Symmetry analysis for the Ruddlesden-Popper systems Ca3Mn2O7and Ca

A. B. Harris

¹

Abstract

We perform a symmetry analysis of the zero-temperature instabilities of the tetragonal phase of Ca 3 Mn 2 O 7 and Ca 3 Ti 2 O 7 which is stable at high temperature.We introduce order parameters to characterize each of the possible lattice distortions to construct a Landau free energy which elucidates the proposed group-subgroup relations for structural transitions in these systems. We include the coupling between the unstable distortion modes and the macroscopic strain tensor. We also analyze the symmetry of the dominantly antiferromagnetic ordering which allows weak ferromagnetism. We show that in this phase the weak ferromagnetic moment and the spontaneous ferroelectric polarization are coupled, so that by rotating one of these orderings by applying an external electric or magnetic field one can rotate the other ordering.We discuss the number of different domains (including phase domains) which exist in each of the phases and indicate how these may be observed. First-principles calculations of Yildirim corroborate our assertion that domain walls in the nonferroelectric phase are narrow. We perform a symmetry analysis of the zero-temperature instabilities of the tetragonal phase of Ca 3 Mn 2 O 7 and Ca 3 Ti 2 O 7 which is stable at high temperature. We introduce order parameters to characterize each of the possible lattice distortions to construct a Landau free energy which elucidates the proposed group-subgroup relations for structural transitions in these systems. We include the coupling between the unstable distortion modes and the macroscopic strain tensor. We also analyze the symmetry of the dominantly antiferromagnetic ordering which allows weak ferromagnetism. We show that in this phase the weak ferromagnetic moment and the spontaneous ferroelectric polarization are coupled, so that by rotating one of these orderings by applying an external electric or magnetic field one can rotate the other ordering. We discuss the number of different domains (including phase domains) which exist in each of the phases and indicate how these may be observed. First-principles calculations of Yildirim corroborate our assertion that domain walls in the nonferroelectric phase are narrow. Disciplines Physical Sciences and Mathematics | Physics

Domains and ferroelectric switching pathways inCa3Ti2O7from first principles

“…The same combination of irreps (X − 3 ⊕ X + 2 ) that induces the polar distortion in A2 1 am also can induce this antipolar distortion, when the irreps are taken along different directions in OP space. The key to describing these polar and antipolar structures on an equal footing is to use the full two-dimensional OPs 24,25 to describe the structural distortions in Ca 3 Ti 2 O 7 . This means that both an amplitude Q and a phase θ characterize each distortion.…”

Epitaxial-strain-induced polar-to-nonpolar transitions in layered oxides

“…Within this context, an oxide class referred to as hybrid-improper ferroelectrics (HIF) 11 has garnered interest owing to strong anharmonic interactions among polar and nonpolar BO 6 rotational modes 12,13 . Such multimode interactions are responsible for the appearance of an electric polarization 14 with the layered A 3 B 2 O 7 Ruddlesden-Popper (RP) structure serving as the scaffolding 11,15,16 …”

“…Within this context, an oxide class referred to as hybrid-improper ferroelectrics (HIF) 11 has garnered interest owing to strong anharmonic interactions among polar and nonpolar BO 6 rotational modes 12,13 . Such multimode interactions are responsible for the appearance of an electric polarization 14 with the layered A 3 B 2 O 7 Ruddlesden-Popper (RP) structure serving as the scaffolding 11,15,16 to stabilize the polar ground state structure (that is, Cmc2 1 symmetry) and induce an electric polarization P. The first theoretically proposed HIF RP oxides include Ca 3 B 2 O 7 (B = Ti or Mn) 11 , which subsequently have been confirmed through recent experiments on (Ca,Sr) 3 Ti 2 O 7 single crystals 17 , Ca 3 Ti 2 O 7 and Ca 3 Mn 2 O 7 polycrystals 18 , and Ca 3 (Ti,Mn) 2 O 7 ceramics 19 . In (Ca,Sr) 3 Ti 2 O 7 single crystals, the existence of a switchable P under a small electric field was also demonstrated 17 .…”

Negative Thermal Expansion in Hybrid Improper Ferroelectric Ruddlesden-Popper Perovskites by Symmetry Trapping

“…Recently it has been shown that in perovskite thin films, improper ferroelectricity may be induced via strain coupling of octahedral rotations between different perovskite heterostructure layers [12]. Benedek and Harris [13,14] developed this idea further proposing a novel mechanism where this improper ferroelectricity may be realized in the bulk structure. In this mechanism, instability of the polar phonon mode is driven by the condensation of two nonpolar lattice modes, neither of which are zone centered.…”