Ferroelectric vortex domains in strained ferroelectric membranes have recently garnered significant scientific interest. However, understanding domain evolution under varying strain conditions has been challenging due to experimental limitations in generating precise strain gradients. Our research introduces a novel approach to strain gradient manipulation in single-layer ferroelectric membranes. By experimentally investigating freestanding bent PbTiO3 membranes, we directly observed ferroelectric vortex-like domains. As bending strain increases, c-domains progressively transition to c- and a-mixed domains, with vortex-like structures emerging at a critical bending strain of 5.2%. Complementary atomistic simulations confirm that strain gradients trigger domain formation through continuous dipole rotation at the domain boundaries. This work unveils a strategy for generating sophisticated ferroelectric domain architectures and its mechanism, offering promising pathways for engineering novel polar textures in next-generation electronic devices.

To combat microbiologically influenced corrosion of titanium alloy components in extreme marine environments, a NbTiZrCrCu high-entropy film was developed via magnetron sputtering. The sputtering bias voltage was adjusted to optimize the microstructure, thereby enhancing mechanical properties and corrosion performance in 3.5 wt% NaCl solution. The NbTiZrCrCu film deposited at a bias voltage of -150 V exhibited a nanostructured high-entropy metallic glass, yielding a high hardness (similar to 23.7 GPa). This hierarchical structure resulted in significantly higher impedance and a lower current density (i(corr) similar to 6.45 x 10(-8) Acm(-2)). Mott-Schottky analysis revealed that the passive film exhibited n-type semiconductor characteristics, and the nanostructure promoted the formation of a more stable passive film. XPS and Pourbaix diagrams confirmed the presence of metallic Cu-0 and the chromium-rich oxides (Cr2O3, CuCrO2), which collectively contributed to the enhanced density and stability of the passive film. Furthermore, the incorporation of Cu endowed the NbTiZrCrCu high-entropy metallic glass films with significant antibacterial activity, thus mitigating microbiologically influenced corrosion and providing effective protection for marine equipment.

Molecular dynamics simulations of the well-known ferroelastic material, CaTiO3, reproduce the experimentally observed bulk and wall properties. We show that Landau–Ginzburg potentials are an excellent approach to estimate bulk properties like the phase diagram and the ferroelastic bulk deformation. Most importantly, the known ferroelastic wall properties are reproduced and predicted, when unknown. The main emerging property is the wall polarization Pwall, which is as large as some of the best ferroelectric bulk materials. The temperature dependence of Pwall shows a near-linear decay from room temperature to the transition point. We argue that the most promising experimental technique to test our results is the measurement of the second harmonic generation of domain walls over large temperature intervals.

Ferroelastic domain walls (DWs), traditionally considered functionally restricted due to antagonistic structural order parameters, are revealed to host electrically switchable polar states through synergistic flexoelectric and biquadratic coupling mechanisms. Using large-scale molecular dynamics (MD) simulations on orthorhombic Pnma CaTiO3 (CTO) with (110)-type DWs, this study demonstrates that a thermally-driven structural phase transition within DWs is related to the reduced out-of-phase a-TiO6 octahedral tilt (Glazer tilt notation a-a-c+) model, activating an achiral-to-chiral polar transition. The DW structural phase transition occurs more than 300 K below the bulk transitions, and the z-axis ([001]pc) polar component becomes switchable at temperatures above 1100 K. Electric-field-driven DW switching, mediated by octahedral tilt suppression, DW flexoelectricity and biquadratic coupling, manifests volatile, antiferroelectric-like double hysteresis loops. At room temperature, a critical field of '3.6 x 104 kV/cm triggers polarization reversal by suppressing octahedral tilts both in the DWs and bulk, while thermal broadening of DWs at elevated temperatures (e.g., 1000 K) reduces strain gradients and lowers the coercive field by '42%, enhancing switchability. These results reveal the dual role of DWs as both structural interfaces and active functional elements, offering pathways to manipulate nanoscale polar textures and engineer novel storage/memory/piezoelectric devices leveraging tunable domain-wall functionalities.

