The First Room‐Temperature Ferroelectric Sn Insulator and Its Polarization Switching Kinetics

Abstract

Sr Sn O is the first room-temperature ferroelectric Sn insulator with switchable electric polarization. The ferroelastic twin domains are observed using a polarized optical microscope. The polarization hysteresis loop clearly demonstrates the ferroelectric property. Intriguing polarization switching kinetics are observed through an in situ poling process using a dark-field transmission electron microscopy technique.

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

“…The superlattice reflections and reflection splittings are also found in the SXRD pattern at 300 K. These features indicate the symmetry-lowering from tetragonal to orthorhombic with an enlarged unit cell metric, a p × a p × c p , where a p and c p are the pseudotetragonal 2 2 lattice parameters. The larger cell was also reported in the previous works 36,73 . Note that no impurity phases were detected from either ND or SXRD data.…”

“…The roomtemperature structure of Sr 3 Sn 2 O 7 was previously reported by laboratory XRD and dark-field transmission electron microscopy 36 . We revisit the crystal structure at 300 K by using high-resolution ND, which provides much more accurate oxygen parameters than those obtained from XRD.…”

“…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.…”

Ferroelectric Sr3Zr2O7: Competition between Hybrid Improper Ferroelectric and Antiferroelectric Mechanisms

“…The net remnant electric polarization and coercive electric field are ≈0.3 µC cm −2 and ≈150 kV cm −1 , respectively. The polarization value is comparable to those of polycrystalline Ca 3 Ti 2 O 7 (0.6 µC cm −2 ) and Sr 3 Sn 2 O 7 (0.25 µC cm −2 ), but it is one order of magnitude smaller than that obtained from our DFT calculations (6.75 µC cm −2 ). The smaller polarization value compared to the calculated one is expected from the polycrystalline nature.…”

“…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.…”