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In our work last year (H. Zhu et al., Rhombohedral BiFeO3 thick films integrated on Si with a giant electric polarization and prominent piezoelectricity, Acta Materialia 200 (2020) 305–314), it was demonstrated that the rhombohedral-like, (110)-textured BiFeO3 thick films (∼2 μm) sputter-deposited at 450 °C and 500 °C exhibited ultrahigh polarizations of Pr ∼ 115 μC/cm2 and 135 μC/cm2, respectively. However, it is not sufficient to explain these ultra-high polarizations by a preferential growth mechanism and the effect of a moderate compressive strain. To further clarify the polarization enhancement of the films, the texture characteristics of these BFO thick films were quantitatively analyzed by fitting the rocking curves and pole figures to the March-Dollase model. The results showed that, in addition to the (110)-textured growth of a BFO thick film under a moderate compressive strain, the minority non-(110)-textured grains also contributed to the enhancement of the total polarization. Our study demonstrates that, the ultra-high polarizations of our BFO thick films can be well explained by adding the contribution from non-textured grains to the preferential growth of the film under a compressive strain.

Spectral induced electric polarization provides useful information on geoelectric parameters, which may allow mineral discrimination in exploration geophysics. Electromagnetic coupling between current and potential electrodes equally contributes to understanding the geology but represents the main source of noise in spectral induced electric polarization surveys. In this article, we propose an integrated analysis of these two phenomena in the context of complex resistivity data in order to evaluate their role in exploration geophysics taking into account their specificities. Deepening previous studies of forward modeling and inversion of mutual impedance in the frequency domain, in this present approach, we have employed an expanded apparent complex resistivity function, which includes the inductive effect in its parameters. We developed an integrated inversion of this function using the very fast simulated annealing and least-squares methods to estimate the geoelectric parameters. We also performed tests and applications on synthetic and real data, discussing the benefits of using the proposed complex resistivity model. The approach was applied to data from three profiles of the Copper District of Vale do Curaca, Bahia, Brazil. The results show that it is possible to distinguish between spectral induced polarization and induction in terms of geoelectric parameters distributed in pseudosections and to identify patterns and behaviors for each of them. They constitute an important step toward mineral discrimination via analysis of analogous circuit parameters, a fundamental tool in searching metallic ores.

The ferroelectric material In2Se3 is currently of significant interest due to its built-in polarisation characteristics that can significantly modulate its electronic properties. Here we employ density functional theory to determine the transport characteristics at the metal-semiconductor interface of the two-dimensional multiferroic In2Se3/Fe3GeTe2 heterojunction. We show a significant tuning of the Schottky barrier height as a result of the change in the intrinsic polarisation state of In2Se3: the switching in the electric polarization of In2Se3 results in the switching of the nature of the Schottky barrier, from being n-type to p-type, and is accompanied by a change in the spin polarization of the electrons. This switchable Schottky barrier structure can form an essential component in a two-dimensional field effect transistor that can be operated by switching the ferroelectric polarization, rather than by the application of strain or electric field. The band structure and density of state calculations show that Fe3GeTe2 lends its magnetic and metallic characteristics to the In2Se3 layer, making the In2Se3/Fe3GeTe2 heterojunction a potentially viable multiferroic candidate in nanoelectronic devices like field-effect transistors. Moreover, our findings reveal a transfer of charge carriers from the In2Se3 layer to the Fe3GeTe2 layer, resulting in the formation of an in-built electric field at the metal-semiconductor interface. Our work can substantially broaden the device potential of the In2Se3/Fe3GeTe2 heterojunction in future low-energy electronic devices.

Significantly enhanced photoelectrochemical (PEC) performance of the visible light active photoanodes of ferroelectric Bi0.5Na0.5TiO3 nanostructure has been demonstrated by tuning the electrical polarization of the film. The photocurrent density of unpoled Bi0.5Na0.5TiO3 photoanode increases from 0.48 mA cm−2 at 1 V with respect to Ag/AgCl to 1.21 mA cm−2 after negative poling, whereas it decreases to 0.18 mA cm−2 after positive poling. The incident photon-to-current conversion efficiency (IPCE) of the nanostructure photoanodes has been observed to vary from 5% to 28% just by changing the direction of electric polarization. The change in the PEC performance and enhancement in the IPCE value after switching the polarization state of Bi0.5Na0.5TiO3 photoanodes have been attributed to the modification in the band bending at the interface of semiconductor electrode/electrolyte, leading to facilitate the increment in photogenerated charge transfer efficiency. The modulation in the band bending and variation in the charge transfer method after switching the polarization state are confirmed by Mott-Schottky (M-S) and electrochemical impedance spectroscopy (EIS) measurements. Our work provides a new visible light active ferroelectric nanostructure material for efficient visible light active photoelectrochemical performance.

International audience; Fe4Nb2O9 and Co4Nb2O9 are antiferromagnetic compounds belonging to the M4M′2O9 series (M = Mn, Fe, Co; M′ = Nb, Ta), whose structure (P[3 with combining macron]c1) derives from the Cr2O3 corundum one. By mixing cobalt and iron in a 1 : 1 ratio, an Fe2Co2Nb2O9 oxide has been synthesized. Its structural, magnetic and electric characterization studies confirm that its unit cell volume (V = 331.19(1) Å3), Néel temperature (TN = 58 K) and dielectric permittivity are intermediate between those of the Fe4Nb2O9 and Co4Nb2O9 end members. The neutron diffraction study evidences an Fe:Co random occupation of the (4d) Wyckoff sites. Its antiferromagnetic structure, refined in the C2/c′ magnetic space group, shows magnetic moments in the planes of the honeycomb (HC) layers of the M4M′2O9 structure, and stacked along c, as for Fe4Nb2O9 and Co4Nb2O9. However, the magnetic field induced magnetization M(H) of Fe2Co2Nb2O9 below TN differs strongly from both end members, exhibiting a sublinear dependence. A similar rounded shape of the electric polarization P(H) curve is evidenced, in marked contrast to the linear M(H) and P(H) behaviours observed below the spin-flop magnetic field for this class of linear magnetoelectric materials. As a result, Fe2Co2Nb2O9 exhibits larger P values and steeper P responses to H at low H than both Fe4Nb2O9 and Co4Nb2O9 end members. This result is explained by a microscopic model based on the Fe and Co mixed occupation. Substitutional disorder locally allows for stronger magnetoelectric couplings and its effect does not cancel on average. This chemical substitution effect opens a new route to enhance the magnetoelectric response of honeycomb antiferromagnets.

