Ferroelastic Domain Walls Research Articles

Imaging Ferroelastic Domain Walls in Hybrid Improper Ferroelectric Sr3Sn2O7.

We combined synchrotron-based near field infrared spectroscopy and atomic force microscopy to image the properties of ferroelastic domain walls in Sr3Sn2O7. Although frequency shifts at the walls are near the limit of our sensitivity, we can confirm semiconducting rather than metallic character and widths between 20 and 60 nm. The latter is significantly narrower than in other hybrid improper ferroelectrics like Ca3Ti2O7. We attribute this trend to the softer lattice in Sr3Sn2O7, which may enable the octahedral tilt and rotation order parameters to evolve more quickly across the wall without significantly increased strain. These findings are crucial for the understanding of phononic properties at interfaces and the development of domain wall-based devices.

Effects of Ferroelastic Domain Walls on the Macroscopic Transport and Photoluminescent Properties of Bulk CsPbBr3 Single Crystals.

The all-inorganic halide perovskite CsPbBr3 has emerged as an excellent class of semiconductive and optoelectronic materials, in which its excellent properties are strongly related to the dynamics of its microstructures, i.e., ferroelastic domain walls. Here, the influence of ferroelastic domain walls on the macroscopic charge transport and photoluminescent properties in bulk single-crystal CsPbBr3 is experimentally and intrinsically studied across wide temperature intervals. The larger area of the same domain orientation, along with denser and thinner domain walls in a bulk CsPbBr3 single crystal, is formed through the Pnma↔P4/mbm↔Pm3̅m phase transitions. Remarkable motion of the domain walls near the P4/mbm↔Pm3̅m transition point is observed using in situ polarized optical microscopy. We initially observed a sharp decrease in resistivity after inducing larger areas with long-range order and denser, thinner domain walls in the temperature range from 273 to 343 K upon heating. In addition, the ferroelastic domain walls modulate exciton-phonon interactions and enhance radiative recombination in the CsPbBr3 single crystal, which correlates with the decrease in resistivity. These results will motivate strategies to design high-performance semiconductive and optoelectronic materials or devices by inducing specific ferroelastic domain walls in metal halide perovskites.

Anelastic and Magnetic Properties of Polycrystalline La0.6Sr0.4Fe1−xCuxO3−δ

Perovskite La0.6Sr0.4Fe1−xCuxO3−δ (x = 0, 0.05, 0.1, and 0.2) polycrystalline samples have been synthesized in air and investigated by X‐Ray diffraction, scanning electron microscope, magnetization, and mechanical spectroscopy. An antiferromagnetic transition is observed around 300 K, while no corresponding anomaly is observed in the mechanical spectrum, indicating the absence of conventional magnetoelastic coupling. For La0.6Sr0.4FeO3, an internal friction peak (P1) presents around 140 K and shifts to lower temperatures with increasing Cu‐doping content. Meanwhile, a magnetic anomaly is also observed around P1 peak temperature. As explained, the P1 peak is related to the freezing of the ferroelastic domain walls, and the mechanical energy dissipation is induced by the lagging variation of the octahedral tilting under the alternating stress. This work suggests a peculiar magnetic property of the octahedra within ferroelastic domain walls.

Electronic Properties of W’ Twin Walls in Ferroelastic BiVO4

AbstractTopological defects in ferroic materials can exhibit intrinsic properties that differ from the bulk. Here， structural and electronic variations of non‐prominent (W’) ferroelastic twin domain walls are investigated in BiVO4, a widely investigated photocatalytic material. Using aberration‐corrected scanning transmission electron microscopy (STEM), a kink configuration of the sharp ferroelastic twin wall with an altered electronic structure is revealed. Nanoscale conductivity measurements by conductive atomic force microscopy (c‐AFM) show higher conductivity at twin walls compared to non‐conductive bulk domains. Electronic structure investigation by electron energy loss spectroscopy (EELS) shows a higher density of oxygen vacancies and possible polaron accumulation at the wall. These findings reveal the electronic properties of BiVO4 domain walls, which are interesting for nanoscale‐engineered catalytic concepts of BiVO4 and materials design for photochemistry‐relevant applications.

