ELECTRON AND X-RAY-DIFFRACTION STUDY OF K2SRTI10O22

The single-phase compound K2SrTi10O22 was prepared by solid-state reaction. It crystallizes in the monoclinic system, space group C2/m with a = 15.314(2), b = 3.7865(6), and c = 15.439(2) Å, β 102.68(1)°, and Z = 2. The structure was determined from 1674 reflections collected on a Enraf-Nonius CAD4 automatic diffractometer with MoKα radiation. The final R index and weighted Rw index are 0.057 and 0.061, respectively. K2SrTi10O22 belongs to the family of titanates (A2Ti6O13)n-A′Ti4O9 with A = Na, K, Rb, A′ = Ba, Sr, Pb, and n = 1, 2, 3, ⋯, first described by Raveau et al., with n = 1. The covalent framework is built up of the intergrowth of two types of structural units: A2Ti6O13 and hypothetical A’ Ti4O9. Both units are characterized by zigzag ribbons of, respectively, 2 × 3 and 2 × 2 edge-sharing octahedra joined by corners sharing to form tunnels along the [001] direction. The tunnels accommodate the K+ cation on the A′ site, whereas the A site is occupied by Sr2+/K+ cations. Electron diffraction study shows diffuse streaks parallel to the (a, c) plane leading to a doubling of the b parameter. This suggests a one-dimensional ordering of K atoms and vacancies along the b axis, on the one hand, and Sr/K atoms on the other hand. © 1993 Academic Press, Inc.