Crystallographic studies of Ba(12)Nb(8-x)TaxCo(4)O(36) (x=1,3,4,5,7)

摘要

Crystal structures and X-ray reference powder diffraction patterns have been determined for the Ba(12)Nb(8-x)TaxCo(4)O(36) (x = 1, 3, 4, 5, 7) series. Ba12Nb8-xTaxCo4O36 crystallize in the cubic perovskite structure with a space group Pm (3) over bar m (No. 221) and the lattice parameter increasing from a = 4.08732(3) angstrom to a = 4.08894 (2) = as x varies from 1 to 7. The Goldschmidt distortion parameter for the entire series is about 1.05 (1.0488-1.0506), being similar to that of the cubic end member Ba3Nb2CoO9. Transmission electron microscopy of the composition Ba12Nb4Ta4Co4O36 (or Ba3(NbTaCo)O-9) revealed nanoscale 1: 2 ordering of Nb/Ta and Co, manifested in the presence of the diffuse superlattice reflections. As this ordering is limited to short range, the average structures were still refined assuming the ideal-perovskite cubic symmetry. X-ray powder diffraction patterns of the studied compounds have been submitted to the Powder Diffraction File (PDF). (C) 2017 Elsevier Masson SAS. All rights reserved.