Effect of Ni-Doping on Seebeck Coefficient of LaCoO3 System

The aim of this study is discussing the results achieved on undoped and Ni-doped bulk LaCoO₃ 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-xNi_xO₃ 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 LaCoO₃ system showed a large negative Seebeck coefficient, but it changed to positive value with increasing temperature while the LaCo_0.95Ni_0.05O₃ 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 Co³⁺ in LaCoO₃ by Ni²⁺. LaCoO₃ was chosen for this thermoelectric test because cobalt oxides have extensive applications.