Thermoelectric properties of Fe2(Ti1−xNbx)O5 pseudobrookite ceramics with low thermal conductivity

Fe2(Ti1-xNbx)O5 (x = 0, 0.005, 0.01, 0.02, 0.05) pseudobrookite with high relative densities have been prepared by solid state reaction and conventional sintering. The solubility of Nb in Fe2TiO5 is low, in between x = 0.01 and 0.02. Introducing Nb into Fe2TiO5 within the solubility limit improves the electrical conductivity and decreases the absolute value of the Seebeck coefficient. Small polaron hopping model is applied to explain the electrical conduction of Fe2(Ti1-xNbx)O5, as verified by the linear fit of the electrical conductivity and the temperature independent Seebeck coefficient above approximately 600 K. All compositions show low thermal conductivity, about 1-1.5 Wm−1K−1 from 673 K to 1000 K. It is found that similar ZT value (∼ 0.006) is obtained for Fe2(Ti1−xNbx)O5 with x = 0.01 and 0.02 at 1000 K.