High-temperature order/disorder transition in the thermoelectric Cu ₃SbSe₃

We report the results of an investigation on the structural evolution of a potential new thermoelectric material, Cu₃SbSe₃, as a function of temperature from 25 to 390 °C. From high-temperature x-ray diffraction data, the refined lattice parameters were seen to change nonlinearly, but continuously, with temperature, with an increased rate of thermal expansion in the a and b lattice parameters from around 125 °C to 175 °C and negative thermal expansion in the c axis from around 100 °C to 175 °C. Crystallographic charge flipping analysis indicated an increase in the disorder of the copper cations with temperature. This reversible order/disorder phase transition in Cu₃SbSe₃ affects the transport properties, as evidenced by thermal conductivity measurements, which change from negative to positive slope at the transition temperature. This structural change in Cu₃SbSe₃ has implications for its potential use in thermoelectric generators.