968 3.945 3.877 3.932 4.046 3.923 3.923

log,,K”

65.44 61.99 66.24 71.03 67.22 68.66 67.95 66.04 72.43 67.87 66.99 66.36 65.72 66.63 68.93 68.37 69.06

-{G”(T)-W(298.15 J K-l mol-’ 173.0 163.4 177.3 192.8 180.3 185.9 183.9 171.9 198.6 184.0 179.0 179.9 118.4 182.5 188.6 187.1 189.6

-41.1 -39.7 -42.6 -45.8 -42.3 -43.8 -43.0 -39.6 -46.1 -42.6 -39.1 -40.9 -40.2 -42.2 -42.6 -41.9 -42.3

K)}/T AH,(298.15 K) a AH”{298.15 K, CuzTe(c)}_O __~ kJmol-’ kJ mol-’

D If the copper content of the vapour is accounted for by assuming that the vapour consists of 90 moles per cent tellurium and 10 moles per cent CuTe(g), then the following must be added to the values listed in table 2: 0.05 to --log,,(p,/atm), -log&,/atm), and -log,O(pl,M,/atm); +0.3 to AH,(298.15 K)/kJ mol-‘; and -0.3 to AHP(298.15 K, CuaTe(c)}/kJ mol-‘.

1138 1141 1160 1178 1182 1197 1213 1234 1235 1235 1252 1268 1283 1286 1288 1304 1315

ii

TABLE 2. The dissociation pressures of Cu,Te(c) and the values of AH={298.15 K, reaction (lo)} and AHY{298.15 K, Cu,Te(c)} derived by the use of the third-law method

908

K. C. MILLS -4

-7

I

I

I

I

I

I

I

I

0.9

0.8

10’ K/T FIGURE 1. Values of log&/atm) against (lo3 K/T) for CuaTe(c). x , Te(g); 0, T%(g); A, total pressure; 0, total pressure reported by Kochnev and Zaidman.‘3) TABLE 3. Thermodynamic data for Te(c), Te(g), Tez(g), &Te(c), Ag,Te(c), Ag,.,,Te(c), and for Agl.BTe(c). The standard states of solid and gaseous phases are the crystalline solid and the ideal gas, respectively, at the standard pressure 101 325 Pa and at the reference temperature 298.15 K, except for Ag,.,Te(c) where 400 K was adopted T z 298 500 600 700 2 1000 1100 AH”(298.15K) kJ mol-1

Te(c)

Te(g)

--(G”(T) - H”(400 K)}/T - H”(298.15 K)}/T J K-l mol-’ J K-l mol-l Tez(g) C&Te(c) Ag,Te(c) Ag,,,,Te(c) Agl.,Te(c)

49.50 52.57 54.93 57.40

182.6 184.9 186.7 188.4 190.0 191.6 193.1 194.6

258.9 263.0 266.1 269.3 272.3 275.2 278.0 280.7

211.7

160.4

-{G’(T)

o

134.7 143.9 151.5 160.5 169.1 177.4 185.0 192.1

153.5 166.4 176.2 185.2 193.4 201.o 208.0 214.6

133.9 143.7 151.4

173.6 177.9 183.0

AHi(298.15 K, Cu,Te(c)) of -47 and -41.5 kJ mol-’ were calculated from the (sulphide/telluride) and (selenide/telluride) ratios, respectively. Thus the estimated values of AHF(298.15 K, Cu,Te(c)} are in reasonable agreement with the value calculated from the pressure measurementsobtained in this investigation. Ag2’W) Decomposition of Ag,Te(c) can be considered to occur by the reaction: Ag,Te(c) = 2Ag(c) + aTe(g) + ((1 - cr)/2}Te,(g). The values of log,,p,, log,,p,, and log,,p,,,, are given in table 4.

(14)

1045 1058 1070 1076 1080 1098 1100 1110 1112 1121 1125 1129 1129 1140 1143

T E

1.275 7.091 7.018 6.984 6.883 6.715 6.698 6.757 6.616 6.530 6.452 6.443 6.387 6.313 6.275

--loihWatm) 6.846 6.648 6.621 6.610 6.477 6.335 6.321 6.254 6.270 6.192 6.095 6.105 6.018 5.968 5.928

0.223 0.220 0.251 0.268 0.245 0.263 0.266 0.279 0.291 0.298 0.282 0.298 0.272 0.293 0.290

a

4.383 4.229 4.325 4.378 4.214 4.187 4.188 4.229 4.242 4.213 4.098 4.157 4.016 4.052 4.017

log,&”

54.79

mol-1

54.12 55.67 56.51 55.19 55.96 56.09 56.65 57.32 51.55 56.65 57.47 56.05 57.05 56.88

J K-l

-{G”(T)-H”(298.15

K)}/T

144.8 142.8 148.1 150.9 146.7 149.4 149.9 152.7 154.0 154.9 152.0 154.7 150.1 153.5 152.9

A&(298.15 kJ mol-1

K)

pressures of Ag,Te(c) and the values of A&(298.15 K, reaction (14)} K, Ag,Te(c)} derived by the use of the third-law method

