Pressure‐Induced Multiferroics via Pseudo Jahn–Teller Effects and Novel Couplings

Abstract

of 7) 1604513PbHfS 3 , and SnHfS 3 . [2][3][4][5][6] Recent studies also revealed that iodate compounds, such as CH 3 NH 3 PbI 3 (which presents a high photovoltaic conversion) and CsSnI 3 can also crystallize in the NH 4 CdCl 3 -type structure. [7,8] Xu et al. further predicted, by using a first-principles-based genetic algorithm, that the NH 4 CdCl 3 -type structure can also become the ground state of many ABO 3 oxides and ABF 3 fluorites, when under high enough pressure. [9] Considering its generality and its occurrence after the perovskite (Pv) and post-perovskite (pPv) structures when gradually increasing the hydrostatic pressure in various ABO 3 and ABF 3 compounds, the NH 4 CdCl 3 -type structure is named as post-post-perovskite (ppPv) in ref.[9] -which is the convention we will also adopt in this paper.Interestingly, as far as we can tell, the post-post-perovskite structure has never been found (or predicted) to display an electrical polarization or the so-called Jahn-Teller (JT) distortions -intimately related to magnetism and electronic structure -in any material, including ABO 3 and ABF 3 systems. This is in line with the common belief that hydrostatic pressure suppresses structural distortions of the type that are typically related to electric polarization and Jahn-Teller effects. [10][11][12][13] For instance, experimental and computational works both reported that JT distortions of LaMnO 3 perovskite are reduced under pressure until potentially fully vanishing for a high enough compression. [11][12][13] Similarly, polarization typically results from a competition between long-range Coulomb interactions (which favor ferroelectricity) and short-range interactions (which favor the paraelectric structure), [14] and pressure tips this delicate balance in favor of short-range repulsive effects, thus favoring the paraelectric state. [15,16] Here we use first-principles simulations to predict that such beliefs have to be revisited. More precisely, we discover that applying pressure to many magnetic rare-earth manganites RMnO 3 not only leads to the stabilization of the post-postperovskite structure but also induces pseudo Jahn-Teller effects that, in turn, yield a spontaneous electrical polarization via a previously unknown coupling. Interestingly, the latter coupling only involves the polarization and the mentioned JT distortion; this feature sets the new coupling apart from other trilinear effects, [17,18] in which a third structural distortion appears, as it strongly suggests the possibility of an easier control of JT effects and related electronic properties via the application of Multiferroic materials are currently attracting a lot of interest because of the cross-coupling between their electrical and magnetic properties, which has the potential to lead to novel devices. There is a relatively small number of multiferroics and, hence, various strategies have been proposed to design materials possessing both ordered electric and magnetic dipoles. However, one strategy that has been scarcely investigated...

Improper ferroelectricity at antiferromagnetic domain walls of perovskite oxides

“…However, ferromagnetic and ferroelectric orders are mutually exclusive in a single compound, owing to the fact that magnetism needs non-d 0 configurations for the d electrons of transition metal whereas ferroelectricity typically requires a d 0 configuration [4]. As a result, multiferroic materials are rather rare in nature [5], and discovering new multiferroics as well as understanding the microscopic origins for the simultaneous occurrence of their long-range ordered electric and magnetic dipoles constitute important research directions [3,[6][7][8][9][10][11][12][13].…”

Dynamics of antipolar distortions

“…Examples of these two latter quantities are two different oxygen octahedral tiltings, [1][2][3][4][5][6][7] one oxygen octahedral tiling and one antipolar motion, 8 one Jahn-Teller mode and one antiferrodistortive (or antipolar) distortion, 9,10 or even two pseudo-Jahn-Teller motions. 11 Note also that trilinear energetic couplings do not restrain themselves to polar materials since they can also arise in compounds possessing antipolar cation distortions via their couplings with antiphase and inphase octahedral tiltings. 12 Antipolar systems are important compounds on their own.…”

On the Crystal Chemistry of Inorganic Nitrides: Crystal-Chemical Parameters and Opportunities in the Exploration of Their Compositional Space

“…124,147 Vibronic mixing usually (but not necessarily) occurs between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), with a distortion mode having the same symmetry as the HOMO to LUMO transition. 147 Although occurrence of the PJTE is not encumbered by a priori limitations such as electronic configuration, the PJTE is primarily observed for d 0 transition metals, with resulting non-centrosymmetric behavior responsible for a host of technologically-relevant properties including ferroelectricity, 51,148 ferromagnetism, 149 multiferroicity, 150 piezoelectricity, 51 photocatalysis, 151 nonlinear optics, 51,55 magnetic-dielectric bistability, 101 etc. The PJTE is of particular interest to materials design, for the structural instability resulting from this effect can be controlled by means of electronic rearrangements induced by redox processes, electromagnetic fields, external pressure and more, 147 with potential applications spanning bistable atomic switches, 152-154 and control over sorption characteristics of catalysts to move beyond the Sabatier principle.…”