Ferroelastic Domain Switching Research Articles

Effect of T’-YSZ@Al2O3 core-shell structure on fracture toughness of YSH24 ceramics

To meet the demands of higher operating temperatures in aero-engines, yttrium oxide fully stabilized cubic (C) phase hafnium oxide (YFSH) has emerged as a promising candidate for thermal barrier coatings due to its ultra-high melting and phase transition temperatures. However, its application is constrained by its inherently low fracture toughness. To enhance the fracture toughness of C-HfO2 phase ceramic, the metastable non-equilibrium tetragonal (T’) phase of Y0.08Zr0.92O1.96 (YSZ8) was synthesized using the sol-gel method. An Al2O3 layer was then coated on YSZ, forming a T’-YSZ@Al2O3 core-shell structure (with Al2O3 comprising 20 % of the YSZ volume). The phase organization stability and diffusion resistance of this T’-YSZ@Al2O3 core-shell structure were investigated. Composite ceramic bulks, with compositions x T’-YSZ@Al2O3/(1-x) YSH24 (where x is the volume fraction, x = 0, 0.1, 0.2, 0.3, 0.4), were prepared using spark plasma sintering (SPS). The impact of the T’-YSZ@Al2O3 addition on the fracture toughness of the YSH24 matrix and the toughening mechanisms were analyzed. The results indicate that the introduction of the T’-YSZ@Al2O3 core-shell structure with good structural integrity into YSH24 ceramics prevents phase transitions. As the volume fraction of the core-shell structure increases from x = 0–0.4, the fracture toughness initially rises and then decreases, reaching a maximum of 2.36 MPa·m1/2 at x = 0.3. This value represents a 38.8 % improvement compared to that of the single C-HfO2 phase YSH24 bulks. The primary toughening mechanism is attributed to the ferroelastic domain switching of T’-YSZ within the T’-YSZ@Al2O3 core-shell structure.

Tailoring mechanical, microstructural and toughening characteristics of plasma-sprayed graphene-reinforced samarium niobate coatings for extreme environments

Thermal barrier coatings (TBCs) are advanced ceramic layers applied to metal components to provide insulation and protection against high temperatures in extreme operating environments. This study investigated the effects of graphene nanoplatelet (GNP) reinforcement on samarium niobate (SN: SmNbO4) TBCs for extreme environments. Four ceramic top coat compositions were plasma-sprayed onto Inconel 718 substrates: Yttria-stabilized zirconia (YSZ), SmNbO4 (SN), and SN reinforced with 1 and 1.5 wt% GNPs (SN-1GNP, SN-1.5GNP). The research examined microstructural characteristics, phase evolution, mechanical properties and toughening mechanisms. GNP reinforcement significantly improved coating density, with SN-1.5GNP reaching 97.4 ± 1.64% compared to 91.3 ± 1.69% for SN and 86.6 ± 1.47% for YSZ. Hardness and elastic modulus were enhanced by 86.38% and 57.91% for SN-1GNP, and 101.09% and 65.23% for SN-1.5GNP respectively. Moreover, fracture toughness experienced a significant increase from 1.86 ± 0.4 to 5.48 ± 0.7 MPa·m1/2, facilitated by toughening mechanisms, like splat bridging, GNP pull-out, crack arrest and ferroelastic domain switching. Additionally, the SN-1.5GNP coating exhibited a higher adhesion strength of 36.84 MPa, thereby leading to improved layer distribution and lesser chance of delamination. Compared to YSZ, these findings suggest that GNP-reinforced SN coatings offer enhanced performance for extreme environment applications.

