High temperature crystallographic study of (La0.9Sr0.1)MIIIO3−δ (MIII=Sc, In, and Lu) perovskite proton conductor

Structure refinement was carried out for the powder X-ray diffraction data of A3+B3+O3-type perovskites, (La0.9Sr0.1)MIIIO3−δ (MIII=Sc, In, and Lu) (LSMs) measured in wet air at 873 K. All the diffraction peaks of LSMs could be indexed as an orthorhombic GdFeO3-type structure (space group Pnma, No. 62). For the Sc-compound, the oxygen–oxygen (O–O) bond lengths of intra-ScO6 octahedra were shorter than those of inter-ScO6 ones, suggesting the predominant three-dimensional (3D) proton conduction along the edges of ScO6-octahedra. With increasing the size of B-site (MIII) cation from Sc3+ to Lu3+, the O–O bond lengths and tilting angles of BO6 (MIIIO6) octahedra increased. For the Lu-compound, the O–O bond lengths of intra-LuO6 octahedra were almost the same as those of the inter-LuO6 ones, suggesting the predominant one-dimensional (1D) proton conduction along O1–O1 and O2–O2 sites on the vertices of BO6 octahedra. This change in proton conduction pathway from 3D to 1D would result in the lowering of proton mobility, hence in lower proton conductivity.