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PbNb2O6 (PN)-based piezoceramics are considered important materials used in high temperatures. Whereas, the main problem of PN-based ceramic is its low electrical performance such as piezoelectric constant (d33), severely restricting its practical applications. Here, based on the principle of regulating structure and performance via defect engineering, a new way of artificially tailoring point defects by A-site nonstoichiometry is implemented in this study. The results show that the PN-based ceramics with A-site deficiency exhibit significantly enhanced dielectric and piezoelectric properties. Particularly, the relative dielectric permittivity (er) increased by 165% (from 197 to 523) and the d33 increased by 177% (from 30 to 83 pC/N) while maintaining a high Curie temperature (TC ~ 543 °C), and the resultant superior comprehensive performance is nearly highest in PN-based ceramic system. The X-ray photoelectron spectrometer and Raman spectra reveal that A-site deficiency leads to a decreased level of oxygen vacancies and NbO6 octahedral distortion as well as disorderly motions of A-site cations, which further causes the markedly decreased domain size exhibited in piezoresponse force microscopy (PFM) images. Consequently, the improved domain structure gives rise to improved dielectric and piezoelectric properties. The results of this work provide a simple and effective strategy to improve the dielectric and piezoelectric properties while keeping a high TC in the PN-based ceramics system, meeting the urgent demands of high-temperature applications.

The effect of temperature and electric field on phase transitions, dielectric relaxation behavior, and macroscopic electrical performances of Pb(In1/2Nb1/2)O3-0.49 Pb(Mg1/3Nb2/3)O3-0.27PbTiO3 (PIMNT27) single crystals were studied. The nanosized domains of unpoled crystals and the engineered domains of DC electric field poled crystals were intuitively recorded by piezoresponse force microscopy (PFM). The distribution of nanosized domains with different sizes and patterns induced by domain switching and domain wall motion under different poling fields and temperatures were also studied to understand the effect of nanosized domains on phase transitions, piezoelectric, and electromechanical properties.

Flexoelectricity in thin films has emerged as an effective electromechanical response owing to appealing scaling law and universal existence. However, current studies show limited out-of-plane converse flexoelectric effect (CFE) of ultra-thin transition metal dichalcogenides (TMDs) when compared to their conventional in-plane piezoresponse. Here, we report converse flexoresponse of atomically thin TMDs such as molybdenum disulfide (MoS2) and tungsten diselenide (WSe2) which exceeds their intrinsic in-plane piezoresponses. Our piezoresponse force microscopy (PFM) measurements revealed strongly enhanced CFE of the atomically thin MoS2 and WSe2 than their bulk counterpart (∼700% enhancement in MoS2, ∼400% enhancement in WSe2). We observed an anomalous reduction in converse flexoresponse in the monolayer structure attributed to a puckering deformation. By inducing a built-in in-plane tension to reduce puckering, we estimated the CFE of monolayer WSe2 to be 8.14 pm/V, the highest among the atomically thin TMDs.

Single-phase multiferroic materials that allow the coexistence of ferroelectric and magnetic ordering above room temperature are highly desirable, motivating an ongoing search for mechanisms for unconventional ferroelectricity in magnetic oxides. Here, we report an antisite defect mechanism for room temperature ferroelectricity in epitaxial thin films of yttrium orthoferrite, YFeO3, a perovskite-structured canted antiferromagnet. A combination of piezoresponse force microscopy, atomically resolved elemental mapping with aberration corrected scanning transmission electron microscopy and density functional theory calculations reveals that the presence of YFe antisite defects facilitates a non-centrosymmetric distortion promoting ferroelectricity. This mechanism is predicted to work analogously for other rare earth orthoferrites, with a dependence of the polarization on the radius of the rare earth cation. Our work uncovers the distinctive role of antisite defects in providing a mechanism for ferroelectricity in a range of magnetic orthoferrites and further augments the functionality of this family of complex oxides for multiferroic applications., Ferroelectricity in orthoferrite perovskites has stimulated intense research, but the mechanism remains unclear. Here, the authors propose an antisite defect mechanism for introducing ferroelectricity in magnetically ordered YFeO3 and the family of rare earth orthoferrites.

International audience; Lead-free Barium Zirconate Titanate thin films synthesized by sol-gel process were deposited on platinized silicon substrates. Atomic and piezoresponse force microscopies analysis have revealed low values for the surface roughness and local piezoelectric loops, respectively. Nanoscopic piezoelectric and ferroelectric properties decrease with zirconium content increasing. Dielectric measurements were made up to 1 MHz at room temperature. The highest dielectric permittivity and tunability are obtained for 10% of zirconium. Dielectric loss tangent decreases with frequency, zirconium content and electric field increasing. Thin films with 20% of zirconium could be particularly interesting for electronic applications.

Dielectric energy storage materials are becoming increasingly popular due to their potential superiority, for example, excellent pulse performance as well as good fatigue resistance. Although numerous studies have focused on lead-free dielectric materials which possess outstanding energy storage characteristics, the results are still not satisfying in terms of achieving both large discharging energy density (Wd) and high discharging efficiency (η) under low electric fields, which is crucial to be conducted in miniatured electronic components. Here, we adopt the strategy of domain engineering to develop sodium bismuth titanate (Bi0.5Na0.5TiO3)-based ceramics employed in the low-field situation. Remarkably, a large Wd of 2.86 J/cm3 and an ultrahigh η of 90.3% are concurrently obtained in 0.94(Bi0.5Na0.5)0.65(Ba0.3Sr0.7)0.35TiO3-0.06 Bi(Zn2/3Nb1/3)O3 system when the electric field is as low as 180 kV/cm. Additionally, the ceramic shows brilliant thermal endurance (20-160 °C) and frequency stability (0.1-100 Hz) with high Wd (>1.48 J/cm3) together with an ultra-high η (>90%). What's more, the ceramic displays a fast charge-discharge time (t0.9 = 109.2 ns). The piezoresponse force microscopy (PFM) results reveal that the introduced Bi(Zn2/3Nb1/3)O3 disrupts the microdomains of (Bi0.5Na0.5)0.65(Ba0.3Sr0.7)0.35TiO3 ceramics and promotes the formation of nanodomains, leading to enhanced energy storage properties. The current work may arouse interest in developing low-field high-performing dielectric capacitors for energy storage application.

