A new alkali metal titanotantalate, KTi 2Ta 5O 17—A compound that exhibits the “chemically twinned” rutile structure

Abstract

KTi 2Ta 5O 17 crystallizes in the orthorhombic system with unit-cell dimensions (from single-crystal data) a = 6.672(4) Å, b = 8.948(5) Å, c = 21.403(9) Å and space group Cmcm, Z = 4. The structure was solved using three-dimensional Patterson and Fourier techniques. Of the 1034 reflections measured by counter techniques, 704 with I ≥ 3 σ( I) were used in the least-squares refinement of the model to a conventional R of 0.041 ( ωR = 0.043). The structure consists of edge- and corner-shared tantalum octahedra joined such that tunnels are formed in which the potassium ions are located. Slabs of octahedra are of the rutile (TiO 2) type related to one another by mirror planes (in which the potassium ions are located), producing a structure that may be considered as a “chemical twin” of the rutile structure.