Field-induced Phase Transition Research Articles

Giant strains of 0.70% achieved via a field-induced multiple phase transition in BNT-based relaxor antiferroelectric ceramics

Giant strains of 0.70% achieved via a field-induced multiple phase transition in BNT-based relaxor antiferroelectric ceramics

Design and development of a new lead-free BiFeO3-BaTiO3 quenched ceramics for high piezoelectric strain performance

Designing a new high-performance lead-free ceramic has become a cutting-edge research topic due to growing concerns about the toxic nature of lead-based materials. In this work, a convenient strategy of compositional design and domain engineering is applied to the lead-fee BiFeO3-BaTiO3 ceramics which provides a flexible polarization free-energy profile for domain switching. Here, simultaneously enhanced dynamic piezoelectric constant (d33* ≈ 772 pm/V) and a good thermal-stability (Δd33* ≈ 26% over the temperature of 20–180 °C) are achieved with a high Curie temperature (TC) of 432 °C. This high piezoelectric strain performance is collectively attributed to multiple effects such as thermal quenching, suppression of defect charges by donor doping, chemically induced local structure heterogeneity, and electric field-induced phase transition. Furthermore, the addition of BT content decreased octahedral tilting that reduce anisotropy for domain switching and increased in tetragonality (cT/aT) providing a wider polar length for B-site cation displacement, leading to high piezoelectric strain performance. Atomic-resolution transmission electron microscopy and piezoelectric force microscopy combined with X-ray diffraction results strongly support the origin of high piezoelectricity. The high and temperature-stable piezoelectric strain response of this work is superior to those of other lead-free ceramics. The synergistic approach of composition design and the concept present here for the origin of high strain response provides a paradigm for the development of new materials for high-temperature piezoelectric actuator applications.

Field-induced anisotropic magnetic phase transitions and tricritical phenomena in GdCr6Ge6

Field-induced anisotropic magnetic phase transitions and tricritical phenomena in GdCr6Ge6

Electric field induced phase transition in multicomponent ceramics based on PbMg1/3Nb2/3O3–PbTiO3

Multicomponent ceramics based on PbMg1/3Nb2/3O3–PbTiO3 system were studied using X-ray diffraction at high electric fields. It was shown that electric field induced phase transition from initial pseudocubic phase to tetragonal one occurs at E > 5 kV/cm. Analysis of the intensities of the 200 X-ray peak components reveals the parameters of the tetragonal unit cell (с = 4.036 Å and а = 4.021 Å) and the degree of preferential domain orientation (≈ 35%) at E = 12 kV/cm. The results of X-ray diffraction studies are in a good agreement with the field-induced behavior of the macroscopic responses: strain, polarization, and dielectric permittivity.

Large reversible magnetocaloric effect in antiferromagnetic Er3Si2C2 compound

The magnetic properties, magnetic phase transition and magnetocaloric effects (MCE) of Er3Si2C2 compound were investigated based on theoretical calculations and experimental analysis. Based on the first principles calculations, the antiferromagnetic (AFM) ground state type in Er3Si2C2 compound was predicted and its electronic structure was investigated. The experimental results show that Er3Si2C2 compound is an AFM compound with the Néel temperature (TN) of 7 K and undergoes a field-induced first-order magnetic phase transition from AFM to ferromagnetic (FM) under magnetic fields exceeding 0.6 T at 2 K. The magnetic transition process of Er3Si2C2 compound was investigated and discussed. The values of the maximum magnetic entropy change (−ΔSMmax) and the refrigeration capacity (RC) are 17 J/(kg·K) and 193 J/kg under changing magnetic fields of 0–5 T, respectively. As a potential cryogenic magnetic refrigerant, the Er3Si2C2 compound also provides an interesting research medium to study the magnetic phase transition process.

Effect of memory behavior on electric-field-induced phase transition and electrocaloric response in antiferroelectric ceramics

Field-induced phase transition in antiferroelectric (AFE) materials always facilitates giant positive/negative electrocaloric (EC) responses for a promising cooling application, while it is not only associated with external field conditions but also applied field history, i.e., memory behavior. Herein, we demonstrate that memory behavior increases the likelihood of observing an EC response when the operating field is parallel to the pre-poling field, as compared to the antiparallel condition. Additionally, when the temperature is slightly above the AFE-ferroelectric (FE) phase transition temperature, the field-off process induces a two-step microstructure change, characterized by a rapid domain rotation followed by a slow phase transition, which finally produces an abnormal EC heat flow signal. Through a Landau theory analysis, this kinetic behavior is contributed to the competition between the ferroelectric (FE) order pinned by memory behavior and the thermal agitation favored AFE state. This work deepens the understanding of the phase transition in the ferroelectric system.

