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The methods of purification and single crystal growth of six II – V semiconducting compounds are discussed and crystallographic data are presented. The six compounds, representing three stoichiometries, are Cd8As2 , CdAs2 , normalCdSb , Zn3As2 , ZnAs2 , and normalZnSb . The compounds are thermally dissociated in the vapor phase, and the solid‐vapor equilibria of four of the compounds has been measured. Because of the thermal instability, crystal pulling was carried out in sealed quartz tubes employing magnetic suspension of the seed. Through purification of the elements and single crystal growth, high purity was attained in most of the compounds. The highest purity is represented in CdAs2 with an electron carrier concentration of 5×1014 cm−3 .

Vaporization, / S(ideal) -S(real), estimated Compression, R In P 76.48 ± 0.20 30.44 0.03 -6.47 S°( ideal gas at 1 atm.) 100.48 ± 0.20 Table V Thermodynamic Properties at 298.16°K. 4C(c, graphite) + 6H2(g) + Pb(c) = (CH3)4Pb (liq or g) Liquid Gas /°23a.ií, kcal. mole-1 + 23.5 + 32.6 AS/°2g8.i6, cal. deg.-1 mole-1 -131.7 -107.7 AF/°298.1e, kcal. mole-1 + 62.8 + 64.7 Log Kf 298*16 -46.0 -47.4differed from the reliable one found subsequently by the rotating-bomb method by 39 kcal. mole-1, but in the opposite direction from the difference found for tetramethyllead.The Pb-C Thermochemical Bond Energy and Bond Dissociation Energy.-The Pb-C thermochemical bond energy was calculated from the heat-of-formation values of both tetramethyllead (Table V) and tetraethyllead (ref. 1). The heat of vaporization of tetraethyllead AHy09S.16 was estimated to be 13 kcal. mole-1, the values of heat of atomization of elements were obtained from Circular 50011 and the other bond energies were assigned the values I?(C-H) = 98.85 kcal. and E(C-C) = 83.1 kcal., given by Cass, et al.12 The values obtained for ¿(Pb-C) are 34.9 kcal. for tetramethyllead and 31.7 kcal. for tetraethyllead.The difference of 3.2 kcal. corresponds to 12.8 kcal. in the heat of atomization. Thus, the assumption of constant bond energies is a poor approximation for these compounds.The average Pb-C bond dissociation energy, one fourth of AH298.16 for the gas-phase reaction PbÉ4 = Pb + 4B, was calculated by use of Field and Franklin's13 values of 31 and 24 kcal. mole-1 for AHf of methyl and ethyl radicals, respectively. The values thus obtained were 34 kcal. for tetramethyllead and 32 kcal. for tetraethyllead, or approximately the same as the thermochemical bond energies calculated above.

Analysis of pressure measurements has led to the determination of the vapor species resulting from the reaction of normalGaAs with I . The reaction determined from the analysis is 2normalGaAsfalse(normalsfalse)+GaI3false(normalvfalse)←3 normalGaIfalse(normalvfalse)+½As4false(normalvfalse) in the range 560°–850°C. The equilibrium constant is given by the equation, lognormalKp=−23,650/T+19.4 . The enthalpy calculated for the reaction is 54.1 kcal/mole of normalGaAs . A similar analysis for the system normalGa‐GaIx resulted in the determination of the reaction 2normalGafalse(normallfalse)+GaI3false(normalvfalse)←3normalGaIfalse(normalvfalse) in the range 420°–650°C. The equilibrium constant for this reaction is given by lognormalKp=11,000/T+12.4 . The enthalpy for the reaction is 25.2 kcal/mole of Ga. By combining the two equilibria in the region of overlapping temperatures, the arsenic pressures in equilibrium with normalGaAs along the three‐phase line are obtained. In the range 560°–640°C the predominant reaction is normalGaAsfalse(normalsfalse)⇄normalGafalse(normallfalse)+½As2false(normalvfalse) . The enthalpy calculated for this reaction is 44.4 kcal/mole of normalGaAs . The dissociation pressures are in good agreement with extrapolations from two previous measurements made at higher temperatures.