Effect of Ni-Doping on Seebeck Coefficient of LaCoO<sub>3</sub> System

The aim of this study is discussing the results achieved on undoped and Ni-doped bulk LaCoO 3 samples synthesized by solid-state reaction. The crystal structures of the samples were analyzed by x – ray diffraction (XRD) and Rietveld refinement of the XRD patterns was used to test the quality of the samples, the results of this procedure confirmed a single phase of LaCo 1-x Ni x O 3 for (x=0 and 0.05) with rhombohedral crystal structure (space group :). The main interest in this class of materials is the possibility of improving the values of Seebeck coefficient and electrical resistivity through chemical doping . The Seebeck coefficient and electrical resistivity were investigated from room temperature (RT) to 450 K, near RT the LaCoO 3 system showed a large negative Seebeck coefficient, but it changed to positive value with increasing temperature while the LaCo 0.95 Ni 0.05 O 3 composition showed a positive Seebeck coefficient throughout all the temperature range. Hence, within this study the Ni substitution led to decrease the electrical resistivity of the samples to one order of magnitude as a result of the partial substitution of Co 3+ in LaCoO 3 by Ni 2+ . LaCoO 3 was chosen for this thermoelectric test because cobalt oxides have extensive applications.