Enhanced mechanical properties and atomic-scale mechanisms of ferroelastic domain switching for GdNbO4-La2Zr2O7 materials

Optimization of mechanical properties in La2Zr2O7 (LZO) ceramics, composites and coatings is an on-going requirement for their practical application. Herein, the contribution of monoclinic (La, Gd)NbO4 (m-LGNO) enhancement of fracture toughness by ∼56% reveals its capability to be a prominent toughening agent. Due to the ferroelastic nature of LGNO, ferroelastic switching takes place within the stress concentrated regions, giving rise to significant strain energy relaxation. Atomic-scale evidence reveals that ferroelastic 94°/86° domain switching can occur, yielding merged 94° domains and newly formed 86° domains. The relevant strains induced by ferroelastic domain switching are quantified up to 8.06% and 6.20% in shear and normal strain, respectively. Such domain switching strains highlight their contribution to accommodate external mechanical loading for the 50 mol% GNO-LZO composite. The results indicate that the unique ferroelastic nature and 94°/86° ferroelastic domain switching in m-LGNO cooperatively provide a significant toughening effect.

Mechanism of nucleation in ferroelastic domain switching

The mechanism of domain nucleation during ferroelastic domain switching is revealed by utilizing phase-field simulations. A complete compression-tension hysteresis loop is simulated, and the results show the nucleation of new domains at domain walls (DW). Due to relaxation of strain energy, the coherent DWs of the surviving domains often form features like steps, crevices and corners, and nucleation of new domains primarily takes place at these sites in a repeated fashion. The change in elastic strain energy around these sites is sufficient to provide the energy necessary for ferroelastic domain nucleation (FDN). The present simulations reveal that the apparent ellipsoidal shape of a nucleus might be an oblate spheroid when the nucleation takes place at a crevice. The present work also reveals that nucleation of triangular shaped domains is equally probable, and they take place at the steps or corners of DWs.

Ferroelastic strain control of multiple nonvolatile resistance tuning in Cr:In2O3/PMN-PT(111) multiferroic heterostructures

Strain can significantly affect the electronic structure and functional properties of dilute magnetic semiconductors. As a wide bandgap transparent semiconductor, doped In2O3 has also received extensive attention for the modulation of physical properties by lattice strain due to its excellent functional properties. Here, we epitaxially grew the Cr:In2O3 thin film on the (111)-oriented 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN–PT) ferroelectric single-crystal substrate. By applying an electric field to PMN–PT, multiple reversible and nonvolatile resistance states can be achieved at room temperature. Utilizing in situ XRD, different strain states corresponding to different resistance states induced by the ferroelastic domain switching of the PMN–PT were characterized. Based on first-principles calculations, the influence of lattice strain on the resistivity of the Cr:In2O3 was discussed. These results offer a route for the design of multiple-valued nonvolatile memory devices and multiple functional magneto-electric devices based on dilute magnetic semiconductors.

Intermediate multidomain state in single-crystalline Mn-doped BiFeO3 thin films during ferroelectric polarization switching

A intermediate multidomain state and large crystallographic tilting of 1.78° for the (hh0)pc planes of a (001)pc-oriented single-domain Mn-doped BiFeO3 (BFMO) thin film were found when an electric field was applied along the [110]pc direction. The anomalous crystallographic tilting was caused by ferroelastic domain switching of the 109° domain switching. In addition, ferroelastic domain switching occurred via an intermediate multidomain state. To investigate these switching dynamics under an electric field, we used in situ fluorescent X-ray induced Kossel line pattern measurements with synchrotron radiation. In addition, in situ inverse X-ray fluorescence holography (XFH) experiments revealed that atomic displacement occurred under an applied electric field. We attributed the atomic displacement to crystallographic tilting induced by a converse piezoelectric effect. Our findings provide important insights for the design of piezoelectric and ferroelectric materials and devices.

Reversible Mechanical Switching of Ferroelastic Stripe Domains in Multiferroic Thin Films.

The application potential of ferroelectric thin films largely relies on the controllability of their domain structure. Among the various proposed strategies, mechanical switching is being considered as a potential alternative to replace electrical switching for control of the domain structure of ferroelectric thin films via, e.g., the flexoelectric effect. So far, studies on mechanical switching are confined to out-of-plane polarization switching in ferroelectric thin films, which are in pristine or prepoled single-domain states. In this work, we report reversible in-plane mechanical switching of the monoclinic phase (MC phase) stripe domains in BiFeO3 thin films can be realized by scanning tip force. Via controlling the fast scan direction of the scanning probe microscopy tip and the magnitude of the tip force, the effective trailing field induced by the local tip force can be rotated to consequently switch the net in-plane polarization of the two-variant stripe domain patterns by either 90° or 180°. Moreover, the monoclinic to rhombohedral (MC-R) phase transition occurs during mechanical switching with the distribution of R-phase domains dependent on the switching paths. These results extend our current understanding of the mechanical switching behavior in ferroelectric thin films and should be instructive for their future applications.

