Hybrid Improper Ferroelectricity in Columnar (NaY)MnMnTi₄O₁₂

Abstract

We show that cation ordering on A site columns, oppositely displaced via coupling to B site octahedral tilts, results in a polar phase of the columnar perovskite (NaY)MnMnTi 4 O 12 . This scheme is similar to hybrid improper ferroelectricity found in layered perovskites, and can be considered a realisation of hybrid improper ferroelectricity in columnar perovskites. The cation ordering is controlled by annealing temperature and when present it also polarises the local dipoles associated with pseudo-Jahn-Teller active Mn 2 + ions to establish an additional ferroelectric order out of an otherwise disordered dipolar glass. Below T N � 12 K, Mn 2 + spins order, making the columnar perovskites rare systems in which ordered electric and magnetic dipoles may reside on the same transition metal sublattice.

Anisotropic Thermal Expansion and a Second-Order Charge Order Transition in the Ferrimagnetic Dy2CuZnMn4O12 Perovskite with Triple A-Site Cation Ordering

“…The parent structure of the A 2 A′A″B 4 O 12 perovskites has P 4 2 / nmc symmetry and is formed through large tilts of the a + a + c – type . This symmetry is retained in the majority of examples of such perovskites. , The next most commonly observed symmetry is P 4 2 / n , which is produced through full or partial rock-salt-type B-cation orderings, A 2 A′A″B 2 B′ 2 O 12 . , The less common symmetries are P 4 2 mc (which is formed through polar distortions in CaMnTi 2 O 6 , CaMnTi 2– x V x O 6 , and NaYMnMnTi 4 O 12 ) and Pmmn (which is formed through layered-type B-cation ordering in RMn 3 O 6 (R = Gd to Tm) , and R 2 CuMnMn 4 O 12 (R = Dy and Y) due to partial or full charge ordering of Mn 3+ and Mn 4+ , respectively). The presence of charge-ordered structures based on the same element could suggest the existence of temperature-driven charge-(dis)­ordered transitions as observed in simple perovskites (e.g., half-doped R 3+ 0.5 A 2+ 0.5 MnO 3 ) or quadruple perovskites (e.g., ACu 3 Fe 4 O 12 ) .…”