Hidden Antipolar Order Parameter and Entangled Néel-Type Charged Domain Walls in Hybrid Improper Ferroelectrics

Abstract

Hybrid improper ferroelectricity (HIF) denotes a new class of polar instability by the mixture of two octahedral-distortion modes and can feature the coexistence of abundant head-to-head and tail-to-tail polar domains, of which the domain walls tend to be charged due to the respective screening charges with an opposite sign. However, no such coexisting carriers are available in the materials. Using group-theoretical, microscopic, and spectroscopic analyses, we establish the existence of a hidden antipolar order parameter in model HIF (Ca,Sr)_{3}Ti_{2}O_{7} by the condensation of a weak, previously unnoticed antipolar lattice instability, turning the order-parameter spaces to be multicomponent with the distinct polar-antipolar intertwining and accompanied formation of Néel-type twinlike antipolar domain walls (few nanometers) between the head-to-head and tail-to-tail domains. The finite-width Néel walls and correlated domain topology inherently lift the polar divergences between the domains, casting an emergent exemplification of charged domain-wall screening by an antipolar ingredient.

Spatially resolved steady-state negative capacitance

“…This is what makes it possible to estimate the local energy density and therefore the local permittivity. Only mapping out the local polarization [30][31][32][33] would not be enough to probe local permittivity. It is also important to note that the vortices lead to a full rotation of the polarization from up to down within just 4 nm (see Fig.…”

Physics and applications of charged domain walls

“…22 Presently, high-resolution and scanning TEM techniques allow for observation of individual atomic displacements and, hence, give information about the internal CDW structure. With these techniques, CDWs were documented in single crystals of LiNbO 3 , 27 YMnO 3 , 28 and (Ca,Sr) 3 Ti 2 O 7 , 29,30 thin films of BiFeO 3 , 8,[31][32][33] PbTiO 3 , 34 and PZT, [35][36][37][38][39][40] and ceramics of BiFeO 3 , 41 (K,Na)NbO 3 , 42 TmMnO 3 , 43 and LuMnO 3 . 43 TEM techniques, supplemented by analyses of the energy losses of electrons (EELS) were employed recently to detect elemental components of the material in the vicinity of CDWs.…”

“…43 TEM techniques, supplemented by analyses of the energy losses of electrons (EELS) were employed recently to detect elemental components of the material in the vicinity of CDWs. 30,[38][39][40][41] Other methods were also in use: scanning electron microscopy for observations of the intersections of CDWs with etched surfaces of LiNbO 3 crystals, 44 high-resolution X-ray photoemission electron microscopy to visualize and characterize conducting DWs in ErMnO 3 , 45 low-energy electron microscopy (electron backscattering) to image CDWs in LiNbO 3 crystals. 46 High-resolution TEM studies have provided crucial information about the widths of domain walls.…”

Enhanced hybrid improper ferroelectricity in Fe/Nb cosubstituted Ca3Mn2O7 ceramics

“…12,40,43,50 The linear fitting results are depicted by red dash lines with the critical τ value [Color figure can be viewed at wileyonlinelibrary.com] there are the rather simple antiparallel 180°-type domain configurations in Ca 3 [Mn 0.5 (Fe 0.5 Nb 0.5 ) 0.5 ] 2 O 7 , and this is similar to the situation in Ca 3 Ti 2 O 7 . [43][44][45] The previous work has also demonstrated that engineering the phase transition by chemical substitution is a useful method to modulate the domain configurations in ferroelectrics. 46,47 The 180°-type ferroelectric domains are relevant to the low-energy polarization switching path for Ca 3 Ti 2 O 7 , which is via a local antipolar stacking domain wall.…”