Electrical conductivityand thermo-EMF of cobaltite gallates LaCo1-xGaxO3

Abstract

It has been found that in LaCo_1-xGa_xO₃ system increase of the substitution degree х from 0 to 0,95 leads to the gradual electrical conductivity (σ) decrease. Within 300-1050 K temperature range for samples LaCo_1-xGa_xO₃ with х ≤ 0,5 there are three linear parts on the curve lnσ - Т^-1, where electrical conductivity activation energies have been calculated for the low, intermediate and high temperature ranges. Electrical conductivity activation energy ( Е_А) for samples at different temperatures has been also estimated using derivatives^{d In σ}/_d(T-1). The E_A temperature dependence for LaCo_1-xGa_xO₃ at 0 ≤ х ≤ 0,5 passes through a maximum that indicates the temperature for beginning of semiconductor - metal phase transition (T_EA,max). It has been shown that the thermo-EMF coefficient (S) for LaCo_1-xGa_xO₃ (0,1 ≤ х ≤ 0,3) at room temperature is negative, increasing with temperature rising, going through zero at 435-530 K, reaching the maximum at 500-650 K and then dropping down. It has been established that the temperatures corresponding to the maximum S and Е_А values are identical.