Layered perovskite compounds were synthesized by means of solid-state reactions, and their crystal structures were determined by means of Rietveld analysis. The compounds had tetragonal symmetry for La, Pr and Nd, while orthorhombic symmetry was observed for the remainder. Stabilization of the compounds was considered with respect to the relative sizes of the rare earth and alkali metal ions. The decrease in symmetry was considered to be introduced by a mismatch between TiO2 and LnO2 layers. Ionic conductivity was observed at high temperatures, and was attributed to inter-layer Na ions. The ionic conductivity of NaLaTiO4, with a single perovskite layer, was much higher than that of Ti3La2Na2O10, with a triple perovskite layer. The high ionic conductivity was attributed to weak interactions between the perovskite layer and the inter-layer Na ions.

K.Toda, Y.Kameo, S.Kurita, M.Sato: Journal of Alloys and Compounds, 1996, 234, 19-25