Ionic and p-type electronic conduction in LaGa(Mg, Nb)O3−δ perovskites

Solid solution formation has been found in the perovskite-type system LaGa0.85−xMg0.15(Nb0.33Mg0.66)xO3−δ (x=0−0.20). With increasing x, oxygen ionic conductivity of the perovskites decreases, whilst p-type electronic conduction at temperatures above 1000 K increases. Oxygen-ion transference numbers in air were determined by e.m.f. and Faradaic efficiency methods, varying in the range 0.77–0.96, decreasing with increasing x and temperature. The electron transference numbers of the end-member phase, LaGa0.85Mg0.15O3−δ, do not exceed 0.08 at temperatures of 870–1170 K and oxygen partial pressures from 10 to 1.01×105 Pa. Thermal expansion coefficients of LaGa0.85−xMg0.15(Nb0.33Mg0.66)xO3−δ ceramic materials are independent of composition, varying in the range (10.0±0.2)×10−6 K−1. Values of the activation energy for the total electrical conductivity are 104–106 kJ mol−1 at 670–1000 K, and 67–76 kJ mol−1 at 1000–1200 K.