High-temperature thermoelectric properties of BaFe_xTi_1−xO_3−δ ceramics

Abstract

High-temperature thermoelectric properties of BaFe_xTi_1−xO_3−δ (BFT100x) ceramics in air were investigated. Crystal structures of BFT100x ceramics were found to be a mixture of tetragonal or cubic provskite and hexagonal BaTiO₃ phases for x = 0.05–0.20, and a single phase of hexagonal BaTiO₃ for x > 0.30. X-ray diffraction pattern of BFT90 revealed a mixture of hexagonal BaTiO₃ and monoclinic Ba₂Fe₂O₅ phases. Conductivity of BFT100x increased with increase in temperature and Fe concentration. This increase in conductivity originated from the substitution of Ti⁴⁺ with Fe³⁺, which increased the oxygen vacancy of the system. A maximum conductivity of 3.1 × 10² S/m was obtained for BFT90 at 1100 K. Activation energy calculated by resistivity decreased with increase in Fe concentration. Seebeck coefficient of BFT100x increased with increase in temperature and decreased with increase in Fe concentration for x = 0.40–0.80. These results suggested an increase in carrier concentration. Seebeck coefficient of BFT90 was larger than that of BFT80, which is attributable to the mixed structure of BFT90. Power factor of BFT100x increased with increase in temperature and Fe concentration. These results suggested that BaFe_xTi_1−xO_3−δ with mixed structure of hexagonal and monoclinic phases have good potential for enhancing the thermoelectric properties of BaFe_xTi_1−xO_3−δ ceramics.