New Route to Ordered Double Perovskites: Synthesis of Rock Salt Oxides, $Li_4MWO_6$, and Their Transformation to $Sr_2MWO_6$ $(M = Mg, Mn, Fe, Ni)$ via Metathesis

We describe a solid-state metathesis route for the synthesis of double perovskite oxides, $Sr_2MWO_6$ $(M= Mg, Mn, Fe, Ni)$, that enabled us to obtain cation-ordered phases at a considerably lower temperature $(\sim750^oC)$ than what is employed in conventional synthesis of these materials. The method involves reaction of appropriate rock salt related precursor oxides of the formula $Li_4MWO_6$ with anhydrous $SrCl_2$ in the solid state at $750^oC$ for 1-2 days. For this purpose, rock salt precursor oxides were designed and synthesized for the first time. Cation ordering in the $Sr_2MWO_6$ products obtained was investigated by Rietveld refinement of powder X-ray diffraction data. We believe that the strategy described here is general and could be extended for the synthesis of functional double perovskites at relatively mild conditions