Great importance has been attached to magnetoelectric coupling in multiferroic thin films owing to their extremely practical use in a new generation of devices. Here, a film of [(n-C3H7)4N][FeIIIFeII(dto)3] (1; dto = C2O2S2) was fabricated using a simple stamping process. As was revealed by our experimental results, in-plane ferroelectricity over a wide temperature range from 50 to 300 K was induced by electron hopping between FeII and FeIII sites. This mechanism was further confirmed by the ferroelectric observation of the compound [(n-C3H7)4N][FeIIIZnII(dto)3] (2; dto = C2O2S2), in which FeII ions were replaced by nonmagnetic metal ZnII ions, resulting in no obvious ferroelectric polarization. However, both ferroelectricity and magnetism are related to the magnetic Fe ions, implying a strong magnetoelectric coupling in 1. Through piezoresponse force microscopy (PFM), the observation of magnetoelectric coupling was achieved by manipulating ferroelectric domains under an in-plane magnetic field. The present work not only provides new insight into the design of molecular-based electronic ferroelectric/magnetoelectric materials but also paves the way for practical applications in a new generation of electronic devices.

Ex-situ local switching is a useful method for studying the domain structure evolution during polarization reversal in the individual grains of the ferroelectric ceramics. In this paper, the local ...

The effect of substitution of lithium cations in the sublattice A of sodium bismuth titanate on the parameters of the crystal structure, microstructure, dielectric and local piezoelectric propertie...

Highly conductive domain walls in insulating ferroelectric LiNbO3 (LNO) single-crystal thin films with atomic smoothness are attractive for use in high-density integration of the ferroelectric domain wall random access memory (DWRAM) because of their excellent reliability and high read currents. However, downscaling of the memory size to the nanoscale could cause poor polarization retention. Understanding the size-dependent electrical performance of a memory cell is therefore crucial. In this work, highly insulating X-cut LNO thin films were bonded to SiO2/Si wafers and lateral mesa-like cells were fabricated on the film surfaces, where contact occurred with two-sided electrodes along the polar z-axis. Under application of an in-plane electric field above a coercive field (Ec), the domain within each memory cell was switched to be antiparallel to the unswitched referencing domain at the bottom; this resulted in the formation of a conducting domain wall, which enables the nondestructive readout strategy of the DWRAM. The cell, which has a lateral length (l) above a critical size (l0) of 105 nm, is found to be a mixture of two phases across the cell area. The inner area of the cell suffers from poor polarization retention because Ec = 150 kV/cm, as demonstrated by in-plane piezoresponse force microscopy imaging. In comparison, the outer periphery domains, which have lengths of 70 nm (∼l0/2), show good retention but require a much higher Ec of 785 kV/cm. The relevant physics is discussed as phase reconstruction occurs after release of the in-plane compressive strain near the outer regions; the results show good agreement with those of one-dimensional thermodynamic calculations and phase-field simulations. The measured current-voltage curves demonstrated a sudden enhancement of the wall current across the cell when l < l0, thus implying higher readout wall currents and better retention for the DWRAM at higher storage densities.

1% Sm substituted PMN-29PT ([Sm0.01Pb0.985][(Mg1/3Nb2/3)0.71Ti0.29]O3) textured ceramics with a Lotgering factor of up to 80 % were successfully prepared. The dielectric, ferroelectric and piezoelectric properties have been investigated in detail for both textured and non-textured ceramics. The heterogeneous templates are found to be critical for the change in relaxor behaviors, leading to the reduced Tf, Tm, emax and Pr in textured ceramics. The textured ceramics show an enhanced d33 of 810 pC/N, about 1.6 times greater than their randomly oriented ceramic counterparts. The domain structures and their responses to applied electric fields have been studied using piezoresponse force microscopy, signifying the enhanced extrinsic contributions by the increased domain wall densities and dynamics. The improved dielectric and piezoelectric properties are discussed and explained from the view point of extrinsic contributions in textured ceramics. The results demonstrate that the textured Sm-PMN-PT piezoelectric ceramics could be promising high performance piezoelectrics with low cost.

Metal halide perovskite (MHP) solar cells have attracted worldwide research interest. Although it has been well established that grain, grain boundary, and grain facet affect MHPs optoelectronic properties, less is known about subgrain structures. Recently, MHP twin stripes, a subgrain feature, have stimulated extensive discussion due to the potential for both beneficial and detrimental effects of ferroelectricity on optoelectronic properties. Connecting the ferroic behavior of twin stripes in MHPs with crystal orientation will be a vital step to understand the ferroic nature and the effects of twin stripes. In this work, we studied the crystallographic orientation and ferroic properties of CH3NH3PbI3 twin stripes, using electron backscatter diffraction (EBSD) and advanced piezoresponse force microscopy (PFM), respectively. Using EBSD, we discovered that the orientation relationship across the twin walls in CH3NH3PbI3 is a 90° rotation about ⟨110⟩, with the ⟨030⟩ and ⟨111⟩ directions parallel to the direction normal to the surface. By careful inspection of CH3NH3PbI3 PFM results including in-plane and out-of-plane PFM measurements, we demonstrate some nonferroelectric contributions to the PFM responses of this CH3NH3PbI3 sample, suggesting that the PFM signal in this CH3NH3PbI3 sample is affected by nonferroelectric and nonpiezoelectric forces. If there is piezoelectric response, it is below the detection sensitivity of our interferometric displacement sensor PFM (