Investigation on degree of non-ergodicity and local piezoelectric properties in Na0.5Bi0.5TiO3–BiFeO3–PbTiO3 system

Knowledge of the statics and dynamics of ferroelectric domains is of immense importance since they are directly correlated with macroscopic polarization and strain. For the present work, piezoresponse force microscopy (PFM) is used to afford insight into field-induced phase transitions and local switching properties of a (1–2x)Na0.5Bi0.5TiO3–xBiFeO3–xPbTiO3 system for compositions, x = 0.01, 0.03, 0.05, and 0.07. Rietveld analysis of x-ray diffraction data reveals crystallization of the compound in single and dual phases in the chosen compositions. Upon the application of a local electric field, a phase transition from relaxor to normal ferroelectric (FE) is observed for all samples. A decrease in degree of non-ergodicity is realized within this composition range, which is found by analyzing the stability of field-induced ferroelectric domains. The field-induced FE domains for lower concentrations of x are found to be irreversible and a reversible nature was found for higher values of x. In addition, spatial variations of local switching parameters are investigated with the help of switching spectroscopic-PFM and a maximum local d33 was found for compositions having dual phases.

Discovery of Nanoscale Electric Field‐Induced Phase Transitions in ZrO2

AbstractThe emergence of ferroelectric and antiferroelectric properties in the semiconductor industry's most prominent high‐k dielectrics, HfO2 and ZrO2, is leading to technology developments unanticipated a decade ago. Yet the failure to clearly distinguish ferroelectric from antiferroelectric behavior is impeding progress. Band‐excitation piezoresponse force microscopy and molecular dynamics are used to elucidate the nanoscale electric field‐induced phase transitions present in ZrO2‐based antiferroelectrics. Antiferroelectric ZrO2 is clearly distinguished from a closely resembling pinched La‐doped HfO2 ferroelectric. Crystalline grains in the range of 3 – 20 nm are imaged independently undergoing reversible electric field induced phase transitions. The electrically accessible nanoscale phase transitions discovered in this study open up an unprecedented paradigm for the development of new nanoelectronic devices.

Field induced phase transition and magnetic phase diagram of multiferroic Ca2CoSi2O7

Magnetic phase transitions are important for the application of individual materials toward modern spintronics and sensing. Using high-resolution sound velocity and pyrocurrent measurements, we have obtained a detailed magnetic phase diagram of multiferroic Ca2CoSi2O7 for magnetic fields applied along the crystallographic [100]- and [001]-directions. The magneto-acoustic measurements were conducted for both longitudinal and transverse modes in both static and pulsed magnetic fields up to 17 and 68 T, respectively. Distinct anomalies with significant changes in sound velocity and sound attenuation were observed at the onset of the structural and magnetic phase transitions. Interestingly, results obtained for fields parallel to the [100]-direction reveal a hysteresis and step-like decrements in ultrasound indicating a transition into a different metastable structural distortion below TN and at magnetic fields between 4 and 10 T that has not been previously reported. We believe that this field-induced distorted structure phase may be the cause of the subsequent phase transition at 11 T. At low temperatures, a softening of the lattice within the ordered phases is also observed, which may be due to residual spin fluctuations.

Magnetic field induced reentrant multipolar ordering in the distorted kagome-lattice antiferromagnet Dy3Ru4Al12

We report on ultrasonic and magnetocaloric-effect measurements of the hexagonal antiferromagnet ${\mathrm{Dy}}_{3}{\mathrm{Ru}}_{4}{\mathrm{Al}}_{12}$ having a distorted kagome lattice. We observed a pronounced softening of the transverse modulus, ${C}_{44}$, above 30 T applied along [100], indicating an as-yet-unidentified magnetic field induced phase transition. We determined the field-temperature phase diagrams using pulsed magnetic fields up to 55.2 T, applied along [100] and [001]. Optimizing crystal-electric-field parameters within the mean-field approximation, we conclude that the enhancement of the field induced phase-transition temperature is due to electric quadrupolar and magnetic octupolar mediated interactions. We propose that the order parameter of the magnetic field induced phase transitions is the electric quadrupole ${O}_{zx}$, facilitated by octupole-mediated interactions.

