Crystal structure and thermoelectric properties of mechanically activated LaCoO3

Abstract

Background:

Crystal structure of rare-earth LaCoO₃ cobalt oxide subjected to high energy mechanical activation has been studied. In the temperature range of 300–800 K, the electrical conductivity and Seebeck coefficient were measured. Thermal conductivity was measured at 300–480 K.

Methods:

Comparative analysis of thermoelectric properties of the samples prepared by standard solid-state reaction and using high-energy mechanical activation was carried out.

Findings:

It was found that the experimental X-ray diffraction patterns are best described within the model that allows the coexistence of two domains in samples with the same crystal symmetry, but different lattice a and c parameters. The percentage ratio of these domains in the samples depends significantly on the size of the initial particles in the solid-state synthesis reaction and the annealing temperature. Mechanical activation and increase of synthesis temperature result in change of Seebeck coefficient sign and significant decrease of electrical resistivity. The Seebeck coefficient of non-activated samples takes positive values over the entire temperature range and decreases monotonically with increasing temperature, in contrast to mechanically activated samples exhibiting ambipolar behavior.