Polar and antipolar polymorphs of metastable perovskiteBiFe0.5Sc0.5O3

Abstract

A metastable perovskite BiFe 0.5 Sc 0.5 O 3 synthesized under high-pressure (6 GPa) and high-temperature (1500 K) conditions was obtained in two different polymorphs, antipolar P nma and polar I ma2, through an irreversible behavior under a heating/cooling thermal cycling. The I ma2 phase represents an original type of a canted ferroelectric structure where Bi 3+ cations exhibit both polar and antipolar displacements along the orthogonal [110] p and [110] p pseudocubic directions, respectively, and are combined with antiphase octahedral tilting about the polar axis. Both the P nma and the I ma2 structural modifications exhibit a long-range antiferromagnetic ordering with a weak ferromagnetic component below T N ∼ 220 K. Analysis of the coupling between the dipole, magnetic, and elastic order parameters based on a general phenomenological approach revealed that the weak ferromagnetism in both phases is mainly caused by the presence of the antiphase octahedral tilting whose axial nature directly represents the relevant part of Dzyaloshinskii vector. The magnetoelectric contribution to the spontaneous magnetization allowed in the polar I ma2 phase is described by a fifth-degree free-energy invariant and is expected to be small.

Magnetic structure of an incommensurate phase of La-dopedBiFe0.5Sc0.5O3: Role of antisymmetric exchange interactions

“…The part of the antisymmetric exchange related to octahedral tilting was considered in detail in Ref. [17]. It has been shown that the axial distortions associated with the octahedral rotations are responsible for the weak ferromagnetic properties of antiferromagnetically ordered perovskites with a G-type spin configuration.…”

“…On heating, the antipolar P nma phase of BiFe 0.5 Sc 0.5 O 3 was found to transform into the polar R3c phase identical to that of BiFeO 3 . Subsequent cooling below the transition temperature resulted in onset of a polar phase with the I ma2 symmetry, where the ferroelectric-like displacements of Bi 3+ cations along the [110] p pseudocubic direction are combined with the antiphase octahedral tilting about the polar axis [17]. It has also been shown that both the P nma and the I ma2 polymorphs of BiFe 0.5 Sc 0.5 O 3 exhibit a long-range antiferromagnetic ordering with a weak ferromagnetic component below about 220 K. The antiferromagnetic configuration was found to be of a G type (where the Fe/Sc nearest neighbors in all three directions have antiparallel spins).…”

“…This offers a unique opportunity to study the structure-properties relationship using distinct structural modifications of the same material. It has been recently shown that the metastable perovskite BiFe 0.5 Sc 0.5 O 3 can be stabilized in two different polymorphs via an irreversible behavior under heating/cooling thermal cycling [17]. As-prepared BiFe 0.5 Sc 0.5 O 3 ceramics obtained by quenching under high pressure were characterized by a complex antipolar structure with the P nma symmetry and the √ 2a p × 4a p × 2 √ 2a p type superstructure (a p is the pseudocubic unit cell).…”

Magnetic Properties of the Bi0.65La0.35Fe0.5Sc0.5O3 Perovskite

“…The system demonstrates a rich phase diagram. Three consecutive phases with different crystal structures appear as the lanthanum content is increased: the as-prepared phase with x ≤ 0.05 is an antipolar Pnma [6], an incommensurately modulated phase with the Imma(00γ)s00 superspace group [7] is observed for 0.10 ≤ x ≤ 0.30, and a non-polar Pnma phase [8] is stable at x ≥ 0.35.…”

“…Bi 1−x La x Fe 0.5 Sc 0.5 O 3 perovskites are the rare examples of single-phase multiferroics which were recently obtained under high-pressure conditions [6][7][8]. The system demonstrates a rich phase diagram.…”