Electric Field Induced Phase Transformation Research Articles

Structural distortion in ferroelectric HfO2 – The factor that determines electric field-induced phase transformation

The origin of the wake-up effect and the factor that determines the amount of the wake-up effect in ferroelectric (FE) HfO2 were systematically investigated. By observing both the waking-up and the phase transformation induced by electric field cycling on the same scale, we clarified that the wake-up effect in our FE-HfO2 system is dominated by the phase transformation induced by electric field cycling. Nevertheless, other mechanisms might be prominent in other FE-HfO2 systems. In our study, we found an anomalous structural distortion induced in both FE and none-FE HfO2 films. We hypothesized that structural distortion is the factor that governs the phase transformation to be induced by electric field cycling. We verified our hypothesis by conducting a series of experiments to clarify the factor that determines the amount of anomalous structural distortion, and that the amount of structural distortion would be the universal factor that determines the amount of the phase transformation. We found that the structural distortion is originating from the shrinkage in the volume of HfO2 films during crystallization due to the difference in the densities among the crystallized phases. Finally, we verified that the amount of structural distortion can be regarded as the universal factor that determines the amount of phase transformation to be induced by electric field cycling.

Uncovering the symmetry of the induced ferroelectric phase transformation in polycrystalline barium titanate

Microstructural design is a widespread approach to tailor the properties of functional materials with the size effect being an effective constraint that modifies physical phenomena. In this work, we investigate the grain size effect on the properties and the electric field induced phase transformation behavior in barium titanate. A broad range of unimodal average grain size distribution between 0.4 and 15 μm was successfully sintered avoiding abnormal grain growth. Samples with a grain size close to the range of 1–2 μm, balancing microstructural strain, presence, and mobility of domain walls to allow the field induced crystal phase transformation, showed optimal electromechanical and dielectric properties. By means of in situ high energy x-ray diffraction and a high-resolution multianalyzer detector, we distinguish and quantify a tetragonal–orthorhombic phase transformation induced by an electric field, providing unambiguous proof of this induced phase transformation. These results contribute to the understanding of fundamental questions about the piezoelectric effect in barium titanate and consequently other similar systems.

Revealing intrinsic and extrinsic piezoelectric contributions in phase coexistence system of PbTiO3-BiScO3

PbTiO3-BiScO3 ceramics possess high piezoelectricity and high Curie temperature simultaneously, presenting a very promising candidate for high-temperature actuators and transducers. Figuring out the underlying piezoelectric mechanisms is of great importance for its application. Herein, we reveal the quantified intrinsic and extrinsic contributions to the high electrostrain of the morphotropic composition with phase coexistence by employing the advanced in situ electrical biasing high-energy synchrotron X-ray diffraction combined with the STRAP (strain, texture, and Rietveld analysis for piezoceramics from diffraction) methodology. An electric field-induced phase transformation is observed between the coexisting tetragonal and rhombohedral phases. It is found that the tetragonal phase contributes most of the domain switching strain, while the predominant lattice strain is from the rhombohedral phase. With phase fraction changes, the quantitative results demonstrate that the field-induced electrostrain is mainly contributed by the intrinsic lattice strain. In contrast, the high irreversible domain switching strain dominates the large remanent strain. It implies that transforming the large remanent strain into reversible strain would be a strategic direction to improve the piezoelectric response. The present results provide a further understanding of the high piezoelectricity and could help to advance the application of PbTiO3-BiScO3.

The role of intermediate S-polymorph towards high piezoelectricity in La-doped BiFeO3 epitaxial thin films

Mixed phases with stripe patterns are considered as a prerequisite for remarkable piezoelectric properties in epitaxial BiFeO3 (BFO) thin films. Among the mixed phases in BFO epitaxial thin films, the vital role in achieving high piezoelectric response is attributed to the intermediate S-polymorph that bridges the transition between rhombohedral and tetragonal phases. However, the correlation between the S-phase and the piezoelectric strain in mixed-phase BFO has not been understood well due to the lack of a probe technique that can investigate the structural and electromechanical variations simultaneously. Here, using the time-resolved X-ray microdiffraction technique, we investigate the electric field induced phase transformation dynamics of a mixed-phase epitaxial La-doped BFO (BLFO) thin film. The BLFO thin film exhibits phase transformations between monoclinic MC and tilted MC, S/tilted S (Stilt) phases under an applied electric field. Among the competing phases, we found that the S- or tilted S-phases exhibit the highest piezoelectric strain variation up to 0.7% at an electric field pulse of strength 1.3 MV/cm and width 5 μs. The present study correlates the high piezoelectric response in mixed-phase BLFO thin films with the presence of S/Stilt -phases, which offers a useful pathway into designing strain-engineered ultra-high piezoelectric BFO thin films.