Several methods have been used to detect defects or debonds nondestructively in materials or construction. Each of these nondestructive testing methods has advantages and limitations. Generally, they are suitable for testing a certain range or a specific type of material and structure and some of them require careful analysis to identify the features of the defects. The present work proposes a nondestructive testing method based on electro-acoustic technique (NDTPEA) to detect internal defects of dielectric materials, which can identify the defects from the original stress wave generated at the internal defect surface. Electric polarization occurs in the dielectric under the action of a high-voltage electric field. When the intensity of the electric field changes suddenly, the polarization charge generates a stress wave. If there are defects, such as cracks and debonding, in the medium, the position and size of the internal defects of the insulating material can be determined according to the stress wave. The waveform and velocity of stress wave is measured by a PVDF film. According to the velocity and time of the stress wave in the dielectric, the position of the internal defects or debonding of the specimen can be determined. The maximum error for measuring the wave transmission time is 1 ns, and the maximum measurement error in the defect thickness direction was 0.00253 mm. In the NDTPEA, the detected wave originates from the vibration of the polarized charge at the defect, i.e., the defect is the source of the stress wave. The measured stress wave does not undergo any reflection or refraction, and the waveform is truly regular, without coupling factors. The wave shape and time characteristics can all reflect the characteristics of the defects.

Two-dimensional (2D) photocatalytic material is a vital project for modern solar energy conversion and storage. Despite a vast family of potential 2D photocatalysts that is demonstrated, their commercial applications are severely limited because of fast photogenerated electron-hole recombination. Here, based on first-principles, we propose a general paradigm to boost the separation of photoexcited charge carriers in 2D photocatalysts by stacking engineering. Taking the emerging water splitting photocatalyst MoSi2N4 as an example, we show that specific interlayer stacking-induced electric polarization plays a significant role in altering the electronic properties and thus the suppressed recombination rate of photoexcited carriers. Moreover, we find that the catalytic performance can be further controlled by vertical strain. These generalized findings not only highlight the importance of stacking-induced electric polarization but also offer new prospects for the design and application of 2D photocatalysts.

Magnetoelectric materials that allow magnetic-field control of electric polarization are promising candidates for high-density data storage and spintronic devices. In this paper, the ferroelectric, magnetic, and magnetoelectric properties of NiFe2O4/PbZ0.5T0.5O3, CoFe2O4/PbZ0.5T0.5O3, NiFe2O4/PbZ0.5T0.5O3/CoFe2O4, and NiFe2O4/PbZ0.5T0.5O3/NiFe2O4 heterostructures have been carried out using the Monte Carlo simulation in the framework of the Heisenberg model. The effects of the temperature on magnetization, electric polarization, and their susceptibilities were examined. The calculated interfacial magnetoelectric coupling interaction Jme for NiFe2O4/PbZ0.5T0.5O3 and CoFe2O4/PbZ0.5T0.5O3 interfaces permitted to predict the magnetoelectric voltage coefficient for these heterostructures and controlling the polarization via a magnetic field. Interestingly, a high magnetoelectric voltage coefficient of 650 and 1405 mV cm−1 Oe−1 was predicted in NiFe2O4/PbZ0.5T0.5O3/CoFe2O4 and NiFe2O4/PbZ0.5T0.5O3/NiFe2O4, respectively. Moreover, the effect of Jme on M-H and P–H hysteresis loops and the magnetoelectric voltage coefficient was studied.

An equivalent circuit model backed deep neural network (DNN) is introduced to develop a broadband frequency selective surface (FSS). Shielding effectiveness (SE) and resonant frequency are inputs and shielding structure parameters are the outputs of the DNN. Moreover, three different configurations of DNN are investigated to get a minimum mean square error of 2.99 × $10^{-6}$ between targeted and observed outputs. The size of FSS is 0.30 $\lambda _0$ × 0.30 $\lambda _0$ and the total thickness of the shielding structure is only 0.1 mm. The variation in resonance frequency is only 0.08 GHz when the angle of incidence changes from $\theta$ = $0^\circ$ to $\text{80}^\circ$ for transverse electric polarization. Furthermore, a fractional bandwidth of 80 ${\%}$ is achieved with a resonance at 10 GHz. The broad shielding bandwidth, ultrathin, polarization-insensitivity, wide angular stability attained by using a new, very simple, and miniaturized geometry are a few key features of the proposed structure. The results obtained from DNN are validated using full-wave simulation and by measurement of the fabricated prototype. SE performance concurs well among all demonstrate the effectiveness of the aforementioned technique for electromagnetic interference shielding application.

In materials showing a linear magnetoelectric (ME) effect, unconventional functionalities can be anticipated such as electric control of magnetism and nonreciprocal optical responses. Thus, the search for new linear ME materials is of interest in materials science. Here, using a recently proposed design principle of linear ME materials, which is based on the combination of local structural asymmetry and collinear antiferromagnetism, we demonstrate that an anion-deficient fluorite derivative, Mn3Ta2O8, is a new linear ME material. This is evidenced by the onset of magnetic-field-induced electric polarization in its collinear antiferromagnetic phase below TN = 24 K. Furthermore, we also find an antiferroelectric-like phase transition at TS = 55 K, which is attributable to an off-center displacement of magnetic Mn2+ ions. The present study shows that Mn3Ta2O8 is a rare material that exhibits both ME and antiferroelectric-like transitions. Thus, Mn3Ta2O8 may provide an opportunity to investigate the physics associated with complicated interactions between magnetic (spin) and electric dipole degrees of freedom.

