Crystallography in Material Science

We have investigated the nuclear density distributions in LaGaO3based perovskites, LaGaO3 (LG), (La0.9Sr0.1)GaO3(LSG), La(Ga0.9Mg0.1)O3(LGM), and (La0.8Sr0.2)(Ga0.8Mg0.15Co0.05)O3(LSGMC), to elucidate the ionic conduction path and disorder of oxide ions at elevated temperatures. Neutron diffraction data were collected in the temperature range from 26 to 1405oC in air, using a diffractometer HERMES installed at JRR-3M in JAERI (Tokai). The data obtained were analyzed by the combination technique of Rietveld analysis (using a computer program RIETAN-2000) and a maximumentropy method (MEM)-based pattern fitting (using a computer program PRIMA). At ca. 1400°C, the oxide ions were localized near the equilibrium (ideal) positions for LG, while they spread over a wide area around the ideal positions for LSG and LGM. For LSGMC, the conduction path of oxide-ion was observed; the conduction path was not along the straight line between the ideal oxygen positions, but exhibited an arc shape away from the B-site cations (Ga0.8Mg0.15Co0.05) [1]. The difference in nuclear density distribution is presumed to arise from the difference in oxide-ion conductivity of these compounds.