Piezoelectric Force Microscopy Research Articles

Bi-piezoelectric effect assisted ZnO nanorods/PVDF-HFP spongy photocatalyst for enhanced performance on degrading organic pollutant

Piezoelectric field engineering has been recently proved to restrain the photogenerated carrier recombination both in the bulk and on the surface of photocatalyst. Herein, we proposed a bi-piezoelectric ZnO nanorods (NR)/PVDF-HFP spongy film that can utilize water flow vibration to boost the photocatalytic degradation of organic dye. The composite photocatalyst can be deformed by water flow to generate an integrated piezoelectric field from PVDF-HFP and ZnO NR, which can considerably drive the separation and transfer of photogenerated charge carriers in ZnO NR. As a result, the ZnO NR/PVDF-HFP spongy film shows a ∼ 3 fold increase in reaction rate constant of degrading methyl orange (MO) with irradiation as flow speed increases from 200 rpm to 1000 rpm. A model about the bi-piezoelectric effect of ZnO NR/PVDF-HFP was configurated according to a series of characterization by piezoelectric force microscopy (PFM) and photoluminescence (PL). This work demonstrates the contribution of the bi-piezoelectric effect to photocatalytic water decontamination and provides a promising strategy to use dual-sustainable energy— solar and water energy.

Enhanced energy storage performance of 0.88(0.65Bi0.5Na0.5TiO3-0.35SrTiO3)-0.12Bi(Mg0.5Hf0.5)O3 lead-free relaxor ceramic by composition design strategy

Dielectric ceramic capacitors with high energy density are one of the great bright energy storage devices. Here, the Bi0.5Na0.5TiO3, 0.75Bi0.5Na0.5TiO3-0.25SrTiO3, 0.65Bi0.5Na0.5TiO3-0.35SrTiO3 and 0.88(0.65Bi0.5Na0.5TiO3-0.35SrTiO3)-0.12Bi(Mg0.5Hf0.5)O3, (abbreviated as BNT, BNT-25ST, BNT-35ST and BNST-BMH, respectively) ceramics were produced by solid state sintering method. The influence of solid solution of SrTiO3 and Bi(Mg0.5Hf0.5)O3 doping in Bi0.5Na0.5TiO3 on crystal structure, microstructure, electrical and energy storage performance were evaluated systematically. By optimizing ceramics composition, high breakdown field and slim hysteresis loops were simultaneously realized due to enhanced band gap, refined grain size and nano-domains formed, which can be verified by the transmission electron microscope (TEM), piezoelectric force microscope (PFM) and ultraviolet–visible spectrum. Therefore, an ultrahigh recoverable energy density of 5.59 J/cm3 with brilliant efficiency of 85.3% is realized in BNST-BMH ceramic. Besides, the BNST-BMH also exhibits prominent temperature stability at 20–140 °C, superior fatigue resistance beyond 105 cycles and outstanding frequency stability at 1–200 Hz. Our work offers a novel way for designing dielectric capacitors and also proves that BNST-BMH is indeed a great hopeful dielectric energy storage material in pulse power electronics.

Flexible Interconnected Cu‐Ni Nanoalloys Decorated Carbon Nanotube‐Poly(vinylidene fluoride) Piezoelectric Nanogenerator

AbstractHerein, high‐performance flexible and stable Cu‐Ni nanoalloy decorated carbon nanotube (CNT) reinforced poly(vinylidene fluoride) (PVDF) based piezoelectric nanogenerator is presented for the first time with very high current and power density. The formation of crystalline β‐phase is confirmed using FT‐IR and Raman spectra analysis. HR‐TEM study reveals the formation of Cu‐Ni nanoalloys with well‐defined interconnected structure with CNT. The Cu‐Ni nanoalloy decorated CNT‐PVDF nanogenerator device exhibits a high output voltage of 12 V and high current density of 0.3 µA cm−2 compared to pristine PVDF nanogenerator (4 V and 10 nA cm−2). Very high power density of 204 µW cm−3 is obtained from the nanocomposite nanogenerator. Piezoelectric force microscopy study reveals very high piezoelectric charge coefficient (d33) of about 160 pm V−1 from Cu‐Ni decorated CNT‐PVDF. Very stable output performance with almost no degradation till 1500 cycles is observed from the Cu‐Ni nanoalloy CNT‐PVDF nanogenerator. Such high stability is due to its dramatic improved high tensile strength of 60 MPa. Very high dielectric constant of 500 is observed from Cu‐Ni decorated CNT‐PVDF as compared to pristine PVDF (ε’ ≈ 20). The dramatic increase in output performance even under without electrical poling is discussed in light of self‐dipole alignment, in‐situ poling, high d33, interfacial polarization, and enhanced dielectric properties.

Deepening of domains at e-beam writing on the −Z surface of lithium niobate

The focus of this study was to investigate the peculiarities of the domains created by an electron beam (e-beam) in a surface layer of congruent lithium niobate (LiNbO3, LN), which are comparable to the depth of e-beam charge penetration. Direct e-beam writing (DEBW) of different domain structures with a scanning electron microscope was performed on the polar −Z cut. Accelerating voltage 15 kV and e-beam current 100 pA were applied. Different patterns of local irradiated squares were used to create domain structures and single domains. No domain contrast was observed by the piezoelectric force microscopy technique. Based on chemical etching, it was found that the vertices of the domains created do not reach the surface level. The average deepening of the domain vertices was several hundred nanometers and varied depending on the irradiation dose and the locations of the irradiated areas (squares) relative to each other. Computer simulation was applied to analyze the spatial distribution of the electric field in the various irradiated patterns. The deepening was explained by the fact that in the near-surface layer there is a sign inversion of the normal component of the electric field strength vector, which controls the domain formation during DEBW. Thus, with the help of the e-beam, domains were created completely located in the bulk, in contrast to the domains that are nucleated on the surface of the −Z cut during polarization inversion with an atomic force microscope tip. The detected deepening of e-beam domains suggests the possibility of creating ‘head-to-head’ domain walls in near-surface-layer LN by DEBW.

Highly a-oriented growth and enhanced ferroelectric properties of Bi3TaTiO9 thin films

Ferroelectric perovskites are favored for integrated device applications due to their high dielectric constants and strong piezoelectric responses. However, the commonly used lead zirconate titanate system has disadvantages such as toxicity, current leakage, and fatigue. As an alternate lead-free material, this study examines the strain-induced ferroelectric properties of Bi3TaTiO9 (BTTO) thin films. BTTO thin films grown on single crystal Rh and Nb-doped SrTiO3 (Nb:STO) substrates via a pulsed laser deposition were compared. The Rh substrate has induced compressive stress in the BTTO thin film, whereas the Nb:STO substrate has induced tensile stress in the BTTO thin film. The BTTO thin film grown on the Rh substrate displayed a highly a-oriented crystallinity compared with the Nb:STO substrate. Significantly, the BTTO thin film on the Rh substrate exhibited improved ferroelectric properties, such as stronger hysteretic behavior, faster polarization switching, and higher piezoelectric coefficients. The surface morphologies and ferroelectric domains of the BTTO thin films were investigated via atomic force microscopy and piezoelectric force microscopy. Our findings provide insights into strain-engineered ferroelectric thin films and their potential device applications.

Design of piezoelectric ZnO based catalysts for ammonia production from N2 and H2O under ultrasound sonication

Using mechanical waste energy to drive the ammonia production from N2 and water under ambient conditions is of great significance yet still very challenging. In this work, we designed ZnO microrods and ZnO-Ag heterostructures that exhibited high activity, selectivity, and stability in the production of ammonia under ultrasound sonication. Combining the piezoelectric force microscopy (PFM), temperature programed desorption of N2 (N2-TPD), electron spin resonance (ESR), electrochemical analysis with finite element numerical simulation, we found that the size and morphology of ZnO greatly impacted the shape deformation as well as the piezoelectric potential across the material, while the oxygen vacancies were essential for the adsorption and activation of N2. Loading Ag NPs onto ZnO could further enhance the N2 fixation activity by generating local strain at the Ag-ZnO interface, enhancing the chemical adsorption of N2, and facilitating the separation of piezo-generated electrons and holes. Our work demonstrates the design principles of highly active piezoelectric catalysts for N2 fixation.

Comprehensive Characterization of PVDF Nanofibers at Macro- and Nanolevel.

This study is focused on the characterization and investigation of polyvinylidene fluoride (PVDF) nanofibers from the point of view of macro- and nanometer level. The fibers were produced using electrostatic spinning process in air. Two types of fibers were produced since the collector speed (300 rpm and 2000 rpm) differed as the only one processing parameter. Differences in fiber’s properties were studied by scanning electron microscopy (SEM) with cross-sections observation utilizing focused ion beam (FIB). The phase composition was determined by Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy. The crystallinity was determined by differential scanning calorimetry (DSC), and chemical analysis of fiber’s surfaces and bonding states were studied using X-ray photoelectron spectroscopy (XPS). Other methods, such as atomic force microscopy (AFM) and piezoelectric force microscopy (PFM), were employed to describe morphology and piezoelectric response of single fiber, respectively. Moreover, the wetting behavior (hydrophobicity or hydrophilicity) was also studied. It was found that collector speed significantly affects fibers alignment and wettability (directionally ordered fibers produced at 2000 rpm almost super-hydrophobic in comparison with disordered fibers spun at 300 rpm with hydrophilic behavior) as properties at macrolevel. However, it was confirmed that these differences at the macrolevel are closely connected and originate from nanolevel attributes. The study of single individual fibers revealed some protrusions on the fiber’s surface, and fibers spun at 300 rpm had a core-shell design, while fibers spun at 2000 rpm were hollow.

Stacking Engineered Room Temperature Ferroelectricity in Twisted Germanium Sulfide Nanowires

AbstractGroup‐IV monochalcogenides have emerged with immense potential to be used as ferroelectric materials in recent times. However, in most of them, ferroelectricity is limited by the presence of inversion symmetry in their natural crystal structure. Here, an experimental observation of ferroelectric order at room temperature by introducing Eshelby twist in Germanium sulfide (GeS) nanowires is reported. The twisted nanowires are synthesized by low‐pressure chemical vapor deposition. The existence of room temperature ferroelectricity in a single nanowire is confirmed by electrical measurements, piezoelectric force microscopy, and second harmonic generation spectroscopy. Density functional theory calculations reveal that the twist in the GeS nanowires breaks the inversion symmetry where the inversion symmetry breaking phonon modes get hardened giving rise to ferroelectricity. These results are expected to be useful in making non‐volatile memory devices, flexible electronics, electronic sensors, and neuromorphic computing.

Interfacial ferroelectricity in rhombohedral-stacked bilayer transition metal dichalcogenides.

van der Waals materials have greatly expanded our design space of heterostructures by allowing individual layers to be stacked at non-equilibrium configurations, for example via control of the twist angle. Such heterostructures not only combine characteristics of the individual building blocks, but can also exhibit physical properties absent in the parent compounds through interlayer interactions1. Here we report on a new family of nanometre-thick, two-dimensional (2D) ferroelectric semiconductors, where the individual constituents are well-studied non-ferroelectric monolayer transition metal dichalcogenides (TMDs), namely WSe2, MoSe2, WS2 and MoS2. By stacking two identical monolayer TMDs in parallel, we obtain electrically switchable rhombohedral-stacking configurations, with out-of-plane polarization that is flipped by in-plane sliding motion. Fabricating nearly parallel-stacked bilayers enables the visualization of moiré ferroelectric domains as well as electric field-induced domain wall motion with piezoelectric force microscopy. Furthermore, by using a nearby graphene electronic sensor in a ferroelectric field transistor geometry, we quantify the ferroelectric built-in interlayer potential, in good agreement with first-principles calculations. The new semiconducting ferroelectric properties of these four new TMDs opens up the possibility of studying the interplay between ferroelectricity and their rich electric and optical properties2-5.

Controlling polarization direction in epitaxial Pb(Zr0.2Ti0.8)O3 films through Nb (n-type) and Fe (p-type) doping

Fe (acceptor) and Nb (donor) doped epitaxial Pb(Zr0.2Ti0.8)O3 (PZT) films were grown on single crystal SrTiO3 substrates and their electric properties were compared to those of un-doped PZT layers deposited in similar conditions. All the films were grown from targets produced from high purity precursor oxides and the doping was in the limit of 1% atomic in both cases. The remnant polarization, the coercive field and the potential barriers at electrode interfaces are different, with lowest values for Fe doping and highest values for Nb doping, with un-doped PZT in between. The dielectric constant is larger in the doped films, while the effective density of charge carriers is of the same order of magnitude. An interesting result was obtained from piezoelectric force microscopy (PFM) investigations. It was found that the as-grown Nb-doped PZT has polarization orientated upward, while the Fe-doped PZT has polarization oriented mostly downward. This difference is explained by the change in the conduction type, thus in the sign of the carriers involved in the compensation of the depolarization field during the growth. In the Nb-doped film the majority carriers are electrons, which tend to accumulate to the growing surface, leaving positively charged ions at the interface with the bottom SrRuO3 electrode, thus favouring an upward orientation of polarization. For Fe-doped film the dominant carriers are holes, thus the sign of charges is opposite at the growing surface and the bottom electrode interface, favouring downward orientation of polarization. These findings open the way to obtain p-n ferroelectric homojunctions and suggest that PFM can be used to identify the type of conduction in PZT upon the dominant direction of polarization in the as-grown films.

Electric-Field-Induced Room-Temperature Antiferroelectric-Ferroelectric Phase Transition in van der Waals Layered GeSe.

Searching van der Waals ferroic materials that can work under ambient conditions is of critical importance for developing ferroic devices at the two-dimensional limit. Here we report the experimental discovery of electric-field-induced reversible antiferroelectric (AFE) to ferroelectric (FE) transition at room temperature in van der Waals layered α-GeSe, employing Raman spectroscopy, transmission electron microscopy, second-harmonic generation, and piezoelectric force microscopy consolidated by first-principles calculations. An orientation-dependent AFE-FE transition provides strong evidence that the in-plane (IP) polarization vector aligns along the armchair rather than zigzag direction in α-GeSe. In addition, temperature-dependent Raman spectra showed that the IP polarization could sustain up to higher than 700 K. Our findings suggest that α-GeSe, which is also a potential ferrovalley material, could be a robust building block for creating artificial 2D multiferroics at room temperature.

Force‐Electric Coupling of Nanoscale Ferroelectric Domains Based on Piezoelectric Force Microscopy (PFM)

Piezoelectric and ferroelectric materials are widely used in various types of microelectronics due to their excellent mechanical and electrical coupling characteristics. In recent years, piezoelectric force microscopy has developed into a powerful tool for analyzing nanoscale ferroelectric materials. However, quantitative analysis based on PFM is difficult to properly study it. This article studies the related issues of PFM quantitative analysis. First, the relationship between the effective piezoelectric coefficient and piezoelectric coefficient of different materials is analyzed from the PFM nanometer scale to analyze the force‐electric coupling effect. The study found that the effective piezoelectric coefficient is closely related to the intrinsic electroelastic constant of the material. Secondly, the analysis of the nanoscale piezoelectric deformation of ferroelectric materials shows that under the conductive SPM probe, as the clustering with the probe increases, the in‐plane displacement first increases and then decreases, and the out‐of‐plane displacement gradually decreases. Finally, the half‐width region of the nanoscale ferroelectric response domain was analyzed by PFM. Taking the in‐plane and out‐of‐plane domains of 180° and 90° domains as examples, the relationship between the response boundary domain and the tip radius was analyzed, and the results showed that whether the PFM can effectively solve the problem of detection and analysis depends on the half‐width of the response boundary domain, and the resolution of the vertical PFM is higher than that of the lateral PFM.

Self-powered visible light photodetector based on BixFeO3 film

In this study, the self-powered photodetector based on photovoltaic effect was obtained from Bi x FeO 3 (x = 1, 1.3, 1.5, 1.7) films. In order to study the origin of the photovoltaic effect, the self-polarized structure and defect distribution of the films were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, and piezoelectric force microscopy. In addition, the responsivity (1515 μA/W) and detectivity (1.35Χ10 11 Jones) are achieved in the Bi 1.5 FeO 3 film at zero bias after receiving 0.2 mW/cm 2 of irradiation light in the wavelength of 500 nm. The rise and decay time of the photocurrent without bias reaches ∼6 ms and ∼15 ms respectively, and did not weaken after a 11 min cycling test. The self-polarized structure and defect dipoles play an important role in the photovoltaic effect of Bi x FeO 3 self-powered photodetector. This work lays a foundation for applications in Bi x FeO 3 self-powered photodetection.

