Ferroelastic Domain Switching Research Articles

Fracture Behaviors and Ferroelastic Deformation in W/Cr Co‐Doped Bi4Ti3O12 Ceramics

In this paper, the influence of Cr2O3 additive (y = 0~0.4 wt%) on fracture behaviors, ferroelastic deformation, and mechanical strengths of Bi4Ti2.95W0.05O12.05 (BTW) Aurivillius ceramics was investigated. For these W/Cr co‐doped Bi4Ti3O12 ceramics (BTW–yC), SEM analysis on their fractured surfaces demonstrate that the transgranular fracture is the main fracture mechanism, however, the intergranular fracture also exists in the sample at y = 0.3. Impedance analyses based electrical resonance show that their Poisson's ratio and Young's modulus vary with y in a similar trend, while the frequency constant and elastic compliance exhibit a contrary varying trend with y. On the other hand, under the Vickers indentation, the crack propagation in BTW–yC ceramics takes the form of the long‐straight extension, small‐angle deflection, and short‐distance branching at y = 0, 0.2, and 0.4, respectively. In the uniaxial compression tests, the stress–strain behavior of ceramics consist of three stages, i.e., linear elastic deformation, ferroelastic domain switching, and microcrack propagation. The ferroelastic domain switching tends to form the resistance for the microcrack propagation. Furthermore, uniaxial bending tests prove that the fracture strength is dependent on the grain size and fracture toughness, Overall, the sample at y = 0.1 gains a better mechanical strength among BTW–yC ceramics.

Electric-Field-Control of Non-Volatile Magnetization Switching in Multiferroic CoFeB/(011)-PMN-PT Heterostructures

The giant converse magnetoelectric coupling (GME) was observed in the multiferroic Co40Fe40B20/(011)-0.7Pb (Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructures at room temperature in this investigation. A tunability of magnetization by electric field along the [100] direction was up to-66.7% at-10 Oe bias magnetic fields. Moreover, the non-volatile magnetization switching was found after removal of bipolar electric field. The corresponding remanent magnetic states even without the assistance of bias magnetic fields were stable and could be modulated synchronously by a sequence of pulse electric fields. The 90o rotation of easy axis and non-symmetrical ferroelastic domain switching contributed to the above results. This work is of great significance in designing ultra-low power and non-volatile magnetoelectric memories and other spintronic devices at room temperature.

Elastic properties of freeze-cast La0.6Sr0.4Co0.2Fe0.8O3–δ

Apparent Young’s, shear and bulk moduli and Poisson’s ratio of freeze-cast La0.6Sr0.4Co0.2Fe0.8O3–δ (LSCF), envisaged as porous substrate for dense LSCF oxygen transport layers, were investigated at room temperature by a quasi–static hysteresis compression test as a function of the longitudinal strain which was measured in longitudinal direction. Ferroelastic domains were confirmed via electron microscopy. The apparent elastic parameters showed extrema related to ferroelastic domain switching. Apparent Young’s and shear moduli revealed minimum values, while bulk modulus and Poisson’s ratio demonstrated maximum values due to the transverse strain contributed by ferroelastic domain switching. Results are discussed with respect to the behavior and values of the elastic parameters that has been reported previously for dense LSCF.

Control of magnetic relaxation by electric-field-induced ferroelectric phase transition and inhomogeneous domain switching

Electric-field modulation of magnetism in strain-mediated multiferroic heterostructures is considered a promising scheme for enabling memory and magnetic microwave devices with ultralow power consumption. However, it is not well understood how electric-field-induced strain influences magnetic relaxation, an important physical process for device applications. Here, we investigate resonant magnetization dynamics in ferromagnet/ferroelectric multiferroic heterostructures, FeGaB/PMN-PT and NiFe/PMN-PT, in two distinct strain states provided by electric-field-induced ferroelectric phase transition. The strain not only modifies magnetic anisotropy but also magnetic relaxation. In FeGaB/PMN-PT, we observe a nearly two-fold change in intrinsic Gilbert damping by electric field, which is attributed to strain-induced tuning of spin-orbit coupling. By contrast, a small but measurable change in extrinsic linewidth broadening is attributed to inhomogeneous ferroelastic domain switching during the phase transition of the PMN-PT substrate.