Ferroelastic materials (materials with switchable spontaneous strain) often are centrosymmetric, but their domain walls are always polar, as their internal strain gradients cause polarization via flexoelectricity. This polarization is generally not switchable by an external electric field, because reversing the domain wall polarity would require reversing the strain gradient, which in turn would require switching the spontaneous strain of the adjacent domains, destroying the domain wall in the process. However, domain wall polarization can also arise from biquadratic coupling between polar and non-polar order parameters (e.g. octahedral tilts in perovskites). Such coupling is independent of the sign of the polarization and thus allows switching between +P and -P. In this work, we seek to answer the question of whether the polarization of domain walls in ferroelastic perovskites is switchable, as per the symmetric biquadratic term, or non-switchable due to the unipolar flexoelectric bias. Using perovskite calcium titanate (CaTiO3) as a paradigm, molecular dynamics calculations indicate that high electric fields broaden the ferroelastic domain walls, thereby reducing flexoelectricity (as the domain wall strain gradient is inversely proportional to the wall width), eventually enabling switching. The polarization switching, however, is not ferroelectric-like with a simple hysteresis loop, but antiferroelectric-like with a double hysteresis loop. Ferroelastic domain walls thus behave as functional antiferroelectric elements, and also as nucleation points for a bulk phase transition to a polar state.

Ferroelastic domain walls (DWs) offer a unique platform for engineering dynamic magnetism through controlled symmetry breaking. Here, we demonstrate deterministic magnetic field generation in reconfigurable DW networks using nanocavity-patterned ferroelastic matrices. Atomistic simulations reveal that propagating kinks along polar twin walls induce strain-gradient polarization and displacement current vortices, producing localized magnetic fields (similar to 10-7-10-6 T) via flexoelectric coupling. These fields exhibit scale-free avalanche dynamics with universal power-law exponents, mirroring mechanical energy release events during kink nucleation and depinning transitions. To overcome intrinsic disorder limitations, we mimic lithographically defined nanocavities that guide orthogonal DW propagation with cycle-to-cycle reproducibility, achieving local field enhancement compared to stochastic networks. Scanning superconducting quantum interference device (SQUID) microscopy on SrTiO3 detects out-of-plane magnetic signatures (similar to 10-7T) persisting for milliseconds, quantitatively matching simulations and indicating extended lifetimes. Crucially, kink velocity-dependent dynamic magnetism is established through synchronized magnetic and energy jerk profiles, resolving the atomic-scale mechanism linking DW motion to emergent magnetism. This work establishes a multiscale framework for defect-engineered ferroelastic materials, bridging atomic-scale polarization dynamics, mesoscale DW circuit design, and macroscale nonvolatile memory functionality. By decoupling magnetic responses from intrinsic disorder, our approach advances ferroelastic DW networks toward practical applications in strain-programmable spintronics and ultrahigh-density racetrack memories.

Abstract The ultrahigh flexibility and elasticity achieved in freestanding single-crystalline ferroelectric oxide membranes have attracted much attention recently. However, for antiferroelectric oxides, the flexibility limit and fundamental mechanism in their freestanding membranes are still not explored clearly. Here, we successfully fabricate freestanding single-crystalline PbZrO3 membranes by a water-soluble sacrificial layer technique. They exhibit good antiferroelectricity and have a commensurate/incommensurate modulated microstructure. Moreover, they also have good shape recoverability when bending with a small radius of curvature (about 2.4 μm for the thickness of 120 nm), corresponding to a bending strain of 2.5%. They could tolerate a maximum bending strain as large as 3.5%, far beyond their bulk counterpart. Our atomistic simulations reveal that this remarkable flexibility originates from the antiferroelectric-ferroelectric phase transition with the aid of polarization rotation. This study not only suggests the mechanism of antiferroelectric oxides to achieve high flexibility but also paves the way for potential applications in flexible electronics.