Fabrication, structural and piezoelectric force microscopy analyses of nanorod ZnO-PVDF thin films

Piezoelectric nanogenerators are composite nanostructure films with a capability of the mechanical-to-electrical energy conversion for potential applications in self-sustained, low-powered electronic devices. In this work, Zinc Oxide (ZnO) nanorods served as piezoelectric materials and they were grown by two steps: (1) Spray Pyrolysis and (2) Hydrothermal Method on copper foils. Afterwards, poly (vinylidene difluoride) (PVDF) was spin-coated on ZnO nanorods with a spinning speed of 500 rpm. After spin-coating, the PVDF films were either air-cooled or heated at 100 °C for 10 min. Piezoelectric Force Microscopy (PFM) was performed to investigate the piezoelectric and ferroelectric behaviour of PVDF and the increment of piezoelectric response by adding ZnO nanorods to PVDF. Then, the ZnO film, pristine PVDF film and ZnO-PVDF were assembled with Al foil on top to construct nanogenerators for comparison. Lastly, the measurement of electric output voltage was carried out using energy conversion circuit.

Progress of functionalized atomic force microscopy in the study of the properties of nanometric dielectric materials

The rapid development of the electrical and electronic industry requires components with miniaturization, flexibility, and intelligence. As an important material for the preparation of electronic components, dielectric materials need to have excellent dielectric properties such as high breakdown electric field, high energy storage density and low dielectric loss. Due to the lack of ultra-high resolution characterization tools, the research on the improvement of dielectric material properties has remained at the macroscopic level in the past. The invention of atomic force microscopy, a measurement instrument with nanoscale high resolution, has shown unique advantages in the study of nanodielectrics, and the birth of functional atomic force microscopy has made important contributions to characterize the electrical, optical, and mechanical properties of nano-dielectric micro-regions. In this paper, we review the progress of atomic force microscopy, electrostatic force microscopy, Kelvin probe force microscopy, piezoelectric response force microscopy and atomic microscopy-infrared spectroscopy in the study of nanodielectric applications. Firstly, their structures and principles are introduced; secondly, their recent research progress in studying the microscopic morphology, interfacial structure, domain behavior and charge distribution in the nanometer region of dielectric materials is presented, and finally, the problems in the existing research and possible future research directions are discussed.

Progress of application of functional atomic force microscopy in study of nanodielectric material properties

The rapid development of the electrical and electronic industry requires components with miniaturization, flexibility, and intelligence. Dielectric materials, as important materials for the preparation of electronic components, are required to have excellent dielectric properties such as high breakdown electric field, high energy storage density and low dielectric loss. Owing to the lack of ultra-high resolution characterization tools, the research on the improvement of dielectric material properties stopped at a macroscopic level in the past. Atomic force microscopy, a measurement instrument which possesses a nanoscale high resolution, shows unique advantages in the study of nanodielectrics, and the advent of functional atomic force microscopy has made important contributions to characterization of the electrical, optical, and mechanical properties of nano-dielectric micro-regions. In this paper, we review the progress of atomic force microscopy, electrostatic force microscopy, Kelvin probe force microscopy, piezoelectric response force microscopy and atomic microscopy-infrared spectroscopy in the study of nanodielectric applications. Firstly, their structures and principles are introduced; secondly, their recent research progress of studying the microscopic morphology, interfacial structure, domain behavior and charge distribution in the nanometer region of dielectric materials is presented, and finally, the problems in the existing research and possible future research directions are discussed.

Unveiling Center‐Type Topological Defects on Rosettes of Lead Zirconate Titanate Associated to Oxygen Vacancies

AbstractUnderstanding the formation of topological defects in ferroelectric materials can provide access to their unusual physics, invaluable for possible applications of domain engineering in nanoelectronics. The present study shows the spontaneous formation of center‐type topological defects in lead zirconate titanate (PZT) films, characterized by a strong in‐plane radial electromechanical response on rosette‐like structures, as revealed by piezoelectric response force microscopy. Multi‐modal electron and X‐ray based techniques provide a comprehensive set of tools for delving at atomic scale the local chemistry, electronic, and crystalline structures. The elemental surface‐sensitivity of soft X‐ray absorption shows chemical segregation and drastic changes in the titanium electronic structure, which have been associated to oxygen vacancies, leading to a mechanism that describe the polarization symmetry on the rosettes. X‐ray nanofluorescence experiments revealed titanium segregation, corroborating with the absorption and low energy electron microscopy images. Taking advantage of a nanobeam, 2D nanodiffraction maps probed the complex microstructure of the domains, revealing its mosaicity and lattice strain at the nanoscale. This study highlights a complex topological structure and provides, by the simultaneous application of a set of analytical tools, a broad comprehension of the formation of center‐type ferroelectric topological defects in PZT.

