Synthesis, structures and phase transitions in the double perovskites Sr 2- x Ca x CrNbO 6

Abstract

The synthesis and crystal structures of nine members of the rock-salt ordered double perovskites Sr2-xCaxCrNbO6 is presented. The crystal structures of the end members of the series Sr2CrNbO6 and Ca2CrNbO6 were refined using powder neutron diffraction data and are cubic in Fm over(3, -) m and monoclinic in P21/n, respectively, in both cases there being considerable anti-site Cr-Nb mixing. Variable temperature and/or composition studies suggest a direct first-order P21/n to Fm over(3, -) m transition, a suggestion supported by selected area electron diffraction studies. Crown