HEAT-CAPACITY AND THERMODYNAMIC PROPERTIES OF SYNTHETIC HEAZLEWOODITE, NI3S2, AND OF THE HIGH-TEMPERATURE PHASE NI3+/-XS2

The heat capacity of synthetic heazlewoodite (Ni3S2) was measured over the temperature range 5 K to 350 K by equilibrium adiabatic calorimetry and compared with earlier results. High-temperature results on this phase and on (two-phase) Ni2.9S2 were obtained through the transition regions and up to about 1000 K. In addition to comparing the post-(834 K)-transitional heat capacity with that of fast ionic conductors it is discussed phenomenologically with Helmholtz-energy modelling for the phase transformation. Thermodynamic functions have been evaluated and selected values are, for R = 8.3144 J·K-1·mol-1: (Cp, m / R Δ0T Smo / R Φmo / R T / K; (1 / 5) Ni3 S2 2.844 3.204 1.469 298.15; 4.614 9.033 4.609 1000; Cp, m / R Δ298.15 KT Smo / R Δ298.15 KT Hmo / R T / K; (1 / 4.9) Ni2, 9 S2 2.386 0 0 298.15; 4.667 5.613 3704.4 980). © 1991 Academic Press Limited All rights reserved.