Orthorhombic GeSe is a promising thermoelectric material. However, large band gap and strong covalent bonding result in a low thermoelectric figure of merit, zT≈0.2. Here, we demonstrate a maximum zT≈1.35 at 627 K in p-type polycrystalline rhombohedral (GeSe)0.9 (AgBiTe2 )0.1 , which is the highest value reported among GeSe based materials. The rhombohedral phase is stable in ambient conditions for x=0.8-0.29 in (GeSe)1-x (AgBiTe2 )x . The structural transformation accompanies change from covalent bonding in orthorhombic GeSe to metavalent bonding in rhombohedral (GeSe)1-x (AgBiTe2 )x . (GeSe)0.9 (AgBiTe2 )0.1 has closely lying primary and secondary valence bands (within 0.25-0.30 eV), which results in high power factor 12.8 μW cm-1 K-2 at 627 K. It also exhibits intrinsically low lattice thermal conductivity (0.38 Wm-1 K-1 at 578 K). Theoretical phonon dispersion calculations reveal vicinity of a ferroelectric instability, with large anomalous Born effective charges and high optical dielectric constant, which, in concurrence with high effective coordination number, low band gap and moderate electrical conductivity, corroborate metavalent bonding in (GeSe)0.9 (AgBiTe2 )0.1 . We confirmed the presence of low energy phonon modes and local ferroelectric domains using heat capacity measurement (3-30 K) and switching spectroscopy in piezoresponse force microscopy, respectively.

The lead-free 0.96NaNbO3-0.04CaSnO3 ceramics with rare-earth dopants (La, Sm and Lu) (NCLn100x) were prepared and characterized. It is found that a certain amount of La substitution stabilizes the antiferroelectric (AFE) phase but alleviates the lattice distortion in the fresh samples. Re-entrant-like characteristics are observed in the temperature – dielectric constant curves with the room temperature P phase gradually replaced by a possible R phase. Relaxor-like hysteresis loops with suppressed hysteresis loss and remanent polarization were obtained at high La content, achieving a relatively high Wre of 2.1 J/cm3 at a low electric field (250 kV/cm). The relaxation behaviors of the ferroelectric (FE) domain measured by piezoresponse force microscopy suggest an even long characteristic relaxation time of field-induced FE phase, which is different from the situations of other AFE perovskites. Via an explanatory defected diatomic chain model, we propose that a much larger mass of substitutive ion than the origin one helps to induce low-frequency localized mode, which is believed to be in favor of the formation of polar nano-regions and hence strengthens the dynamic stability of FE phase during electric field loading. Our research provides a further understanding of the tuning strategy for enhancing the antiferroelectricity of the NaNbO3-based system.

Piezoelectric response in two-dimensional (2D) materials has evoked immense interest in using them for various applications involving electromechanical coupling. In most of the 2D materials, piezoelectricity is coupled along the in-plane direction. Here, we propose a technique to probe the in-plane piezoelectric coupling strength in layered nanomaterials quantitively. The method involves a novel approach for in-plane field excitation in lateral Piezoresponse force microscopy (PFM) for 2D materials. Operating near contact resonance has enabled the measurement of the piezoelectric coupling coefficients in the sub pm/V range. Detailed methodology for the signal calibration and the background subtraction when PFM is operated near the contact resonance of the cantilever is also provided. The technique is verified by estimating the in-plane piezoelectric coupling coefficients (d11) for freely suspended MoS2 of one to five atomic layers. For 2D-MoS2 with the odd number of atomic layers, which are non-centrosymmetric, finite d11 is measured. The measurements also indicate that the coupling strength decreases with an increase in the number of layers. The techniques presented would be an effective tool to study the in-plane piezoelectricity quantitatively in various materials along with emerging 2D-materials.

The dependence of electromechanical behavior on strain in ferroelectric materials can be leveraged as parameter to tune ferroelectric properties such as the Curie temperature. For van der Waals materials, a unique opportunity arises because of wrinkling, bubbling, and Moire phenomena accessible due to structural properties inherent to the van der Waals gap. Here, we use piezoresponse force microscopy and unsupervised machine learning methods to gain insight into the ferroelectric properties of layered CuInP2S6 where local areas are strained in-plane due to a partial delamination, resulting in a topographic bubble feature. We observe significant differences between strained and unstrained areas in piezoresponse images as well as voltage spectroscopy, during which strained areas show a sigmoid-shaped response usually associated with the response measured around the Curie temperature, indicating a lowering of the Curie temperature under tensile strain. These results suggest that strain engineering might be used to further increase the functionality of CuInP2S6 through locally modifying ferroelectric properties on the micro- and nanoscale.

BiFeO3-BaTiO3 is a promising high-temperature piezoelectric ceramic that possesses both good electromechanical properties and a Curie temperature (TC). Here, the piezoelectric charge constants (d33) and strain coefficients (d*33) of (1 - x)BiFeO3-xBaTiO3 (BF-xBT; 0.20 ≤ x ≤ 0.50) lead-free piezoelectrics were investigated at room temperature. The results showed a maximum d33 of 225 pC/N in the BF-0.30BT ceramic and a maximum d*33 of 405 pm/V in the BF-0.35BT ceramic, with TCs of 503 and 415 °C, respectively. To better understand the performance enhancement mechanisms, a phase diagram was established using the results of XRD, piezoresponse force microscopy, TEM, and electrical property measurements. The superb d33 of the BF-0.30BT ceramic arose because of its location in the optimum point in the morphotropic phase boundary, low oxygen vacancy (VO··) concentration, and domain heterogeneity. The superior d*33 of the BF-0.35BT ceramic was attributed to a weak relaxor behavior between coexisting macrodomains and polar nanoregions. The presented strategy provides guidelines for designing high-temperature BF-BT ceramics for different applications.

