Preparation and Crystal Structure of K2YNb5O15−δ

Abstract

Single crystals of new reduced potassium yttrium niobate, K2YNb5O15−δwere prepared in a H2atmosphere at 1200°C. Potassium yttrium niobate crystallizes in the orthorhombic space groupCmmmwitha= 10.316(1),b= 15.257(1), andc= 3.914(1) Å,Z= 2, and the finalRfactors areR= 0.046 andRw= 0.047 for 1077 unique reflections. The crystal structure is built up by corner-sharing of NbO6octahedra and the three-dimensional framework formed by the Nb5O15units is same as that of the NaNb6O15F-type structure. The Y3+ion is located in a distorted perovskite-like cavity and the K+ion is in a pentagonal tunnel. Reduced potassium yttrium niobate, K2YNb5O15−δ, is oxidized without deterioration in crystallinity at about 450°C, and the oxidized phase, K2YNb5O15, transforms to the tetragonal tungsten bronze-type structure at 1150°C.