Potassium Disorder in the Defect Pyrochlore KSbTeO 6 : A Neutron Diffraction Study

摘要

KSbTeO 6 defect pyrochlore has been prepared from K 2 C 2 O 4 , Sb 2 O 3 , and 15% excess TeO 2 by solid-state reaction at 850 °C. Direct methods implemented in the software EXPO2013 allowed establishing the basic structural framework. This was followed by a combined Rietveld refinement from X-ray powder diffraction (XRD) and neutron powder diffraction (NPD) data, which unveiled additional structural features. KSbTeO 6 is cubic, a = 10.1226(7) ?, space group F d 3 ˉ m , Z = 8 and it is made of a mainly covalent framework of corner-sharing (Sb,Te)O 6 octahedra, with weakly bonded K + ions located within large cages. The large K-O distances, 3.05(3)–3.07(3) ?, and quite large anisotropic atomic displacement parameters account for the easiness of K + exchange for other cations of technological importance.