Domains and ferroelectric switching pathways inCa3Ti2O7from first principles

Abstract

Hybrid improper ferroelectricity, where an electrical polarization can be induced via a trilinear coupling to two non-polar structural distortions of different symmetry, has recently been experimentally demonstrated for the first time in the n=2 Ruddlesden-Popper compound Ca3Ti2O7. In this paper we use group theoretic methods and first-principles calculations to identify possible ferroelectric switching pathways in Ca3Ti2O7. We identify low-energy paths that reverse the polarization direction by switching via an orthorhombic twin domain, or via an antipolar structure. We also introduce a chemically intuitive set of local order parameters to give insight into how these paths are relevant to switching nucleated at domain walls. Our findings suggest that switching may proceed via more than one mechanism in this material.

Infrared nano-spectroscopy of ferroelastic domain walls in hybrid improper ferroelectric Ca3Ti2O7

“…1(a)] decomposes into three distinct distortions: an out-of-phase octahedral tilt (a − a − c 0 in Glazer notation [40]) that transforms like the X − 3 irreducible representation of the high-symmetry prototype structure I4/mmm, an in-phase octahedral rotation (a 0 a 0 c + in Glazer notation) that transforms as X + 2 , and a polar distortion that transforms like Γ − 5 . Each distortion is represented by a structural order parameter with amplitude Q and phase φ [24]. For the chosen setting of the orthorhombic axes relative to the tetragonal axes the twin domains are labelled by different settings of the space group symbol: A2 1 am (twin A) and Bb2 1 m (twin B).…”

“…Ferroics also have naturally occurring heterogeneities in the form of domains and domain walls [8][9][10][11][12][13][14][15][16][17][18]. This is especially true for Ca 3 Ti 2 O 7 , a hybrid improper ferroelectric [19,20] where the polarization arises from a trilinear coupling mechanism [21][22][23] and abundant charged domain walls have been observed [19,20,24]. Atomic-and piezo-force imaging reveal the different orientations of directional order parameters and domain wall character, providing a physical playground for graph theory.…”

“…Atomic-and piezo-force imaging reveal the different orientations of directional order parameters and domain wall character, providing a physical playground for graph theory. Like other counterpart materials [16,17], ferroelectric domain walls in Ca 3 Ti 2 O 7 are anisotropic and more conducting than their surroundings -although the domains themselves are insulating [19,20,24]. Theoretical modeling and electron diffraction experiments recently revealed that polarization rotates across the ferroelectric walls in a manner that is more Néel-than Ising-like [25].…”

“…Ferroelastic walls in Ca 3 Ti 2 O 7 are linear and separate different structural twin domains [20]. Because the boundaries connect domains with different spontaneous strain states, mechanical compatibility conditions determine their orientation [24,26,27]. These ferroelastic walls are also 90 • ferroelectric walls.…”

Polarization switching dynamics and switchable diode effect in hybrid improper ferroelectric Ca3Ti2O7 ceramics

“…Moreover, optical spectroscopy and band gap analysis of single crystals CTO samples have been investigated through theoretically calculation and experimental verification . Nowadnick et al used group theory methods and first‐principles calculations to investigate the possible ferroelectric switching pathway in CTO with low‐energy barriers via an orthorhombic twin domain, an antipolar stacking domain, or a rhombohedral‐like phase . In a report by Huang et al, the high‐energy antiphase boundaries and ferroelastic tilting and rotation domain walls were found to dominate the nucleation controlled kinetics of polarization flipping in a CTO single crystal .…”