Theory and experimental evidence of phonon domains and their roles in pre-martensitic phenomena

AbstractPre-martensitic phenomena, also called martensite precursor effects, have been known for decades while yet remain outstanding issues. This paper addresses pre-martensitic phenomena from new theoretical and experimental perspectives. A statistical mechanics-based Grüneisen-type phonon theory is developed. On the basis of deformation-dependent incompletely softened low-energy phonons, the theory predicts a lattice instability and pre-martensitic transition into elastic-phonon domains via ‘phonon spinodal decomposition.’ The phase transition lifts phonon degeneracy in cubic crystal and has a nature of phonon pseudo-Jahn–Teller lattice instability. The theory and notion of phonon domains consistently explain the ubiquitous pre-martensitic anomalies as natural consequences of incomplete phonon softening. The phonon domains are characterised by broken dynamic symmetry of lattice vibrations and deform through internal phonon relaxation in response to stress (a particular case of Le Chatelier’s principle), leading to previously unexplored new domain phenomenon. Experimental evidence of phonon domains is obtained by in situ three-dimensional phonon diffuse scattering and Bragg reflection using high-energy synchrotron X-ray single-crystal diffraction, which observes exotic domain phenomenon fundamentally different from usual ferroelastic domain switching phenomenon. In light of the theory and experimental evidence of phonon domains and their roles in pre-martensitic phenomena, currently existing alternative opinions on martensitic precursor phenomena are revisited.

In-situ structural investigations of ferroelasticity in soft and hard rhombohedral and tetragonal PZT

Despite the technological importance of hard and soft PZT, Pb(Zr,Ti)O3, ceramics, the mechanisms of ferroelectric hardening and softening remain widely discussed in the literature. The hardening and softening phenomena have traditionally been investigated in relation with dielectric manifestations such as aging of the dielectric susceptibility and constriction of the polarization-electric field hysteresis loop. Here, we present a systematic investigation of the ferroelectric and ferroelastic properties of soft and hard PZT in both the tetragonal and rhombohedral phases. A particular focus has been devoted to ferroelastic domain switching by characterizing the macroscopic mechanical constitutive behavior and in-situ synchrotron X-ray diffraction during compression. It is demonstrated that variation of the ordering state of point defects in PZT ceramics affects the switching behavior of both ferroelectric and ferroelastic domains under mechanical or electrical fields. Softening of the mechanical and electrical properties of originally hard PZT ceramics was conferred by quenching the materials from above the Curie temperature. The present findings are discussed with respect to the current understanding of hardening-softening transitions in ferroelectric materials.

Realization of face-shear piezoelectric coefficient d36 in PZT ceramics via ferroelastic domain engineering

The piezoelectric face-shear (d36) mode may be the most useful shear mode in piezoelectrics, while currently this mode can only exist in single crystals of specific point groups and cut directions. Theoretically, the d36 coefficient vanishes in piezoelectric ceramics because of its transversally isotropic symmetry. In this work, we modified the symmetry of poled PZT ceramics from transversally isotropic to orthogonal through ferroelastic domain switching by applying a high lateral stress along the “2” direction and holding the stress for several hours. After removing the compression, the piezoelectric coefficient d31 is found much larger than d32. Then, by cutting the compressed sample along the Zxt±45° direction, we realized d36 coefficients up to 206pC/N, which is measured by using a modified d33 meter. The obtained large d36 coefficients in PZT ceramics could be very promising for face-shear mode resonators and shear horizontal wave generation in nondestructive testing.

Epitaxial PbZrxTi1−xO3 Ferroelectric Bilayers with Giant Electromechanical Properties