Neuromorphic computation is based on memristors, which function equivalently to neurons in brain structures. These memristors can be made more efficient and tailored to neuromorphic devices by using ferroelastic domain boundaries as fast diffusion paths for ionic conduction, such as of oxygen, sodium, or lithium. In this paper, we show that the local memristor generates a second, unexpected feature, namely, weak magnetic fields that emerge from moving ferroelastic needle domains and vortices. The vortices appear near ferroelastic “junctions” that are common when the external stimulus is a combination of electric fields and structural phase transitions. Many ferroelastic materials show such phase transitions near room temperatures so that device applications display a “multiferroic” scenario where the memristor is driven electrically and read magnetically. Our computer simulation study of an elastic spring model suggests magnetic fields in the order of 10−7 T, which opens the way for a fundamentally new way of running neuromorphic devices. The magnetism in such devices emerges entirely from intrinsic displacement currents and not from any intrinsic magnetism of the material.

The elastic interaction between kinks (and antikinks) within domain walls plays a pivotal role in shaping the domain structure, and their dynamics. In bulk materials, kinks interact as elastic monopoles, dependent on the distance between walls, and typically characterised by a rigid and straight domain configuration. In this work we investigate the evolution of the domain structure as the sample size decreases, by means of in-situ heating techniques on free-standing samples. A significant transformation is observed: domain walls exhibit pronounced curvature, accompanied by an increase in both domain wall and junction density. This transformation is attributed to the pronounced influence of kinks, inducing sample warping, where 'dipole dipole' interactions are dominant. Moreover, we experimentally identify a critical thickness range that delineates a cross-over between the monopolar and dipolar regimens and corroborated this by detailed atomic simulations. These findings are relevant for in-situ TEM studies and for the development of novel devices based on free-standing ferroic thin films and nanomaterials.

The possibility to use ferroelastic materials as components of neuromorphic devices is discussed. They can be used as local memristors with the advantage that ionic transport is constraint to twin boundaries where ionic diffusion is much faster than in the bulk and does not leak into adjacent domains. It is shown that nano-scale ferroelastic memristors can contain a multitude of domain walls. These domain walls interact by strain fields where the interactions near surfaces are fundamentally different from bulk materials. We show that surface relaxations (∼image forces) are curtailed to short range dipolar interactions which decay as 1/d2 where d is the distance between domain walls. In bigger samples such interactions are long ranging with 1/d. The cross-over regime is typically in the range of some 200–1500 nm using a simple spring interaction model.

Precursor elastic effects are investigated in a displacive anharmonic spring model and shown to extend greatly into the paraelastic phase. Weak precursor effects can be detected near 2T(tr), where T-tr is the ferroelastic transition temperature. The precursor effects become strong at T<1.7T(tr.) Two effects were identified in our two-dimensional model: the symmetry-breaking strain e(3) (epsilon(xy)) leads to softening of the elastic modulus C-33, while the nonsymmetry-breaking strain e(1)+e(2) (epsilon(xx)+epsilon(yy)) leads to hardening of C11. The strain e(3 )is proportional to the order parameter and scales as |e(1)+e(2)| similar to e(23). The temperature evolutions of the elastic moduli are surprisingly well described by power laws and Vogel-Fulcher equations. The power-law exponents are similar to-0.5 for Delta C-33 and similar to-1 for Delta C-11, Delta(C-11+C-12) and Delta(C-11-C-12). The Vogel-Fulcher temperatures are very similar, while the Vogel-Fulcher energies differ between the excess elastic moduli. The origin of the precursor effect is the evolution of short-range order in the paraelastic phase which gives rise to a characteristic local nanostructure. In the case of the symmetry-breaking strain, this microstructure resembles dynamical twinning patterns corresponding to the ferroelastic nanostructure, which weakens the material. In the case of the nonsymmetry-breaking strain, we find density fluctuations which make the material harder.