Robust Ferroelasticity and Carrier Dynamics Across the Domain Wall in Perovskite‐Like van der Waals WO2I2

AbstractAs a new group of van der Waals (vdWs) ferroic materials, transition metal dioxydihalides MO2X2 (M: Mo, W; X: halogen) with a perovskite‐like structure are theoretically predicted to exhibit intriguing physics and versatile ferroic characteristics, which is not achieved experimentally as far as it is known. In this work, the robust ferroelasticity in vdWs WO2I2 with the switching strain as low as ≈0.3%, accompanied with the striped optical contrast between adjacent domains, spot splitting of selected area electron diffraction (SAED) patterns at domain wall, and 90° domain wall is demonstrated. With the aid of ab‐initio calculations, the origin of ferroelasticity in WO2I2 is unveiled, where the imaginary phonon mode in the high‐symmetry paraelastic phase leads to the spontaneous displacement of W atom away from the center of the [WO4I2] octahedron, resulting in the switchable spontaneous strain under an external strain field. Moreover, transient absorption microscopy (TAM) measurements demonstrate that the diffusion of photogenerated carriers is significantly hindered by the ferroelastic domain walls. This study provides deep insights into the ferroic order and domain wall in perovskite‐like vdWs MO2X2 for new physics and functionalities.

Strain-affected ferroelastic domain walls in RbMnFe charge-transfer materials undergoing collective Jahn-Teller distortion.

Many rubidium manganese hexacyanoferrate materials, with the general formula Rb x Mn[Fe(CN)6](x+2)/3·zH2O, exhibit diverse charge-transfer-based functionalities due to the bistability between a high temperature MnII(S = 5/2)FeIII(S = 1/2) cubic phase and a low-temperature MnIII(S = 2)FeII(S = 0) tetragonal phase. The collective Jahn-Teller distortion on the Mn sites is responsible for the cubic-to-tetragonal ferroelastic phase transition, which is associated with the appearance of ferroelastic domains. In this study, we use X-ray diffraction to reveal the coexistence of 3 types of ferroelastic tetragonal domains and estimate the spatial extension of the strain around the domain walls, which represents about 30% of the volume of the crystal.

Observation of dislocation-controlled domain nucleation and domain-wall pinning in single-crystal BaTiO3

Electro-mechanical interactions between topological defects and domain walls play a key role in the macroscopic response of bulk and thin-film ferroelectrics. The applications of ferroelectrics are derived from their inherent ability to nucleate new domains and to move the domain walls that separate adjacent domains. Here, we report dislocation-mediated domain nucleation in single-crystal BaTiO3, achieved by dislocations generated via high-temperature uniaxial compression on a notched sample. We also present a direct observation of domain-wall pinning of 90° ferroelastic domain walls by dislocations using in situ transmission electron microscopy. Dense and well-aligned “forest” dislocations, featuring {100}⟨100⟩ slip systems oriented in the out-of-plane [001] direction, exclusively nucleate in-plane domain variants. We reveal that the 90° domain walls are strongly pinned by imprinted dislocations due to the presence of their associated stress fields. Our findings may advance our understanding of the control of defects in ferroelectrics and propose a strategy applicable to both emerging nanoelectronic and bulk applications.

Ferroelastic twin domain patterns and polar domain walls of BiVO4 thin films via phase-field simulations