A phase-field model for study of ferroelastic deformation behavior in yttria stabilized zirconia

A modified phase-field model coupled with linear elasticity is formulated to study the effect of ferroelastic domain switching on the deformation behavior of tetragonal-prime yttria-stabilized zirconia. Simulations are performed under uniaxial tension and compression using realistic domain microstructures. This work provides new insights into the mechanism of ferroelastic deformation by studying the evolution of domains under different loading directions and strain rates. The model predicts realistic stress-strain curves consisting of stress-plateaus with accurate domain switching behavior without setting a switching criterion based on a critical stress for nucleation of new domains. The results reveal that the origin of coercive stress lies in the balance between the energy absorbed by the domain switching process and the externally applied energy. Loading in different directions but parallel to the spontaneous strain results in different levels of coercive stress as domain switching absorbs different amounts of energy. For the same reason when the strain-rate increases, the coercive stress also increases. This work establishes the relation between the coercive stress and microstructural changes during ferroelastic domain switching.

In situ study on enhanced plastic deformability of Lanthanum-doped Bismuth ferrite processed by flash sintering

BiFeO3 is a promising multiferroic material for versatile device applications due to its co-existence of magnetic (i.e., antiferromagnetic) and ferroelectric ordering at room temperature. While its functional properties have been extensively investigated, the exploration of its mechanical behavior was limited mostly to the thin-film form of BiFeO3. In this work, we conducted in situ micropillar compression experiments to investigate the deformation behavior of La-doped BiFeO3 (La-BFO) samples processed by both conventional and flash sintering methods. The conventionally sintered La-BFO exhibited limited deformability at room temperature and 450 °C. In contrast, the deformability of the flash-sintered La-BFO specimens was substantially improved by nearly 100% at both testing temperatures. Detailed post-mortem studies suggest that preexisting dislocations and wide anti-phase boundaries introduced during flash sintering can toughen flash-sintered La-BFO by easing dislocation migration and ferroelastic domain switching. This study provides a fresh perspective to design an advanced multifunctional system with improved mechanical properties.

The effect of ferroelastic domains and ultrahigh‐density dislocations on fracture toughness of high entropy niobates

AbstractThis study investigates the fracture toughness and toughening mechanism of (La0.2Nd0.2Sm0.2Eu0.2Y0.2)NbO4, a high entropy material characterized by a high thermal expansion coefficient and low thermal conductivity. Our finding demonstrates a noteworthy 50% increase in fracture toughness for (La0.2Nd0.2Sm0.2Eu0.2Y0.2)NbO4 (∼3.09 MPa m0.5) compared to YNbO4 (∼2.11 MPa m0.5). The superior fracture toughness for (La0.2Nd0.2Sm0.2Eu0.2Y0.2)NbO4 can be attributed to the two key factors: relatively easy ferroelastic domain switching and the presence of ultrahigh‐density dislocations (∼7 × 108 mm−2). The enhanced ferroelastic toughening in (La0.2Nd0.2Sm0.2Eu0.2Y0.2)NbO4 is associated with its distinct characteristics, large atomic radius (RA), significant tetragonality (c/a ratio), and low monoclinic β angle. These factors contribute to larger spontaneous strain, larger coercive strain, and lower transformation strain, respectively. These properties facilitate the formation and switching of the ferroelastic domains. In addition, the interactions between the large strain field surrounding the dislocations and the cracks facilitate crack deflection and bridging. The combined effect of ferroelastic toughening and ultrahigh‐density dislocations ultimately leads to the significant improvement in the fracture toughness of (La0.2Nd0.2Sm0.2Eu0.2Y0.2)NbO4.

