528. Superconducting transition of strong-coupling thin films

Abstract

High temperature reaction calorimetry has been applied in a thermochemical study of solid and liquid phases in the quasi-binary system Ag2S-Sb2S3. Direct synthesis calorimetry of stibnite, Sb2S3, at 880 K and 768 K, from the elements yields a mean value for the standard enthalpy of formation, ΔH0ƒ, stibnite, 298 K = −129.72 ± 3.75 kJ mol−1; this value is about 12 kJ mol−1less exothermic than a previously reported value obtained by fluorine combustion calorimetry.The enthalpies of formation at 298 K of the sulfosalts α-miargyrite (AgSbS2) and hexagonal pyrargyrite (Ag3SbS3) from their endmember component sulfides (Ag2S and Sb2S3) were determined to be −4.1 ± 2.3 kJ mol−1 and −7.8 ± 0.8 kJ mol−1, respectively. The enthalpy of transformation of ordered monoclinic α-miargyrite to disordered cubic β-miargyrite at 298 K was determined to be +8.7 ± 1.4 kJ mol−1. If the equilibrium temperature for this transformation is equal to 650 K, this implies an entropy of transformation of about +13.3 J/K mol.Liquid mixtures of solid Ag2S and liquid Sb2S3 at 880 K were studied by solid-liquid reaction calorimetry, and by dilution calorimetry, with pure liquid Sb2S3. Measurements of the solid-liquid enthalpies of mixing yielded the following linear expression ΔHS-LmixXAg2S = −6.35 + 13.33XAg2S(kJ mol−1)), based on experiments with values of Xag2S ranging from 0.1 to 0.86. This equation is consistent with a symmetrical, regular solution model and implies that the heat of fusion of Ag2S at 880 K (for XAg2S = 1.00) is 6.98 kJ mol−1. Our data yield an average value for ΔCps-l, Ag2S of about 4 joules K−1 mol−1. The approximate partial enthalpies of solution of liquid Sb2S3, obtained from the dilution experiments, are consistent with the expression ΔH̄Sb2S3 ≈ −13.33(XAg2S)2kJ mol−1.