This paper presents a systematic study of room temperature magnetoelectric properties of lead-free (1 − x) Bi0.9La0.1FeO3/xLa0.7Sr0.3MnO3 (x = 0, 0.1, 0.2) composites synthesized via solid-state reaction route. We investigated the crystal structure, morphology, elemental presence, dielectric parameters, and electric polarization properties. Magnetization versus field study shows an enhancement in magnetization values as we add La0.7Sr0.3MnO3 (LSMO) to the Bi0.9La0.1FeO3 (BLFO) samples. The magnetoelectric (ME) coupling coefficient increases from 10.21 to 23.16 mVcm−1Oe−1 as the concentration of LSMO varies from x = 0 to 0.2. The observed linear dependence of voltage generation with modulating AC field point toward the direct application of the material in a variety of next-generation low power consuming memory devices, spintronics, sensors, etc.

The mechanical characteristics of piezoelectric ceramic fibers can be improved by embedding the fibers in a metal matrix. The compressive stress generated during the embedding process, however, limits the polarization of piezoelectric ceramic composites. To study and determine the relationship between the mechanical and piezoelectric properties of piezoelectric ceramics, we analyzed the crystallographic orientation of piezoelectric ceramics embedded in an aluminum matrix via electron backscatter diffraction. The orientation of the crystals before and after the polarization of the piezoelectric fibers, in which residual stresses were generated during embedding, was evaluated. Furthermore, the residual stresses were reduced by heat treatment, and the resultant angle of orientation was evaluated before and after polarization. Results showed that, as the residual stresses were relieved, the orientation of the piezoelectric ceramic crystals changed to reveal increased polarization. Our analysis shows that the crystal orientation of piezoelectric ceramics is impacted by the residual compressive stress that arises from embedding the piezoelectric fiber in the aluminum matrix; it also illustrates the hindering effect of residual stress on the polarization of piezoelectric ceramics.

Antiferroelectric (AFE) materials, featuring an antiparallel alignment of electric dipoles in the adjacent sublattices, are keeping a great promise toward solid-state refrigeration applications on account of their electrocaloric (EC) effects. Although extensive studies have been performed on inorganic oxide counterparts (e.g., PbZrO3 and AgNbO3), metal-free molecular AFE alternatives with the above-room-temperature EC activities are quite scarce but urgently demanded in terms of environmental issues. Herein, we present a new metal-free molecular AFE, cyclohexylmethylammonium bromide (CMB), which exhibits the unusual antiferroelectric-ferroelectric-paraelectric phase transitions around 364 and 368 K upon heating. The phase transition temperatures are much higher than the majority of known molecular AFE materials. The practical utilization level of electric polarization (∼6 μC/cm2) is clearly evidenced by the typical double polarization-electric field hysteresis loops. Strikingly, large positive and negative EC responses with the temperature changes (ΔT) of 4.2 and -3 K are achieved under an electric field of 20 kV/cm. The origin of its antiferroelectricity and EC properties is elucidated by the antipolar reorientation of cations along with displacement of bromine anions, being distinct from the known mechanism of inorganic oxides. Such intriguing AFE behaviors, including large polarization and EC effects, reveal great potentials of CMB for the solid-state refrigeration. This study sheds light on further exploration of new AFE candidates toward environmentally friendly solid-state cooling devices.

The dielectric behavior of polycrystalline graphite is addressed by assimilating the DC electric polarization, AC permittivity, DC electret behavior, and their grain-size dependence. The AC-permittivity-related polarization is weaker than the DC-electret-related polarization, involving fewer carriers, because the depolarization is slower than polarization. The DC-current-induced polarization is even weaker than the AC-permittivity-related polarization, involving even fewer carriers. A decrease in the grain size increases the fraction of carriers that participate in the DC-polarization/AC-permittivity/DC-electret through carrier-atom interaction at the grain boundaries, thereby increasing the permittivity and the electret's electric field. The electric field increases with increasing resistivity and increasing inter-electrode distance l. DC-polarization/DC-depolarization and electret discharge/charge are faster for a smaller grain size. Both electric field and the reciprocal of the capacitance increase linearly with l, suggesting a model of dipoles in series. The amount of charge at each end of the overall dipole is greater for a smaller grain size, while the discharge time per unit electret-participating charge is shorter. In spite of the decrease in the fraction of carriers that participate with increasing l, the electret energy density is much increased by increasing l, because it depends on the power density and discharge time, both of which increase with l.

High density Ba4Sm2Fe2Nb8O30 (BSFN) multiferroics ceramics with tetragonal tungsten bronze structure had been prepared by microwave sintering (MS) for 30min and conventional sintering (CS) methods for 4 h at 1275 °C. Single tungsten bronze phase and equiaxial grains are obtained for the MS BSFN ceramics, while a small amount secondary phase of SmNbO4 is observed in the CS BSFN ceramics with columnar grains. Compared to Ba4Sm2Fe2Nb8O30 ceramics prepared by CS method, enhanced dielectric, ferroelectric and magnetic properties are achieved for the MS BSFN ceramics. The values of electric polarization Pr and coercive electric field Ec are 2.11 μC/cm2 and 7.14 kV/cm for the MS BSFN ceramics, respectively. Meantime, the magnetic polarization Mr of 0.410emu/g and coercive magnetic field Hc of 2930Oe are also obtained for the MS BSFN ceramics. Based on the density, crystal structure, point defect and grain, the reasons of enhanced dielectric, ferroelectric and magnetic properties are discussed for the MS BSFN ceramics It is indicated that Ba4Sm2Fe2Nb8O30 is an intrinsic room temperature multiferroic materials.

