Thermoelectric and Magnetic Properties of Bi0.5Na0.5TiO3-Doped NaxCoO2 Ceramics

Bi0.5Na0.5TiO3 (BNT)-doped NaxCoO2 (NCO) ceramics with a variation in doping concentration of 0.00, 0.01, 0.03, 0.05, 0.07 mol fraction were prepared using a conventional solid state reaction with a firing condition of 950 degrees C for 18 h. Metallic-like conduction behavior was observed for all samples with less dependence on temperature for the electrical conductivity when BNT was added. For all compositions, the major charge carrier was a positive hole, and charge compensation effects seemed to be more prominent with the addition of BNT, resulting in a decrease of the Seebeck coefficient. The addition of BNT (0.03 and 0.05) reduced the thermal conductivity of NCO, and doping with BNT caused a decrease in the ZT of the NCO ceramic mainly due to the electrical conductivity and the Seebeck coefficient. The maximum ZT of the undoped NCO was about 0.3 in the high temperature range. A vibrating sample magnetometer was used to measure the magnetic properties of this solid solution system. The BNT seemed to have a small effect on the magnitude of the susceptibility although the valence fluctuation of Co ions was expected to be the main cause of the compositional dependence behavior.