Thermoelectric, thermodynamic, and structural properties in Cu1.94A0.02Se (AÂ =Â Al, Ga, and In) polycrystalline compounds

We investigated the thermoelectric and thermal stability properties of cation doped polycrystalline compounds of Cu1.94A0.02Se (A = Al, Ga, and In). The maximum ZT value of the In-doped sample (0.8 at 973 K) was also lower than the previous Al-doped one (1.0 along the layer plane and 1.5 along the inter-layer plane at 973 K). Thermo-gravimetric analysis (TGA) showed that the dissociation temperature of the doped compounds was significantly enhanced compared with the parent compound Cu2−xSe indicating the enhancement of thermal stability by cation doping. The enhancement of thermodynamic stability might be related to hybridization of cation elements with Se. However, thermal hysteresis behavior was observed upon heating to 90 °C and cooling to room temperature, with 0.28% reduction of lattice volume, indicating that the Se evaporation during thermal cycling cannot be resolved completely in spite of the enhancement of thermal stability by cation doping.94