Giant electromechanical response viaferroelastic domain switching is achieved in epitaxial (001) ferroelectric tetragonal (T) PbZr0.3Ti0.7O3/rhombohedral (R) PbZr0.55Ti0.45O3 bilayers, grown on La0.67Sr0.33MnO3 buffered SrTiO3 substrates. X‐ray diffraction and transmission electron microscopy show that the domain structure of the T films is tuned as a function of its thickness, from a fully a1/a2‐domains (30 nm thick T layer) to a three domain stress‐free c/a1/c/a2 polytwin state (100 nm thick T layer). A large switchable polarization is found up to 65 μC cm−2. Quantitative piezoelectric force microscopy reveals enhanced piezoelectric coefficients, with d33 coefficients ranging from 250 to 350 pm V−1, which is up to seven times higher than the nominal PbZrxTi1−xO3 thin film values. These are attributed to the motion of nanoscale ferroelastic domains. Fatigue testing proves that these domains are reversible and repeatable up to 107 cycles. In‐situ X‐ray synchrotron measurements reveal that the ferroelastic domain switching is promoted by a pulsating strain effect imposed by the R layer. The study reports a fundamental understanding of the origin of giant piezoelectric coefficients in epitaxial ferroelectric bilayers.

Electric-field control of non-volatile magnetization switching without external-magnetic-field bias in CoFeB/(011)-PMN-0.3PT heterostructures

Electric-field control of non-volatile magnetization switching in the absence of external-magnetic-field bias has been investigated in multiferroic Co40Fe40B20/0.7Pb(Mg1/3Nb2/3)-0.3PbTiO3 (CoFeB/PMN-0.3PT) heterostructure at room temperature. The two non-volatile magnetic states are achieved without magnetic-field bias and can be switched in a reversible and reproducible manner by an electric field. These results are attributed to the modulation of the magnetic anisotropy of the CoFeB layer by as-grown magnetic field and electric-field–induced non-volatile strain through unipolar-electric-field cycling. High-resolution X-ray diffraction studies on the (022) peaks under in situ electric field indicate that the non-volatile strain is closely related to the 71° ferroelastic domain switching ( to ) of the PMN-0.3PT substrate. The corresponding ratio of the ferroelastic domain is electrically changed by 14.1% between the two non-volatile magnetic states. Our results provide a promising path to non-magnetically operating magnetic bits by pure electric field at room temperature.

Anomalous variation of the mechanical behaviour of ferroelastic La0.6Sr0.4Co0.2Fe0.8O3-δ during the ferro-to-paramagnetic transition

Uniaxial compression tests of ferroelastic La0.6Sr0.4Co0.2Fe0.8O3-δ were conducted in the temperature range covering the ferro-to-paramagnetic transition at ∼240 K (Tc). An anomalous variation of mechanical behaviour was observed. The apparent elastic modulus drastically decreases above Tc, whilst it is almost constant below Tc; on the other hand, the critical stress for ferroelastic domain switching decreases monotonically with increasing temperature. Furthermore, the back-switching occurs easily and/or rapidly below Tc, but the material becomes brittle.

Enhancing electrical energy storage density in anti-ferroelectric ceramics using ferroelastic domain switching

Capacitors form an indispensable part of many modern electrical and electronic devices. An ideal capacitor is expected to possess high power and energy density along with enhanced energy recovery characteristics. Anti-ferroelectric materials form a suitable candidate for ceramic-based capacitor applications, owing to their low loss and high energy density. However, these materials show ample room for improvement through physical means. In this regard, the present work deals with mechanical tuning of the energy storage density and recoverable efficiency in known anti-ferroelectric materials. For this study, various configurations of (Pb1−xLax)(Zr0.90Ti0.10)1−x/4O3 (PLZTx) ceramics have been investigated. Both mechanical confinement and temperature applications have been shown to improve the performance characteristics of all selected compositions. This behavior has been explained on the basis of competing ferroelectric and ferroelastic domain rotations. The application of suitable stress/temperature reduces hysteresis losses and delays anti-ferroelectric ↔ ferroelectric phase transformation, which increases the electrical energy storage capacity of these materials. Mechanical confinement was observed to provide an increase in energy storage density and efficiency by approximately 38% and 25%, respectively, for the PLZT4 composition. The highest recoverable energy density of 698 m J cm−3 was achieved under compressive stress of a 100 MPa and 60 kV cm−1 applied electric field.

Strain-induced modulation of magnetic anisotropy in Co/BaTiO3 composite

A uniaxial magnetic anisotropy Co film was grown on a single-crystal BaTiO3 (BTO) substrate. The strain yielded by the voltage-induced ferroelastic domain switching in the BTO substrate was recorded by atomic force microscope and modulated the magnetism of the Co film. The manipulation of the magnetism of the Co film is experimentally demonstrated by voltage dependence of magnetic hysteresis loops measured via magneto-optic Kerr effect.