Phase field study of crack growth in t′ yttria stabilized zirconia with initial domain structures

In this paper, the fracture behavior of t′ yttria stabilized zirconia (YSZ) with initial domain structures is studied with the phase field (PF) method. Firstly, a PF model is proposed to characterize the initial domain structure and the subsequent domain switching in YSZ. After that, the PF model for domain structure evolution is coupled with the variational PF fracture model to simulate crack growth in the multi domain YSZ. The toughening effect induced by the ferroelastic domain switching is evaluated by computing the energy dissipation rate (EDR) along with the crack growth. It is shown that the internal stress field of the initial domain structure has very trivial influence on the crack growth resistance. However, the domain switching in the crack growth process can have significant influences on the fracture resistance. The domain structure evolution can bring about a local toughening or deshielding effect on the crack growth, depending on the crystal orientation. The underlying mechanisms are analyzed in detail. The proposed PF approach is efficient to study the mesoscale fracture behavior of multi domain YSZ and is helpful to assess the integrity of thermal barrier coatings.

Giant room-temperature modulation of magnetic anisotropy by electric fields in CoFeB/(011)-PMN-PT multiferroic heterostructures with two distinct initial magnetic anisotropies

This paper reports that the in situ growth magnetic field (Hg) during magnetic-phase CoFeB deposition impacts the electric-field control of magnetic anisotropy in Co40Fe40B20/(011)-Pb(Mg1/3Nb2/3)0.7Ti0.3O3 [CoFeB/(011)-PMN-PT] composite multiferroic heterostructures at room temperature. In the Hg1 mode (in situ Hg along the [011¯] direction of the ferroelectric PMN-PT substrate), the electric-field-controlled modulation ratios of the magnetic coercivity HC and saturation magnetic field HS are approximately −47% and +156%, respectively. However, in the Hg2 mode (in situ Hg along the [100] direction of the ferroelectric PMN-PT substrate) of the CoFeB/(011)-PMN-PT multiferroic heterostructure, the electric-field-controlled modulation ratios of the magnetic coercivity HC and saturation magnetic field HS can reach as high as +162% and +393%, respectively. Moreover, the electric-field-controlled magnetic coercive field HC exhibits a butterfly shape when plotted versus the applied electric fields in both modes, which matches the in-plane butterfly strain loop of the ferroelectric PMN-PT substrate. However, the electric-field-controlled saturation magnetic field HS presents a square loop, which is very consistent with the ferroelectric loop of the PMN-PT substrate. This result may be ascribed to the distinct pathway of the ferroelastic domain switching in the (011)-oriented PMN-PT substrate. This study provides a new idea for the design of spintronic devices based on multiferroic heterostructures.

Uniaxial stress-dependent dielectric properties and phase transitions of antiferroelectric AgNbO3

Antiferroelectric AgNbO3 ceramic is investigated with a focus on the effects of uniaxial compressive stress on dielectric response and phase transitions as well as its frequency-dependent ferroelastic behavior. The application of uniaxial compressive stress leads to diffused phase transitions, higher phase transition temperatures, and increased permittivity parallel to the stress application direction for low-temperature phase regions (MI, MIIa). The stress-dependent permittivity response at different phase regions reveals the influence of stress on domain wall motion and phase changes. Additionally, loading rate-dependent stress–strain measurements demonstrate easier ferroelastic domain switching under a lower loading frequency, where the coercive stress increases with frequency initially while getting saturated above 5 mHz. This study reveals the impact of external stress, which can alter the dielectric response and affect domain wall movement at different extents depending on the loading frequency and shift phase boundaries of AgNbO3, implying positive prospects of property engineering of energy storage materials by stress application.

