Thermodynamics of copper sulfides IV. Heat capacity and thermodynamic properties of Cu 1.90S from 5 K to 750 K, Cu 1.95S from 5 K to 1000 K, Cu 1.98S from 300 K to 1000 K, and Cu 1.995S from 300 K to 750 K

Abstract

The heat capacities of Cu 1.90S, Cu 1.95S, Cu 1.98S, and Cu 1.995S have been measured by adiabatic-shield calorimetry. All samples have been characterized by powder X-ray diffraction in the temperature interval studied. A revised version of the copper-rich part of the phase diagram is presented. All transitions are characterized by hysteresis in the attainment of equilibrium and a greater or lesser dependence on thermal history and/or thermal recycling. Thermodynamic functions have been evaluated and selected values are, for R = 8.3144 J·K −1·mol −1: C p, m R Δ 0 TS m o R Φ m o R T K ( 1 2.90 ) Cu 1.90S (3.166) 4.654 2.5148 298.15 3.478 8.080 4.9280 700 ( 1 2.92 ) Cu 1.95S 3.109 4.679 2.5353 298.15 3.446 8.145 4.9391 700 3.420 9.361 6.0945 1000 C p, m R Δ 298.15 K TS m o R Δ 298.15 K TH m o (R· K) T K ( 1 2.98 ) Cu 1.98S 3.042 0 0 298.15 3.395 3.529 1643.4 700 3.384 4.723 2646.9 1000 ( 1 2.995 ) Cu 1.995S 3.027 0 0 298.15 (4.02) 3.564 1660.7 700