Ferroelastic phase transitions induced by the orbital and rotation ordering in perovskites |
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Authors: | M. P. Ivliev |
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Affiliation: | (1) Research Institute of Physics, Southern Federal University, pr. Stachki 194, Rostov-on-Don, 344090, Russia |
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Abstract: | The phases formed in cubic crystals upon ferrodistortion and antiferrodistortion orientational ordering of anion polyhedra distorted as a result of the Jahn-Teller effect are established in terms of the statistical model in the mean-field approximation. For the four-sublattice three-minimum model, there are four types of ordered phases, and one of them is the intrinsic ferroelastic (ferrodistortion) phase. The conditions providing the appearance of ordering of a particular type are determined. The effect of orbital ordering on the rotational structural distortions is discussed. The conditions of the formation of ordered phases (D 4h 5 , D 4h 18 ) that are most frequently encountered in perovskites are found within the eight-sublattice three-minimum model. It turns out that, under certain conditions, these phases can coexist in the same crystal and transform into each other. The variants of their mutual transformations are considered. |
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