Spin excitation continuum to topological magnon crossover and thermal Hall conductivity in Kitaev magnets

There has been great interest in identifying a Kitaev quantum spin liquid state in frustrated magnets with bond-dependent interactions. In particular, the experimental report of a half-quantized thermal Hall conductivity in $\alpha$-RuCl$_3$ in the presence of a magnetic field has generated excitement as it could be strong evidence for a field-induced chiral spin liquid. More recent experiments, however, provide a conflicting interpretation advocating for topological magnons in the field-polarized state as the origin of the non-quantized thermal Hall conductivity observed in their experiments. An inherent difficulty in distinguishing between the two scenarios is the phase transition between a putative two-dimensional spin liquid and the field-polarized state exists only at zero temperature, while the behaviour at finite temperature is mostly crossover phenomena. In this work, we provide insights into the finite temperature crossover behavior between the spin excitation continuum in a quantum spin liquid and topological magnons in the field-polarized state in three different theoretical models with large Kitaev interactions. These models allow for a field-induced phase transition from a spin liquid (or an intermediate field-induced spin liquid) to the field-polarized state in the quantum model. We obtain the dynamical spin structure factor as a function of magnetic field using molecular dynamics simulations and compute thermal Hall conductivity in the field-polarized regime. We demonstrate the gradual evolution of the dynamical spin structure factor exhibiting crossover behaviour near magnetic fields where zero-temperature phase transitions occur in the quantum model. We also examine nonlinear effects on topological magnons and the validity of thermal Hall conductivity computed using linear spin wave theory. We discuss the implications of our results to existing and future experiments.

Defect-Induced, Ferroelectric-Like Switching and Adjustable Dielectric Tunability in Antiferroelectrics.

Antiferroelectrics, which undergo a field-induced phase transition to ferroelectric order that manifests as double-hysteresis polarization switching, exhibit great potential for dielectric, electromechanical, and electrothermal applications. Compared to their ferroelectric cousins, however, considerably fewer efforts have been made to understand and control antiferroelectrics. Here, it is demonstrated that the polarization switching behavior of an antiferroelectric can be strongly influenced and effectively regulated by point defects. In films of the canonical antiferroelectric PbZrO3 , decreasing oxygen pressure during deposition (and thus increasing adatom kinetic energy) causes unexpected "ferroelectric-like" polarization switching although the films remain in the expected antiferroelectric orthorhombic phase. This "ferroelectric-like" switching is correlated with the creation of bombardment-induced point-defect complexes which pin the antiferroelectric-ferroelectric phase boundaries, and thus effectively delay the phase transition under changing field. The effective pinning energy is extracted via temperature-dependent switching-kinetics studies. In turn, by controlling the concentration of defect complexes, the dielectric tunability of the PbZrO3 can be adjusted, including being able to convert between "positive" and "negative" tunability near zero field. This work reveals the important role and strong capability of defects to engineer antiferroelectrics for new performance and functionalities.

Tunable polarization-drived superior energy storage performance in PbZrO 3 thin films

Antiferroelectric PbZrO₃ films have great potential to be used as the energy storage dielectrics due to the unique electric field-induced phase transition character. But the phase transition process always accompanies polarization hysteresis effect that induces large energy loss and lowers the breakdown strength, leading to inferior energy storage density as well as low efficiency. In this work, the synergistical strategies by doping smaller ions of Li⁺-Al³⁺ to substitute Pb²⁺ and lowering the annealing temperature from 700℃ to 550℃ are proposed to change the microstructure and tune the polarization character of PbZrO₃ films, excepting to dramatically improve the energy storage performances. The prepared Pb_(1-x)(Li_0.5Al_0.5)_xZrO₃(abbreviated as P_(1-x)(L_0.5A_0.5)_xZO) films exhibit ferroelectric-like (<em>FE</em>) rather than antiferroelectric (<em>AFE</em>) character once the doping content of Li⁺-Al³⁺ ions reaches 6 mol%, accompanying a significant improvement of energy storage density of 49.09 J/cm³,but energy storage efficiency is only 47.94% due to the long-correlation of ferroelectric domains. Accordingly, the low-temperature annealing is carried out to reduce the crystalline degree and the polarization loss. P_0.94(L_0.5A_0.5)_0.06ZO films annealed at 550℃ deliver a linear-like polarization rather than ferroelectric-like behavior annealed at 700℃, the lowered remanent polarization as well as improved breakdown strength (4814 kV/cm) result in the superior energy storage density of 58.7 J/cm³ and efficiency of 79.16%, simultaneously possessing excellent frequency and temperature stability, and good electric fatigue tolerance.

