Structural chemistry of new ion-exchangeable tantalates with layered perovskite structure: New reduced Ruddlesden-Popper phase, Na₂Ca₂Ta₃O₁₀

A new reduced tantalate, Na₂Ca₂Ta₃O₁₀, with layered perovskite structure was synthesized by an intercalation reaction from the parent sodium compound, NaCa₂Ta₃O₁₀. The crystal structures of these compounds were determined by the Rietveld analysis of powder X-ray diffraction pattern. Although the framework of the perovskite layer of intercalation compound is analogous to that of the parent compound, the coordination of interlayer sodium ion in the intercalation compound is clearly distinct from that of the parent compound. The sodium ions within the interlayer of intercalation compound have a rock-salt coordination because of a too strong repulsive force for a tetrahedral coordination. The intercalation compound, Na₂Ca₂Ta₃O₁₀, is the first example of a reduced tantalate with a Ruddlesden-Popper type structure.