Crystal structure of the thortveitite-relatedMphase, (MnxZn1–x)2V2O7(0.75
The determination of the crystal structure of theMphase, (MnxZn1–x)2V2O7(0.75 <x< 0.913), in the pseudobinary Mn2V2O7–Zn2V2O7system forx≃ 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 theMphase has a different triclinic structure in the space groupP-1 withZ= 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 theMphase 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-Mn2V2O7transforms at low temperature to α-Mn2V2O7, the distortions which give rise to theMphase from the β-Mn2V2O7prototype are noticeably less pronounced.