International audience; Herein we investigate the technologically relevant blend of the ferroelectric polymer poly(vinylidene fluorideco-trifluoroethylene), P(VDF-co-TrFE), with the semiconducting polymer poly(3-hexylthiophene), P3HT, by means of a combination of Scanning Probe Microscopy techniques, namely Atomic Force Microscopy, Conductive Force Microscopy, Kelvin Probe Force Microscopy and Piezoresponse Force Microscopy. This combination proves to be a powerful tool for the non-destructive morphological reconstruction of multifunctional nano-structured thin films, as those under study. Each modality allows discerning the two blend constituents based on their functionality, and, additionally, probes layers of different thickness with respect to the films surface. The depth-dependent information that is collected allows a qualitative reconstruction of the blend's composition and morphology both in-plane and out-of-plane of the film. We demonstrate that P3HT exhibits the tendency to reside the film surface at an almost constant composition of 15%, independent of blend's composition. Increasing the P3HT content in the blend results in the segregation of P3HT at the upper layers of the films, partially buried below a P(VDF-co-TrFE) superficial layer. The depletion of P3HT from the substrate/film interface is reflected by the poor existence of conducting pathways that connect the top and bottom planes of the film. The three-dimensional morphology of this polymer blend that is revealed thanks to the employed techniques deviates substantially from the ideal morphology proposed for the efficient performance of the targeted memory devices.

Simultaneous manipulation of multiple boundary conditions in nanoscale heterostructures offers a versatile route to stabilizing unusual structures and emergent phases. Here, we show that a stable supercrystal phase comprising a three-dimensional ordering of nanoscale domains with tailored periodicities can be engineered in PbTiO3–SrRuO3 ferroelectric–metal superlattices. A combination of laboratory and synchrotron X-ray diffraction, piezoresponse force microscopy, scanning transmission electron microscopy and phase-field simulations reveals a complex hierarchical domain structure that forms to minimize the elastic and electrostatic energy. Large local deformations of the ferroelectric lattice are accommodated by periodic lattice modulations of the metallic SrRuO3 layers with curvatures up to 107 m−1. Our results show that multidomain ferroelectric systems can be exploited as versatile templates to induce large curvatures in correlated materials, and present a route for engineering correlated materials with modulated structural and electronic properties that can be controlled using electric fields. Ferroelectric superlattices can present a rich variety of phenomena. Here, in PbTiO3/SrRuO3 superlattices, it is shown that a complex and stable hierarchical supercrystal can form, with the correlated metal of the SrRuO3 layers showing large curvatures.

Controlling the growth of complex relaxor ferroelectric thin films and understanding the relationship between biaxial strain-structural domain characteristics are desirable for designing materials with a high electromechanical response. For this purpose, epitaxial thin films free of extended defects and secondary phases are urgently needed. Here, we used optimized growth parameters and target compositions to obtain epitaxial (40-45 nm) 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3/(20 nm) SrRuO3 (PMN-33PT/SRO) heterostructures using pulsed-laser deposition (PLD) on singly terminated SrTiO3 (STO) and ReScO3 (RSO) substrates with Re = Dy, Tb, Gd, Sm, and Nd. In situ reflection high-energy electron diffraction (RHEED) and high-resolution X-ray diffraction (HR-XRD) analysis confirmed high-quality and single-phase thin films with smooth 2D surfaces. High-resolution scanning transmission electron microscopy (HR-STEM) revealed sharp interfaces and homogeneous strain further confirming the epitaxial cube-on-cube growth mode of the PMN-33PT/SRO heterostructures. The combined XRD reciprocal space maps (RSMs) and piezoresponse force microscopy (PFM) analysis revealed that the domain structure of the PMN-33PT heterostructures is sensitive to the applied compressive strain. From the RSM patterns, an evolution from a butterfly-shaped diffraction pattern for mildly strained PMN-33PT layers, which is evidence of stabilization of relaxor domains, to disc-shaped diffraction patterns for high compressive strains with a highly distorted tetragonal structure, is observed. The PFM amplitude and phase of the PMN-33PT thin films confirmed the relaxor-like for a strain state below ∼1.13%, while for higher compressive strain (∼1.9%) the irregularly shaped and poled ferroelectric domains were observed. Interestingly, the PFM phase hysteresis loops of the PMN-33PT heterostructures grown on the SSO substrates (strain state of ∼0.8%) exhibited an enhanced coercive field which is about two times larger than that of the thin films grown on GSO and NSO substrates. The obtained results show that epitaxial strain engineering could serve as an effective approach for tailoring and enhancing the functional properties in relaxor ferroelectrics.

Present work focuses on detailed temperature-dependent x-ray diffraction, Raman scattering, domain configuration and photoluminescence (PL) studies in the (Ba0·85Ca0.15) (Zr0·10Ti0.90)O3 (BCZT) ceramics. The comprehensive Raman spectroscopy analysis in the present work not only validates the presence of the intermediate orthorhombic phase in BCZT, but also provides evidence of another transition: rhombohedral R3c phase to R3m at low temperature. Temperature behaviour of the lowest frequency transverse optical mode (soft E (TO) phonon) and hard modes were studied. Temperature dependence of peak positions, intensities, and linewidths of Raman phonon modes signalled the presence of phase transitions near −50 ± 5 °C, 0±5 °C, 35±5 °C and 110 ± 10 °C. Evolution of domain morphology occurring with phase transitions above room temperature was studied by piezoresponse force microscopy technique. Analysis of PL spectra revealed disorder/heterogeneity in the sample and indicated the existence of self-trapped excitons. PL spectra is composed of four distinct colour components (∼2.55eV:blue, ∼2.32eV:green, ∼2.08eV:orange and ∼1.78eV:red).

Aligned carbon nanotubes (CNTs) are among the most promising nanostructures in nanoelectronics. However, at the moment, CNTs have not received wide practical application for producing electronic devices, owing to the fact that electrical parameters of devices based on CNTs seriously deviate from those that were theoretically predicted. Previously, these phenomena were not associated with the properties of CNTs and were attributed to the parasitic effects of the environmental impact, and substrate- and interface-related influences. In this paper, using piezoresponse force microscopy, it is shown for the first time that aligned CNTs with a diameter of 52 ± 9 nm and a length of 1.5 ± 0.27 μm have an abnormally large piezoelectric strain coefficient with a value of 203 ± 18 pm V−1, which exceeds the values of typical piezoelectric nanomaterials. It has been established that piezoelectric properties of aligned CNTs lead to the presence of hysteresis in current–voltage characteristics when sawtooth voltage pulses are applied, and cause a significant decrease in conductivity when rectangular voltage pulses are applied. This effect opens up broad prospects for the use of aligned carbon nanotubes for producing nanopiezotronic devices and makes it possible to explain anomalous effects of resistive switching of the CNTs and electronic devices based on them.

