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The stereochemical expression of the ns2 lone pair significantly impacts symmetry breaking and corresponding photoelectric properties. However, hindered by the symmetric octahedral configuration, the Pb2+ 6s2 lone pair in the well‐conductive lead halide hybrid perovskites (LHHP) are normally stereo‐inactive, new approaches to activate the 6s2 lone pair are still greatly desired. Herein, by exploiting a perovskitizer tuning Pb2+ lone pair method, the study successfully obtains a stereo‐active 6s2 in the polar perovskite PA2MHy2Pb3Br10 (PMPB, PA = n‐propylamine, MHy = methylhydrazine), and unprecedentedly performs a multiaxial self‐powered X‐ray detection. In detail, the stereo‐active 6s2 lone pair is caused by the coordination bond between the perovskitizer MHy and Pb atom. Emphatically, the N‐Pb bond induces a large angular distortion parameter (≈45 times larger than other LHHP) and the lowest‐symmetric space group (P1) crystallization. Therefore, PMPB natively contains multiaxial polarization, which acts as the driving force to separate and transport the X‐ray‐generated carriers, thus enabling multiaxial self‐powered X‐ray detection with a low detection limit (129 nGy s−1). This work reveals the relationship between stereo‐active lone pair and polarization and sheds light on future X‐ray detection. [ABSTRACT FROM AUTHOR]

In this report, I studied the structural, morphological, and dielectric properties of new ferroelectric compounds prepared according to the formula Ba0.95Sr0.05Ti1-ySnyO3. The solid-state reaction method enhanced by a high-efficiency metal ball mill was used in the preparation process. The quantitative and qualitative analysis of the XRD patterns confirmed the crystallization of the samples y = 0.00, 0.05 in the tetragonal crystal system and the presence of the tetragonal and cubic crystal systems together in the samples y = 0.10, 0.14. Formation of BaSnO3 impurities in very low percentages in the doped samples. Their prevalence increases with increasing tin content, reaching 8.7% at the ratio y = 0.14. SEM images of the ceramic samples showed the formation of nano-ceramics with a high degree of condensation at the doping ratio y = 0.05. The dielectric analyses showed high thermal stability in the dielectric properties of the ceramic samples y = 0.05, 0.10, which was shown by the flatness of the dielectric constant curve over the entire temperature range studied, where this stability is attributed to the structure of the nano-grains that resist the ferroelectric-paraelectric phase transition. Furthermore, the dielectric properties were interpreted by accurately linking the dielectric measurements with the nano-structural and polar properties. [ABSTRACT FROM AUTHOR]

High carrier recombination causes a huge waste of photogenic charge, which severely restrains the photocatalytic efficiency. Creating polarization electric field by polar photocatalytic materials proves effective to promote charge separation, while developing efficient polarization strategy is challenging and the related micromechanism remains obscure. Here, overall polarization is achieved in Bi2MoO6 single crystal photocatalyst by lateral growth of the nanoplate along {010} facets. Gradual elongation of equatorial Mo─O bonds along the MoO6 octahedral layer occurs, while the length of apical Mo─O bonds basically remains unchanged, thus allowing the large asymmetric distortion of MoO6 octahedron for producing the microscopic polarization. Meanwhile, the lateral growth of Bi2MoO6 nanoplates enables the accumulation of distorted polar units, further increasing the polarization intensities. The inside‐out crystal polarization significantly promotes the separation and migration of photogenerated charge carriers. The finely polarized Bi2MoO6 nanoplates exhibit an exceptional photocatalytic selective oxidation rate of benzyl alcohol (BA) to benzaldehyde (BAD) under visible light irradiation (Conversion (Con.) ≈100% within 30 min, Selectivity (Sel.) ≥95%), over 70.7 times that of original Bi2MoO6 nanosheets, on the condition of comparable O2 adsorption capability. This study advances atomic‐level mechanistic insight into polarized materials toward precise design of high‐performance photocatalysts. [ABSTRACT FROM AUTHOR]

