Studies on structural, redox and electrical properties of Ni-doped strontium titanate materials

Series of nickel-doped strontium titanates porous materials with general formula SrTi1-xNixO3 (where x = 0.00; 0.02; 0.04; 0.06; 0.08 and 0.10) was obtained by wet synthesis method. Materials sintered at 1400 degrees C were tested for structural (XRD analysis), microstructural (SEM) and electrical (conductivity and Seebeck coefficient measurements) as well as oxidizing -reduction (TPR/TPOx methods) properties. Based on the results of structural analysis and the TPR/TPOx experiments, nickel solubility limit in SrTiO3 structure was determined between 2 and 4 mol.% Ni. Moreover, the TPR results indicate not only that nickel is present in the obtained systems in the form of separate oxide phases and embedded in SrTiO3 structure, but also that nickel in the titanate structure adopts +2, +3 and + 4 oxidation state. Seebeck coefficient measurements confirmed presence of nickel as an acceptor dopant in SrTiO3, while measurements of total conductivity (by direct current method -DC) in air atmosphere indicate that an increase of the amount of nickel in the system leads to an increase of the conductivity. In addition, the results of DC measurements suggest mixed electronic-ionic mechanism of conductivity.