Analyses of Electric Field-Induced Phase Transformation by Luminescence Study in Eu3+-doped (Na, K)0.5Bi0.5TiO3 Ceramics.

Most analyses of phase transformations detected by rare earth ions are based on the luminescence spectrum, while in this study we focus on the luminescence decay processes. We prepared Eu3+-doped (Na, K)0.5Bi0.5TiO3 ceramics and studied their phase structure before and after poling by luminescence spectra, decay curves, and X-ray diffraction (XRD). Luminescence spectra indicated that electric fields induced a transformation in (Na0.8, K0.2)0.5Bi0.497Eu0.003TiO3 (NKBET20) ceramic from tetragonal to rhombohedral phase (R phase). Based on the decay kinetics and the Judd–Ofelt theory, decay curves were shown to identify the fraction of the transformation quantitatively. The data from decay curves suggest that with electric fields increasing from 0 to 50 kV/cm, the R phase fraction increases from about 23 to 89% and the tetragonal phase (T phase) fraction decreases from about 77 to 11%. XRD Rietveld analyses further confirmed the results. In this work, the analyses of the phase fractions are simplified by the monoexponential decay of the pure phases and the biexponential decay of the mixed phase, showing an easy and inexpensive way of studying the phase structures of the materials.

Dynamics and grain orientation dependence of the electric field induced phase transformation in Sm modified BiFeO3 ceramics

Sm-Modified BiFeO3 multiferroic ceramics experience two simultaneous electric field induced phase transformations, both of which have strong grain orientation dependences and slow transformation kinetics in the order of several minutes.

In-situ Electric Field-Induced Modulation of Photoluminescence in Pr-doped Ba0.85Ca0.15Ti0.90Zr0.10O3 Lead-Free Ceramics.

Luminescent materials with dynamic photoluminescence activity have aroused special interest because of their potential widespread applications. One proposed approach of directly and reversibly modulating the photoluminescence emissions is by means of introducing an external electric field in an in-situ and real-time way, which has only been focused on thin films. In this work, we demonstrate that real-time electric field-induced photoluminescence modulation can be realized in a bulk Ba0.85Ca0.15Ti0.90Zr0.10O3 ferroelectric ceramic doped with 0.2 mol% Pr3+, owing to its remarkable polarization reversal and phase evolution near the morphotropic phase boundary. Along with in-situ X-ray diffraction analysis, our results reveal that an applied electric field induces not only typical polarization switching and minor crystal deformation, but also tetragonal-to-rhombohedral phase transformation of the ceramic. The electric field-induced phase transformation is irreversible and engenders dominant effect on photoluminescence emissions as a result of an increase in structural symmetry. After it is completed in a few cycles of electric field, the photoluminescence emissions become governed mainly by the polarization switching, and thus vary reversibly with the modulating electric field. Our results open a promising avenue towards the realization of bulk ceramic-based tunable photoluminescence activity with high repeatability, flexible controllability, and environmental-friendly chemical process.

Aliovalent cation ordering, coexisting ferroelectric structures, and electric field induced phase transformation in lead-free ferroelectric Na0.5Bi0.5TiO3

Using first-principles calculations, we show that a specific chemical ordering of Na and Bi in Na0.5Bi0.5TiO3 is responsible for the co-existence of its ferroelectric phases with rhombohedral R3c and monoclinic Cc structures, which are relevant to its morphotropic phase boundary and large piezoelectric response. We identify the signatures of chemical ordering in the calculated phonon spectra and establish the prevalence of A-type ordering through comparison with experiment. We uncover a mechanism of the observed electric field induced Cc to lower energy R3c structural transformation promoted by a hybrid soft mode involving a combination of TiO6 rotations and a polar component.

Stress and electric field induced phase transformation phenomena in [0 1 1]-poled PZN–PT single crystals of [1 0 0]-length cut

For rhombohedral PZN–(4.5–7)%PT single crystals of [ 1 0 0 ] L ( A ) × [ 0 1 ¯ 1 ] W × [ 0 1 1 ] T ( P ) cut, A and P denoting Active and Poled direction respectively, the applied axial compressive stress in the [1 0 0]-length direction and electric field in the [0 1 1] poling direction aid one another to bring about the rhombohedral-to-orthorhombic (R-O) phase transformation in the crystal. On stress and/or field removal, PZN–(4.5–6)%PT single crystals revert back to the rhombohedral state and the original good properties are retained but not for PZN–7%PT single crystal which remains in the overpoled orthorhombic state with degraded properties. The stress and electric field for the R-O phase transformation, i.e. the E RO– σ RO curves, for PZN–4.5%PT, PZN–5.5%PT and PZN–6%PT of said crystal cut are provided which are useful for device design purposes.