In-situ synthesis of gadolinium niobate quasi-binary composites with balanced mechanical and thermal properties for thermal barrier coatings

Yttria-stabilized zirconia (YSZ) has been used as a thermal barrier coating (TBC) material in gas turbines for several decades. Although continuous efforts have been made to develop novel TBC materials that can work at a higher temperature, no single material other than YSZ has all the desired attributes for the TBCs. In this paper, we report the in-situ synthesis of quasi-binary GdNbO4/Gd3NbO7 composites based on the simple Gd2O3-Nb2O5 binary phase diagram. The fracture toughness of these quasi-binary composites is remarkably enhanced compared with the value predicted by the rule of mixtures because the ferroelastic domain switching is more activated due to the residual stress in the quasi-binary composites, which triggers more crack defections due to the enlarged process zone. Additionally, the Gd3NbO7 phase provides a low thermal conductivity due to the substantial chemical inhomogeneity, which diffuses phonons. Gd3NbO7/GdNbO4 exhibits a balanced thermal conductivity of 1.6 W/(m·K) at 1073 K and a toughness value of 2.76 MPa·m0.5, and these values are among the best comprehensive properties that have been obtained for new TBC materials. The work demonstrates a feasible approach of designing a new TBC material with balanced properties and can be easily fabricated.

Effect of airborne-particle abrasion of yttria-containing zirconia dental ceramics on mechanical properties before and after regeneration firing

The zirconia-resin adhesion, crucial in fixed dental prostheses, may be mechanically enhanced by airborne-particle abrasion (APA) induced surface roughening. APA may substantially increase the strength of 3Y-TZP, which is associated with (sub)surface compressive residual stresses through t-m phase transformation. In this work, the effects of APA and regeneration firing (RF) (1000 °C, 15 min) of various zirconia dental ceramics containing 3–5 mol.% of yttria were investigated. The phase composition, (sub)surface microstructural changes, and biaxial flexural strengths coupled with Weibull statistics and fractography were analysed and compared. The results show a significant increase in strength for 3Y and 4Y specimens after APA, ascribed to the t-m transformation toughening. However, APA substantially decreased the strength of 5Y variant. After RF, the ferroelastic domain switching phenomenon was presumably the persisting mechanism to withstand the propagation of APA-induced cracks in 3Y and 4Y zirconias, not being inferior to strength values of the as-sintered counterparts.

Nonvolatile modulation of spin transport in PMN-PT/LiFe5O8/Pt multiferroic heterostructures

Beside playing a keystone role in spin-field-effect transistor, electrical control of spin transport is also of fundamental and practical importance for many other spintronic devices due to the advantages of energy efficiency and versatility. In this work, we demonstrate a significant electrical modulation of spin transport in the PMN-PT/LiFe5O8/Pt heterostructures. The key spin transport parameters, including the spin Hall angle, spin diffusion length, and spin mixing conductance, were extracted through the thickness dependence of spin Hall magnetoresistance. It is found that the spin Hall angle decreases with the decrease in temperature, while the spin diffusion length keeps invariant with temperature, revealing the dominance of D'yakonov–Perel' type spin transport in LiFe5O8/Pt. Remarkably, by applying the electric field onto the piezoelectric PMN-PT substrate, the spin Hall angle of Pt can be modulated 28% and exhibits a nonvolatile hysteresis relationship with the applied electric field, which primarily originates from the modulation of Pt resistivity induced by the strain coupling through the ferroelastic domain switching of the ferroelectric PMN-PT substrate. Our results elucidate the spin transport characteristics in PMN-PT/LiFe5O8/Pt heterostructures and pave the way toward novel spintronic devices with electrically tunable spin current generation and transport processes.

Mild fluctuations in ferroelastic domain switching

We study the avalanche dynamics of shear-induced ferroelasticity by molecular dynamics simulations and statistical analysis. The dynamics of ferroelastic domain switching proceeds by avalanches which are power-law distributed. These avalanches can therefore be classified as wild with an energy exponent near 3. Wildness originates from the interaction between domain boundaries and defects, and jamming between domain boundaries. Concomitantly, mild events also arise but their distributions do not follow power-laws so that these mild energy releases are not scale invariant and exhibit a characteristic energy. We identify several mild domain switching events, namely the motion of single kinks and highly nonlinear relaxations of solitonic waves. The solitonic waves are reflected by domain boundaries, kinks, junctions, and free surfaces. Relaxations during domain switching have different characteristic energies from those created during creep. We observe the coexistence of mild and wild events depending on the external forces acting on the ferroelastic material.

