Domain topology and domain switching kinetics in a hybrid improper ferroelectric

Abstract

Charged polar interfaces such as charged ferroelectric walls or heterostructured interfaces of ZnO/(Zn,Mg)O and LaAlO3/SrTiO3, across which the normal component of electric polarization changes suddenly, can host large two-dimensional conduction. Charged ferroelectric walls, which are energetically unfavourable in general, were found to be mysteriously abundant in hybrid improper ferroelectric (Ca,Sr)3Ti2O7 crystals. From the exploration of antiphase boundaries in bilayer-perovskites, here we discover that each of four polarization-direction states is degenerate with two antiphase domains, and these eight structural variants form a Z4 × Z2 domain structure with Z3 vortices and five distinct types of domain walls, whose topology is directly relevant to the presence of abundant charged walls. We also discover a zipper-like nature of antiphase boundaries, which are the reversible creation/annihilation centres of pairs of two types of ferroelectric walls (and also Z3-vortex pairs) in 90° and 180° polarization switching. Our results demonstrate the unexpectedly rich nature of hybrid improper ferroelectricity.

Domains and ferroelectric switching pathways inCa3Ti2O7from first principles

“…Our finding that this path's intrinsic energy barrier is the same regardless of whether η and η X + 2 , change across the wall. 17 The antipolar path, shown in Fig. 3(a), 5(a), describes switching at the stacking domain wall introduced in Fig.…”

“…The eight polar domains, and a complex network of domain walls between them, have already been detected experimentally. 17,18 An additional type of domain wall that should be present in samples is what we call a "stacking domain wall," illustrated in Fig. 2(c): an interface between a polar domain with polarization P stacked on top of (along [001]) a polar domain with polarization −P.…”

“…10 Recently, it was experimentally demonstrated in the n=2 RP compound Ca 3 Ti 2 O 7 , 16 and a complex domain structure was observed. 17,18 The observation of an unexpectedly low switching barrier and abundant structural domains suggests that these domains may be critical to ferroelectric switching, but the precise pathway by which the polarization reverses remains an open question.…”

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

“…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 . Very recently, employing pulsed laser deposition, Li et al deposited CTO thin films onto SrTiO 3 single‐crystal substrates and found that CTO film exhibits a coercive field of 5 kV/cm at a temperature of 2 K. While the coercive field of bulk CTO single crystal is around 120 kV/cm .…”

Aperiodic topological order in the domain configurations of functional materials

“…These functional materials can exhibit different orientations of the directional orders, thus spatially varying vectors (order parameters) are accommodated through delicate vortex structures. These emergent vortex-like domain configurations in real space are essential for the understanding of the energy hierarchy of different types of domain boundaries 38,42,43 . Another milestone was the discovery of emergent physical propertiesentirely distinct from those of the domainsat the domain boundaries.…”