Polar domain walls in centrosymmetric ferroelastics (e.g., BiVO4 films) give rise to inhomogeneity and offer promises for solar energy conversion applications via expediting charge-carrier separation. However, the origin of polar domain walls and the relationship between them and spontaneous strain from structural phase transition remain elusive at the mesoscale in BiVO4 films. Here, from the perspective of phenomenological thermodynamics, the relationship between four variants of monoclinic (M) phase and the corresponding lattice parameters during the tetragonal-monoclinic (T-M) phase transition is revealed. Using phase-field simulations, it suggests that the formation of four variants of ferroelastic twin domains arises from spontaneous strain from T-M phase transition. Moreover, it is demonstrated that (i) polar domain walls in BiVO4 films originate from the flexoelectric effect induced by strain gradient across the domain walls during phase transition process; (ii) shear strain gradient dominates the contribution to the polarization vectors at the domain walls; (iii) 180° head-to-head or tail-to-tail in-plane polarization configurations emerge at the adjacent domain walls. The stability of several types of ferroelastic domain walls is also analyzed from the point of view of total free energy. These results not only provide a fundamental understanding of the origin of polar domain walls and the formation mechanisms of ferroelastic twin patterns, but also stimulate potential applications of polar domain walls of non-polar BiVO4 films in energy conversion.

Introducing Ferroelasticity into 1D Hybrid Lead Halide Semiconductor by Halogen Substitution Strategy.

Organic-inorganic hybrid lead halide perovskites (OLHPs), represented by (CH3 NH3 )PbI3 , are one of the research focus due to their exceptional performance in optoelectronic applications, and ferroelastic domain walls are benign to their charge carrier transport that is confirmed recently. Among them, the 1DOLHPs feature better stability against desorption and moisture, but related 1D ones possessing ferroelasticity are rarely investigated and reported so far. In this work, the 1D ferroelastic semiconductor (N-iodomethyl-N-methyl-morpholinium)PbI3 ((IDMML)PbI3 ) is prepared successfully by introducing successively halogenate atoms from Cl, Br to I into the organic cation of the prototype (N,N-dimethylmorpholinium)PbI3 ((DMML)PbI3 ). Notably, (IDMML)PbI3 shows the narrow bandgap energy (≈2.34eV) according to the ultraviolet-visible absorption spectrum and the theoretical calculation, and possesses the evident photoconductive characteristic with the on/off ratio of current of ≈50 under the 405nm light irradiation. This work provides a new case for the ferroelastic OLHPs and will inspire intriguing research in the field of optoelectronic.

Influence of kinks on the interaction energy between ferroelastic domain walls in membranes and thin films

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.

Visible-light controlled interfacial magnetoelectric coupling in SrRuO3/BaTiO3 heterostructure

Artificial multiferroics provide a tunable magnetoelastic and magnetoelectric coupling owing to the variety of combinations of ferroelectric and ferromagnetic layers, hence facilitate a better perspective for device applications such as magnetic field sensors and electric write magnetic -read memory devices. The intertwined physical properties can be controlled via external parameters such as electric field, temperature, and magnetic field. Here, we report an additional mode to manoeuvre the magnetoelastic and magnetoelectric coupling in an epitaxial SrRuO3/BaTiO3 multiferroic heterostructure using polarized visible light illumination. The light-induced ferroelastic (FE) domain wall motion in underlying BaTiO3 leads to photostriction and photodomain effects. Consequently, the change in the converse magnetoelastic effects leads to modify the magnetic properties of the above grown SrRuO3 layer. Besides this, we have observed a sharp and persistent changes in the SrRuO3/ BaTiO3 heterostructure, when the system is electrically biased owing to the change in the interfacial converse magnetoelectric coupling. Light controlled magnetization tunability in BaTiO3-based artificial multiferroic can open an alternate way for potential applications in several types of wireless devices and magnetic field sensors, electric write magnetic-read memory devices and other interesting optomechanical systems. Our findings in this context can be proven indeed as a novel prospective for opto-spintronics device applications.

Improved polarization retention in epitaxial BiFeO3 thin films induced by strain relaxation

This study investigated the impact of lattice mismatch strain (LMS) on the polarization retention of epitaxial ferroelectric BiFeO3 (BFO) thin films. The application of varying degrees of LMS on the BFO films was achieved by tuning the film thickness, which was verified through X-ray diffraction and reciprocal space mapping. As the strain was gradually eliminated, the film demonstrated a more saturated hysteresis loop with a reduced negative coercive electric field. Additionally, a significant increase in polarization retention was observed with increasing film thickness, strongly indicating the crucial role of LMS in driving the formation of preferred polarization, which is intimately connected with the built-in field induced by oxygen vacancies-relevant space charge alignment. Moreover, the anisotropic LMS state of the BFO films was utilized to horizontally reverse local polarization in a sub-micrometer scale, revealing that strain accelerates the back-switching of polarization to eliminate the artificially created ferroelastic domain walls. To counteract the strain effect, charge injection of electrons was proposed to enhance the retention of switched polarization by fully suppressing the built-in field and pinning the artificially created domain walls. The findings provide valuable insights into the impact of strain on polarization retention for the development of ferroelectric memories.

