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Knowledge of the thermodynamic equilibria and domain structures of ferroelectrics is critical to establishing their structure–property relationships that underpin their applications from piezoelectric devices to nonlinear optics. Here, we establish the strain condition for strain phase separation and polydomain formation and analytically predict the corresponding domain volume fractions and wall orientations of, relatively low symmetry and theoretically more challenging, monoclinic ferroelectric thin films by integrating thermodynamics of ferroelectrics, strain phase equilibria theory, microelasticity, and phase‐field method. Using monoclinic KxNa1 − xNbO3(0.5 < x < 1.0) thin films as a model system, we establish the polydomain strain–strain phase diagrams, from which we identify two types of monoclinic polydomain structures. The analytically predicted strain conditions of formation, domain volume fractions, and domain wall orientations for the two polydomain structures are consistent with phase‐field simulations and in good agreement with experimental results in the literature. The present study demonstrates a general, powerful analytical theoretical framework to predict the strain phase equilibria and domain wall orientations of polydomain structures applicable to both high‐ and low‐symmetry ferroelectrics and provide fundamental insights into the equilibrium domain structures of ferroelectric KxNa1 − xNbO3 thin films that are of technology relevance for lead‐free dielectric and piezoelectric applications. [ABSTRACT FROM AUTHOR]

Oxygen vacancy is the most common type of point defects in functional oxides, and it is known to have profound influence on their properties. This is particularly true for ferroelectric oxides since their interaction with ferroelectric polarization often dictates the ferroelectric responses. Here, we study the influence of the concentration of oxygen vacancies on the stability of ferroelectric domain walls (DWs) in BiFeO3, a material with a relatively narrow bandgap among all perovskite oxides, which enables strong interactions among electronic charge carriers, oxygen vacancies, and ferroelectric domains. It is found that the electronic charge carriers in the absence of oxygen vacancies have essentially no influence on the spatial polarization distribution of the DWs due to their low concentrations. Upon increasing the concentration of oxygen vacancies, charge‐neutral DWs with an originally symmetric polarization distribution symmetric around the center of the wall can develop a strong asymmetry of the polarization field, which is mediated by the electrostatic interaction between polarization and electrons from the ionization of oxygen vacancies. Strongly charged head‐to‐head DWs that are unstable without oxygen vacancies can be energetically stabilized in the off‐stoichiometric BiFeO3−δ with δ ∼ 0.02 where ionization of oxygen vacancies provides sufficient free electrons to compensate the bound charge at the wall. Our results delineate the electrostatic coupling of the ionic defects and the associated free electronic charge carriers with the bound charge in the vicinity of neutral and charged DWs in perovskite ferroelectrics. [ABSTRACT FROM AUTHOR]

Interest in high‐entropy inorganic compounds originates from their ability to stabilize cations and anions in local environments that rarely occur at standard temperature and pressure. This leads to new crystalline phases in many‐cation formulations with structures and properties that depart from conventional trends. The highest‐entropy homogeneous and random solid solution is a parent structure from which a continuum of lower‐entropy offspring can originate by adopting chemical and/or structural order. This report demonstrates how synthesis conditions, thermal history, and elastic and chemical boundary conditions conspire to regulate this process in Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O, during which coherent CuO nanotweeds and spinel nanocuboids evolve. We do so by combining structured synthesis routes, atomic‐resolution microscopy and spectroscopy, density functional theory, and a phase field modeling framework that accurately predicts the emergent structure and local chemistry. This establishes a framework to appreciate, understand, and predict the macrostate spectrum available to a high‐entropy system that is critical to rationalizing property engineering opportunities. [ABSTRACT FROM AUTHOR]

HfO2‐based ferroelectrics offer promises for next‐generation nonvolatile nanoscale devices owing to excellent CMOS compatibility and robust ferroelectricity at the nanoscale. However, fundamentally understanding the mechanism of polarization reversal and domain dynamics is challenging because the role of the spacer layer at the domain level in HfO2‐based ferroelectrics remains elusive. Here, it is realized that visualization of time‐resolved dynamics of nanoscale domain configurations in the epitaxial Hf0.5Zr0.5O2 thin films using phase‐field simulations. Scale‐free domain independent switchability (namely, irreducible stable polar domain down to 1 nm lateral size) and sharp domain walls that originate from weak interactions between adjacent domains characterized by the reduced gradient energy coefficient, which unravels the mesoscale mechanism of spacer layer in domain dynamics are demonstrated. Meanwhile, it is revealed that 180° polarization switching is dominated by the nucleation of a new domain with a high nucleation density, well described by the nucleation‐limited switching model. This study not only provides a fundamental mesoscale mechanism of the spacer layer, but also stimulates further studies on the manipulation of ultra‐scaled single domain state for designing high‐density and fast‐speed HfO2‐based ferroelectric memory. [ABSTRACT FROM AUTHOR]

The magnetoelectric effect is technologically appealing because of its ability to manipulate magnetism using an electric field rather than magnetic field or current, thus providing a promising solution for the development of energy‐efficient spintronics. Although 180° magnetization switching is vital to spintronic devices, the achievement of 180° magnetization switching via magnetoelectric coupling is still a fundamental challenge. Herein, voltage‐driven full resistance switching of a magnetic tunnel junction (MTJ) with dipole interaction on a ferroelectric substrate through switchable parallel/antiparallel magnetization alignment is demonstrated. Parallel magnetization alignment along the y direction is obtained under a bias magnetic field. By rotating the magnetic easy axis via strain‐mediated magnetoelectric coupling, the parallel magnetizations in the MTJ reorient to the x axis with opposite paths because of dipole interaction, thus resulting in antiparallel alignment. Moreover, this voltage switching of MTJs is nonvolatile owing to variations in dipole interaction and can be well understood via phase field simulations. The results provide an avenue to realize electrical switching of MTJs and are significant for exploring energy‐efficient spintronic devices. [ABSTRACT FROM AUTHOR]

Understanding the electromechanical breakdown mechanisms of polycrystalline ceramics is critical to texture engineering for high‐energy‐density dielectric ceramics. Here, an electromechanical breakdown model is developed to fundamentally understand the electrostrictive effect on the breakdown behavior of textured ceramics. Taking the Na0.5Bi0.5TiO3‐Sr0.7Bi0.2TiO3 ceramic as an example, it is found that the breakdown process significantly depends on the local electric/strain energy distributions in polycrystalline ceramics, and reasonable texture design could greatly alleviate electromechanical breakdown. Then, high‐throughput simulations are performed to establish the mapping relationship between the breakdown strength and different intrinsic/extrinsic variables. Finally, machine learning is conducted on the database from the high‐throughput simulations to obtain the mathematical expression for semi‐quantitatively predicting the breakdown strength, based on which some basic principles of texture design are proposed. The present work provides a computational understanding of the electromechanical breakdown behavior in textured ceramics and is expected to stimulate more theoretical and experimental efforts in designing textured ceramics with reliable electromechanical performances. [ABSTRACT FROM AUTHOR]

Piezoresponse force microscopy (PFM) is used for investigation of the electromechanical behavior of the head‐to‐head (H‐H) and tail‐to‐tail (T‐T) domain walls on the non‐polar surfaces of three uniaxial ferroelectric materials with different crystal structures: LiNbO3, Pb5Ge3O11, and ErMnO3. It is shown that, contrary to the common expectation that the domain walls should not exhibit any PFM response on the non‐polar surface, an out‐of‐plane deformation of the crystal at the H‐H and T‐T domain walls occurs even in the absence of the out‐of‐plane polarization component due to a specific form of the piezoelectric tensor. In spite of their different symmetry, in all studied materials, the dominant contribution comes from the counteracting shear strains on both sides of the H‐H and T‐T domain walls. The finite element analysis approach that takes into account a contribution of all elements in the piezoelectric tensor, is applicable to any ferroelectric material and can be instrumental for getting a new insight into the coupling between the electromechanical and electronic properties of the charged ferroelectric domain walls. [ABSTRACT FROM AUTHOR]

Order–disorder transitions are widely explored in various vortex structures in condensed matter physics, that is, in the type‐II superconductors and Bose–Einstein condensates. In this study, the ordering of the polar vortex phase in [Pb(Zr0.4Ti0.6)O3]n/(SrTiO3)n (PZT/STO) superlattices is investigated through phase‐field simulations. With a large tensile substrate strain, an antiorder vortex state (where the rotation direction of the vortex arrays in the neighboring ferroelectric layers are flipped) is discovered for short‐period PZT/STO superlattice. The driving force is the induced in‐plane polarization in the STO layers due to the large tensile epitaxial strain. Increasing the periodicity leads to antiorder to disorder transition, resulting from the high energy of the head‐to‐head/tail‐to‐tail domain structure in the STO layer. On the other hand, when the periodicity is kept constant in short‐period superlattices, the order–disorder–antiorder transition can be engineered by mediating the substrate strain, due to the competition between the induction of out‐of‐plane (due to interfacial depolarization effect) and in‐plane (due to strain) polarization in the STO layer. The 3D ordering of such polar vortices is still a topic of significant current interest and it is envisioned that this study will spur further interest toward the understanding of order–disorder transitions in ferroelectric topological structures. [ABSTRACT FROM AUTHOR]

Piezoelectric nanocomposites with oxide fillers in a polymer matrix combine the merit of high piezoelectric response of the oxides and flexibility as well as biocompatibility of the polymers. Understanding the role of the choice of materials and the filler‐matrix architecture is critical to achieving desired functionality of a composite towards applications in flexible electronics and energy harvest devices. Herein, a high‐throughput phase‐field simulation is conducted to systematically reveal the influence of morphology and spatial orientation of an oxide filler on the piezoelectric, mechanical, and dielectric properties of the piezoelectric nanocomposites. It is discovered that with a constant filler volume fraction, a composite composed of vertical pillars exhibits superior piezoelectric response and electromechanical coupling coefficient as compared to the other geometric configurations. An analytical regression is established from a linear regression‐based machine learning model, which can be employed to predict the performance of nanocomposites filled with oxides with a given set of piezoelectric coefficient, dielectric permittivity, and stiffness. This work not only sheds light on the fundamental mechanism of piezoelectric nanocomposites, but also offers a promising material design strategy for developing high‐performance polymer/inorganic oxide composite‐based wearable electronics. [ABSTRACT FROM AUTHOR]

Antiferroelectric (AFE) materials are of great interest owing to their scientific richness and their utility in high‐energy density capacitors. Here, the history of AFEs is reviewed, and the characteristics of antiferroelectricity and the phase transition of an AFE material are described. AFEs are energetically close to ferroelectric (FE) phases, and thus both the electric field strength and applied stress (pressure) influence the nature of the transition. With the comparable energetics between the AFE and FE phases, there can be a competition and frustration of these phases, and either incommensurate and/or a glassy (relaxor) structures may be observed. The phase transition in AFEs can also be influenced by the crystal/grain size, particularly at nanometric dimensions, and may be tuned through the formation of solid solutions. There have been extensive studies on the perovskite family of AFE materials, but many other crystal structures host AFE behavior, such as CuBiP2Se6. AFE applications include DC‐link capacitors for power electronics, defibrillator capacitors, pulse power devices, and electromechanical actuators. The paper concludes with a perspective on the future needs and opportunities with respect to discovery, science, and applications of AFE. [ABSTRACT FROM AUTHOR]

Flexoelectricity is an electromechanical coupling effect in which electric polarization is generated by a strain gradient. In this investigation, a potassium sodium niobite/poly(vinylidene fluoride‐trifluoroethylene) (KNN/PVDF‐TrFE)‐based nanocomposite is fabricated, and the flexoelectric effect is used to enhance the photovoltaic current (Ipv) in the nanocomposite. It is found that both a pyroelectric current and photovoltaic current can be generated simultaneously in a light illumination process. However, the photovoltaic current (Ipv) in this process contributes ≈85% of the total current. When assessing the effect of flexoelectricity with a curvature of 1/20, the Ipv of the curved KNN/PVDF‐TrFE (20%) (K/P‐20) composite increased by ≈13.9% compared to that of the flat K/P‐20 nanocomposite. Similarly, at a curvature of 1/20, the Ipv of the K/P‐20 nanocomposite is 71.6% higher than that of the PVDF‐TrFE film. However, the photovoltaic effect induced by flexoelectricity is much higher than the increased polarization from flexoelectricity, so this effect is called as the flexophotovoltaic effect. Furthermore, the calculated energy conversion efficiency of the K/P‐20 film is 0.017%, which is comparable to the previous research result. This investigation shows great promise for PVDF‐based nanocomposites in ferroelectric memory device applications. [ABSTRACT FROM AUTHOR]

The discovery of superconductivity in twisted graphene bilayers with a magic twisting angle ≈1.1° has opened up a wide range of potential twistronic device possibilities. In this work, the twisting effects in spintronic devices are explored. In particular, a material prototype integrating spintronics, straintronics, and twistronics is developed by stacking a twisted CoFe2O4 (CFO) bilayer membrane on a Pb(Mg1/3Nb2/3)O3‐PbTiO3 (PMN‐PT) membrane. Phase‐field simulations are performed to study the magnetic domain configurations and switching in CFO bilayers under piezostrains. An emerging interlayer parallel‐to‐antiparallel magnetic transition of the twisted CFO bilayer induced by appropriate piezostrain pulses generated from the PMN‐PT membrane is discovered. Such a strain‐induced parallel‐to‐antiparallel magnetic transition is non‐volatile and reversible, arising from the synergistic interaction among spin, strain, and twisting order parameters. The present work provides a paradigm for designing novel spinotropic devices by taking advantage of the emerging phenomena generated by twisting. [ABSTRACT FROM AUTHOR]

Inorganic/organic dielectric nanocomposites have been extensively explored for energy storage applications for their ease of processing, flexibility, and low cost. However, achieving simultaneous high energy density and high efficiency under practically workable electric fields has been a long‐standing challenge. Guided by first‐principles calculations of interface properties and phase‐field simulations of the dynamic dielectric breakdown process, superhierarchical nanocomposites of ferroelectric perovskites, layered aluminosilicate nanosheets, and an organic polymer matrix are designed and simultaneous high energy density of 20 J cm−3 and high efficiency of 84% at a low electric field of 510 MV m−1 are achieved. This is the highest energy density of all the state‐of‐the‐art dielectric polymer nanocomposites with energy efficiency > 80% at a low electric field of <600 MV m−1. Strong atomic hybridization, large ionic displacement, the enhanced breakdown strength through forming charge‐blocking layers, and the superhierarchical microstructure with gradient interfaces are responsible for the high performances. This superhierarchical structuring modulation strategy is generally applicable to composites for different functionalities and applications. [ABSTRACT FROM AUTHOR]

Ferroelectric polymers have been regarded as the preferred matrix for high‐energy‐density dielectric polymer nanocomposites because of their highest dielectric constants among the known polymers. Despite a library of ferroelectric polymer‐based composites having been demonstrated as highly efficient in enhancing the energy density, the charge–discharge efficiency remains moderate because of the high intrinsic loss of ferroelectric polymers. Herein, a systematic study of the oxide nanofillers is presented with varied dielectric constants and the vital role of the dielectric match between the filler and the polymer matrix on the capacitive performance of the ferroelectric polymer composites is revealed. A combined experimental and simulation study is further performed to specifically investigate the effect of the nanofiller morphology on the electrica properties of the polymer nanocomposites. The solution‐processed ferroelectric polymer nanocomposite embedded with Al2O3 nanoplates exhibits markedly improved breakdown strength and discharged energy density along with an exceptional charge–discharge efficiency of 83.4% at 700 MV m−1, which outperforms the ferroelectric polymers and nanocomposites reported to date. This work establishes a facile approach to high‐performance ferroelectric polymer composites through capitalizing on the synergistic effect of the dielectric properties and morphology of the oxide fillers. [ABSTRACT FROM AUTHOR]

Interfaces play an important role during phase transition and interfacial chemical reactions. In this paper, three different methods are introduced to analyze the explicit dynamics of the diffuse interface by means of phase‐field model, and these methods are based on three independent perspectives: non‐dispersive propagation of the interfacial waveform, the flux density and sources/sinks analysis of continuity equation, and the moving interfacial coordinate transformation. These theoretical derivations not only present the relationship between the diffuse interfacial velocity and the effect of driving force and interfacial curvature, but also clarify the equivalent method between the phase‐field dynamics and the sharp‐interfacial dynamics, which reveals the physical meaning of the diffuse interfacial dynamical equation from different perspectives. The present study advances the understanding of the interfacial phase transition and provides theoretical insights for the phase‐field model and numerical simulation. [ABSTRACT FROM AUTHOR]

Ferroelectric domain walls, topological entities separating domains of uniform polarization, are promising candidates as active elements for nanoscale memories. In such applications, controlled nucleation and stabilization of domain walls are critical. Here, using in situ transmission electron microscopy and phase‐field simulations, a controlled nucleation of vertically oriented 109° domain walls in (110)‐oriented BiFeO3 (BFO) thin films is reported. In the switching experiment, reversed domains that are nucleated preferentially at the nanoscale edges of the "crest and sag" pattern‐like electrode under external bias subsequently grow into a stable stripe configuration. In addition, when triangular pockets (with an in‐plane polarization component) are present, these domain walls are pinned to form stable flux‐closure domains. Phase field simulations show that i) field enhancement at the edges of the electrode causes site‐specific domain nucleation, and ii) the local electrostatics at the domain walls drives the formation of flux closure domains, thus stabilizing the striped pattern, irrespective of the initial configuration. The results demonstrate how flux closure pinning can be exploited in conjunction with electrode patterning and substrate orientation to achieve a desired topological defect configuration. These insights constitute critical advancements in exploiting domain walls in next generation ferroelectronic devices. [ABSTRACT FROM AUTHOR]

A domain wall‐enabled memristor is created, in thin film lithium niobate capacitors, which shows up to twelve orders of magnitude variation in resistance. Such dramatic changes are caused by the injection of strongly inclined conducting ferroelectric domain walls, which provide conduits for current flow between electrodes. Varying the magnitude of the applied electric‐field pulse, used to induce switching, alters the extent to which polarization reversal occurs; this systematically changes the density of the injected conducting domain walls in the ferroelectric layer and hence the resistivity of the capacitor structure as a whole. Hundreds of distinct conductance states can be produced, with current maxima achieved around the coercive voltage, where domain wall density is greatest, and minima associated with the almost fully switched ferroelectric (few domain walls). Significantly, this "domain wall memristor" demonstrates a plasticity effect: when a succession of voltage pulses of constant magnitude is applied, the resistance changes. Resistance plasticity opens the way for the domain wall memristor to be considered for artificial synapse applications in neuromorphic circuits. [ABSTRACT FROM AUTHOR]

Application of scanning probe microscopy techniques such as piezoresponse force microscopy (PFM) opens the possibility to re‐visit the ferroelectrics previously studied by the macroscopic electrical testing methods and establish a link between their local nanoscale characteristics and integral response. The nanoscale PFM studies and phase field modeling of the static and dynamic behavior of the domain structure in the well‐known ferroelectric material lead germanate, Pb5Ge3O11, are reported. Several unusual phenomena are revealed: 1) domain formation during the paraelectric‐to‐ferroelectric phase transition, which exhibits an atypical cooling rate dependence; 2) unexpected electrically induced formation of the oblate domains due to the preferential domain walls motion in the directions perpendicular to the polar axis, contrary to the typical domain growth behavior observed so far; 3) absence of the bound charges at the 180° head‐to‐head (H–H) and tail‐totail (T–T) domain walls, which typically exhibit a significant charge density in other ferroelectrics due to the polarization discontinuity. This strikingly different behavior is rationalized by the phase field modeling of the dynamics of uncharged H–H and T–T domain walls. The results provide a new insight into the emergent physics of the ferroelectric domain boundaries, revealing unusual properties not exhibited by conventional Ising‐type walls. [ABSTRACT FROM AUTHOR]

Ferroelectric materials owning a polymorphic nanodomain structure usually exhibit colossal susceptibilities to external mechanical, electrical, and thermal stimuli, thus holding huge potential for relevant applications. Despite the success of traditional strategies by means of complex composition design, alternative simple methods such as strain engineering have been intensively sought to achieve a polymorphic nanodomain state in lead‐free, simple‐composition ferroelectric oxides in recent years. Here, a nanodomain configuration with morphed structural phases is realized in an epitaxial BaTiO3 film grown on a (111)‐oriented SrTiO3 substrate. Using a combination of experimental and theoretical approaches, it is revealed that a threefold rotational symmetry element enforced by the epitaxial constraint along the [111] direction of BaTiO3 introduces considerable instability among intrinsic tetragonal, orthorhombic, and rhombohedral phases. Such phase degeneracy induces ultrafine ferroelectric nanodomains (1–10 nm) with low‐angle domain walls, which exhibit significantly enhanced dielectric and piezoelectric responses compared to the (001)‐oriented BaTiO3 film with uniaxial ferroelectricity. Therefore, the finding highlights the important role of epitaxial symmetry in domain engineering of oxide ferroelectrics and facilitates the development of dielectric capacitors and piezoelectric devices. [ABSTRACT FROM AUTHOR]

