Synthesis and Structures of Reduced Niobates with Four Perovskite-like Layers and Their Semiconducting Properties

Carriers were successfully doped into RbCa₂NaNb₄O₁₃ by the substitution of Sr²⁺ for Na⁺, yielding electroconducting niobates with a layered structure consisting of four perovskite-like layers. Single-phase products of polycrystalline RbCa₂Na_1-xSr_xNb₄O₁₃ (x = 0.2 and 0.4) were synthesized by the solid-state reaction of RbCa₂Nb₃O₁₀, Sr₅Nb₄O₁₅, Nb₂O₅, and Nb metal. The solid solutions were indexed based on a tetragonal structure, corresponding to the end-member RbCa₂NaNb₄O₁₃. With the increase in the amount of strontium substitution, an expansion of the c-axis was observed while the a-axis was essentially constant. The products showed semiconducting properties.