MS16-P23 1:3 A-site ordering in perovskite structures: group theoretical analysisThe quadruple perovskites AA'3B4O12 are characterized by an extremely wide variety of intriguing physical properties, which make them demanded for various applications [1,2]. Using group-theoretic analysis, we found all possible 1:3 A-site ordered low-symmetry phases, which can be formed from a parent Pm-3m perovskite structure (archetype) as a result of real or hypothetical (virtual) phase transitions due to different structural mechanisms (ordering and displacement of atoms, anion octahedral tilts). For each of the low-symmetry phases, the complete condensate of order parameters (proper and improper order parameters), the calculated structure, including the space group, the primitive cell multiplication, the distribution of atoms over the Wyckoff positions and the structural formula were determined. All phases were systematized according to the types of structural mechanisms responsible for their formation, and the group-subgroup relations between the phases were investigated. Special attention is paid to the structural mechanisms for the low-symmetry phase’s formation of the compounds known from experimental data, such as: CaCu3Ti4O12, CaCu3Ga2Sn2O12, CaMn3Mn4O12, Ce1/2Cu3Ti4O12, LaMn3Mn4O12 and others. For the first time, the variability in the choice of the proper order parameters, which generate 1: 3 A-site ordered low-symmetry phases, highlights the fundamental significance of the complete condensate of the order parameters in the description of structural phase transitions. The constructed map of the 1:3 A-site ordered quadruple perovskites can be used to identify new phases and interpret experimental results, determine the structural mechanisms responsible for the formation of low-symmetry phases as well as to understand the structural genesis of the perovskite-like phases. The obtained non-model group-theoretical results in combination with crystal-chemical data and first principles calculations can be a starting point for the design of new functional materials with a perovskite structure.
The reported study was funded by RFBR - research projects no.16-32-60025 mol_a_dk.
 Shimakawa, Y. (2008). Inorg. Chem., 47, 8562-8570.
 Belik, A.A.. (2018). Dalt. Trans., 47, 3209-3217.Keywords: quadruple perovskites, group-theoretical analysis, order parameter