Emergent Noncentrosymmetry and Piezoelectricity Driven by Oxygen Octahedral Rotations in n = 2 Dion–Jacobson Phase Layer Perovskites

Abstract

The loss of centrosymmetry via oxygen octahedral rotations is demonstrated in the n = 2 Dion-Jacobson family of layered oxide perovskites, A′LaB 2 O 7 (A′ = Rb, Cs; B = Nb, Ta). Ab initio density functional theory calculations predict that all four materials should adopt polar space groups, in contrast to the results of previous experimental studies that have assigned these materials to the centrosymmetric P4/ mmm space group. Optical second harmonic generation experiments confi rm the presence of a noncentrosymmetric phase at ambient temperature. Piezoresponse force microscopy experiments also show that this phase is piezoelectric. To elucidate the symmetry-breaking and assign the appropriate space groups, the crystal structure of CsLaNb 2 O 7 is refi ned as a function of temperature from synchrotron X-ray diffraction data. Above 550 K, CsLaNb 2 O 7 adopts the previously determined centrosymmetric P4/ mmm space group. Between 550 and 350 K, the symmetry is lowered to the noncentrosymmetric space group A mm 2. Below 350 K, additional symmetry lowering is observed as peak splitting, but the space group cannot be unambiguously identifi ed.

Ferroelectric Sr3Zr2O7: Competition between Hybrid Improper Ferroelectric and Antiferroelectric Mechanisms

“…Here, we demonstrate that ferroelectricity emerges by layering nonpolar perovskite SrZrO 3 with nonpolar rock salt‐structured SrO to form the n = 2 Ruddlesden–Popper (RP) A 3 B 2 O 7 structure . We show that Sr 3 Zr 2 O 7 is a hybrid improper ferroelectric (HIF), whereby ferroelectricity with an electric polarization P occurs from a combination of two nonpolar lattice modes, Q 1 and Q 2 , interacting through a trilinear term of the form PQ 1 Q 2 .…”

New Type of 2D Perovskites with Alternating Cations in the Interlayer Space, (C(NH2)3)(CH3NH3)nPbnI3n+1: Structure, Properties, and Photovoltaic Performance

“…The (½, 0) case results in an 'eclipsed' configuration of the layers along the stacking direction. The structural chemistry of the DJ oxide perovskites has recently undergone a resurgence after the predictions that such structures can exhibit ferroelectricity [31][32] using certain material design principles. 33 Despite the abundance of DJ perovskites in oxides, 34 this structural type is hitherto unknown in the hybrid halide perovskites.…”

Phase Transition Behavior of the Layered Perovskite CsBi0.6La0.4Nb2O7: A Hybrid Improper Ferroelectric

“…Strayer et al [12] listed all models corresponding to the simple combinations of octahedral tilts for this structural family (see Supplementary information in Reference [12]). Specifically, the definition of simple combinations here means that there are four distinct octahedral tilts modes to be considered, viz.…”

“…These ideas have been described in more detail by Benedek et al [3,4]. Although the a − a − c + tilt system is predicted to be a stable option for DJ phases of the type AA'B 2 O 7 , recent experimental work has shown that other related polymorphs are possible, and a tilt system a − b 0 c + , in polar space group Amm2, has been reported in CsLaNb 2 O 7 in the range 350 < T < 550 K [12] (curiously an earlier single crystal X-ray study of CsLaNb 2 O 7 reported the adoption of the aristotype tetragonal structure, P4/mmm at 296 K [13]). Moreover, a recent experimental and theoretical study of the triple-layer DJ phase CsBi 2 Ti 2 NbO 10 has suggested that a proper rather than improper mechanism drives the polarity of the ambient temperature phase [14].…”