Novel laminated multiferroic heterostructures for reconfigurable microwave devices

Voltage tuning of magnetism is fundamentally and technically important for fast, compact and ultra-low power electronic devices. Multiferroic heterostructures, simultaneously exhibiting distinct ferroelectric and ferromagnetic properties, have caught a lot of attentions because of the capability of controlling magnetism by a voltage via a strain-mediated magnetoelectric (ME) coupling. In these materials, a voltage-induced strain is involved to create an effective magnetic field and change ferromagnetic resonance frequency in the coupled ferromagnetic phases through magnetoelastic interactions. Therefore, the devices made of such materials are compact, ultra-fast and energy efficient, providing new functionalities for microwave components. This paper will review the recent progress of multiferroics and their applications in microwave devices from different aspects, including the creation of the novel laminated multiferroic heterostructures with a strong ME coupling, the realization of the multiferroics based on tunable microwave signal processors and the investigation of nonvolatile tuning of microwave properties using ferroelastic domain switching in multiferroic heterostructures. These tunable multiferroic heterostructures and devices offer great opportunities for realizing the next generation of tunable magnetic microwave components, ultra-low power electronics and spintronics.

Electric-field-controlled interface strain coupling and non-volatile resistance switching of La1-xBaxMnO3 thin films epitaxially grown on relaxor-based ferroelectric single crystals

We have fabricated magnetoelectric heterostructures by growing ferromagnetic La1-xBaxMnO3 (x = 0.2, 0.4) thin films on (001)-, (110)-, and (111)-oriented 0.31Pb(In1/2Nb1/2)O3-0.35Pb(Mg1/3Nb1/2)O3-0.34PbTiO3 (PINT) ferroelectric single-crystal substrates. Upon poling along the [001], [110], or [111] crystal direction, the electric-field-induced non-180° domain switching gives rise to a decrease in the resistance and an enhancement of the metal-to-insulator transition temperature TC of the films. By taking advantage of the 180° ferroelectric domain switching, we identify that such changes in the resistance and TC are caused by domain switching-induced strain but not domain switching-induced accumulation or depletion of charge carriers at the interface. Further, we found that the domain switching-induced strain effects can be efficiently controlled by a magnetic field, mediated by the electronic phase separation. Moreover, we determined the evolution of the strength of the electronic phase separation against temperature and magnetic field by recording the strain-tunability of the resistance [(ΔR/R)strain] under magnetic fields. Additionally, opposing effects of domain switching-induced strain on ferromagnetism above and below 197 K for the La0.8Ba0.2MnO3 film and 150 K for the La0.6Ba0.4MnO3 film, respectively, were observed and explained by the magnetoelastic effect through adjusting the magnetic anisotropy. Finally, using the reversible ferroelastic domain switching of the PINT, we realized non-volatile resistance switching of the films at room temperature, implying potential applications of the magnetoelectric heterostructure in non-volatile memory devices.

Voltage control of metal-insulator transition and non-volatile ferroelastic switching of resistance in VOx/PMN-PT heterostructures.

The central challenge in realizing electronics based on strongly correlated electronic states, or ‘Mottronics', lies in finding an energy efficient way to switch between the distinct collective phases with a control voltage in a reversible and reproducible manner. In this work, we demonstrate that a voltage-impulse-induced ferroelastic domain switching in the (011)-oriented 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-PT) substrates allows a robust non-volatile tuning of the metal-insulator transition in the VOx films deposited onto them. In such a VOx/PMN-PT heterostructure, the unique two-step electric polarization switching covers up to 90% of the entire poled area and contributes to a homogeneous in-plane anisotropic biaxial strain, which, in turn, enables the lattice changes and results in the suppression of metal-insulator transition in the mechanically coupled VOx films by 6 K with a resistance change up to 40% over a broad range of temperature. These findings provide a framework for realizing in situ and non-volatile tuning of strain-sensitive order parameters in strongly correlated materials, and demonstrate great potentials in delivering reconfigurable, compactable, and energy-efficient electronic devices.