Perovskite ABO3 oxides that have Bi and Pb at the A site and transition metals at the B site, when stabilized by high-pressure synthesis at several gigapascals, provide a rich parameter space of fascinating properties. Stereochemical 6 s2 lone pairs of Bi3+ and Pb2+ induce polar or antipolar distortions. 6 s2 and 6 s0 (Bi5+ and Pb4+) charge degree of freedom enable intermetallic charge transfer transitions. The structural distortion and the charge degree of freedom are coupled with magnetism of transition metals, resulting in various functionalities. In particular, we highlight magnetization reversal by electric field and polarization rotation in BiFe1− xCo xO3, negative thermal expansion in modified BiNiO3 and PbVO3, and systematic charge distribution changes in Pb MO3 ( M = 3 d transition metal).

Nowadays, several research groups are extensively trying to develop by synthesizing and characterizing single/co-doped single-phase bismuth ferrite (BFO) in order to get a highly efficient eco-friendly multifunctional devices. In this process, this report is an attempt to provide the detailed studies of structural, dielectric, impedance and ferroelectric properties of Bi(Fe0.85Dy0.15)O3 ceramic fabricated via the solid-state reaction method. Analysis of X-ray diffraction (XRD) data confirms a single phase of orthorhombic symmetry. The average crystallite (particle) size is found to be in the order of ~ 41 nm. The field emission scanning electron microscopy (FE-SEM) spectrum shows a homogeneous grain distribution of the sample. The elemental composition examined by means of energy dispersive X-ray spectroscopy (EDXS) shows the existence of constituent elements of the sample. The electrical measurements and analysis, carried out using a computer-controlled phase sensitive multimeter (PSM) in a frequency range of 1 kHz–1 MHz at different sets of temperature (25–325 °C), provide many interesting features to explain further conduction mechanism. The dielectric analysis exhibits high value of dielectric constant (ɛr) and small value of dielectric loss (tanδ). Due to the effect of electronic and space charge polarization, the ɛr value falls with an increasing frequency. The frequency–temperature dependence of impedance and electrical modulus analysis reveals the presence of semiconductor nature and non-Debye type of relaxation process in the sample. The analysis of ac-conductivity (σac) with respect to frequency and temperature obeys the universal Jonscher’s power law. The electric polarization study shows an enhancement in ferroelectric property of the material. Hence, based on the significant enhancement in electrical and ferroelectric properties of the Bi(Fe0.85Dy0.15)O3 material, the material may be considered for some applications.

The mechanism of the magnetoelectric coupling of spins of Ni2+ and Cu2+ ions with the applied electric field in (Ni, Cu)B2O4, caused by the coupling of 3d electrons with the electric field and by the spin–orbit coupling, is analyzed. It is shown that the ordering of spins in the ab crystallographic plane of the crystal induces the electric polarization along the c axis of the crystal, and this polarization is mainly related to nickel ions. To obtain the electric polarization in the CuB2O4 antiferromagnet, it turns out to be necessary to apply the magnetic field in the ab plane.

The luminescence modulation behavior of lanthanide ion doped materials possesses great potential for applications in sensing, display and anti-counterfeiting devices. Unlike traditional tuning methods for chemical compositions, novel rare-earth doped ferroelectric oxides exhibit attractive luminescence modulation effects via electric polarization engineering, and enrich the development of multifunctional devices. In this work, Sm3+ doped KSr2Nb5O15 ceramics with abundant ferroelectric and luminescent properties were synthesized. The samples show different relaxation behaviors and ferroelectric features upon chemical and structural factors caused by Sm3+ doping, such as average ionic radii, local tolerance factors, and chemical bonds. After polarization at 20 kV/cm for 20 min, a considerable increase (~40%) in the luminescent emission intensity was obtained in 4 mol. % Sm3+ doped KSr2Nb5O15 ceramics. The related luminescence modulation mechanism was attributed to controlling the environmental symmetry around Sm3+ by the electric polarization.

The average electric polarization arising in a two-layer, nanosized, ferromagnetic film with a combined uniaxial and cubic anisotropy and a vortical distribution of magnetization is studied numerically. Allowance for the cubic anisotropy leads to a multifold increase in the average electric polarization in samples with a positive constant of cubic anisotropy and a significant decrease in samples with a negative constant of cubic anisotropy. Analysis of the hysteresis of the average electric polarization in a magnetic field perpendicular to the film revealed striking differences in the field dependences in films with different cubic anisotropy. If the cubic anisotropy is positive, then the maxima of the average polarization curves shift to the region of low magnetic fields upon an increase in the anisotropy constant. The intensity of the maxima becomes larger, and the hysteresis practically disappears. For films with a negative constant of cubic anisotropy, the maxima of the average polarization curves shift to the region of high fields upon an increase in this constant and the intensity of the maxima becomes significantly smaller.

Y-type hexaferrites with non-collinear conical magnetic structures, which induce electric polarization (P), are prospective single-phase multiferroics with broad applications, such as magnetic sensors, energy convertors, and memory devices, among others. Y-type hexaferrites have attracted considerable attention. In this study, we investigated the magnetoelectric properties of Ba0.7Sr1.3CoZnFe11AlO22 single crystals with Y-type hexaferrite structures by replacing half of Zn2+ ions with Co2+ ions. A transition from a screw order to the ferromagnetic is observed at TN2 = 356 K in Ba0.7Sr1.3CoZnFe11AlO22 single crystals. The electric polarization (P) and magnetoelectric coupling coefficient ( α ) reach a maximum of 130 μC/m2 and 16667 ps/m at T = 30 K and E = 880 kV/m, respectively. Most importantly, the in-plane Hab induced P can be fully reversed by applying in-plane Hab and it maintains a non-zero value even when the applied magnetic field is zero. Since the P does not decay and repeats many times under a fluctuating low magnetic field, it is important for potential applications in new types of non-volatile memory devices.