Atomically thin two-dimensional (2D) van der Waals materials have exhibited many exotic layer-dependent physical properties including electronic structure, magnetic order, etc. Here, we report a striking even–odd layer dependent oscillation in the ferroelectric polarization of 2H-stacked few-layer α-In2Se3 nanoflakes. As characterized by piezoresponse force microscopy (PFM), when the in-plane (IP) electric polarization of 2H-stacked α-In2Se3 films is electrically aligned, the out-of-plane (OOP) polarization of the odd-layer (OL) samples is obviously larger than that of the even-layer (EL) ones. Similarly, samples with electrically aligned OOP polarization also show even–odd layer dependent IP polarization. Such an even–odd oscillation, as confirmed by the density functional theory calculations, can be attributed to the strong intercorrelation of the IP and OOP electric polarization of the α-In2Se3 monolayers and the special 2H-stacking structure of a 180 degree IP rotation with respect to the adjacent layers. Moreover, a negative differential resistance, interestingly, is induced by the polarization flip with a small coercive field of ∼1.625 kV cm−1, and its peak-to-valley ratio can be tuned up to ∼7 by the gate. This work demonstrates that the delicate stacking geometry of multilayer α-In2Se3 can bring an interesting even–odd ferroelectric effect, enriching the layer-dependent physical properties of the 2D materials family.

New opportunities in the development and commercialization of novel photonic and electronic devices can be opened following the development of technology-compatible arbitrary-shaped ferroelectrics encapsulated in a passive environment. Here, we report and experimentally demonstrate nanoscale tailoring of ferroelectricity by an arbitrary pattern within the nonferroelectric thin film. For inducing the ferroelectric nanoregions in the nonferroelectric surrounding, we developed a technology-compatible approach of local doping of a thin (10 nm) HfO

Four different functional properties at room temperature were found in Ba12Fe28Ti15O84 quaternary ferrite ceramics: a thermoelectric character with a prominent Seebeck coefficient of -400 μV/K, a strong ferrimagnetic character and weak magnetoresistivity, non-linear dielectric character (tunability) and ferro/piezoelectric response. The complex crystalline structure with a naturally occurring self-organized layered structure was mapped by High Resolution Transmission Electron Microscopy. A n-type conduction was found for optimized samples, consistent with the negative Seebeck coefficient. The presence of magnetic domains with a lateral size ranging from few hundreds of nanometers, up to few microns, extended over several grains indicates a strong intergranular magnetic interaction. Local ferroelectric switching as revealed by piezoresponse force microscopy showed a relatively weak effective piezoelectric coefficient with a remnant value of 0.5 p.m./V and a clockwise cycling direction, which was attributed to an effective negative piezoelectric coefficient. The switching behavior was described as originating from the material’s nanoscale layered complexity, with a strong anisotropy of its dielectric and ferro/piezoelectric local properties.

Bi0.5Na0.5TiO3 (BNT)-based ferroelectrics have received more and more attention due to their environment-friendliness and large maximum polarization. Herein, the enhanced energy-storage properties of BNT-based ceramics were successfully prepared by introducing multi-ions (La3+, K+, Al3+, Nb5+, Zr4+) to improve the breakdown strength and simultaneously suppress the remnant polarization. An excellent discharge energy-storage density (Wd) of 3.24 J cm−3 and a high energy-storage efficiency (η) of 82 % under 200 kV cm-1 have been recorded for Bi0.44La0.06(Na0.82K0.18)0.5Ti0.90(Al0.5Nb0.5)0.08Zr0.02O3 ceramic. Meanwhile, the outstanding thermal stability with Wd of 1.84–1.96 J·cm−3 were also achieved in 25−125 °C at 140 kV cm-1. More importantly, piezoresponse force microscopy reveals that the threshold voltage for inducing long range order enhances while the stability of polar nanoregions (PNRs) on the nanoscale decreased with the increase of La doping amount, leading to more linear polarization behavior and higher energy-storage properties. These results promote the practical applications of BNT-based ferroelectrics in advanced pulsed power systems.

Substrate bias was applied for AlN deposition on rolled Ni sheet during pulse DC reactive sputtering to overcome the difficulty caused by thermal expansion mismatch between Ni substrate and AlN upon substrate heating. It was shown by Piezoresponse Force Microscopy (PFM) that the quality of the deposited AlN layer depends strongly on the negative substrate bias, i.e., the energy transferred via the bombardment of the accelerated positive ions on the sample. As the negative substrate bias becomes larger, the so formed layer shows higher piezoresponse, and better homogeneity. A Z-cut LiNbO3 single crystal was used as a reference to correct the PFM signals. The highest average d33 piezoelectric coefficient value, achieved at − 100 V substrate bias, is 3.4 pm/V indicating the feasibility of AlN deposition on rolled Ni substrate for vibration energy harvesting applications.

Lead-free piezoelectric thin films of composition (1-x)Bi0.5Na0.5TiO3-xBi0.5K0.5TiO3-0.03SrZrO3 (x = 15, 17.5, 20 and 22.5%) have been created using the sol-gel spin coating approach over a Pt/Ti/SiO2/Si substrate. The X-ray diffraction profiles suggest that a remarkable transition from tetragonal to rhombohedral-phase passing by a morphotropic phase boundary (MPB) occurs at x values from 17.5 to 22.5%. Additionally, the surface morphology, piezoelectric response, ferroelectric behavior, and energy storage properties were also investigated. Piezoresponse force microscopy (PFM) depicted a strong piezoelectric and ferroelectric behavior at a very localized size; at x = 17.5%. The piezoelectric behavior was enhanced and reached values of the recoverable energy storage density (Jrec) and the energy storage efficiency (η) of 3.27 J/cm3, and 39.9%, respectively. Such materials are anticipated to play an important role in lead-free devices.