Nonvolatile memory based on the extension–retraction of bent ferroelastic domain walls: A phase field simulation

Herein, a prototype nonvolatile bent ferroelastic domain wall (DW) memory based on extension–retraction of DWs in a top electrode/bent ferroelastic DWs/bottom electrode architecture is demonstrated and the effects of mechanical condition, electrical condition, and the material parameter on ferroelastic DWs in PbTiO3 ferroelectric thin films are studied by phase field modeling. Misfit strain can be used to drive the bend of DWs in PbTiO3 thin film, resulting in a change of ferroelastic domain size, bending degree, and conductivity. Stable and reversible switching of DWs between the extendible state with high conductivity and the retractile state with low conductivity can be realized, resulting in an apparent resistance change with a large ON/OFF ratio of >102 and an excellent retention characteristic. The extension and retraction speed, corresponding to data writing speed, can be adjusted by the electric field magnitude and distributions. The memory speed increases by 5% under a homogeneous electric field and 6% under an inhomogeneous probing electric field, after the buildup of space charges in a ferroelectric thin film, and the fastest memory speed is obtained at tip potential φ = 1.8. Moreover, polarization orientations of a and c domains separated by bent ferroelastic DWs do not affect memory performance. This paper can guide the development of new ferroelectric domain wall memory.

Digital and analog resistive switching in Lu-doped piezoelectric [formula omitted] film

Recently, in the field of artificial intelligence, neuromorphic devices have received significant attention for building artificial neural networks. Nano-scale resistive random access memory (RRAM) is one of the emerging electrical components for neuromorphic computing. In the present study, the synaptic characteristics are investigated in the piezoelectric BiFe1−xLuxO3 (BFLO) and Bi1−xLuxFeO3 (BLFO) (x = 0.05) based RRAM devices in a vertical configuration. Both devices show bipolar resistive switching behavior with good endurance characteristics. However, analog switching with potentiation and depression response is observed in Ag/BFLO/FTO device. The change in resistance and leakage current flow across the device is explained by the space charge limiting current conduction mechanism with regard to thermally generated and injected charge carriers. Both films possess strong electro-mechanical response with the ferroelectric and ferro-elastic domain walls oriented along 710, 1090, and 1800 directions. The electro-mechanical response and resistive switching properties make the materials viable for sensing, energy harvesting, and non-volatile memory technology. Moreover, the BFLO-based synaptic device has potential application in neuromorphic computation.

Domain wall nature of sketched LaAlO3/SrTiO3 nanowires

The rich electron correlations and highly coherent transport in reconfigurable devices sketched by a conductive atomic force microscope tip at the $\mathrm{LaAl}{\mathrm{O}}_{3}/\mathrm{SrTi}{\mathrm{O}}_{3}$ interface have enabled the oxide platform an ideal playground for studying correlated electrons and quantum technological applications. Why these one-dimensional devices possess enhanced properties over the two-dimensional interface, however, has remained elusive. Here, we provide evidence that one-dimensional $\mathrm{LaAl}{\mathrm{O}}_{3}/\mathrm{SrTi}{\mathrm{O}}_{3}$ nanowires are intrinsically ferroelastic domain walls by nature through thermodynamic study. We have observed spreading resistance anomalies under thermostimulus and temperature cycles with characteristic temperatures matching domain-wall polarity. This information is crucial in understanding the novel phenomena including superconductivity and high mobility quantum transport.