Although it is established that the force-induced electric polarization field of piezoelectric semiconductors can be used to tune the transfer rate of photoexcited charge carriers, there is still a lack of successful strategies to effectively improve the photocatalytic reactivity and solar-to-chemical conversion efficiency (SCC) of piezoelectric materials. Here, we are the first to prepare and study a kind of catalyst based on nanopiezoelectric heterostructures of LiNbO3-type ZnTiO3·TiO2 and tetragonal BaTiO3 with Pt or FeOx nanoparticle modification (i.e., ZBTO-Pt or ZBTO-FeOx) for reactive species generation. With respect to the production of •OH and •O2- radicals, higher amounts were observed in piezophotocatalysis relative to those for individual piezo- and photocatalysis. Benefiting from the charge transfer resistance decreases by the deposition of Pt and FeOx, the amounts of •OH radicals formed on ZBTO-Pt and ZBTO-FeOx were approximately 48 and 21% higher than that on isolated ZBTO during piezophotocatalysis, and for the amounts of •O2- radicals the enhancements were approximately 11 and 6%, respectively. Furthermore, the concentrations of H2O2 formed on ZBTO-Pt and ZBTO-FeOx under piezophotocatalysis reached approximately 315 and 206 μM after 100 min of reaction (and was still increasing) corresponding to 0.10 and 0.06% SCCs, respectively, which were also much higher than the concentrations and SCCs observed for piezo- and photocatalysis. The enhancements of piezophotocatalytic activities with these piezoelectric materials were related to the mechanical strain exerted on ZBTO, which generated a larger electric polarization field than those on ZnTiO3·TiO2 and BaTiO3 as analyzed by a finite element method. This high-intensity electric polarization field accelerated the separation and transportation of photoexcited charge carriers in the highly sunlight responsive nanopiezoelectric heterostructures based on ZBTO-Pt and ZBTO-FeOx.

The temperature-frequency dependences of the dielectric permittivity and conductivity of Li2O-Fe2O3-Al2O3 ceramics in the temperature range of 298-648 K were obtained by impedance spectroscopy. Their analysis indicates the presence of a fractal-like structure in the studied samples, the effect of which is manifested at low temperatures. To study the phenomenon of electric polarization associated with this structure, we used the generalized law of Jonscher. A significant dependence of the dispersion of dielectric and conductive properties of these spinel ceramics on the temperature and aluminum content in them was revealed.

Wideband and polarization-insensitive operation are key issues for electro-optic modulators. An electro-absorption modulator based on graphene-silicon nitride hybrid waveguide has been proposed. Geometric parameters are investigated through finite element method to enhance the interaction between the optical mode and the graphene. For a 200-µm-long hybrid waveguide, a modulation depth (MD) of 20 dB can be obtained when Femi level varies from 0.2 to 0.6 eV. The MD difference between the transversal electric polarization and transversal magnetic polarization (ΔMD) can be restrained to 4 × 10−3 dB at 1550 nm. A low average ΔMD of 0.2 dB within the wavelength range from 1100 to 1645 nm can be obtained. The 3 dB-bandwidth of 53 GHz and a power consumption is 0.687 pJ/bit can be obtained. The proposed modulator has potentials for on-chip signal processing.

Insulator-based dielectrophoresis (iDEP) has been increasingly used for particle manipulation in various microfluidic applications. It exploits insulating structures to constrict and/or curve electric field lines to generate field gradients for particle dielectrophoresis. However, the presence of these insulators, especially those with sharp edges, causes two nonlinear electrokinetic flows, which, if sufficiently strong, may disturb the otherwise linear electrokinetic motion of particles and affect the iDEP performance. One is induced charge electroosmotic (ICEO) flow because of the polarization of the insulators, and the other is electrothermal flow because of the amplified Joule heating in the fluid around the insulators. Both flows vary nonlinearly with the applied electric field (either DC or AC) and exhibit in the form of fluid vortices, which have been utilized to promote some applications while being suppressed in others. The effectiveness of iDEP benefits from a comprehensive understanding of the nonlinear electrokinetic flows, which is complicated by the involvement of the entire iDEP device into electric polarization and thermal diffusion. This article is aimed to review the works on both the fundamentals and applications of ICEO and electrothermal flows in iDEP microdevices. A personal perspective of some future research directions in the field is also given.

Phase transitions in small spherical particles of multiferroics were investigated in the framework of the Ginzburg-Landau phenomenological theory. Using the expression of free energy for magnetizat...

Two-dimensional (2D) Janus materials with mirror asymmetry exhibit fascinating physical properties, implying wide applications in nanoscale optoelectronic and piezoelectric devices. However, intrinsic ferromagnetic (FM) Janus monolayers with high Curie temperature (Tc) and large magnetic anisotropic energy (MAE) are rarely reported. By performing the first-principles calculations, the electronic structure and magnetic properties of stable Janus Mn2PAs monolayer were investigated. We found that Mn2PAs monolayer is FM half-metal with high Tc of 557 K and easy out-of-plane magnetization axis, as well as a small intrinsic electric polarization. Additionally, Mn2PAs monolayer under biaxial strain from -10% to 10% remains to be FM half-metallic. More importantly, the MAE reaches a maximum value of ~ 578 μeV per Mn atom under 8% tensile strain and changes direction under compressive strain larger than 2%, which mainly attributes to the variation of (py, pz)/(py, px) orbital matrix elements of As/P atom. The desired and robust ferromagnetism and half-metallicity with 100% spin-polarization of Janus Mn2PAs monolayer enrich the application of 2D Janus materials in nanoscale spintronic devices.

