Understanding ferroelectricity in layered perovskites: new ideas and insights from theory and experiments

Abstract

ABO 3 perovskites have fascinated solid-state chemists and physicists for decades because they display a seemingly inexhaustible variety of chemical and physical properties. However, despite the diversity of properties found among perovskites, very few of these materials are ferroelectric, or even polar, in bulk. In this Perspective, we highlight recent theoretical and experimental studies that have shown how a combination of non-polar structural distortions, commonly tilts or rotations of the BO 6 octahedra, can give rise to polar structures or ferroelectricity in several families of layered perovskites. We discuss the crystal chemical origin of the polarization in each of these families -which emerges through a so-called 'trilinear coupling' or 'hybrid improper' mechanism -and emphasize areas in which further theoretical and experimental investigation is needed. We also consider how this mechanism may provide a generic route for designing not only new ferroelectrics, but also materials with various other multifunctionalities, such as magnetoelectrics and electric field-controllable metal-insulator transitions.

Electric Field Control of Jahn-Teller Distortions in Bulk Perovskites

“…Such a coupling was identified in various layered perovskites [8,9,[12][13][14][15], metal-organic framework [16,17], and can even appear in bulk ABO 3 perovskites [18,19]. Interestingly, in Ruddlesden-Popper compounds [9,20] and ABO 3 =A 0 BO 3 superlattices [21], this trilinear coupling appeared as a practical way to achieve electric control of nonpolar antiferrodistortive (AFD) motions associated with the rotation of the oxygen octahedra (i.e., monitoring P with an electric field will directly and sizeably tune the nonpolar modes R 1 and/or R 2 ).Following this spirit, achieving an electric field control of Jahn-Teller distortions can be realized through the identification of a material exhibiting, by symmetry, a similar "trilinear" term involving both the polarization and the Jahn-Teller distortion which, to the best of our knowledge, has not yet been discovered in bulk ABO 3 perovskites [11]. In the present Letter, we identify such conditions and demonstrate, explicitly, an electric field control in bulk perovskites using a combination of symmetry analysis and first-principles calculations.…”

“…Recently, the concept of "hybrid improper ferroelectricity" has emerged within the community of oxide perovskites [8][9][10][11]. This concept is related to an unusual coupling of lattice modes, giving rise in the free energy expansion to a trilinear term −λPR 1 R 2 linking the polar motion P to two independent nonpolar distortions R 1 and R 2 .…”

“…Following this spirit, achieving an electric field control of Jahn-Teller distortions can be realized through the identification of a material exhibiting, by symmetry, a similar "trilinear" term involving both the polarization and the Jahn-Teller distortion which, to the best of our knowledge, has not yet been discovered in bulk ABO 3 perovskites [11]. In the present Letter, we identify such conditions and demonstrate, explicitly, an electric field control in bulk perovskites using a combination of symmetry analysis and first-principles calculations.…”

La2SrCr2O7: Controlling the Tilting Distortions of n = 2 Ruddlesden–Popper Phases through A-Site Cation Order

“…Fortunately, some relief can be found in the recent theoretical and experimental observations that inversion symmetry can be broken in the layered variants of the perovskite structure by the collective rotations of the constituent BO 6 octahedra alone, without the need for cation order. 8 Thus, for example, if the appropriate collective tilting and twisting arrangement of the BO 6 octahedra is induced into an A 3 B 2 O 7 , n = 2 Ruddlesden-Popper phase, 9,10 or an A'AB 2 O 7 , n = 2 Dion-Jacobson phase [11][12][13][14][15] the inversion symmetry of the aristotype structures can be broken to yield NCS materials.…”

Designing new ferroelectrics with a general strategy

“…11 To find more high-performance FEs, improper (including hybrid improper) FEs become an intense research field. 12 The typical example of the conventional improper FEs is hexagonal manganite YMnO 3 , 13 where the FE buckling (P mode) of the Y-O planes is induced by the non-polar MnO 5 polyhedra tilt (Q mode). 13,14 The free energy expansion in this system contains the coupling term (PQ 3 ) between the Q and P, indicating that the non-polar distortion Q must be reversed.…”