Crystal structure, electronic structure, and thermoelectric properties of Ca5Al2Sb6

The electronic structure and transport properties of Ca5Al2Sb6 are investigated by using first-principles calculations and Boltzmann transport theory, respectively. The results show that the partially filled valence band induces a high carrier concentration of about n = 5 × 1019 cm−3. There is a combination of heavy and light bands at the conduction band edge, which may lead to a combination of high Seebeck coefficient and reasonable conductivity. At mid-and-high temperature, the thermoelectric powerfactor, with respect to relaxation time of p-type Ca5Al2Sb6, is higher than that of the n-type within the carrier concentration ranging from −10 × 1021 cm−3 to 10 × 1021 cm−3, without considering the kinds of doping. But with decreasing temperature, the thermoelectric powerfactor with respect to relaxation time of n-type Ca5Al2Sb6 is higher than that of the p-type. The thermoelectric coefficient is increasingly sensitive to carrier concentration with the decreasing temperature. Most strikingly, at 30 K, the thermoelectric powerfactor, with respect to relaxation time, is nearly thirty-five times larger than that of conventional n-type thermoelectric materials. At 300 K, the thermoelectric powerfactor with respect to relaxation time of Ca5Al2Sb6 is equal to that of the conventional p-type thermoelectric materials. Our theoretical calculations give valuable insight on how to improve the thermoelectric performance of Ca5Al2Sb6 under different temperature and doping conditions.