Dynamic integration of aligned nanostructures fabricated on different surfaces has prompted the needs for a novel nanoelectromechanical energy harvester. This study describes the morphologies of as-synthesized zinc oxide (ZnO) nano rod-like structures grown onto a bare sputtered substrate and patterned microcontact electrode (IDE), using a simple chemical bath deposition method (CBD). Local piezoresponse measurements were conducted to detect the piezoelectric response and polarization switching in Zinc oxide nanorods. The morphological characteristics and electromechanical response of the grown nanostructures on the printed electrode have been investigated, as a step towards enhancing the performance of piezoelectric nanogenerators. The growth characteristics and energy harvesting ability of nanostructured ZnO on interdigitated microelectrode (IDE) were reported. AFM analysis indicated that the average seed layer thickness of the ZnO film deposited before the lithographic pattern of the IDE was about ~267.5 nm. The FESEM images and XRD analysis confirmed that the ZnO nanorods possessed a hexagonal wurtzite structure having the c-axis crystal orientation preferentially in the (002) plane. FTIR spectrum confirmed the secondary vibrations of the Zn–O bonding at 669.75 cm−1 even with the adjustment in the microstructural features of ZnO. Finally, the Piezoresponse Force Microscopy (PFM) analysis confirmed the converse piezoelectric response of the grown nanorods.

Characterization of the ionic transport and corresponding electro-elastic deformations in cerium oxide at the nanoscale are important for the understanding of the mechanism of the local response under an external electric field, especially the mechanisms of the ‘non-Newnham’'-type giant electrostriction. Here, we introduce a methodological approach to the analysis of signals in the piezoresponse force microscopy/electrochemical strain microscopy allowing decoupling ionic motion, electrostriction, and electrostatic contributions to the electromechanical signals based on a precise analysis of the electromechanical amplitude and phase as a function of temperature, and AC and DC biases. The ionic motion was demonstrated to be hampered in a 30–300°C temperature range, the typical operational range of commercial SPM microscopes. The local electromechanical response was interpreted as a mixture of the electrostatic-force-meditated response and conventional electrostriction.

Understanding ferroelectric domain switching dynamics at the nanoscale is a great of importance in the viewpoints of fundamental physics and technological applications. Here, we investigated the intriguing polarity-dependent switching dynamics of ferroelectric domains in epitaxial BiFeO3 (001) capacitors using transient switching current measurement and piezoresponse force microscopy. We observed the distinct behavior of nucleation and domain wall motion depending on the polarity of external electric bias. When applying the negative bias to the top electrode, the sideways domain wall motion initiated by only few nuclei was dominant to polarization switching. However, when applying the positive bias, most of domains started to grow from the pre-existed pinned domains and their growth velocity was much smaller. We suggest that the observed two distinct domain switching behavior is ascribed to the interfacial defect layer.

The most abundant protein in the human body, collagen, is widely used in tissue culture and engineering applications, spanning from substrate functionalization to fibrillar architectures and three-dimensional constructs. Collagen piezoelectricity provides an opportunity to exploit electromechanical coupling in these applications, wherein an applied mechanical stress generates charge, which might influence ion screening, protein absorption, and cell response. In type I collagen, the polarization direction follows the fibril orientation. Thus, control of fibril orientation and size in a collagen film or membrane may provide control of the polarization, enabling the creation of regions of uniform polarization direction. Here, aligned substrate-supported type I collagen membranes having fibril sizes from ∼100-500 nm are deposited using different osmotic concentrations (90, 190, and 290 mOsm/kg, from low to high ionic strength) to investigate the correlation between fibril size and piezoelectric properties. Lateral piezoresponse force microscopy is used to show that regions of uniform polarization orientation, as determined through 2D correlation analysis, decrease with increasing fibril size. European Commission Horizon 2020 China Scholarship Council

Non-volatile field-effect transistor (FET) with amorphous Al2O3 dielectric is demonstrated on Si substrate, which is enabled by the voltage modulation of the oxygen vacancy and negative charge dipoles in gate insulator. Ferroelectric-like behavior in TaN/Al2O3/Si0.70Ge0.30 stacks with different thicknesses of Al2O3 is proved by polarization-voltage tests, positive-up and negative-down tests, piezoresponse force microscopy, and electrical measurements. The Al2O3 capacitors attain over 108 cycles’ endurance of polarization versus voltage measurement. A 6.5 nm-thick Al2O3 non-volatile FET achieves a memory window above 0.6 V under ±2 V at 100 ns program/erase (P/E) condition, over 104 cycles P/E endurance, and >105s data retention at room temperature.

Interactions between grain boundaries and domain walls were extensively studied in ferroelectric films and bicrystals. This knowledge, however, has not been transferred to polycrystalline ceramics, in which the grain size represents a powerful tool to tailor the electromechanical and dielectric response. Here, we relate changes in dielectric and electromechanical properties of a bulk polycrystalline Pb(Zr0.7Ti0.3)O3 to domain wall interactions with grain boundaries. Samples with grain sizes in the range of 3.9–10.4 μm were prepared and their microstructure, crystal structure, and dielectric/electromechanical properties were investigated. A decreasing grain size was accompanied by a reduction in large-signal electromechanical properties and an increase in small-signal relative permittivity. High-energy diffraction analysis revealed increasing microstrains upon decreasing the grain size, while piezoresponse force microscopy indicated an increased local coercive voltage near grain boundaries. The changes in properties were thus related to strained material volume close to the grain boundaries exhibiting reduced domain wall dynamics.

In this paper, we study ferroelectric domain structures, optical properties, as well as domain dynamic performances induced by external in-plane electric field of Eu-doped lead magnesium niobate-lead titanate [Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT)] transparent ceramics mainly via piezoresponse force microscopy (PFM). It is found that Eu doping play a significant role on the domain structures and domain switching behavior in PMN-PT transparent ferroelectrics. For some compositions the switching of domain structures exhibit a normal evolutionary trend, while for the compositions with low Eu doping content, unusual anisotropic polarization switching behaviors were obtained in macrodomain regions under in-plane bias in the Eu-doped PMN-PT transparent ceramics.

The possibility of confining interlayer excitons in interfacial moire patterns has recently gained attention as a strategy to form ordered arrays of zero-dimensional quantum emitters and topological superlattices in transition metal dichalcogenide heterostructures. Strain is expected to play an important role in the modulation of the moire potential landscape, tuning the array of quantum dot-like zero-dimensional traps into parallel stripes of one-dimensional quantum wires. Here, we present real-space imaging of unstrained zero-dimensional and strain-induced one-dimensional moire patterns along with photoluminescence measurements of the corresponding excitonic emission from WSe2/MoSe2 heterobilayers. Whereas excitons in zero-dimensional moire traps display quantum emitter-like sharp photoluminescence peaks with circular polarization, the photoluminescence emission from excitons in one-dimensional moire potentials shows linear polarization and two orders of magnitude higher intensity. These results establish strain engineering as an effective method to tailor moire potentials and their optoelectronic response on demand. The combination of piezoresponse force microscopy and optical measurements reveals the influence of strain in the formation of one-dimensional moire patterns and the resulting behaviour of interlayer excitons in van der Waals heterostructures.

We investigate over a period of a 500 hours the effect of relative humidity (RH) on the retention loss in ferroelectric P(VDF-TrFE) thin films by using piezoresponse force microscopy (PFM). When the copolymer films are exposed to more water molecules, more domain reversal is observed, especially in upward domains. Interestingly, the retention loss behavior based on a stretched exponential model can be distinctly classified depending on the RH conditions. We conjecture that the absorption and the desorption of water molecules in the P(VDF-TrFE) polymers have a great influence on the reversal of ferroelectric domains.

The orthorhombic phase of GeSe, a structural analogue of layered SnSe (space group: Pnma), has recently attracted attention after a theoretical prediction of high thermoelectric figure of merit, zT > 2. The experimental realization of such high performance in orthorhombic GeSe, however, is still elusive (zT ≈ 0.2). The rhombohedral phase of GeSe, a structural analogue of GeTe (space group: R3m), previously stabilized at high pressure (2 GPa) and high temperature (1600 K), is promising due to its theoretically predicted ferroelectric instability and the higher earth abundance of Se compared to Te. Here, we demonstrate high thermoelectric performance in the rhombohedral crystals of GeSe, which is stabilized at ambient conditions by alloying with 10 mol % AgBiSe2. We show ultralow lattice thermal conductivity (κL) of 0.74-0.47 W/mK in the 300-723 K range and high zT ≈ 1.25 at 723 K in the p-type rhombohedral (GeSe)0.9(AgBiSe2)0.1 crystals grown using Bridgman method. First-principles density functional theoretical analysis reveals its vicinity to a ferroelectric instability which generates large anomalous Born effective charges and strong coupling of low energy polar optical phonons with acoustic phonons. The presence of soft optical phonons and incipient ferroelectric instability in (GeSe)0.9(AgBiSe2)0.1 are directly evident in the low temperature heat capacity (Cp) and switching spectroscopy piezoresponse force microscopy (SS-PFM) experiments, respectively. Effective scattering of heat carrying acoustic phonons by ferroelectric instability induced soft transverse optical phonons significantly reduces the κL and enhances the thermoelectric performance in rhombohedral (GeSe)0.9(AgBiSe2)0.1 crystals.

To tackle the global restriction on the use of lead-based materials, a feasible strategy of developing a piezoelectric ceramic with a ferroelectric- and relaxor-coexisted hybrid state is proposed in order to reduce the energy barrier as well as to assist polarization rotation. A significantly enhanced piezoelectric coefficient, d33, of 173 pC/N along with a broadened high-temperature stability above 300 °C has been obtained. Further probing via piezoresponse force microscopy unveils the grain boundary-governed domain structures with complicated configurations, suggesting close correlations with the coexistence of ferroelectric and relaxor states. This work demonstrates a recipe for establishing a novel grain-based ferroelectric-relaxor hybrid state with improved piezoelectric performance, which can further be beneficial for realistic applications.

The photovoltaic properties of ferroelectric films have been extensively studied due to their potential applications in the fields of photodetection, energy conversion harvesting and storage. However, the effect of the gradient distribution of oxygen vacancies on the photovoltaic properties remains unclear. Herein, we prepared BiFeO3 (BFO) and two types of gradient calcium-doped BiFeO3 (BiFeO3/Bi0.95Ca0.05FeO2.975/Bi0.90Ca0.10FeO2.950/Bi0.85Ca0.15FeO2.925: BCFO-1 and Bi0.85Ca0.15FeO2.925/Bi0.90Ca0.10FeO2.950/Bi0.95Ca0.05FeO2.975/BiFeO3: BCFO-2) films deposited on fluorine-doped tin oxide glass substrates. Piezoresponse force microscopy studies indicate the upward self-polarization phenomenon in BFO and BCFO-1 films, while the downward self-polarization phenomenon in BCFO-2 films. The J–V characteristic curves show rectifier behaviors for these films due to the configuration of oxygen vacancies. For photovoltaic response, the open circuit voltage of BCFO-1 films is more than 2 times higher than that of BFO films, and the short-circuit photocurrent densities of BCFO-1 and BCFO-2 films are increased by nearly 32 and 6 times, respectively. The direction and magnitude of photovoltaic response are possibly associated with the energy band modulation governed by self-polarization and the gradient distribution of oxygen vacancies. The work demonstrates the merits of gradient doping with lower valence cation towards enhanced photovoltaic properties with high stability for ferroelectric oxides.

High-performance environment-friendly piezoelectric potassium sodium niobate (KNN)-based thin films have been emerged as promising lead-free candidates, while their substrate-dependent piezoelectricity faces the lack of high-quality information due to restraints in measurements. Although piezoresponse force microscopy (PFM) is a potential measuring tool, still its regular mode is not considered as a reliable characterization method for quantification. After combining machine-learning enabled analysis using PFM datasets, it is possible to measure piezoelectric properties quantitatively. Here we utilized advanced PFM technology empowered by machine learning to measure and compare the piezoelectricity of KNN based thin films on different substrates. The results provide a better understanding of the relationship between structures and piezoelectric properties of the thin films.