Enhancing the piezoelectricity of CaBi4Ti4O15 (CBT) ceramics is crucial for improving their application potential in high-temperature piezoelectric devices. Here, we propose a strategy involving the introduction of larger Na/Bi ions at the A-site, effectively inhibiting the tilt of oxygen octahedra and flattening the potential energy profile. This flattening enhances the variation in polarization under external fields. Concurrently, substituting Nb/Mn at the B-site increases the deviation between positive and negative ionic centers, leading to stronger spontaneous polarization, while the induced defect dipoles restrict oxygen vacancy migration and increase the direct current resistivity (ρdc). The flattened potential energy profile and increased spontaneous polarization significantly enhance the overall performance of CBT ceramics, with the piezoelectric constant (d33) reaching 25 pC/N when the Curie temperature (TC) = 752 °C. Piezoresponse force microscopy (PFM) and transmission electron microscopy (TEM) revealed submicron-long rectangular domains and nanoscale domains in the modified composition, indicating a high density of domain walls. This study presents an effective approach for enhancing the piezoelectric properties of bismuth layered-structured ferroelectrics (BLSFs), thereby improving the application potential of BLSFs at high temperatures.

In this report, I studied the structural, morphological, and dielectric properties of new ferroelectric compounds prepared according to the formula Ba0.95Sr0.05Ti1-ySnyO3. The solid-state reaction method enhanced by a high-efficiency metal ball mill was used in the preparation process. The quantitative and qualitative analysis of the XRD patterns confirmed the crystallization of the samples y = 0.00, 0.05 in the tetragonal crystal system and the presence of the tetragonal and cubic crystal systems together in the samples y = 0.10, 0.14. Formation of BaSnO3 impurities in very low percentages in the doped samples. Their prevalence increases with increasing tin content, reaching 8.7% at the ratio y = 0.14. SEM images of the ceramic samples showed the formation of nano-ceramics with a high degree of condensation at the doping ratio y = 0.05. The dielectric analyses showed high thermal stability in the dielectric properties of the ceramic samples y = 0.05, 0.10, which was shown by the flatness of the dielectric constant curve over the entire temperature range studied, where this stability is attributed to the structure of the nano-grains that resist the ferroelectric-paraelectric phase transition. Furthermore, the dielectric properties were interpreted by accurately linking the dielectric measurements with the nano-structural and polar properties.

Improving ferro-piezoelectric properties of niobate-based perovskites is highly desirable for developing eco-friendly high-performance sensors and actuators. Although electro-strain coupling is usually obtained by constructing multiphase boundaries via complex chemical compositions, defect engineering can also create opportunities for novel property and functionality advancements. In this work, a representative tetragonal niobate-based perovskite, i.e., KNbO3, is studied by using first-principles calculations. Two intrinsic types of Nb antisite defect complexes are selected to mimic alkali-deficiency induced excess Nb antisites in experiments. The formation energy, electronic profiles, polarization, and piezoelectric constants are systematically analyzed. It is shown that the structural distortion and chemical heterogeneity around the energetically favorable antisite pair defects, i.e., ( Nb K 4 · + K Nb 4 ′ ), lower the crystal symmetry of KNbO3 from tetragonal to triclinic phase, and facilitate polarization emergence and reorientation to substantially enhance intrinsic ferro-piezoelectricity (i.e., spontaneous polarization Ps of 68.2 μC/cm2 and piezoelectric strain constant d33 of 228.3 pC/N) without complicated doping and alloying. [ABSTRACT FROM AUTHOR]

To obtain high performance optoelectronic devices, ferroelectric materials have received a lot of attention due to the various emerging effects on channel materials induced by the ferroelectric polarization. In this work, a special photodetector with the channel material of a triple-layer MoS2 on a polarized LiNbO3 substrate was fabricated. The device has a high responsivity of 113.1A/W and a high specific detectivity of up to 7.286×1012 Jones under red illumination, while maintaining the rise and fall time of 32 and 22ms, respectively. Meanwhile, the dark current of this device can be as low as 2.66×10−11A with a bias of 5.0V because the channel material MoS2 is almost depleted under the internal electrical field induced by the polarized LiNbO3. This work promises a feasible way for the future development of integrated high-sensitivity photodetectors. [ABSTRACT FROM AUTHOR]

The electric potential stimulation of biological structures in aqueous environments is well-known to be a result of the gating of voltage-gated ion channels. Such voltage-gated ion channels are ubiquitous in the membranes of a wide variety of cells and they play central roles in a wide variety of sensing mechanisms and neuronal functions in biological systems. Experimental studies of ion-channel gating are frequently conducted using path-clamp techniques by placing a cumbersome external electrode in the vicinity of the extracellular side of the ion channel. Recently, it has been demonstrated that laser-induced polarization of nanoscale quantum dots can produce voltage sufficient to gate voltage-gated ion channels. This study specifically focuses on a new method of gating voltage-gated ion channels using 2D structures made of materials exhibiting large naturally occurring spontaneous polarizations, thereby eliminating the need for an external electrode or an illuminating laser. The work presents the use of self-polarizing semiconductor flakes, namely, 2H-SiC, ZnO, and GaN, to produce electric potential that is sufficient to gate voltage-gated ion channels when existing in proximity to it. [ABSTRACT FROM AUTHOR]