Monolayer transition-metal dichalcogenides (TMDs) have provided a platform to investigate the excitonic states at the two-dimensional (2D) limit. The inherent properties of excitons in TMDs, such as the photoluminescence quantum yield, the charge states, and even the binding energy, can be effectively controlled via electrostatic gating, selective carrier doping, or substrate dielectric engineering. Here, aiming for the nonvolatile electrical tunability of excitonic states and thereby the optical property of TMDs, we demonstrate a 2D ferroelectric heterostructure with monolayer MoSe2 and ultrathin CuInP2S6 (CIPS). In the heterostructure, the electric polarization of CIPS results in continuous, global, and large electronic modulation in monolayer MoSe2. With the saturated ferroelectric polarization of CIPS, electron-doped or hole-doped MoSe2 is realized in a single device. The carrier density tunability in the heterostructure is as high as 5 × 1012 cm-2. The nonvolatile behavior of these devices up to 3 months is also characterized. Our results provide a new and practical strategy for low-power consumption and agelong tunable optoelectronic devices.

BaTiO3-based ferroelectrics have been extensively studied due to their large dielectric constants and a high saturated polarization, which have the potential to store or supply electricity of very high energy and power densities. In order to further improve the energy efficiency η and the recyclable energy density Wrec, an A, B-site co-doped (Ba0.95,Sr0.05)(Zr0.2,Ti0.8)O3 ceramic target was used for sputter deposition of film capacitor structures on Si. This film composition reduces the remnant polarization Pr, while the choice of a low-temperature, templated sputtering process facilitates the formation of high-density arrays of columnar nanograins (average diameter d ∼20 nm) and grain boundary dead layers. This self-assembled nanostructure further delays the saturation of the electric polarization, leading to a high energy density Wrec of ∼148 J/cm3 and a high energy efficiency η of ∼90%. Moreover, the (Ba0.95,Sr0.05)(Zr0.2,Ti0.8)O3 film capacitors retain their high energy storage performance in a broad range of working temperature (-175-300 °C) and operating frequency (1 Hz-20 kHz). They are also fatigue-free after up to 2 × 109 switching cycles. Our work provides a new method and a cost-effective processing route for the creation and integration of high-performance dielectric capacitors for energy storage applications.

Magnetoelectric (ME) materials have been attracting extensive attention due to their potential applications. It is important to realize strong ME effect in one single material at sufficiently high temperature, and thus substantial efforts in searching for ME materials with strong ME coupling together and a comprehensive understanding of the underlying mechanism is necessary. Herein we focus on the Mn-doped linear ME material Co4-xMnxNb2O9, in which a large electric polarization driven by magnetic field emerges below its Neel temperature TN, by presenting the detailed characterizations on the structure, magnetism, and ME effect. It is revealed that an increasing Mn substitution x allows largely enhanced TN and gradually suppressed ME coefficient αME. This ME coupling suppression is attributed to the weak spin-orbit interaction of Mn2+ with respect to Co2+. It is indicated that the Dzyaloshinskii-Moriya (DM) interaction plays an important role in the ME coupling. The measured largest αME is found in For Co0.8Mn3.2Nb2O9, reaching up to 9.9 ps/m at 10 K while the TN reaches up to 102 K, exceeding most of the linear ME materials that have been reported.

We study the buckling of flexoelectric semiconductor beams using one-dimensional equations based on the macroscopic theory of flexoelectric semiconductors. Simple solutions for a beam with sliding ends and a simply supported beam with hinged ends are obtained. Results show that when buckling occurs, the mobile charges in the beams redistribute themselves driven by the electric polarization or field accompanying buckling through flexoelectricity. The buckling load increases due to flexoelectric coupling which may be called flexoelectric stiffening. The mobile charges redistribute themselves to screen the polarization or electric field and thus weaken the flexoelectric stiffening.

A group of 0.65(Bi0.5Na0.5)TiO3 -0.35(Sr0.7+x + Bi0.2)TiO3 (BNT-S0.7+xBT) composite ceramic pellets are synthesized using a traditional solid sintering method, where a tunable x, the changeable volume of Sr, is to tailor energy storage through the adjustments of the A-site stoichiometry in BNT-S0.7+xBT. We find that a small excess of Sr2+ ions will result in an extensively tuning on the crystal grain size and even contribute to the A-site disorder and charge fluctuation of BNT-S0.7+xBT. As such, the BNT-S0.7+xBT exhibits a minimum average grain size and a highly compact crystal morphology, and thus, BNT-S0.75BT ceramic exhibits a high dielectric constant (er) of about 5100 at 110 °C. Meanwhile, a relatively thin polarization–electric field (P–E) loop with a high maximum polarization of 42 μC/cm2 and a low remnant electric polarization of 5 μC/cm2 are obtained in a BNT-S0.75BT pellet under 100 kV/cm, corresponding to an energy density of 0.98 J cm−3 and a good η of 70.7%. Attractively, the maximum polarization (Pm) of BNT-S0.75BT ceramic at 25–100 °C hardly decreases, implying excellent temperature stability of polarization performances under high electric field of 100 kV/cm, which favors the energy storage of relaxor ferroelectric ceramics and is valuable to a supercapacitor serving at evaluated high temperature.

Utilizing the magnetostrictive properties of CoFe2O4, we demonstrate reversible room temperature control of the Ti electronic structure in SrTiO3–CoFe2O4 heterostructures, by inducing local and reversible strain in the SrTiO3. By means of X-ray absorption spectroscopy, we have ascertained the changes that take place in the energy levels of the Ti 3d orbitals under the influence of an external magnetic field. The observed Ti electronic state when the sample is subjected to moderately large external magnetic fields and the disappearance of the induced phase upon their removal indicates lattice distortions that are suggestive of the development of a net electric polarization., We show reversible room temperature control of the Ti band structure in SrTiO3–CoFe2O4 heterostructures exploiting CoFe2O4 magnetostriction. Changes as a function of the applied magnetic field suggest the development of a net electric polarization.

