Crystal structure of the thortveitite‐related M phase, (MnxZn1–x)2V2O7 (0.75 < x < 0.913): a combined synchrotron powder and single‐crystal X‐ray study

The determination of the crystal structure of the M phase, (Mn_xZn_1–x)₂V₂O₇ (0.75 < x < 0.913), in the pseudobinary Mn₂V₂O₇–Zn₂V₂O₇ system for x ? 0.8 shows that the previously published triclinic unit‐cell parameters for this thortveitite‐related phase do not describe a true lattice for this phase. Instead, single‐crystal X‐ray data and Rietveld refinement of synchrotron X‐ray powder data show that the M phase has a different triclinic structure in the space group P with Z = 2. As prior work has suggested, the crystal structure can be described as a distorted version of the thortveitite crystal structure of β‐Mn₂V₂O₇. A twofold superstructure in diffraction patterns of crystals of the M phase used for single‐crystal X‐ray diffraction work arises from twinning by reticular pseudomerohedry. This superstructure can be described as a commensurate modulation of a pseudo‐monoclinic basis structure closely related to the crystal structure of β‐Mn₂V₂O₇. In comparison with the distortions introduced when β‐Mn₂V₂O₇ transforms at low temperature to α‐Mn₂V₂O₇, the distortions which give rise to the M phase from the β‐Mn₂V₂O₇ prototype are noticeably less pronounced.