Nanoscale investigation on electric field induced ferroelectric phase transitions in the rhombohedral PMN-PT single crystal

The excellent piezoelectric property of Pb(Mg1/3Nb2/3)O3-PbTiO3(PMN-PT) single crystals has attracted increasing attentions for their application in electromechanical devices. Generally, the electric field induced phase transition is an important contribution to the piezoelectric response. Understanding the pathway of electric field induced phase transition is essential for the practical application of PMN-PT crystals. Here, evolution of the domain structure and surface screening charges during phase transitions in the (001) oriented 0.72PMN-0.28PT crystal were studied at nanoscale via piezo-response force microscopy (PFM) and Kelvin probe force microscopy (KPFM). In combination with confocal polarized Raman spectroscopy, electric field induced phase transitions were locally studied. PFM tip bias poling in 0.72PMN-0.28PT single crystal results in a rhombohedral to monoclinic phase transition. And the monoclinic phase relaxes back to the rhombohedral at elevated temperatures. Our work provides nanoscale investigations on the electric field induced phase transition, and will be instructive for the practical application of PMN-PT single crystals.

Effect of the Annealing Conditions on the Strain Responses of Lead-Free (Bi0.5Na0.5)TiO3–BaZrO3 Ferroelectric Thin Films

Bismuth sodium titanate (Bi0.5Na0.5)TiO3 (BNT)–based thin films have attracted large attention for the production of modern precise micro–devices due to their outstanding strain responses. However, obtaining good electrical properties and low leakage current in BNT-based thin films is still a great challenge. In this work, 0.945(Bi0.5Na0.5)TiO3–0.055BaZrO3 (BNT–5.5BZ) thin films were deposited by the chemical solution deposition (CSD) method and annealed under two different conditions. This work describes a careful research study on the influence of the annealing conditions on the crystalline structure, morphology, and electrical performance of the BNT–5.5BZ thin films. The films exhibited a dense structure and excellent electrical properties following an optimized thermal treatment process. An ultra–high strain response of 1.5% with a low dielectric loss of ~0.03 was obtained in the BNT–5.5BZ thin films after post-annealing in an O2 atmosphere. The results of this work show that the enhanced strain response was mainly due to a reversible field-induced phase transition between the ferroelectric phase and the relaxation state. The post-annealing treatment is an effective method to optimize the electrical properties of BNT–based films, providing many opportunities for the application of ferroelectric devices.

Alkali-earth metal ion inducing multiphase transition of lanthanum-free Pb(Zr0.5Sn0.5)O3 ceramics improves the energy storage properties

Constructing the stepwise phase transition can delay the polarization process of antiferroelectric ceramics, possessing certain significance for improving the energy storage density. However, the common multiphase transitions are obtained in the rare-earth ions doped PbZrO3-based systems. In the present work, the multiphase transition can also be induced in the lanthanum-free Pb(Zr0.5Sn0.5)O3 matrix with mere doping of the alkali-earth metal ion Sr. The introduction of Sr endows the matrix with a higher lattice distortion and the reduced phase-transition temperature. Moreover, related to the induced stepwise electric field-induced phase transition, the energy storage properties are remarkably enhanced to 10.5 J/cm3 and 83.2% when the substitution content of Sr is 3 mol. %. Sr modification can adjust the phase structure by regulating the phase stability of the matrix and suppress the leakage current originating from the structural changes. This work provides a successful attempt that the phase structure and energy storage performance of antiferroelectric ceramics can also be effectively controlled through cheaper and simpler element modification. The optimized energy storage performance provides a new material selection for pulsed power devices.

