Crystal structures of some niobium and tantalum oxides. VII. K 4+5 xTa 16− xO 42 ( x ≈ 0.3)

Abstract

K 4+5 x Ta 16− x O 42 crystallizes in the hexagonal system with unit-cell dimensions (from single-crystal data) a = 9.085(6), c = 12.254(8) Å and space group P6 3 mcm , Z = 1 . The structure was solved by Patterson and Fourier techniques and refinement by full-matrix least-squares methods using 271 reflections, measured by counter techniques, with I ⩾ 3.5 σ ( I), resulted in an R of 0.060 ( R w = 0.051). The structure consists of units of six octahedra, edge- and corner-shared to one another, that are linked by corner sharing through a single octahedron. This structure provided the “key” to other structures in the K 2O:Ta 2O 5 and Rb 2O:Nb 2O 5 systems. Its significance in this respect is discussed.