Investigations of electronic minority charge carrier conductivity in La0.9Sr0.1Ga0.8Mg0.2O2.85

The perovskite structured material LaGaO3 doped with 10 mol-% strontium and 20 mol-% magnesium was prepared by two different wet-chemical synthesis routes. The total conductivity was measured in air and under an oxygen partial pressure of 10−20 bar. There was a decrease by 10 % in 4 days when the atmosphere was changed from air to 10−20 bar. This process is reversible. Hebb-Wagner measurements resulted in values for the electronic minority charge carrier conductivities in pure oxygen of log σh [S/cm]=−4.02 and log σe [S/cm]=−15.5 for the holes and electrons, respectively, at 600 °C. In the partial pressure range 10−3 bar≤p(O2)≤1 bar, a slope of +1/4 was observed for d(log (σh)) / d(log (p(O2)) at T=600, 650 and 700 °C. That is in agreement with the assumption of a large number of oxygen vacancies. The diffusion coefficient of the holes was evaluated from the relaxation curves to be 1.1*10−7 cm2/s at 600 °C. Degradation effects were observed under highly reducing conditions which are attributed to the formation of gallium-platinum alloys and the loss of gallium oxide if O2 is available in the gas phase.