On the Heat Capacity of Cu2Se

Abstract

Copper selenide is a promising thermoelectric material. One of the reasons for its high efficiency is its low thermal conductivity that can be connected with the decrease of heat capacity with temperature. The possibility of the decrease of heat capacity with the increase of temperature in this material can be connected with the liquid-like behavior of copper ions. In order to reveal the influence of this factor, measurements of constant pressure heat capacity cp and calculations of constant volume heat capacity cV were performed for cubic β-Cu2Se at temperatures T = 450–1000 K. Both calculations and measurements made in the present work demonstrate only a small decrease of heat capacity with temperature. The temperature dependence of cp reasonably correlates with the literature data. But, cV values showed a similar trend only up to 770 K; at higher temperatures, the values obtained previously by other authors are considerably smaller. As the diffusion of copper atoms was taken into account in our calculations, the comparison suggests that small cV values obtained at T > 770 K previously are connected mainly with large thermal expansion of Cu2Se in this temperature range.