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 RbCa2Na1xSrxNb4O13 (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.