Nitrogen-vacancy (NV) centers in diamond can be used as quantum sensors to image the magnetic field with nanoscale resolution. However, nanoscale electric-field mapping has not been achieved so far because of the relatively weak coupling strength between NV and electric field. Using individual shallow NVs, here we succeeded to quantitatively image the contours of electric field from a sharp tip of a qPlus-based atomic force microscope (AFM), and achieved a spatial resolution of ~10 nm. Through such local electric fields, we demonstrated electric control of NV's charge state with sub-5 nm precision. This work represents the first step towards nanoscale scanning electrometry based on a single quantum sensor and may open up new possibility of quantitatively mapping local charge, electric polarization, and dielectric response in a broad spectrum of functional materials at nanoscale., Comment: 32 pages, 5 figures

Two-dimensional (2D) ferroelectric (FE) hybrid organic-inorganic perovskites (HOIPs) are promising for potential applications as miniaturized flexible ferroelectric/piezoelectric devices. Recently, several 2D HOIPs [e.g., Ruddlensden-Popper type HOIP BA2PbCl4 (BA = C6H5CH2NH3+)] were reported to possess room-temperature ferroelectricity. However, the underlying microscopic mechanisms for ferroelectricity in 2D HOIPs remain elusive. Here, by performing first-principles calculations and symmetry mode analysis, we demonstrate that there exists a cooperative coupling between A-site organic molecules and B-site inorganic Pb2+ ions that is essential to the ferroelectricity in 2D BA2PbCl4. The nonpolar ground state of the closely related compounds BA2PbBr4 and BA2PbI4 can also be explained in terms of the weakened cooperative coupling. We further predict that 2D BA2PbF4 displays in-plane ferroelectricity with a higher Curie temperature and larger electric polarization. Our work not only reveals the unusual FE mechanism in 2D HOIPs but also provides a solid theoretical basis for the rational design of 2D multifunctional materials.

We report the structural, magnetic, and electrical properties of a new family of doubly ordered perovskites NaLnNiWO6 (Ln = La, Pr, Nd, Sm, Eu, Gd, and Tb), synthesized at high-pressure (4.5 GPa) and high-temperature (1000 °C) conditions. These materials crystallize in the monoclinic structure with the polar space group P21 as revealed by neutron diffraction (Ln = La), X-ray diffraction, and second-harmonic-generation (SHG) studies. These compounds exhibit a combined layered ordering of A-site cations and rock-salt ordering of B-site cations with octahedral tilting, which breaks the inversion symmetry and results in a polar structure. The magnetic and heat capacity measurements reveal the antiferromagnetic order of Ni2+ ion moments in the temperature range of 23–30 K, depending on the Ln ion. Analysis of neutron powder diffraction data for the La compound reveals that the Ni2+ spins couple antiferromagnetically along the a- and c-directions and ferromagnetically along the b-axis, consistent with the propagation vector, k = (1/2, 0, 1/2). In contrast to the compounds with smaller lanthanide ions (Ln = Y, Dy, Ho, and Yb), these compounds do not exhibit measurable electric polarization at TN but show a dielectric anomaly.

In this paper, single-phase orthoferrite NdFeO3 crystals with the space group of Pbnm were successful prepared via mild hydrothermal method. The NdFeO3 crystal performs a weak antiferromagnetic behavior by magnetic measurement. The Dzyaloshinskii Moriya interaction in NdFeO3 crystal causes an additional canting of the antiferromagnetically ordered spins which induce the ferroelectricity. The saturation electric polarization result is 0.0163 μC/cm2 with coercive field of 6.68 kV/cm, and the Curie temperature is 430 K. So we present the direct experimental evidences that the NdFeO3 sample simultaneously exists the ferroelectricity and weak antiferromagnetic at room temperature. This work can develop a route to obtain more species of multiferroic compounds with perovskite structure.

The classical theory is incapable of explaining the size-dependent behavior of small-scale structures. This theory also fails to describe a linear response of electric polarization to the temperature gradient. The mentioned effects can be explained by the local gradient theory of electrothermoelasticity that alongside the mechanical, thermal, and electromagnetic processes considers the effect of the changes in material microstructure on the solid behavior. Within the local gradient theory, the above changes in the material microstructure are linked with the process of the local mass displacement. The basic equations of this theory were obtained earlier based on the continuum-thermodynamic approach. In this study, the variational approach for the formulation of linear boundary-value problems of the local gradient electrothermoelasticity is proposed. Using this approach, the fundamental equations and proper boundary conditions which describe the physical behavior of the linear continuum are derived. The usefulness of the proposed theory is verified based on two simple problems. Namely, the theory is used to study the response of the electric polarization of the isotropic layer to the temperature gradient and to investigate the coupled field in a simply-supported piezoelectric nanobeam subjected to the distributed uniform force. A generalized mathematical model of the Bernoulli–Euler electroelastic beam is formulated. It is shown that the resulting local gradient beam model can capture the size-depending behavior of the piezoelectric beam at the nanoscale. The results obtained in this study are general and can be useful for modeling new devices based on size, thermopolarization, and piezoelectric effects.