Understanding the leakage current caused by charge transport and local accumulation in dielectric oxides is critical for predicting and extending the lifetime of dielectric‐based electronic devices. The internal interfaces such as grain boundaries (GBs) inside a dielectric induce local strain and charge segregation and thus further influence the charge transport behavior. In this work, we employ computational modeling based on the Schottky barrier model and nonlinear Nernst‐Planck transport equation is used to study the oxygen vacancy transport and leakage current evolution in a SrTiO3 thin film under a DC bias with planar electrodes. It is found that in polycrystalline SrTiO3, the GB‐bounded donors create an electric potential barrier and a local depletion region near the GBs, impeding the oxygen vacancy transport and suppressing the leakage current increase compared to a single crystal SrTiO3 thin film. The effects of temperature, the magnitude of an applied field, the number density of GBs, the GB‐bounded donor concentration, and the depletion layer width on the leakage current evolution are systematically investigated. The simulation results are compared with the analytical solutions, as well as with existing theoretical and experimental reports. This work thus helps shed light to the grain‐structure dependent electrostatic behaviors in dielectric thin films under different intrinsic and extrinsic conditions. [ABSTRACT FROM AUTHOR]

Wintersweet (Chimonanthus praecox L.) is an important ornamental plant in China with a pleasant floral scent. To explore the potential mechanisms underlying differences in the fragrances among genotypes of this plant, we analyzed floral volatile organic compounds (VOCs) from two different genotypes: SW001, which has little to no fragrance, and the scented genotype H29. The major VOCs in H29 were linalool, trans‐β‐ocimene, benzyl acetate, methyl salicylate, benzyl alcohol (BAlc) and methyl benzoate. The most important aroma‐active compound in H29, linalool, was emitted at a low concentration in SW001, which had markedly higher levels of trans‐β‐ocimene than H29. Next, to investigate scent biosynthesis, we analyzed the transcriptome and proteome of fully open flowers of the two genotypes. A total of 14 443 differentially expressed unigenes and 196 differentially expressed proteins were identified. Further analyses indicated that 56 differentially expressed genes involved in the terpenoid and benzenoid biosynthesis pathways might play critical roles in regulating floral fragrance difference. Disequilibrium expression of four terpene synthase genes resulted in diverse emission of linalool and trans‐β‐ocimene in both genotypes. In addition, the expressions of two CpMYC2 transcription factors were both upregulated in H29, implying that they may regulate linalool production. Notably, 16 of 20 genes in the benzenoid biosynthesis pathway were downregulated, corresponding to the relatively low level of benzenoid production in SW001. The lack of benzyl acetate might indicate that SW001 may lack substrate BAlc or functional acetyl‐CoA:benzylalcohol acetyltransferase. [ABSTRACT FROM AUTHOR]

The electrical behavior of iron‐doped strontium titanate (Fe:SrTiO3) single crystals equilibrated at 900°C and quenched below 400°C at various oxygen partial pressures (PO2) was investigated via impedance spectroscopy and compared to defect chemistry models. Fe:SrTiO3 annealed and quenched between 1.2 × 10−14 and 2.0 × 10−4 Pa PO2 exhibits a conduction activation energy (EA) around 0.6 eV, consistent with ionic conduction of oxygen vacancies. However, sudden changes in EA are found to either side of this range; a transition from 0.6 to 1 eV is found in more oxidizing conditions, while a sudden transition to 1.1 and then 0.23 eV is found in reducing PO2 These transitions, not described by the widely used canonical model, are consistent with predictions of transitions from ionic to electronic conductivity, based on first principles point defect chemistry simulations. These models demonstrate that activation energies in mixed conductors may not correlate to specific conduction mechanisms, but are determined by the cumulative response of all operative conduction processes and are very sensitive to impurities. A comparison to electrically degraded Fe:SrTiO3 provides insight into the origins of the conductivity activation energies observed in those samples. [ABSTRACT FROM AUTHOR]

Abstract: Strain and applied external electric fields are known to influence domain evolution and associated ferroelectric responses in ferroelectric thin films. Here, phase‐field simulations are used to predict equilibrium domain structures and polarization‐field (P‐E) hysteresis loops of lead zirconate titanate (PZT) thin films under a series of mismatch strains, ranging from strongly tensile to strongly compressive. In particular, the evolution of domains and the P‐E curves under different applied strains reveal the mesoscale mechanism, the appearance of in‐plane polarization during domain switching, that is responsible for a relatively small coercive field and remnant polarization. A Landau energy distribution is analyzed to better understand the domain evolution under various strain conditions. The results provide guidance for choice of mismatched strains to yield the desired P‐E hysteresis loops and the domain structures. [ABSTRACT FROM AUTHOR]