Thermal and electrical properties of gadolinium sulfides at high temperatures

A study is made into the temperature dependence of the thermal conductivity, electrical conductivity, thermoelectromotive force, thermal expansion coefficient, and heat capacity in the temperature range from $300$ to $1200$ K for polycrystalline gadolinium sulfides $\mathrm{GdSy}(y=1.495-1.487)$ produced both by recrystallization pressing and by crystallization from a melt. The role of the mechanisms of heat and charge transfer is estimated depending on the composition. The reasons for changes in their electrical and thermal properties are analyzed. The thermoelectric efficiency is calculated. It is demonstrated that $Z\ge0.6\times10^{-3}$ K$^{-1}$ at $T\ge1000$ K.