Ferroelasticity and spin-state transitions of LaCoO3

A uniaxial compression test of polycrystalline lanthanum cobaltite (LCO) was performed to investigate mechanical behavior of LCO in the temperature range of 83–553 K. Prepared by solid-state reaction, the electrical resistivity and the linear expansion coefficient of polycrystalline LCO, measured between 80 and 1273 K, exhibit distinct changes attributed to spin-state transitions of cobalt ions around 100–200 K and 400–600 K, but are relatively constant between 200 and 400 K. The stress-strain curve obtained under uniaxial compression shows strong nonlinearity due to ferroelastic domain switching process between 83 and 553 K. Initial Young's moduli, critical stress, and dissipated energy evaluated from the stress-strain curves decrease by about a half with increasing the temperature, whereas there was no drastic changes even around the spin-state transition temperatures. The initial modulus agrees with the temperature dependence of the apparent Young's modulus measured under low-stress cyclic loading.

Ferroelastic domain switching dynamics under electrical and mechanical excitations.

In thin film ferroelectric devices, switching of ferroelastic domains can significantly enhance electromechanical response. Previous studies have shown disagreement regarding the mobility or immobility of ferroelastic domain walls, indicating that switching behaviour strongly depends on specific microstructures in ferroelectric systems. Here we study the switching dynamics of individual ferroelastic domains in thin Pb(Zr0.2,Ti0.8)O3 films under electrical and mechanical excitations by using in situ transmission electron microscopy and phase-field modelling. We find that ferroelastic domains can be effectively and permanently stabilized by dislocations at the substrate interface while similar domains at free surfaces without pinning dislocations can be removed by either electric or stress fields. For both electrical and mechanical switching, ferroelastic switching is found to occur most readily at the highly active needle points in ferroelastic domains. Our results provide new insights into the understanding of polarization switching dynamics as well as the engineering of ferroelectric devices.

Bipolar loop-like non-volatile strain in the (001)-oriented Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals

Strain has been widely used to manipulate the properties of various kinds of materials, such as ferroelectrics, semiconductors, superconductors, magnetic materials, and “strain engineering” has become a very active field. For strain-based information storage, the non-volatile strain is very useful and highly desired. However, in most cases, the strain induced by converse piezoelectric effect is volatile. In this work, we report a non-volatile strain in the (001)-oriented Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals and demonstrate an approach to measure the non-volatile strain. A bipolar loop-like S-E curve is revealed and a mechanism involving 109° ferroelastic domain switching is proposed. The non-volatile high and low strain states should be significant for applications in information storage.

Molecular dynamics study on the nature of ferroelasticity and piezoconductivity of lanthanum cobaltite

Abstract Lanthanum cobaltite systems are known to exhibit unique characteristics under mechanical stress such as ferroelasticity and piezoelasticity. In the present study, molecular dynamics simulation on LaCoO3 was performed to investigate the nature of these characteristics. Under uniaxial compression, the material can accommodate the highest stress in the c direction, i.e., hexagonal c-axis, and this orientation preference is related to displacement of oxygen-ions due to rhombohedrally-distorted CoO6 octahedron. The elastic deformation before ferroelastic domain switching process, where domains are re-oriented to make the hexagonal c-axis parallel to the stress axis, could be attributed to a change in the Co O bond length, whereas the elastic deformation after the switching process could be mostly due to the tilt of CoO6 octahedron. The general lattice deformation (Co Co) proceeds continuously during the whole deformation process. The Co O Co bond angle shows a linear correlation to stress, which could be related to the piezoconductivity.

The effect of domain patterns on 180° domain switching in BaTiO3 crystals during antiparallel electric field loading

In this Letter, the effect of domain pattern on 180° domain switching behavior in BaTiO3 crystals was investigated by using polarized light microscopy during antiparallel electric field loading. Results show that for nearly perfectly in-plane poled specimen, 180° domain switching is accomplished by successive antiparallel domain nucleation and forward domain wall motion; whereas for specimen with in-plane a-a domain pattern, 180° domain switching is achieved by two-step 90° ferroelastic domain switching. This discrepancy is explained by combined effects of the depolarization field and the mechanical constraint from the adjacent domains during 90° ferroelastic domain switching.