The effects of (Ho, Nb) co-doping on the electrical, luminescent properties and electronic structure of Bi0.5(Na0.82K0.18)0.5Ti1-x(Ho0.5Nb0.5)xO3 (x = 0, 0.010, 0.015, 0.020, 0.025, and 0.030, abbreviated as BNKTxHN) ceramics were investigated. XRD analysis showed that Ho3+ and Nb5+ ions completely entered the crystal structure of BNT-based ceramics, forming a stable perovskite structure. SEM confirmed the polycrystalline nature and relatively uniform grain structure of the samples. The doping of (Ho, Nb) destroyed the long-range ferroelectricity of BNT-based ceramics, resulting in the transition from ferroelectric phase to relaxor ferroelectric phase. The maximum unipolar strain of 0.32% was obtained by introducing (Ho, Nb) with a concentration of x = 0.020. Under excitation at 453 nm, a strong green emission peak appears at 550 nm, corresponding to the energy level transition of 5S2 -> 5I8, while the weak red emission centered at 658 nm is due to the energy level transition from 5F5 -> 5I8. As the amount of doping increases, the luminous intensity first increases and then decreases. The first-principle method based on density functional theory was used to calculate the energy band structure and density of the system states. The calculated results show that the band gap width (Eg) decreases with the increase of doping amount, and the electron cloud density distribution of the energy level orbit is very stable. Reducing the band gap makes it easier for electrons to absorb photon energy, which may explain the micro-mechanism of changing luminous intensity.

In thin samples, such as membranes, kinks inside ferroelastic domain walls interact through “dipolar” interactions following a 1/d 2 decay, where d is the distance between the walls. Simultaneously, the samples relax by bending. Bending is not possible in thick samples or can be suppressed in thin films deposited on a rigid substrate. In these cases, wall-wall interactions decay as 1/d , as monopoles would do. In free-standing samples, we show a wide crossover regime between “dipolar” 1/d 2 interactions and “monopolar” 1/d interactions. The surfaces of all samples show characteristic relaxation patterns near the kink, which consists of ridges and valleys. We identify the sample bending as the relevant image force that emanates from kinks inside walls in thin samples. When samples are prevented from bending by being attached to a substrate, the dipolar force is replaced by “monopolar” forces, even in thin samples. These results are important for transmission electron microscopy imaging, where the typical sample size is in the dipolar range while it is in the monopolar range for the bulk.

(Bi0.5Na0.5)0.935Ba0.065(Zn1/3Nb2/3)xTi(1−x)O3-0.005Er (BNBT-xZN-Er) multifunctional ceramics were prepared by a traditional solid-phase reaction method. The ferroelectric, dielectric, and photoluminescence properties of BNBT-xZN-Er ceramics doped with different (Zn1/3Nb2/3)4+ complex ions were systematically investigated. The results emerge that (Zn1/3Nb2/3)4+ can be completely diffused in the BNBT-xZN-Er ceramics lattice. With the addition of complex ions, the long-range ferroelectric order of BNBT-xZN-Er ceramics was significantly disrupted, and the electric field-induced strain responses was promoted. The maximum bipolar strain of 0.35% was obtained by introducing (Zn1/3Nb2/3)4+ with a concentration of x = 0.0100, corresponding to d33* (Smax/Emax) of 500 pm/V. Two dielectric anomaly peaks emerge at TR−E and Tm due to the transformation of the phase. Additionally, the ceramics have bright up-conversion photoluminescence properties under a 980 nm laser light source, exhibiting intense green emission bands at 526 and 547 nm. The results illustrate that the BNBT-xZn-Er ceramics exhibit excellent ferroelectric properties and also obtain bright up-conversion green photoluminescence properties.

Kinks interact with other kinks and antikinks elastically in ferroelastic domain walls and other interfaces in ferroic materials. In thin samples, suitable for transmission electron-microscopy, the interaction is purely dipolar with no indication of monopolar or higher order contributions. Kinks and antikinks attract each other while kink-kink interactions are repulsive. When the kinks are situated in two parallel twin walls, they display the same attraction/repulsion. We argue that this interaction constitutes, part or all, the elusive wall-wall interaction in ferroelastics. The dipolar interactions over distances d between the kinks and between walls decay as 1/d2 when the samples have some nanoscale size. Nanoscale samples bend and tilt when kinks are introduced with typical bent regions of some 1 nm and tilt angles of some 1.2 degrees. Multiple kinks will enhance the effect systematically and bent and modulated twin walls are predicted.

