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Crystal structure of the thortveitite‐related M phase, (Mn x Zn 1– x ) 2 V 2 O 7 (0.75 < x < 0.913): a combined synchrotron powder and single‐crystal X‐ray study
Author(s) -
Knowles Kevin M.,
Sil Anjan,
Stöger Berthold,
Weil Matthias
Publication year - 2018
Publication title -
acta crystallographica section c
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.304
H-Index - 17
ISSN - 2053-2296
DOI - 10.1107/s2053229618010458
Subject(s) - triclinic crystal system , monoclinic crystal system , crystallography , crystal structure , crystal twinning , superstructure , x ray crystallography , materials science , rietveld refinement , phase (matter) , single crystal , diffraction , chemistry , physics , microstructure , optics , organic chemistry , thermodynamics
The determination of the crystal structure of the M phase, (Mn x Zn 1– x ) 2 V 2 O 7 (0.75 < x < 0.913), in the pseudobinary Mn 2 V 2 O 7 –Zn 2 V 2 O 7 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‐Mn 2 V 2 O 7 . 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‐Mn 2 V 2 O 7 . In comparison with the distortions introduced when β‐Mn 2 V 2 O 7 transforms at low temperature to α‐Mn 2 V 2 O 7 , the distortions which give rise to the M phase from the β‐Mn 2 V 2 O 7 prototype are noticeably less pronounced.