4層のペロブスカイト骨格をもつMCa₂NaNb₄O₁₃ (M=Rb, Na) の構造解析とイオン伝導性

抄録

Layered perovskite, RbCa₂NaNb₄O₁₃, with four units of perovskite layer was synthesized by solid state reaction. A sodium ion-exchanged compound, NaCa₂NaNb₄O₁₃⋅1.7H₂O, was also synthesized by ion-exchange reaction of a rubidium compound with NaNO₃ molten salt. The anhydrous sodium ion-exchanged compound was stable in the temperature range from 350 to 600°C in an ambient atmosphere. The crystal structures of the three materials were determined using the Rietveld method by powder XRD data. The most reliable solutions were obtained for the structural model assuming that the site for a large cation within the perovskite layer, corresponding to the A site for an ideal perovskite, is occupied by the mixed species with the atomic ratio of Ca:Na=2/3:1/3. The structures of these compounds are substantially the same as those of MLaNb₂O₇ (M=Rb, Na) except for the thickness of the perovskite layer. A fairly high ion conductivity attributed to the interlayer cation was observed at high temperatures for the sodium compound.