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

Abstract

Abstract:The phase behavior of the layered perovskite CsBi 0.6 La 0.4 Nb 2 O 7 , of the Dion-Jacobson family, has been studied by high-resolution powder neutron diffraction between the temperatures of 25 < T < 850 • C. At ambient temperature, this material adopts the polar space group P2 1 am; this represents an example of hybrid improper ferroelectricity caused by the interaction of two distinct octahedral tilt modes. Within the limits of our data resolution, the thermal evolution of the crystal structure is consistent with a first-order transition between 700 and 750 • C, with both tilt modes vanishing simultaneously, leading to the aristotype space group P4/mmm. This apparent "avalanche transition" behavior resembles that seen in the related Aurivillius phase SrBi 2 Nb 2 O 9 .

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 . The role played by the two nonpolar structural distortions—oxygen octahedral rotations (OOR, out‐of‐plane rotational modes) and oxygen octahedral tilts (OOT, in‐plane rotational modes)—in stabilizing ferroelectricity is determined using a combination of synchrotron X‐ray diffraction (SXRD), neutron powder diffraction (NPD), optical second harmonic generation (SHG), and first‐principles density functional theory (DFT) calculations.…”

Hybrid Improper Ferroelectricity in (Sr,Ca)3Sn2O7 and Beyond: Universal Relationship between Ferroelectric Transition Temperature and Tolerance Factor in n = 2 Ruddlesden–Popper Phases

“…This form of ferroelectricity should be prevalent in perovskiterelated materials because the octahedral rotations/tilts are ubiquitous structural distortions 21 (which are primarily of geometric origin and are driven by the size mismatch of the constituent ions). Indeed, a number of layered perovskites have been proposed as potential hybrid improper ferroelectrics through the integrated approach of symmetry arguments and first-principles calculations [22][23][24][25][26][27][28][29][30] , some of which have been experimentally confirmed to exhibit switchable polarization [31][32][33][34][35][36][37][38] , or at least crystalize in polar structures [39][40][41][42][43][44][45][46] . One can now utilize group theory to elucidate symmetry breaking caused by given distortions and identify whether their combinations result in a polar symmetry, and then the ferroelectricity.…”

“…Recent theoretical work has developed a new mechanism for achieving a ferroelectric state, whereby two nonpolar structural distortions, commonly rotations or tilts of BO 6 octahedra, cooperatively give rise to a net polar symmetry and induce a macroscopic polarization as a byproduct. − This novel mechanism, called hybrid improper ferroelectricity, , is active in layered perovskite oxides like Ruddlesden–Popper (RP) , and Dion–Jacobson phases and has opened a new avenue for the rational design of ferroelectric materials. − This form of ferroelectricity, of geometric origin, should be prevalent in perovskite-related compounds, because the octahedral rotations/tilts are ubiquitous structural distortions (which are predominantly driven by the size mismatch of the constituent ions). Indeed, a number of layered perovskites have been proposed as potential hybrid improper ferroelectrics through the integrated approach of symmetry arguments and first-principles calculations, − some of which have been experimentally confirmed to exhibit switchable polarization − or at least crystallize in polar structures. − One can now utilize group theory to elucidate symmetry breaking caused by given distortions and identify whether their combinations result in a polar symmetry and then the ferroelectricity. For real technological applications, on the other hand, it is important to evaluate key parameters of ferroelectrics, including polarization, coercive field, and Curie temperature ( T C ).…”

Ferroelectricity of Dion-Jacobson layered perovskites CsNdNb$_2$O$_7$ and RbNdNb$_2$O$_7$

“…The value of ǫ ′ r at room temperature in our samples are comparable to those in other n = 2 DJ niobates (ǫ ′ r = 10−60). 23,24,32,37 IV. CONCLUSION…”