view article

Figure 1
The RT A21am structure of Ca3Mn2O7 (Guiblin et al., 2002BB13) 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.

ISSN: 2053-2733
Follow Acta Cryst. A
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds