Understanding Ferroelectric Phase Transitions and Domain Switching by Phase-field Modeling

The temperature in the ferroelectric and ferromagnetic materials may rise due to energy dissipation under loading. Thermal effects on the mechanical behavior in ferroelectric/ferromagnetic materials are investigated theoretically in this paper. First, the influence of stresses induced by domain switching on the subsequent domain switching and domain reversal process in ferroelectrics is investigated. Based on the electrical saturation model, the influence of thermal effect on the domain switching is studied, and the changes of stress and electric intensity factors brought by thermal effect are obtained. The accumulative influence of temperature rise on the domain switching zone and fracture behavior of ferroelectrics under cycle electric field is studied. Second, the above approach of ferroelectric materials is extended to analyze the thermal effect in ferromagnetic materials. Using the magnetic saturation model, the temperature fields around the tip of a narrow elliptic hole are calculated under different conditions. It is found that the magnitude of temperature increment strongly depends upon the geometrical shape of the hole, the frequency and wave shape of the magnetic loading. This study is helpful to gain a deep understanding of the fracture and fatigue behavior of ferroelectric/ferromagnetic materials.

In this study, a generalized inverse-pole-figure (IPF) method has been suggested to analyze domain switching in polycrystalline ferroelectrics including composition of morphotropic phase boundary (MPB). Using the generalized IPF method, saturated domain orientation textures of single-phase polycrystalline ferroelectrics with tetragonal and rhombohedral symmetry have been analytically calculated and the results have been confirmed by comparison with the results from preceding studies. In addition, saturated domain orientation textures near MPBs of different multiple-phase polycrystalline ferroelectrics have been also analytically calculated. The results show that the generalized IPF method is an efficient method to analyze not only domain switching of single-phase polycrystalline ferroelectrics but also MPB of multiple-phase polycrystalline ferroelectrics.

Ordered coalescence of nano-crystals in alkaline niobate ceramics with high remanent polarization

Ferroelectric domain switching within individual nanoscale grains of a 100 nm thick polycrystalline PbZr0.2Ti0.8O3 thin film has been shown to depend on the relative crystallographic orientation of the adjacent grains. Using Piezoresponse Force Microscopy, the significance of local microstructure on the domain switching was demonstrated. Different regions within grains show different coercive fields under the same external electric field. In addition, neighboring grains also show a collective switching pattern, facilitating/suppressing switching on both sides of the grain boundaries compared to the center of the grain. These experimental observations were supported by numerical simulation demonstrating that changing the crystallographic orientation of a grain affects the switching loop of the neighboring grains. Based on both experimental and numerical simulation, the conclusion can be made that microstructural modulation of the local electric and stress field can significantly affect individual grain switching in polycrystalline thin films.

Simulations of gradual domain-switching in polycrystalline ferroelectrics using an optimization-based, multidomain-grain model

Domain switching kinetics in ferroelectric PbTiO3 nanostructures

Fracture mechanics of piezoelectric materials – Where are we right now?

Ferromagnetic resonance with applied electric fields has been used to investigate the magnetoelectric effect in a Fe/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 heterostructure. The out-of-plane magnetoelectric effect follows a butterfly behavior in response to electric field, consistent with the linear piezoelectric strain-mediated mechanism. In contrast, the in-plane magnetoelectric effect exhibits a loop-like dependence on electric field. In addition, a relaxation of the in-plane resonant field has been observed after the ferroelectric domains are switched. The loop-like feature and the time-dependent response suggest that the in-plane magnetoelectric coupling involves the 109° switching and relaxation of ferroelectric domains.

Diffraction provides an effective means to characterize ferroelectric materials under dynamic loading conditions. This paper describes a typical time-resolved diffraction setup and one example of a time-dependent strain response to an applied electric field in a piezoelectric lead zirconate titanate (PZT) ceramic.

