Sol–Gel Synthesis and Characterisation of Nanostructured LaNiO<SUB>3−<I>x</I></SUB> for Thermoelectric Applications

Nanostructured LaNiO3−x (x> 0) was prepared at low temperature between 500–800 C by the sol–gel method. Their potentials as a thermoelectric material were investigated. The minimum temperature to form the LaNiO3−x phase in air was 600 C. The samples sintered between 600 and 800 C had a grain size of 18–31 nm and showed a metallic behaviour with the linear temperature dependence of electrical resistivity and Seebeck coefficient. The electrical conductivity at room temperature varied from 581 to 810 S/cm and the thermal conductivity from 0.580 to 0.886 Wm−1 K−1. Negative Seebeck coefficient was observed for all the samples, indicating that the likely charge carrier was electron, which was confirmed by the Hall-effect measurements. The absolute value of the Seebeck coefficient was 12–15 V/K at 300 K and increased approximately linearly with temperature in the measured range up to 550 K. The attainable ZT so far was 0.034 at 550 K and would rise to 0.15 at 1000 K, which was comparable to the values of other promising n-type oxide thermoelectrics currently under development, such as Nb/La-doped SrTiO3 and Al-doped ZnO.