Narrowband absorption spectrum is usually a critically important factor for a plasmonic absorber that works as a biosensor for narrower bandwidth which refers to higher sensitivity of sensor. To realize plasmonic biosensor of narrow bandwidth, absorption property of plasmonic absorber has been usually investigated under normally incident light with transverse magnetic polarization. Here we present numerically a structure of graphene-based metasurface to obtain reflection spectrum of narrow bandwidth, while incident light is at oblique angle and with transverse electric polarization in the infrared range. The presented structure includes a dielectric layer on top side, a buffer dielectric layer, graphene film, a dielectric layer of high refractive index with high-aspect-ratio nanotrench array, and a metal substrate. As a plasmonic absorber, its absorption bandwidth is $\text{0.5}$ nm wide, and its peak absorption reaches 97% at the resonant wavelength. As a refractive index sensor, its bulk sensitivity and figure of merit are $\text{500}$ nm/RIU and $\text{1000/}$ RIU (“RIU” is abbreviation of “Refractive Index Unit” and as unit of refractive index), respectively. It shows a novel configuration of obtaining narrow bandwidth plasmonic absorbers using transverse electric polarized incident light at oblique incidence angle. The presented graphene-based structure has a strong potential in biosensing applications, such as platform for sensing refractive index variation on the nanoscale while probing neural stem cell activities in the period of cell development.

One of the most important lead-free piezoelectric compounds that has been studied extensively belongs to alkali niobate family, the sodium-potassium niobium (KNN) compound. In this study, KNN/PVDF composite was fabricated through hot compression molding of the components and its mechanical, thermal and electrical properties were studied. For this purpose, KNN was first synthesized by solid-state reaction during two-step calcination and its structural evolution was studied using XRD. Composite samples were prepared at different KNN to PVDF weight ratios. The powder mixture was then formed into disks by hot compression molding. The microstructure of the composite samples was investigated by SEM. The prepared samples were perfectly dense with a density in the range of 97.44% to 99.11% of the theoretical density. The thermal properties of the prepared composites were evaluated by thermogravimetric analysis and it was observed that final weight loss due to material degradation was reduced with increasing KNN weight percent. In addition, samples with higher KNN contents showed increased Young's modulus and yield strength values in compression. In order to investigate the electrical properties, the dielectric constant, dielectric loss factor, piezoelectric charge and voltage coefficients and electric polarization were studied. The results showed that the dielectric constant increased with KNN content. The same trend was observed in the piezoelectric charge coefficient and the dielectric loss factor of the PVDF/KNN composites. At 80 wt% KNN, the composite showed a distinct ferroelectric behavior with a remanent polarization of 0.255 μC/cm2 and 20.5 kV/cm coercivity. According to the results of the present study, hot compression molding is an effective method for producing KNN/PVDF composites with improved mechanical and thermal properties compared to its constituents.

The electrification of ice has been a subject of research since 1940, mostly in the context of charge generation in thunderstorms. This generation of electric charge is spontaneous, distinct from applying an external electric field to affect the diffusive growth of ice crystals. Here, we exploit the spontaneous electrification of ice to reveal a surprising phenomenon of jumping frost dendrites. We use side-view high-speed imaging to experimentally observe frost dendrites breaking off from mother dendrites and/or the substrate to jump out-of-plane toward an opposing polar liquid. Analytical and numerical models are then developed to estimate the attractive force between the frost dendrites and liquid, in good agreement with the experimental results. These models estimate the extent of charge separation within a growing sheet of frost, which is caused by mismatches in the mobilities of the charge carriers in ice. Our findings show that the unexpected jumping frost event can serve as a model system for resolving long-standing questions in atmospheric physics regarding charge separation in ice, while also having potential as a deicing construct.

This work provides the first report of the effect of the dielectric behavior on the conduction behavior of solder. The lead-free solder studied contains 96 wt% tin and 4 wt% silver. The electric polarization stems from the interaction of the valence electrons with the atoms. The fraction of valence electrons that participate in the initial polarization is of the order of 10–9. The injected electrons play a minor role compared to the valence electrons of the solder in the polarization. The efficiency of the injected electrons in promoting the polarization decreases with the increasing number of injected electrons. Due to the polarization under a constant applied DC current (30–100 mA), the apparent electrical resistivity increases beyond the true resistivity. The rate of apparent resistivity increase diminishes as the time of current application increases. The fractional increase is 0.10% at 130 s of 100-mA current application. The higher is the current, the greater are the degree and rate of polarization at a given time. The current effect saturates above ~ 90 mA. Upon reversal of the polarity of the applied current, depolarization (followed by reverse polarization) occurs. The rates of depolarization and reverse polarization, as indicated by the rate of apparent resistivity increase, increase with increasing current. These rates decrease with increasing time. At the same current and respective time, the rates of polarization and depolarization are essentially equal, but the rate of reverse polarization is much below that of the initial polarization. Furthermore, the nearly saturated degree of reverse polarization is much below that of the initial polarization. This indicates a partially irreversible effect of the initial polarization that hinders the reverse polarization.

The dynamics of direct-current-induced electric polarization/depolarization of a conductive material (graphite) are studied. Forward-current polarization and reverse-current depolarization cause the apparent resistivity to increase by ≤ 2.2% and ≤1.0%, respectively. Polarization-related carrier-atom interaction engagement occurs more readily than depolarization-related disengagement. The number n of carriers that participate increases with the number NI of injected electrons; the rate of the n increase decreases with increasing NI. The efficiency of carrier-atom interaction (indicated by n/NI, ≤1.2 × 10−17) decreases with increasing NI (≤1.2 × 1020). For the same NI, the fraction of carriers that participate (n/(NI + Nc), where Nc = number of inherent carriers) increases with increasing current (rate of electron injection). At a particular current, this fraction increases and then decreases with increasing NI. The polarization/depolarization rate decreases as polarization/depolarization proceeds. At a given polarization/depolarization time, the rate and degree of polarization are higher than those of depolarization. The above fraction is higher for polarization (≤8.5 × 10−18) than depolarization (≤4.7 × 10−18). The difference between polarization and depolarization agrees with the apparent-resistivity asymmetry and true electret character indicated by the open-circuited DC electric field of 1.0 × 10−5 V/m. The above fraction is lower than the fraction of carriers that participate in the electret discharge (4.9 × 10−4) by 14 orders of magnitude.