High-temperature stability study of the oxygen-ion conductor La0.9Sr0.1Ga0.8Mg0.2O3-x

La0.9Sr0.1Ga0.8Mg0.2O3-x (LSGM) has been prepared by a complexing sol-gel p rocess and characterised by X-ray diffraction, thermogravimetric-differenti al thermal analysis (TG-DTA) and conventional weight analysis. The room-tem perature structure is orthorhombic, space group Pnma, with a = 5.5340(14), b = 5.5074(22), c = 7.8003(31) Angstrom. After heating at 1000 degrees C, t he lattice parameters of LSGM shift a little, and La4SrO7 and SrLaGaO4 sepa rate from the parent phase, which may further affect other properties. The weight change of LSGM at 750 degrees C is insignificant and the phase is al so stable after heating at 750 degrees C in a hydrogen atmosphere for a tot al of 132 h. Defect chemistry modelling supports the view that LSGM is not single phase at 1000 degrees C.