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K. Knowles, A. Sil, B. Stöger, M. Weil:
"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";
Acta Crystallographica Section C, - (2018), 74; S. 1079 - 1087.

The determination of the crystal structure of the M phase, (MnxZn1-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\overline{1} 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.

http://dx.doi.org/10.1107/S2053229618010458