Polarization Evolution in Morphology-Engineered Freestanding Single-Crystalline BaTiO₃ Membranes

Abstract

The ferroelectric properties in single-crystalline perovskite oxide can be engineered by strain, which is conventionally achieved via interfacial lattice mismatch between a substrate and an epitaxial ferroelectric overlayer. To realize the continuous tuning of strain in ferroelectrics and explore its functionality in the morphology of freestanding membranes, in this study, we have performed a comprehensive investigation on flexible BaTiO3 (BTO) membranes with varied wrinkle patterns. The freestanding BTO membranes can be obtained from the rigid epitaxial heterostructures by water-dissolving the Sr3Al2O6 (SAO) sacrificial interlayer, and the different varied wrinkle patterns are gained by tailoring the mixing ratios of polydimethylsiloxane (PDMS) supporters following the thermal strain and elastic theory. Then, we have found that the spontaneous polarization switching behavior of freestanding wrinkled BTO membranes is curvature-dependent, and the coercive field of BTO can be reduced by 15.03% once it suffers ∼1.34% tensile and compressive strain. Our study provides a convenient and robust approach to morphological changes of ferroelectrics and holds great promising potential for applications in flexible oxide electronics.

Extreme Enhanced Curie Temperature and Perpendicular Exchange Bias in Freestanding Ferromagnetic Superlattices

“…On the basis of the great enhancement of H eb in SL with n = 4 after releasing from the STO substrate, we systematically study the ferromagnetic properties of SLs in different states, as shown in Figure 4a. By controlling the transfer process, 37 we can fabricate freestanding SLs with two typical morphologies: flat and wrinkle surfaces (Figure S7 of the Supporting Information). The exchange bias field and coercive field of freestanding samples are much larger than those of rigid samples, while M s of freestanding samples become smaller.…”

Strain‐Induced Toroidal Polar States in Wrinkled Ferroelectric Polymer by Phase‐Field Simulations

“…Certain external stimuli such as mechanical force [31,32] and thermal perturbation [33,34] can induce a buckling-instability mode in thin film systems, resulting in out-of-plane (OOP) deformation. Recent advancements in thin film fabrication have led to the discovery of peculiar instability patterns in flexible ferroelectric thin films, [35][36][37][38] including the regular concentric surface wrinkles ob-served in ferroelectric P(VDF-TrFE) polymer. [27] The concentric "target" structure at the center of the wrinkles features a circular convex deformation, with continuous undulations spreading outwards in a "wave" shape.…”

“…The modulation of the morphology of wrinkles through adjustments to the thickness of the film system, material parameters, or external conditions has been theoretically and experimentally demonstrated to influence the strain state within wrinkles and the distribution of domain structures in ferroelectric films. [20,35,37,38] exhibits three ferroelectric phase patterns, marked by different symbols and colors, and the background strain distribution map shows the strain ratio between the outermost valley i-position and peak ii-position in Figure 1a. At small wavelengths, the wrinkle wavelength and amplitude are approximately equal, leading to a large strain ratio between the valley and peak.…”

“…The modulation of the morphology of wrinkles through adjustments to the thickness of the film system, material parameters, or external conditions has been theoretically and experimentally demonstrated to influence the strain state within wrinkles and the distribution of domain structures in ferroelectric films. [ 20,35,37,38 ] Figure 1b displays the wavelength‐amplitude phase diagram of these wrinkles obtained through morphological engineering. The diagram exhibits three ferroelectric phase patterns, marked by different symbols and colors, and the background strain distribution map shows the strain ratio between the outermost valley i ‐position and peak ii ‐position in Figure 1a.…”

Electrode Effect on Ferroelectricity in Free-Standing Membranes of PbZr0.2Ti0.8O3

“…Free-standing ferroelectric oxide membranes have attracted extensive research interests recently as they provide a versatile playground to explore low dimensional ferroelectricity and corrugation-enabled flexoelectricity. − Being free of the clamping effect from the epitaxial substrates, crystalline oxide membranes based on PbTiO 3 , Pb­(Zr,Ti)­O 3 , BaTiO 3 , and their heterostructures exhibit various exotic properties, such as slow domain wall (DW) motion, unconventional electromechanical coupling, , enhanced piezoelectric coefficient, and bubble domain formation , that can be reversibly switched by an electric field . The flexible nature also facilities strain engineering via stretchable or corrugated base layers, which leads to substantial modulation of their bandgap, coercive field ( E c ), , dielectric permittivity, ferroelastic domains, and photovoltaic response . Unlike epitaxial complex oxide heterostructures, whose preparation imposes stringent requirements for the structural similarity between the constituent layers, ferroelectric oxide membranes can be easily integrated with the mainstream Si platform ,, and two-dimensional (2D) van der Waals materials , for developing flexible nanoelectronics, optics, and energy applications. ,, It also possesses distinct advantages compared with ferroelectric polymers and 2D van der Waals ferroelectrics for its high Curie temperature ( T C ), large polarization ( P ), and scalable synthesis.…”