Mixed conductivity in La(Ga,Mg,Nb)O3-delta perovskites

Solid-solution formation has been found in the perovskite-type system LaGa0 .85-xMg0.15(Nb0.33Mg0.66)(x)O3-delta (x = 0-0.20). Increasing dopant concen tration leads to lower oxygen ionic conductivity and, at temperatures above 1000 K, higher p-type electronic conductivity. Oxygen-ion transference num bers in air were determined to vary in the range 0.78 to 0.96, decreasing w ith increasing x and temperature. Thermal expansion coefficients of ceramic samples of LaGa0.85-xMg0.15(Nb0.33Mg0.66)(x)O3-delta were calculated in a temperature range of 300 to 1100 K to be essentially independent of composi tion, varying in the range (10.0 +/- 0.2) x 10(-6) K-1. Values of the activ ation energy for the total electrical conductivity in air are 104-106 kJ/mo l in the temperature range 670 - 1000 K and 67 - 76 kJ/mol in the temperatu re range 1000 - 1200 K. The method of synthesis was found to affect both th e symmetry of the perovskite unit cell and phase composition. The presence of second phases led to a dramatic decrease in conductivity.