The study of domain switching and dielectric breakdown behavior of ferroelectrics together with their relations is crucial for understanding the essence of ferroelectric physics and exploring their applications. In this work, a phase-field method is developed to reveal the coupled domain structure and dielectric breakdown evolution in a ferroelectric single crystal (FSC) by employing the Ginzburg-Landau kinetic equation and Griffith type energy criterion. Results show that the domain switching mobility, symbolizing the speed of polarization evolution, has a significant influence on ferroelectric properties, namely coercive field, dielectric breakdown strength (DBS), discharge energy density (DED), and energy storage efficiency (ESE). It is found that FSC with the higher domain switching mobility always displays a lower coercive field and smaller remanent electric displacement (or polarization) together with a higher DBS, accounting for a higher DED and ESE. Such findings can provide effective guidance in understanding and designing high-DBS and high-energy-density ferroelectrics. In addition, the defect concentration has a significant influence on the DBS and the pattern of breakdown paths.

Ferroelectric domain switching on the surface of a lithium niobate thin film can be induced by the tip of a scanning probe microscope, and gives rise to both regular and chaotic spatiotemporal patterns. Moreover, the long-range interactions that govern these phenomena can be tuned by varying temperature, humidity, domain spacing and tip bias.

We report on electrically switchable polarization and ferroelectric domain scaling over a thickness range of 5–100 nm in BiFeO3 films deposited on [110] vicinal substrates. The BiFeO3 films of variable thickness were deposited with SrRuO3 bottom layer using the pulsed laser deposition technique. The domains are engineered into preferentially oriented patterns due to substrate vicinality along the [110] direction. The domain width scales closely with the square root of film thickness, in agreement with the Landau–Lifschitz–Kittel (LLK) law. Switching spectroscopy piezo-response force microscopy provides clear evidence for the ferroelectric switching behavior in all the films.

Self-doping of the h-LuMnxO3±δ (0.92 ≤ x ≤ 1.12) phase and changes in the sintering time are applied to investigate the formation and annihilation of antiphase ferroelectric (FE) domains in bulk ceramics. The increase in the annealing time in sintering results in growth of FE domains, which depends on the type of vacancy, 6-fold vortices with dimensions of the order of 20 μm being observed. Interference of planar defects of the lattice with the growth of topological defects shows breaking of 6-fold symmetry in the self-doped ceramics. The role of grain boundaries in the development of topological defects has been studied. Dominance of the atypical FE domain network in very defective h-LuMnxO3±δ lattices saturated with Mn vacancies (x < 1) was also identified in the current study. After a long annealing time, scattered closed-loops of nano-dimensions are often observed isolated inside large FE domains with opposite polarization. Restoring of the polarization after alternative poling with opposite electrical fields is observed in FE domains. Stress/strain in the lattice driven by either planar defects or chemical inhomogeneity results in FE polarization switching on the nanoscale and further formation of nano-vortices, with detailed investigation being carried out by electron microscopy. Pinning of FE domains to planar defects is explored in the present microscopy analysis, and nano-scale observation of lattices is used to explain features of the ferroelectricity revealed in Piezo Force Microscopy images of the ceramics.

The use of ferroelectric polarization to promote electron–hole separation has emerged as a promising strategy to improve photocatalytic activity. Although ferroelectric thin films with planar geometry have been largely studied, nanostructured and porous ferroelectric thin films have not been commonly used in photo-electrocatalysis. The inclusion of porosity in ferroelectric thin films would enhance the surface area and reactivity, leading to a potential improvement of the photoelectrochemical (PEC) performance. Herein, the preparation of porous barium titanate (pBTO) thin films by a soft template-assisted sol–gel method is reported, and the control of porosity using different organic/inorganic ratios is verified by the combination of scanning electron microscopy and ellipsometry techniques. Using piezoresponse force microscopy, the switching of ferroelectric domains in pBTO thin films is observed, confirming that the ferroelectric polarization is still retained in the porous structures. In addition, the presence of porosity in pBTO thin films leads to a clear improvement of the PEC response. By electrochemical poling, we also demonstrated the tuning of the PEC performance of pBTO thin films via ferroelectric polarization. Our work offers a simple and low-cost approach to control the morphology optimization of ferroelectric thin films, which could open up the development of materials with great potential for PEC applications.

The domain-switching process of monoclinic K0.25Na0.75NbO3single crystals were studied byin situpolarized light microscopy and X-ray diffraction.