--loglo(ptot&tm)

4. The dissociation and AH”{298.15

7.048 6.843 6.844 6.849 6.694 6.569 6.557 6.503 6.531 6.458 6.347 6.372 6.260 6.230 6.187

TABLE

-34.6 -33.7 -34.9 -35.5 -34.2 -34.6 -34.7 -35.9 -35.5 -35.5 -34.7 -35.3 -34.1 -34.8 -34.6

AHF(298.15 K, AgaTe( kJ mol-1

910

K. C. MILLS -3

u

,

I

I

I

I

q 0

-4

-7

-8 0.9

0.8

1.0

lo3 K/T FIGURE 2. Values of log&/atm) against (lo3 K/T) for Ag,Te(c). A, total pressure; 0, total pressure reported by Zhiteneva et af.(*)

x, Te(g); 0,

Te,(g);

The relation between the logarithm of the pressure and (l/T) for Te(g), Tez(g), and the total pressure are given by the equations: log,,(p,/atm) = - 11795(T/K)-‘+4.021, (15) log,,(p,/atm) = -9952(T/K)-1 +2.490, (16) logl,,(~tota,/atm) = - 10756(T/K)-’ + 3.460, (17) and are shown in figure 2. A value of A&(298.15 K, Ag,Te(c)} can be calculated from these partial pressures by the third-law method. The standard entropy, S”(298.15 K, Ag,Te(c)} = (153.5 + 1.0) J K-’ mol-‘, was calculated from a third-law evaluation of Gibbs energy dataW-W by use of the calorimetric value,(9) AHF(298.15 K, Ag,Te(c)} = -(36.0 + 0.4) kJ mol-‘. Values of -{G”(T)-H” (298.15 K)}/T for Ag,Te(c),(14’ Te(g), and Te,(g)‘13’ are given in table 3 and the values of - {G”(T) -H”(298.15 K)}/Tfor Ag(c) are those listed by Hultgren et a/.(“) Calculated values for the enthalpy of reaction (14), AH,.(298.15K) and of AH,” (298.15 K, Ag,Te(c)} are given in table 4. The mean value, A.HF(298.15K, Ag,Te(c)} = -(34.8 ) 3.0) kJ mol-‘, obtained from the dissociation pressure measurements,is in good agreement with the calorimetric value.“) Pressuremeasurementsfor Ag,Te(c) have also been recorded by Zhiteneva et ~1.~~) for the temperature range 1073 to 1303 K; these values of pressure are higher than

DISSOCIATION

PRESSURES OF TELLURIDES

911

those recorded in this investigation by almost a factor of 10. Moreover, for the data of Zhiteneva el al., a plot of log r,,pt0talagainst the reciprocal of temperature shows a marked change of slope at 1198 K; the enthalpy associated with this transition has a value, AK,,,,, { 1198 K, Ag,Te(c)} = - 159 kJ mol- ‘, which is highly improbable. A value of A&(298.15 K, Ag,Te(c)) = - 14 kJ mol-’ was calculated from these pressuresC4’using the third-law method. Ag, .JW Kiukkola and Wagner(6) have reported that this phase is stable at 573 K between the compositions, Ag,.,,Te and Ag, .ssTe.t Thus dissociation can be considered to occur by the reaction: Ag,.,,Te(c) = 0.955Ag,Te(c) + O.O23Te,(g). (18) The dissociation pressuresfor the temperature range 600 to 672 K are given in table 5 and figure 3. The temperature dependence of the pressure is given by logl&Jatm) = log,,(p,/atm) = - 8959(T/K)- ’ +8.135. (19) Kiukkola and Wagner@) have recorded activity measurements at 573 K for the two-phase region, Ag ,.,,Te(c) + Ag,Te(c); the value log,,(p,/atm) = -7.11, was calculated from their data. The discrepancy between this value and that calculated from equation (19) log,,(p,/atm) = -7.50, can be attributed to the variation of TABLE 5. The dissociation pressures of Agl.*Te(c)

600 z!i:

7.002 6.234 6.418

631 647 641

5.991 5.663 5.890

625

6.313

672

5.214

‘\ -6 E

IO3 K/T FIGURE

3. Values of log&/atm)

against (lo3 K/T) for Agl.9Te(c).

t It has been assumed that the values of -{G”(T) - H”(400 K)}/Tand A&‘(400 K) for Ag,,,,Te(c) and Ag1.88Te(c) are the same as the values for Ag,.,Te(c). The values of -{G”(T) - H”(400 K)}/T for Ag,.,Te(c) were calculated by assuming that S”{298.15 K, Ag,.,Te(c)} = S”(298.15 K, Agl.,,Te(c)h

912

K. C. MILLS

the homogeneity range of the Ag,.,Te phase with temperature and to the uncertainties in the extrapolation of the dissociation pressure equation. As this phase decomposes at temperatures below 393 K, (l 7, thermodynamic properties for Ag,.,Te(c) have been calculated for a reference temperature of 400 K. Values of - {G”(T) - H”(400 K)}/T f or unit amount of Ag,.,Te(c)t listed in table 3 were calculated from the value S”(298.15 K, Ag,.,,Te(c)] due to Walsh et al.(lO) and from heat capacities determined from an extrapolation of low-temperature values.(“) Third-law evaluations of galvanic cell@)results and the present dissociation pressures yield values for AH,“{400 K, Ag,.,Te(c)} of -(36.2 -t 3.0) and -(36.6 + 3.5) kJ mol-‘, respectively.