(Bi 0.5 Na 0.5 ) 0.935 Ba 0.065 (Zn 1/3 Nb 2/3 ) x Ti (1− x ) O 3 -0.005Er (BNBT- x ZN-Er) multifunctional ceramics were prepared by a traditional solid-phase reaction method. The ferroelectric, dielectric, and photoluminescence properties of BNBT- x ZN-Er ceramics doped with different (Zn 1/3 Nb 2/3 ) 4+ complex ions were systematically investigated. The results emerge that (Zn 1/3 Nb 2/3 ) 4+ can be completely diffused in the BNBT- x ZN-Er ceramics lattice. With the addition of complex ions, the long-range ferroelectric order of BNBT- x ZN-Er ceramics was significantly disrupted, and the electric field-induced strain responses was promoted. The maximum bipolar strain of 0.35% was obtained by introducing (Zn 1/3 Nb 2/3 ) 4+ with a concentration of x = 0.0100, corresponding to d 33 * ( S max / E max ) of 500 pm/V. Two dielectric anomaly peaks emerge at T R−E and T m due to the transformation of the phase. Additionally, the ceramics have bright up-conversion photoluminescence properties under a 980 nm laser light source, exhibiting intense green emission bands at 526 and 547 nm. The results illustrate that the BNBT- x Zn-Er ceramics exhibit excellent ferroelectric properties and also obtain bright up-conversion green photoluminescence properties.

Flexoelectricity in twinned ferroelastic thin films generates polarity inside twin walls. The electrical dipoles are typically aligned parallel to twin walls while out-of-plane dipoles are induced elastically by an atomic force microscopy (AFM) tip or by atomic steps in the substrate. Molecular dynamics modeling shows that the out-of-plane dipoles form polar vortex structures next to the domain walls. Flexoelectricity, e.g., by moving AFM tips, produces displacement currents inside these vortices. We estimate that these displacement currents generate magnetic fields with moments in the order of 10−9 μB per atomic layer.

Enhancing the electromechanical response by engineering domain boundaries in multiferroics has become a highly active research field in recent years. The starting point is the discovery that ferroelastic twin walls are polar inside a nonpolar matrix. The density of such twin walls is then greatly enhanced by forming complex twin patterns. Our computer simulations show that the interaction of nanocavities with differently charged configurations with twin boundaries generates strong piezoelectricity in ferroelastic (nonferroelectric) crystals. Cavity-induced domain patterns statistically break the inversion symmetry of a sample even when the cavities themselves obey inversion symmetry with relatively weak emerging piezoelectricity (d similar to 10(-3) pm/V). Stronger piezoelectricity occurs in noncentrosymmetric charged cavity arrangements with a coefficient of d similar to 10(-1) pm/V. Structurally, the electric field polarizes and shifts the nanocavities by the displacement of trapped surface charges. The related strain fields interact with the ferroelastic domains, which act as soft bridges between the nanocavities. This leads to a significant deformation of the entire sample and hence to enhanced piezoelectricity. Our simulation results point to new directions for designing and enhancing electromechanical nanodevices based on ferroelastic templates even when the bulk material is structurally centrosymmetric.

Ferroelastic twin boundaries often have properties that do not exist in bulk, such as superconductivity, polarity etc. Designing and optimizing domain walls can hence functionalize ferroelastic materials. Using atomistic simulations, we report that moving domain walls have magnetic properties even when there is no magnetic element in the material. The origin of a robust magnetic signal lies in polar vortex structures induced by moving domain walls, e.g., near the tips of needle domains and near domain wall kinks. These vortices generate displacement currents, which are the origin of magnetic moments perpendicular to the vortex plane. This phenomenon is universal for ionic crystals and holds for all ferroelastic domain boundaries containing dipolar moments. The magnetic moment depends on the speed of the domain boundary, which can reach the speed of sound under strong mechanical forcing. We estimate that the magnetic moment can reach several tens of Bohr magnetons for a collective thin film of 1000 lattice planes and movements of the vortex by the speed of sound. The predicted magnetic fields in thin slabs are much larger than those observed experimentally in SrTiO3/LaAlO3 heterostructures, which may be due to weak (accidental) forcing and slow changes of the domain patterns during their experiments. The dynamical multiferroic properties of ferroelastic domain walls may have the potential to be used to construct localized magnetic memory devices in future.