Ferroelastic and 90∘ ferroelectric domains in Bi2WO6 single crystals

High-quality single crystals of [Formula: see text] are grown using a flux method. With different flux growth recipes, we aim to control the crystallization temperature to be lower and higher than the ferroelectric transition temperature, resulting in mono-domain and multi-domain [Formula: see text] crystals, respectively. Abundant ferroelastic orthorhombic twin domains are observed in the multi-domain crystals under an optical microscope. PFM studies unveil the 90[Formula: see text] polarization change across those ferroelastic domain walls, as well as the absence of 180[Formula: see text] ferroelectric domains in the as-grown multi-domain crystals, indicating a high energy cost of 180[Formula: see text] ferroelectric domains. Moreover, a 45[Formula: see text] tilt of the 90[Formula: see text] ferroelectric domain walls is discovered, and this tilt creates a new type of charged 90[Formula: see text] ferroelectric walls, which have not been observed in other bulk ferroelectrics.

Oxygen transport at a ferroelastic domain wall in CaTiO3

The formation and migration of charged oxygen vacancies at a ${90}^{\ensuremath{\circ}}(100)[001]$ domain wall in orthorhombic ${\mathrm{CaTiO}}_{3}$ were studied by means of atomistic simulation techniques. The segregation-energy profiles of an oxygen vacancy across the wall were revealed through careful discrimination to display hyperbolic secant forms, with a domain-wall width consistent with that obtained from a tilt-angle analysis. Equilibrium distributions of oxygen vacancies across the ferroelastic domain wall in a nominally undoped (weakly acceptor-doped) sample were calculated self-consistently (assuming a sech segregation-energy profile) for various temperatures. The calculations indicate a positively charged domain wall, arising from high vacancy concentrations, compensated by negative space-charge layers, in which vacancies are depleted. The activation barriers for oxygen-vacancy migration along the domain wall, determined from nudged-elastic-band calculations, revealed that the long-range diffusion of oxygen vacancies along the wall is neither strongly enhanced nor strongly hindered.

Ferroelastic Domain Walls in BiFeO3as Memristive Networks

Electronic conduction along individual domain walls (DWs) is reported in BiFeO3(BFO) and other nominally insulating ferroelectrics. DWs in these materials separate regions of differently oriented electrical polarization (domains) and are just a few atoms wide, providing self‐assembled nanometric conduction paths. Herein, it is shown that electronic transport is possible also from wall‐to‐wall through the dense network of as‐grown DWs in BFO thin films. Electric field cycling at different points of the network, performed locally by conducting atomic force microscopy (cAFM), induces resistive switching selectively at the DWs, both for vertical (single wall) and lateral (wall‐to‐wall) conduction. These findings are the first step toward investigating DWs as memristive networks for information processing andin-materiocomputing.

Competition between Ferroelectric and Ferroelastic Domain Wall Dynamics during Local Switching in Rhombohedral PMN-PT Single Crystals.

The possibility to control the charge, type, and density of domain walls allows properties of ferroelectric materials to be selectively enhanced or reduced. In ferroelectric-ferroelastic materials, two types of domain walls are possible: pure ferroelectric and ferroelastic-ferroelectric. In this paper, we demonstrated a strategy to control the selective ferroelectric or ferroelastic domain wall formation in the (111) single-domain rhombohedral PMN-PT single crystals at the nanoscale by varying the relative humidity level in a scanning probe microscopy chamber. The solution of the corresponding coupled electro-mechanical boundary problem allows explaining observed competition between ferroelastic and ferroelectric domain growth. The reduction in the ferroelastic domain density during local switching at elevated humidity has been attributed to changes in the electric field spatial distribution and screening effectiveness. The established mechanism is important because it reveals a kinetic nature of the final domain patterns in multiaxial materials and thus provides a general pathway to create desirable domain structure in ferroelectric materials for applications in piezoelectric and optical devices.

Wall-wall and kink-kink interactions in ferroelastic materials

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 $1/{d}^{2}$ 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 $1.{2}^{\ensuremath{\circ}}$. Multiple kinks will enhance the effect systematically and bent and modulated twin walls are predicted.