Tailoring high-energy storage NaNbO3-based materials from antiferroelectric to relaxor states

Reversible field-induced phase transitions define antiferroelectric perovskite oxides and lay the foundation for high-energy storage density materials, required for future green technologies. However, promising new antiferroelectrics are hampered by transition´s irreversibility and low electrical resistivity. Here, we demonstrate an approach to overcome these problems by adjusting the local structure and defect chemistry, delivering NaNbO3-based antiferroelectrics with well-defined double polarization loops. The attending reversible phase transition and structural changes at different length scales are probed by in situ high-energy X-ray diffraction, total scattering, transmission electron microcopy, and nuclear magnetic resonance spectroscopy. We show that the energy-storage density of the antiferroelectric compositions can be increased by an order of magnitude, while increasing the chemical disorder transforms the material to a relaxor state with a high energy efficiency of 90%. The results provide guidelines for efficient design of (anti-)ferroelectrics and open the way for the development of new material systems for a sustainable future.

Self-doped graphite nanobelts

We report that mechanical deformation of graphite with cavity shock waves introduces a new group of charge carriers, with both effective mass and native concentration one order of magnitude above those found in the pristine material. Their nature, however, remains quasi-2D. Our results show that defects introduced during mechanical exfoliation have the potential to unlock oscillatory behavior above 50 T in graphite, thus providing a new probe for field-induced electronic phase transitions in the material.

Spin reorientation in easy-plane kagome ferromagnet Li9Cr3(P2O7)3(PO4)2

We report the successful growth and characterization of Li9Cr3(P2O7)3(PO4)2 single crystal, and investigate its magnetic properties under external magnetic fields via magnetization and heat capacity measurements. Our study reveals that Li9Cr3(P2O7)3(PO4)2 is an easy-plane kagome ferromagnet with S = 3/2, as evidenced by the Curie–Weiss temperature of 6 K which implies a ferromagnetic exchange coupling in the material. Under zero magnetic field, Li9Cr3(P2O7)3(PO4)2 undergoes a magnetic transition at T C = 2.7 K from a paramagnetic state to a ferromagnetically ordered state with the magnetic moment lying in the kagome plane. By applying a c-axis directional magnetic field to rotate the spin alignment from the kagome plane to the c-axis, we observe a reduction in the magnetic transition temperature as the field is increased. We construct a magnetic phase diagram as a function of temperature and magnetic field applied parallel to the c-axis of Li9Cr3(P2O7)3(PO4)2 and find that the phase boundary is linear over a certain temperature range. Regarding that theoretically, the field-induced phase transition of the spin reorientation in the easy-plane ferromagnet can be viewed as the ferromagnetic magnon Bose–Einstein condensation (BEC), the phase boundary scaling of field-induced (B ∥ c) magnetic transition in Li9Cr3(P2O7)3(PO4)2 can be described as the quasi-2D magnon BEC, which has been observed in other ferromagnetic materials such as K2CuF4.

Field-induced second-harmonic generation induced by distorted soft chiral crystal

The nonlinear optical response of soft chiral crystal system-blue-phase (BP) liquid crystals was studied experimentally using a second-harmonic-generation (SHG) microscope. With the aid of the SHG microscope (SHM), the internal coupling between the polarization and structural deformation was visualized in a short time. In this study, a fringing field, formed at the electrode edges, causes lattice deformation of the cubic BPs, which contributes to the flexoelectric-optic response and field-induced SHG at low frequencies. Using the SHM, we can observe the spatial distribution of the induced polarization in the BPs, and the mean SHG intensity of the cubic BP depends quadratically on the strength of the electric field at a lower value. As the applied electric field increases, the structure of the BPs transfers to the chiral nematic phase (N*), and then the SHG intensity remains constant. Compared to the mean intensities of the SHG signal in N* and the different BPs in the low electric field, the SHG signal caused by the lattice deformation in BPs is weaker in N* and depends on the cubic structure of the BPs. The experimental results demonstrate that through the SHM, the influence of the inhomogeneous electric field on the BPs can be exhibited clearly because the response of the SHG signal in BPs is sensitive to field-induced lattice deformation and phase transitions between the BPs and chiral nematic. This will help us elucidate the mechanism of the secondary electro-optical response in BPs and for further improvement and development of high-performance photonic devices using BPs.