Doping effect on crystal structure and conduction property of fast oxide ion conductor LaGaO3-based perovskite

In order to discuss oxide ion conduction mechanism for LaGaO3-based perovskite compounds, doping effects were investigated using two kinds of solid solutions whose oxygen vacancy concentrations are the same: one is La0.9Sr0.1Ga0.9Mg0.1O2.9 with A-site and B-site substitutions and the other is LaGa0.8Mg0.2O2.9 with only B-site substitution. Conductivity measurements showed that La0.9Sr0.1Ga0.9Mg0.1O2.9 had a circumstance whereby oxide ion could more easily diffuse in the perovskite structure than in LaGa0.8Mg0.2O2.9. Structural analyses using neutron diffraction found out the following three differences: the first finding was that the saddle point formed by two A-site cations and one B-site cation in La0.9Sr0.1Ga0.9Mg0.1O2.9 was larger than that in LaGa0.8Mg0.2O2.9 due to larger displacements of A-site and B-site cations; the second was that the doubly doping with Sr and Mg was more effective for reduction of GaO6 octahedral tilt angles than the doping with Mg; the last was that La0.9Sr0.1Ga0.9Mg0.1O2.9 had larger oxygen displacement than LaGa0.8Mg0.2O2.9. It was considered that these structurally related parameters dominated the high oxide ion conduction in LaGaO3-based perovskite compounds.