Review of experimental progress of hybrid improper ferroelectricity in layered perovskite oxides

Abstract

The primary order parameter of hybrid improper ferroelectricity (HIF) is not spontaneous polarisation but nonpolar modes such as oxygen octahedral rotations (OORs), antipolar, or even Jahn–Teller distortions; therefore, the HIF mechanism may be applied as an effective pathway to tune electronic bandgaps, control orbitals, and create multiferroicity. Most of the current experimental research on HIF is focused on layered perovskite oxides; therefore, this review focuses on the recent progress of experimental studies on HIF materials with the Ruddlesden–Popper (R–P) and Dion–Jacobson (D–J) structures. Experimental research on double-layered R–P oxides is included, and the linear relationship between the Curie temperature and tolerance factor has been established. Moreover, the coexistence of polar and weak ferromagnetic phases has been observed in iron-based double-layered R–P oxides at room temperature. The recent discovery of ferroelectricity in A-site cation-ordered triple-layered R–P oxides has significantly expanded the HIF field. HIF has also been confirmed in caesium- and rubidium-based double-layered D–J oxides, and complex OOR modes have been observed in D–J oxides. Although significant progress has been achieved for HIF materials in layered perovskite oxides, extensive research is required to reveal the mysteries of HIF and to create single-phase multiferroics in HIF materials.

Symmetry Analysis of Magnetoelectric Effects in Perovskite-Based Multiferroics

“…Ruddlesden-Popper (RP) structures are attracting considerable attention due to the recently discovered high-temperature ferroelectric properties and the prospects for their potential implementation as multiferroics at room temperature [11]. The presence of ferroelectric properties, the so-called hybrid improper ferroelectricity (HIF), was theoretically predicted in double-layered perovskite compounds Ca 3 Mn 2 O 7 and Ca 3 Ti 2 O 7 , and then detected experimentally in Ca 3−x Sr x Ti 2 O 7 single crystals [20], and in Ca 3 (Ti 1−x Mn x ) 2 O 7 ceramics [21].…”

Second Harmonic Generation in the Polar A′SmNb2O7 (A′ = Rb, Cs) Dion–Jacobson Layered Perovskites

“…The subsequent work of Benedek using the HIF mechanism on several of the ( n = 2) DJ phases supported the polar structures observed experimentally in the A′ANb 2 O 7 (A′ = Rb, Cs, A = Bi; A′ = Cs, A = Nd) members and predicted polar ground states for other A′ANb 2 O 7 (A′ = Rb, Cs; A = Y, La) oxides necessitating thorough structural determinations. The recognition of HIF through experimental evidence has been demonstrated in several of the layered DJ and RP oxides as reviewed by Lightfoot et al and in the recent more elaborate review by Liu and co-workers …”

“…The recognition of HIF through experimental evidence has been demonstrated in several of the layered DJ and RP oxides as reviewed by Lightfoot et al 7 and in the recent more elaborate review by Liu and co-workers. 40 Particularly in the DJ series, both ferroelectricity and piezoelectricity of polycrystalline CsBiNb 2 O 7 were proven experimentally by Chen et al 41 for the first time with a piezoelectric constant of 8 pC/N and a T c (Curie point) of 1033 ± 5 °C and reported a T c of 1098 ± 5 °C with a piezoelectric constant of 5 pC/N for RbBiNb 2 O 7 . The reexamination 42 of the A′LaB 2 O 7 (A′ = Rb, Cs; B = Nb, Ta) oxides resulted in noncentrosymmetric space group structures at room temperature [from synchrotron X-ray diffraction, optical SHG, and piezoelectric force microscope] instead of the structural results based on centrosymmetric tetragonal 43−45 (P4/mmm) or orthorhombic 46,47 (Imma) symmetries.…”

“…The origin could be the chemical pressure induced by the smaller ionic size of Sm 3+ ions in comparison to those of La 3+ , Pr 3+ , and Nd 3+ ions and the distortion arising from the presence of 6s 2 lone pair of Bi 3+ ions. The tolerance factors of the n = 2 DJ compounds have been calculated by Liu and coworkers 40 based on the Shannon's six-coordinate ionic radii. 68 The tolerance factor calculated for RbSmNb 2 O 7 is 0.914 as against the values of 0.919, 0.920, 0.927, and 0.927 obtained for Nd, Pr, La, and Bi, respectively.…”

Dion–Jacobson A′MiiiNaNb3O10 (A′ = Rb, Cs; M(iii) = Sm, Bi) and RbSmNa2Nb4O13 layered perovskites and their luminescent function

“…Notably, the ability of layered oxides to split water and generate hydrogen photolytically is quite remarkable. 29 Apart from the drive to produce polar structures for the development of ferroelectric materials, 30 quite a few of the rare-earth ion-containing layered oxides are found to be useful to develop novel phosphor materials. The latter materials, additionally are being pursued from the point of view of fabricating persistent luminescent materials.…”