Effect of Ni substitution on electrical and thermoelectric properties of LaCoO3 ceramics

LaCo1−xNixO3 (0 ≤ x ≤ 0.2) ceramics were prepared by solid state reaction and their thermoelectric properties were investigated from room temperature (RT) to 400 °C. In the range from RT to 180 °C, LaCoO3 showed a large negative Seebeck coefficient, but it changed to a positive value above 180 °C. However, the Seebeck coefficient became positive in the whole investigated temperature span due to Ni substitution for Co even for a tiny amount, but its absolute value decreased significantly with increasing Ni content. The LaCo0.9Ni0.1O3 composition showed an enhanced power factor with a maximum value of 1.41 × 10−4 W m−1 K−2 at room temperature, which is about 3.5 times higher than that of un-doped LaCoO3. Because the power factor decreased and the thermal conductivity increased apparently with temperature, the ZT values were not increased at elevated temperatures, in spite of a relatively large ZT value of 0.031 at a low temperature (50 °C) obtained in the composition LaCo0.9Ni0.1O3.