Synthesis, structures and phase transitions in the double perovskites Sr2−xCaxCrNbO6

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 Fm3¯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 Fm3¯m transition, a suggestion supported by selected area electron diffraction studies.

The evolution of the structures in the series Sr2−xCaxCrNbO6 has been investigated using a combination of high resolution diffraction methods. The series shows an unusual direct cubic-monoclinic phase transition near x=1.0 with both phase co-existing.Figure optionsDownload as PowerPoint slide