Hybrid Improper Ferroelectricity in Highly Cleavable Single Crystals of Dion‐Jacobson‐Compound CsBiNb2O7

AbstractDion‐Jacobson compound CsBiNb2O7 exhibits supposedly hybrid improper ferroelectricity (HIF), resulting from two different structural distortions. The highly‐cleavable single crystal of CsBiNb2O7 has been successfully grown and found large ferroelectric polarization as large as 30 μC cm‐2 with the coercivity of 310 kV cm‐1 from polarization‐electric field measurements on the crystals. Using piezoelectric force microscopy, a systematic study is on the ferroelectric domain structure and dynamics of CsBiNb2O7, unveiling the rich nature of its domain/domain wall evolution upon poling. The record large switchable polarization in CsBiNb2O7 among HIF compounds brings HIF closer to the real Pb‐free ferroelectric applications and the high cleavability of CsBiNb2O7 crystals provides a unique opportunity to explore ultrathin ferroelectrics with in‐plane polarization.

BNNT-ZnO QDs nanocomposites for improving piezoelectric nanogenerator and piezoelectric properties of boron nitride nanotube

Boron nitride nanotubes (BNNTs) are eco-friendly and lightweight materials with various physical, chemical, piezoelectric and mechanical properties. In particular, their exceptional properties can be exploited for piezoelectric applications. However, it remains a great challenge to improve the efficiency of the piezoelectric properties in the radial direction rather than the longitudinal direction. Thus, design with BNNT-inorganic composite materials is required including the outstanding inorganic piezoelectric materials to induce the improved performance of the piezoelectric properties. Here, we suggest the high-performance piezoelectric device as a nanogenerator based on BNNT-ZnO quantum dots (QDs) nanocomposites. The ZnO QDs were chemically synthesized on the surface of BNNTs by hydrothermal synthesis. As to the critical piezoelectric properties, we have investigated piezoelectric constants of BNNT-ZnO QDs nanocomposites and the difference in piezoelectric properties between out-of-plane and in-plane through conventional piezoelectric force microscopy (PFM) analysis. In addition, we confirmed the piezoelectric effect generated by applying a specific force to the single wire of BNNT-ZnO QDs nanocomposites in the radial direction using in-situ hybrid SEM-PFM technique. The effective piezoelectric coefficient (d33) of the single wire of BNNT-ZnO QDs in the radial direction and the piezoelectric charge coefficient of BNNT-ZnO QDs films were increased by 42.8% (0.340 pm/V) and 41.9% (−60.3 pC/N), respectively, compared to that of the single wire of BNNT and BNNT films. BNNT-ZnO QDs nanocomposites based transparent and flexible piezoelectric device showed excellent piezoelectric properties with a small amount of 0.18 wt%. The piezoelectric performance of nanogenerator with electrically poled BNNT-ZnO QDs nanocomposites was improved by more than 140% and 45%, respectively, compared to those of intrinsic BNNT-ZnO QDs nanocomposites and BNNT. Therefore, this study will pave a new path to the development of innovative materials and devices to generate recycled energy.

Effects of Hf4+ substitute on the enhanced electrostrain properties of 0.7BiFeO3-0.3BaTiO3-based lead-free piezoelectric ceramics

The 0.7Bi1.05FeO3-0.3BaHfxTi(1−x)O3 (BF-BHT-x) ceramics are prepared by using conventional method. The mechanism of large electric-induced strain is studied in detail through Rietveld refinement, transmission electron microscopy (TEM), and piezoelectric force microscopy (PFM). The BF-BHT-0.05 ceramics, which possess the coexistence of cubic (Pm-3m) and rhombohedral (R3c) phase proved by Rietveld refinement and TEM measurement, have the maximum electric-induced strain of Smax = 0.58% at 130 kV/cm (1 Hz). The reduced potential barrier is beneficial to the switching and reorientation of domain under an external electric field due to the coexistence of cubic and rhombohedral phase. A mass of nanodomains embedded into the microdomains, which is conducive to domain switching, are observed obviously through PFM. Therefore, the findings show that the large strain is because the external electric field drives the conversion mixed phase into the major rhombohedral phase, the reduced potential barrier, and the nanodomain in macrodomain.