Thermodynamic properties and superconductivity of natural carrollite (CuCo2S4)

Abstract

The thermodynamic properties of natural carrollite with a formula Cu0.92Co2.07S4 are studied using low temperature heat capacity and high temperature oxidative solution calorimetry. The standard thermodynamic functions at 298.15 K are: Cp,m°, Sm°, Δ0THm°, andΦm° are 158.48 J∙K−1∙mol−1, 176.33 J∙K−1∙mol−1, 28.40 kJ∙mol−1, and 81.07 kJ∙mol−1 with an estimated error of 1%. The enthalpies (ΔfH), entropies (ΔfS), and Gibbs energies of formation (ΔfG) from elements at 298.15 K are: −344.46 ± 12.87 kJ∙mol−1, −45.22 ± 1.81 J∙K−1∙mol−1, and −331.14 ± 1.89 J∙K−1∙mol−1. The stability of carrollite relative to the elements is demonstrated with a negative Gibbs energy (ΔGr°) of formation for several temperatures between 0 and 300 K. A superconductivity transition, which has been observed previously for synthetic carrollite, is confirmed by both the low temperature heat capacity and magnetization measurements.