&l.s4W4 This phase has been reported@ to exist at 573 K between the compositions Ag,.,,Te and Ag,.65Te.t Thus, the dissociation pressure measurements refer to the reaction: Agl.6sTe(C) = 0.873Ag,.s,Te(c)+O.O635Te,(g), (20) the Ag,.sgTe(c) being the tellurium-rich composition of the Ag,.,Te phase.2 TABLE

6. The dissociation

557 566 578 582 593 600 601

7.192 6.930 6.584 6.592 6.168 6.102 6.020

1.6

FIGURE t See footnote $ See footnote

4. Values of log&/atm)

on p. 913. on p. 911.

pressures of Ag,.,,Te(c)

615 617 625 625 626 641

5.695 5.714 5.568 5.694 5.705 5.164

1.7

against (lo3 K/T)

1.8

for Agl.B4Te(c).

DISSOCIATION

PRESSURES OF TELLURIDES

913

The measured dissociation pressures are listed in table 6 and the temperature dependenceof the dissociation pressure is given by the equation: loglO(ptOta,/atm)= Iog,,(p,/atm) = -8091(T/K)-‘+7.377. (21) and shown in figure 4. A value, loglO(pz/atm) = -6.59 at 573 K was derived from the activity data for the two phase region, Ag r.s9Te and Ag,,,,Te, recorded by Kiukkola and Wagner.(6’ This is in reasonable agreement with the value obtained from equation (21), which is log,,(p,/atm) = -6.73. The values of - {G”(T)-H”(298.15 K)}/Tfor unit amount of Ag,.,,Te(c)t listed in table 3 were calculated from an estimated va1ue,(13) S”(298.15 K, Ag ,.64Te(c)} = 133.9 J K-’ mol-‘, and the heat capacities obtained by Mills and Richardson.(‘4’ Second-law and third-law evaluationst of the dissociation pressures yield values of AHF(298.15 K, Ag,.,,Te(c)) of -(29.7 f 5.0) and -(31.6 + 5.5) kJmol-‘, respectively. A third-law evaluationt of the Gibbs energy data listed by Kiukkola and Wagner’@ resulted in a value, AHF(298.15 K, Ag,.,,Te(c)} = -31.6 kJ mol-‘. This work was carried out in the National Physical Laboratory, Teddington. REFERENCES I. Mekler, L. I.; Yashchenkova, V. M.; Buketov, E. A. Tsvet. Met. 1970, 43, 27, through Chem. Abstracts 1970,73, 101 189f. 2. Kozorin, L. G.; Gromakova, Z. I.; Buketov, E. A. Tr. Wim-Met. Inst.. Akad. Nauk Kaz. SSR. 1969, 7, 31, through Chem. Abstracts 1970, 73, 51 453q. 3. Kochnev, M. G.; Zaidman, T. N. Dokl. Akad. Nauk SSSR. 1954,94,65. 4. Zhiteneva, G. M. ; Rumyantsev, Y. M. ; Bolandz, F. M. Tr. Vost-Sib., Filiala, Akad. Nauk SSSR. 1962,41,

121.

5. Kubaschewski, P. Ph.D. Thesis, Gijttingen University, Germany. 1969. 6. Kiukkola, K.; Wagner, C. J. Electrochem. Sot. 1957, 104, 379. 7. Takahashi, T., Yamamoto, 0. J. Electrochem. Sot. 1970, 117, 1. 8. Reinhold, H. Z. Elektrochem. 1934, 40, 361. 9. Pool, M. J. Trans. Amer. Inst. Mining Met. Engrs. 1965,23, 1711. 10. Walsh, P. N.; Art, E. W.; White, D. J. Phys. Chem. 1962, 66, 1946. 11. Gultyaev, P. V.; Petrov, A. Sov. Phys. Solid State 1959, 1, 330. 12. Andon, R. J. L.; Martin, J. F.; Mills, K. C. J. Chem. Sot. A. 1971, 1788. 13. Mills, K. C. Selected Thermodynamic Valrres of Znorganic Sulphides, Selenides and Tellurides: to be published. 14. Mills, K. C.; Richardson, M. J. To be published. 15. Hultgren, R.; Orr, R. L.; Anderson, P. D.; Kelley, K. K. Selected Values of Thermodynamic Properties of Metals and Alloys. John Wiley: New York. 1963. 16. Fabre, C. Ann. Chim. Phys. 1888, 14, 110. 17. Kracek, F. C.; Ksanda, C. J.; Cabri, L. J. Amer. Mineral. 1966, 51, 14.

t The values of -{G”(T) - H”(298.15 K)}/T and A& (298.15 K) for Ag,.,,Te(c) were assumed to be identical to those for Ag1.64Te(c).