NaTaO3 composite ceramics – A new thermoelectric material for energy generation

Increasing energy demand requires the energy harvesting of any dispersed energy in combustion machines, nuclear, geothermal, photovoltaic or solar-thermal devices by thermoelectric materials. NaTaO3 composite material is suggested in this paper for the first time as such material with reasonable high figure-of-merit in the temperature range from 750 to 1273 K. While pure NaTaO3 with perovskite crystal structure is an insulator, ceramic NaTaO3–Fe2O3 (n-type) and NaTaO3–Ag (p-type) composites in mixtures around 30 mol.% are semiconductors with Seebeck coefficients of −250 and 70 mV/K as measured in a self-built device even under closed circuit condtions. The electric conductivity for the n-type material increases from 0.02 mS/m at 773 K to 200 mS/m at 1273 K leading to a power factor of ZT > 4.5 * 10−6 at 900 K and ΔT = 500 K. This material was found by ab initio calculations using the VASP program. The reason for the high Seebeck coefficient is the large effective mass of NaTaO3 m*/m0 = 12, the main factor determining the thermoelectric performance. It is also confirmed, that Fe atoms as dopants enter the Ta-site of NaTaO3, up to 8 at.%, and reduces the bandgap.