Crystal structure of some niobium and tantalum oxides. IV. The structure of KTa 5O 13 and its relationship to the α-PbO 2 structure

Abstract

KTa 5O 13 crystallizes in the orthorhombic system with unit-cell dimensions a = 5.653(3), b = 10.708(5), and c = 16.799(7) Å with space group Pbcm, z = 4. The structure was solved by conventional methods; of 1445 unique reflections measured by counter methods, 982 that obeyed the condition I ⩾ 3 σ( I) were used in the refinement of the model to a conventional R of 0.053 ( R w = 0.052). The structure consists of edge-and corner-shared tantalum-oxygen octahedra joined such that tunnels are formed in which the potassium ions are located. Slabs of octahedra are of the α-PbO 2 type and are related to one another by a mirror plane (in which the potassium ions are located) producing a structure that may be considered as a “chemical twin” of the α-PbO 2 structure.