Effect of La modification on antiferroelectricity and dielectric phase transition in sol–gel grown [formula omitted] thin films

Antiferroelectricity of sol–gel grown pure and La modified PbZrO 3 thin films, with a maximum extent of 6 mol%, has been characterized by temperature dependent P – E hysteresis loops within the applied electric field of 60 MV/m. It has been seen that on extent of La modification electric field induced phase transformation can be altered and at 40 °C its maximum value has been observed at ±38 MV/m on 6 mol% modifications whereas the minimum value is ±22 MV/m on 1 mol%. On La modification the variation of electric field induced phase transformations at 40 °C has been correlated with the temperature of antiferroelectric phase condensation on cooling. The critical electric fields for saturated P – E hysteresis loops have been defined from field dependent maximum polarizations and their variations on La modification show a similar trend as found in their dielectric phase transition temperatures.

Influence of composition and pressure on the electric field-induced antiferroelectric to ferroelectric phase transformation in lanthanum modified lead zirconate titanate ceramics

The electric field-induced phase transformation behavior in lanthanum-doped lead zirconate titanate ceramics was examined by polarization versus electrical field (P-E) measurements carried out from room temperature to 130 degrees C and under hydrostatic pressures from 20 to 300 MPa. The samples with composition (Pb(1-x)La(x))(Zr(0.90)Ti(0.10))(1-x/4)O(3) [PLZT x/90/10; x = 2,3,4 at%] were prepared by the standard solid-state reaction method. The analysis at room temperature under atmospheric pressure showed that the increase in the lanthanum content induces a transformation from the typical ferroelectric hysteresis, observed for PLZT 2,3/90/10, to double-hysteresis loops, typical of antiferroelectric phases, for PLZT 4/90/10 under a strong electric field. Hydrostatic pressure- induced and temperature-induced ferroelectric (FE) to antiferroelectric (AFE) phase transformations were examined. The measured hysteresis loops indicated that the FE-AFE phase transformation depends on both temperature and hydrostatic pressure for PLZT 3/90/10. This composition, which is in a ferroelectric state at room temperature under atmospheric pressure, can be transformed into the antiferroelectric phase by the application of a hydrostatic pressure of 100 MPa or by increasing the temperature to around 90 degrees C. The PLZT 2/90/10 and 4/90/10 compositions displayed predominantly ferroelectric and antiferroelectric behavior, respectively, over the ranges of temperature and hydrostatic pressure examined in the present study.

Study of the structure and electrostrictive property of proton-irradiated P(VDF-TrFE) 56/44 mol% copolymer

High-energy proton (3 MeV) irradiation with dosages ranging from 43 to 200 Mrad have been carried out to investigate the potential for modifying both the structure and property of vinylidene fluoride-trifluoroethylene 56/44 mol% copolymer. The structural and transitional behavior of the irradiated copolymer was studied by X-ray diffraction and differential scanning calorimetry. The polarization hysteresis, relative permittivity properties and electrostrictive strain response of these copolymers were also measured. It was found that the ferroelectric copolymer could be successfully converted to a relaxor at a low proton dosage of about 75 Mrad at ambient temperature. A slim polarization hysteresis loop and a frequency dispersion of the relative permittivity observed in the irradiated copolymer imply that the high-energy protons break up the coherent polarization domains in the ferroelectric copolymer into nanosized regions. In addition, the irradiation leads to a significant change in the ferroelectric-to-paraelectric phase transition behavior. X-ray diffraction measurements show that the crystalline region in the copolymer is converted into a nonpolar phase upon irradiation, and the lattice spacing increases significantly. The electric field induced phase transformation of the nanosized regions between the nonpolar and polar phase leads to a high electrostrictive strain observed in the irradiated copolymer.

Large Strain Ceramics Based on Electric Field-Induced Phase Transformation in Sr-Modified PZT

The electric field-induced antiferroelectric (AFE) to ferroelectric (FE) phase transition in lead strontium zirconate titanate (PSZT) ceramics is studied by polarization, X-ray diffraction, and strain measurements. PSZT compositions with varying strontium and Zr/Ti ratios, located in the ferroelectric, antiferroelectric phase regions, and near the AFE/FE phase boundary are prepared. Electric filed-induced AFE to FE phase change is demonstrated in selected compositions, which also displayed large strains of ∼0.5% in polycrystalline ceramics. The origin of the large induced strain is identified to be the AFE-FE phase transformation by in situ X-ray diffraction studies.