A new electron diffraction approach for structure refinement applied to Ca3Mn2O7

Beanland, R.; Smith, K.; Vaněk, P.; Zhang, H.; Hubert, A.; Evans, K.; Römer, R.A.; Kamba, S.

doi:10.1107/S2053273321001546

Figure 1
The RT A2₁am structure of Ca₃Mn₂O₇ (Guiblin et al., 2002

) and possible intermediate phases. (a) Perspective view of the A2₁am unit cell, Ca atoms blue and MnO₆ octahedra orange. (b) View along [001] showing the upper and lower oxygen octahedra, which twist in-phase about the [001] axis. (c) View along [001] showing the central octahedra, which also twist in-phase about [001]. (d) Projections of the A2₁am structure, as a ball-and-stick model for the upper perovskite block (Mn atoms magenta, oxygen atoms red, Ca atoms blue) and showing oxygen octahedra for the lower perovskite block. The RT structure has X₂⁺ and $[X_{3}^{-}]$ distortions, and appears differently when viewed along [ $[\bar{1}]$ 10] (left) and [110] (right). Note the lack of mirror symmetry: the anti-phase octahedral tilts about [110] and in-phase tilts about [001] split the visible oxygen sites and displace the oxygen atoms adjacent to the Mn atom asymmetrically. (e) A structure with the $[X_{3}^{-}]$ distortion only, with symmetry Aeam. (f) A structure with the X₂⁺ distortion only, with symmetry Amam. For both (e) and (f) the [110] projection is identical to the [1 $[\bar{1}]$ 0] projection.

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ISSN: 2053-2733

Volume 77| Part 3| May 2021| Pages 196-207

https://doi.org/10.1107/S2053273321001546

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