Double perovskites containing hexavalent molybdenum and tungsten: synthesis, structural investigation and proposal of a fitness factor to discriminate the crystal symmetry

Abstract

Double perovskites A^II₂B^IIB^VIO₆ (A^II=Ba, Sr, Ca; B^II=Mg, Ni, Co, Cd, Ca; B^VI=W, Mo, W_0.5Mo_0.5) have been synthesized and their crystal structures investigated by powder X-ray diffraction measurements. In order to discriminate the crystal systems of the double perovskites, a fitness factor is proposed which corresponds to the size matching between the A cation and the cubo-octahedral cavity formed by eight BO₆ octahedrons. The fitness factor can discriminate the crystal systems of obtained compounds more exactly than the well known tolerance factor.

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