Lithium niobate on insulator (LNOI) is widely used in optical, acoustic, domain wall current (DWC)-based integrated circuits and other domain engineering devices, enabling higher material performance, higher domain integration density and more advanced applications. However, there are hidden dangers of thermal failure in these highly integrated domain engineering devices. Therefore, maintaining thermal stability of domain structures in ferroelectric single-crystal thin films is an important and challenging task. Here, thermally induced structure reconstruction of tailored metastable switched domains was research in a 500 nm thick congruent lithium niobate (CLN) thin film, and a method for enhancing the thermal stability of switched domains was proposed. Piezoresponse force microscopy (PFM) and a polyheater are used to accurately monitor the thermal evolution of switched domains in CLN thin film sample. The results indicate the switched domain structures determine the thermal stability, and the enhanced thermal stability of the switched domains increases from 55 to 85 °C–150 °C. In this contribution, the thermal failure in domain engineering devices can be avoided effectively. The investigation paves the way for the development of domain engineering devices based on lithium niobate (LN) thin films.

The positive temperature co-efficient (PTC) of resistivity in BaTiO3 is a grain boundary effect, where the resistivity increases by several orders of magnitude near the transition temperature from ...

Ferroelectric domain structure in BaTiO3 ceramics was studied with nanoscale spatial resolution before and after poling by application of the uniform electric field. Complimentary vector piezorespo...

Calibration technique for lateral piezoresponse force microscopy (PFM) based on lateral force curves measurements is introduced and discussed in terms of relative error connected with experimental ...

We study the interplay between epitaxial strain, film thickness, and electric field in the creation, modification, and design of distinct ferroelastic structures in PbTiO3 thin films. Strain and thickness greatly affect the structures formed, providing a two-variable parameterization of the resulting self-assembly. Under applied electric fields, these strain-engineered ferroelastic structures are highly malleable, especially when a/c and a1/a2 superdomains coexist. To reconfigure the ferroelastic structures and achieve self-assembled nanoscale-ordered morphologies, pure ferroelectric switching of individual c-domains within the a/c superdomains is essential. The stability, however, of the electrically written ferroelastic structures is in most cases ephemeral; the speed of the relaxation process depends sensitively on strain and thickness. Only under low tensile strain-as is the case for PbTiO3 on GdScO3-and below a critical thickness do the electrically created a/c superdomain structures become stable for days or longer, making them relevant for reconfigurable nanoscale electronics or nonvolatile electromechanical applications.

Polarization switching in lead-free (K0.40Na0.60)NbO3 (KNN) single crystals was studied by switching spectroscopy piezoresponse force microscopy (SS-PFM). Acquisition of multiple hysteresis loops on a closely spaced square grid enables polarization switching parameters to be mapped in real space. Piezoresponse amplitude and phase hysteresis loops show collective symmetric/asymmetric characteristics, affording information regarding the switching behavior of different domains. As such, the out-of-plane polarization states of the domains, including amplitudes and phases can be determined. Our results could contribute to a further understanding of the relationships between polarization switching and polarization vectors at the nanoscale, and provide a feasible method to correlate the polarization hysteresis loops in a domain under an electric field with the polarization vector states.

Ferroelectrics exhibit polarization tunable resistance switching behaviors, which are promising for next-generation non-volatile memory devices. For technological applications, thinner nanoscale arrays are expected, which feature with higher density and larger ON/OFF (RON/OFF) ratios in the metal/ferroelectrics/semiconductor heterojunction. Here, we acquire high density BiFeO3 (BFO) nano-islands around 10 nm in thickness displaying a high RON/OFF ratio of 103, comparable to the tunnel junctions. Moreover, both the macroscopic and microscopic resistive switching behaviors of the present BiFeO3 films reveal an unexpected the filamentary-type resistive switching which is modified by the charged domain walls in nano-islands dominated by the center-type domains. Particularly, the charged domain walls spontaneously formed within the BFO nano-islands are proposed as the conductive paths based on the redistribution of carriers under the applied voltages. Potential applications for memories with large RON/OFF ratios of such kind of configurable charged domain walls are demonstrated.

In this study, the underlying physical mechanisms of imprint are addressed in order to obtain a better understanding of the imprint phenomenon of relaxor Pb(Zn1/3Nb2/3)O3-x%PbTiO3 (PZN-x%PT) ferroelectric single crystals. The local domain structure and imprint of Pb(Zn1/3Nb2/3)O3-4.5%PbTiO3 (PZN-4.5%PT) single crystals are investigated by using Piezoresponse Force Microscopy (PFM) and Switching Spectroscopy PFM (SS-PFM) techniques, respectively. The results show that the imprint depends on polarization states. It is also found that surface charge accumulation shows no significant effects on the imprint behaviour of the PZN-4.5%PT single crystals. By studying the annealed samples in the oxygen and argon atmospheres respectively, it is found that the alignment of oxygen vacancy related defect dipoles is one of the origins for the occurrence of imprint. This study provides a better understanding of the imprint phenomenon in ferroelectric materials, which is crucial for the enhancement of the reliability and the advancement of ferroelectric relaxors into the application of ferroelectric devices.

A new polar and magnetic oxide, LuCrWO6, was synthesized under high pressure (6 GPa) and high temperature (1673 K). LuCrWO6 is isostructural with the previously reported polar YCrWO6 (SG: Pna21, no. 33). The ordering of CrO6 and WO6 octahedra in the edge-shared dimers induce the polar structure. The effective size of rare earth, Ln cation does not seem to affect the symmetry of LnCrWO6. Second harmonic generation measurements of LuCrWO6 confirmed the noncentrosymmetric character and strong piezoelectric domains are observed from piezoresponse force microscopy at room temperature. LuCrWO6 exhibits antiferromagnetic behavior, TN, of ∼18 K with a Weiss temperature of -30.7 K.