Ferroelastic deformation mechanism and mechanical properties of [001]-oriented YSZ film by indentation

The ferroelastic properties of zirconia-based ceramics are crucial for their use as structural and functional materials. In this study, [001]-oriented ferroelastic YSZ films are prepared on the (100) SrTiO3 (STO) substrates by pulsed laser deposition (PLD). The mechanical properties and ferroelastic deformation mechanism of the film have been studied in detail through experiments and modeling. The Hardness and Young’s modulus of the YSZ film are 19.3 ± 0.4 GPa and 293.8 ± 5.1 GPa, respectively, which are determined by nanoindentation tests with the continuous stiffness measurement (CSM) mode. Indentation experiments show that a 90° twin domain structure is produced on the surface of the film. By combining TEM and STEM analysis methods, it was experimentally confirmed for the first time that the YSZ film produces ferroelastic deformation under the compressive stress of the indenter, causing the ferroelastic domain switching mechanism. Then the phase field simulation reproduced the ferroelastic domain switching process in the film under the indenter load and obtained the ferroelastic domain switching mechanism of the YSZ film. This proves the fundamental reason for the excellent mechanical properties of the ferroelastic YSZ film.

Self-Organized Ferroelastic Superdomains with Enhanced Piezoresponse in (101)-Oriented Pb(Zr0.2,Ti0.8)O3 Thin Films

Thin film engineering, utilizing proper control of crystalline orientation, strain, thickness, and defect density in thin films, has offered tremendous degrees of freedom for researchers to modify the physical properties, phase stability, and domain architectures in a wide spectrum of functional materials. This work unveils a naturally formed superdomain architecture arising from the low-orientation-symmetry-induced energetically degenerate state in a (101)-oriented tetragonal Pb(Zr,Ti)O3 epitaxial film. Different from conventional (101)-oriented/(110)-oriented domains found in (101)-oriented tetragonal Pb(Zr,Ti)O3 epitaxial heterostructures, these superdomains are composed of (101)-oriented domains with an alternative arrangement of opposite out-of-plane polarizations. Additionally, the conjunction between these superdomains has been found as another variant of the 90° domain wall that can exist in the low-symmetric preferred crystallographic orientation. The superdomains simultaneously exhibit an atypical piezoresponse hysteresis loop with additional metastable states, corresponding to the multistate ferroelastic domain switching process. This work gives distinct insight into the correlation between the domain pattern, lattice symmetry, and polarity switching, offering an effective way for exploring and engineering ultrafine domain features in tetragonal ferroelectrics.

Stress- and frequency-dependent properties of relaxor-like sodium bismuth titanate

Despite the importance of $({\mathrm{Na}}_{1/2}{\mathrm{Bi}}_{1/2})\mathrm{Ti}{\mathrm{O}}_{3}$ as an end member in lead-free ferroelectrics and as an oxide ion conductor, the relaxor/ferroelectric nature remains unclear. In order to understand the relaxor-like behavior, frequency-dependent macroscopic mechanical measurements of polycrystalline $({\mathrm{Na}}_{1/2}{\mathrm{Bi}}_{1/2})\mathrm{Ti}{\mathrm{O}}_{3}$ were performed as a function of poling state, revealing the role of a potential field-induced long-range ferroelectric order on the nonlinear hysteretic stress-strain behavior. The mechanical measurements showed an increase in remanent strain and decrease in coercive stress with electrical poling, consistent with previous studies of relaxors. Electrical poling and mechanical texturing were found to influence the frequency dispersion of the relative permittivity, highlighting the potentially relaxor-like response. Further, the relative permittivity showed a directional dependence with respect to the previously applied electrical and mechanical fields. These data are discussed in conjunction with ex situ stress- and electric-field-dependent piezoresponse force microscopy measurements that revealed a clear ferroelectric domain switching through the application of a sufficiently high electric field, but no change of the domain configuration for uniaxial compressive stresses up to \ensuremath{-}750 MPa. The in situ stress-dependent crystal structure, which was characterized using synchrotron x-ray diffraction, however, indicates stress-induced ferroelastic domain switching as the primary hysteretic process.