Tuning between Proper and Hybrid-Improper Mechanisms for Polar Behavior in CsLn₂Ti₂NbO₁₀ Dion-Jacobson Phases

Abstract

The Dion-Jacobson (DJ) family of perovskite-related materials have recently attracted interest due to their polar structures and properties, resulting from hybrid-improper mechanisms for ferroelectricity in n = 2 systems and from proper mechanisms in n = 3 CsBi 2 Ti 2 NbO 10 . We report here a combined experimental and computational study on analogous n = 3 Cs Ln 2 Ti 2 NbO 10 ( Ln = La, Nd) materials. Density functional theory calculations reveal the shallow energy landscape in these systems and give an understanding of the competing structural models suggested by neutron and electron diffraction studies. The structural disorder resulting from the shallow energy landscape breaks inversion symmetry at a local level, consistent with the observed second-harmonic generation. This study reveals the potential to tune between proper and hybrid-improper mechanisms by composition in the DJ family. The disorder and shallow energy landscape have implications for designing functional materials with properties reliant on competing low-energy phases such as relaxors and antiferroelectrics.

Recent developments in oxide ion conductors: focusing on Dion–Jacobson phases

“…121 In contrast to CsBi 2 Ti 2 NbO 10− δ , CsLa 2 Ti 2 NbO 10− δ was reported to be a single tetragonal phase with a space group of P 4/ mmm from 24 °C to 800 °C (Fig. 13(c)), 172,174 exhibiting no first-order phase transitions. Further examination on the detailed crystal structure of CsLa 2 Ti 2 NbO 10− δ is needed in the future, because reflections forbidden for the primitive tetragonal symmetry are observed.…”

“…Further examination on the detailed crystal structure of CsLa 2 Ti 2 NbO 10− δ is needed in the future, because reflections forbidden for the primitive tetragonal symmetry are observed. 174…”

“…Further examination on the detailed crystal structure of CsLa 2 Ti 2 NbO 10Àd is needed in the future, because reflections forbidden for the primitive tetragonal symmetry are observed. 174 CsM 2 Ti 2 NbO 10Àd oxides (M = Bi and La) have a layered perovskite structure with an inner perovskite layer M(Ti/ Nb1)O 3À3d/10 , two perovskite-like layers M 0.5 (Ti/Nb2)O 3À3d/10 , and a CsO 3À3d/10 rock-salt layer (Fig. 13).…”

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

“…In addition, polar RbBi 2 Ti 2 NbO 10 (S. G. Ima 2) and nonpolar CsBi 2 Ti 2 TaO 10 (S. G. P 4̅) oxides have also been confirmed by SHG and piezoelectricity measurements . Low permittivity values have been reported in the case of CsLn 2 Ti 2 NbO 10 (Ln = La, Nd) phases . We recently reported the incorporation of d 10 (Cd 2+ ) cations and the stabilization of potential ferroelectric-layered perovskites, A′Cd 2 Nb 3 O 10 (A′ = Rb, Cs) (S. G. Ima 2), based on structural refinements and SHG measurements …”

Perovskite-derived structure modulation in the iron sulfate family

“…This resembles the situation seen in the different families of more conventional layered perovskites, i.e., the Ruddlesden-Popper and Dion-Jacobson phases, for III and II, respectively. [35][36][37][38] The actual motif is shown in Fig. 3d, where it is clear that the vertex (Fe in B-site) of the upper layer (green shadow) lies right above the centre of the lower layer (blue shadow).…”