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Figure 3
(a) Ideal perovskite with untilted octahedra. (b) Octahedral tilting by angle a allows one to reduce the distance between the cations B and B′ while the bond length between B and X is maintained. The result is a contraction of the cell volume (highlighted in grey) due to less volume assigned to the A cations. (c) Along the tilting axis, two subsequent octahedra can be tilted in antiphase (here, notation a−) or in phase [notation a+, see (b)]. Cross sections of the PES along the blue lines corresponding to octahedral rotations are given in Fig. 2[link].

IUCrJ
Volume 10| Part 3| May 2023| Pages 309-320
ISSN: 2052-2525
https://doi.org/10.1107/S2052252523002208