Crystal structure refinement of magnesium zinc divanadate, MgZnV₂O₇, from powder X-ray diffraction data

The crystal structure of magnesium zinc divanadate, MgZnV₂O₇, was determined and refined from laboratory X-ray powder diffraction data. The title compound was synthesized by a solid-state reaction at 1023 K in air. The crystal structure is isotypic with Mn_0.6Zn_1.4V₂O₇ (C2/m; Z = 6) and is related to the crystal structure of thortveitite. The asymmetric unit contains two metal sites with statistically distributed magnesium and zinc atoms with the atomic ratio close to 1:1. One (Mg/Zn) metal site (M1) is located on Wyckoff position 8j and the other (M2) on 4h. Three V sites (all on 4i), and eight O (three 8j, four 4i, and one 2b) sites complete the asymmetric unit. The structure is an alternate stacking of V₂O₇ layers and (Mg/Zn) atom layers along [20]. It is distinct from other related structures in that each V₂O₇ layer consists of two groups: a V₂O₇ dimer and a V₄O₁₄ tetra-mer. Mixed-occupied M1 and M2 are coordinated by oxygen atoms in distorted trigonal bipyramidal and octa-hedral sites, respectively.