Ca2CoNbO6: A new monoclinically distorted double perovskite

The new Ca2CoNbO6 double perovskites has been synthesized by solid-state reaction and its crystal structure has been refined using X-ray powder diffraction data. Rietveld fit to the diffraction data shows that the compound is monoclinically distorted and adopts space group P21/n. The cell parameters are: a = 5.4797(1) angstrom, b = 5.6051(1) angstrom, c = 7.8119(2) angstrom, beta = 89.96(1)degrees. The Co and Nb are found to be distributed over the six coordinated octahedral sites in rock salt arrangement. However, nearly identical ionic radii of Co and Nb lead to severe degree of anti-site disorder (31%). The refined Co-O and Nb-O bond lengths are 1.9788(2) angstrom and 2.0642(2) angstrom respectively. (C) 2010 Elsevier Masson SAS. All rights reserved.