NaBiCe/Sc ions were co‐doped into a pure CaBi4Ti4O15 (CBT) ceramic to investigate the synergistic action of multiple factors that induced a high piezoresponse. In comparison to the undoped CBT ceramic, the NaBiCe/Sc co‐doped CBT solid solution exhibited an enhancement in spontaneous polarization (Ps) attributed to the tilting of the oxygen octahedra, enhanced domain reorientation owing to increased grain size, and improved dielectric breakdown strength as a consequence of reduced porosity. The synergistic action of the aforementioned comprehensive factors resulted in excellent electrical properties of Ca0.6(Na0.5Bi0.5)0.4Bi3.97Ce0.03Ti3.925Sc0.075O15 ceramic: piezoelectric coefficient d33 = 25.0 pC/N, remnant polarization Pr = 9.28 μC/cm2, and coercive field Ec = 76.14 kV/cm. Moreover, a significant high direct current resistivity (ρdc = 1.22 × 107 Ω·cm at 500°C) was achieved, and the corresponding conductance mechanism was analyzed through a synergistic approach that combines ultraviolet–visible diffuse reflectance spectra and density functional theory. [ABSTRACT FROM AUTHOR]

The unique spontaneous polarization property of ferroelectric material makes it to be a special catalyst in photocatalysis. The spontaneous polarization property can induce the formation of built-in electric field, which can improve the separation of photoelectrons and holes to affect photocatalytic performance. The internal electric field induced by spontaneous polarization can be influenced by multiple factors such as the morphology, the concentration of defect, the type of doped heteroatoms, as well as the composition of heterostructures. Besides, the preparation method, pretreating temperature, the strength of prepolarized external electric field of ferroelectric-based photocatalysts as well as the strength of external mechanical force or external magnetic field in photocatalytic reactions can influence the photocatalytic effectivity via influencing spontaneous polarization-induced internal electric field. Thus, it is urgently to unveil the mystery of structure-activity relationships for ferroelectric materials-based photocatalysts, which is usually uncertain. With this in mind, this review was provided for the role of various complex influencing factors on ferroelectric materials-based photocatalysis based on the latest advancement in the fields of new energy development, environmental remediation. In the beginning, the basic structure and properties of ferroelectric material are given. Then, popular synthesis methods of ferroelectric-based photocatalysts are summarized. After that, two main mechanisms of ferroelectric photocatalysis are discussed. The research progress of ferroelectric photocatalysis is then given emphatically according to the classification of photocatalytic reactions. Finally, the problems existing nowadays and the challenges facing in the future on the application of ferroelectric materials-based photocatalysts are outlined in the summary and outlook section. [ABSTRACT FROM AUTHOR]

Wurtzite aluminum nitride (AlN) crystal has a non-centrosymmetric crystal structure with only a single axis of symmetry. In an AlN crystal, the electronegativity difference between the Al atom and N atom leads to a distortion of electron cloud distribution outside the nucleus and a spontaneous polarization (SP) along the c-axis direction. The N-polar surface along the directions of [000-1] has higher surface energy than the Al-polar surface along the directions of [0001]. Due to the different atomic arrangement, Al atoms on the Al-polar surface bond with O and OH− in the environment to generate Al2O3·xH2O, which prevents the reaction from occurring inside the crystal. After the Al2O3·xH2O dissolve in an alkaline environment, N atoms have three dangling bonds exposed on the surface, which can also protect OH− from destroying the internal Al-N bonds, so the Al-polar surface is more stable than the N-polar surface. [ABSTRACT FROM AUTHOR]

Phonon anharmonic interactions up to the fourth order and four-body interaction terms, with the consideration of the extra spin–lattice term, direct spin–spin interaction terms, and four spin coupling, are introduced in the earlier modified Ising type of pseudospin model Hamiltonian to account for the investigation of dielectric properties in arsenate-type family of KDP crystals. Cochran's mode frequency and other ferroelectric properties like energy shift and width, electrical permittivity, spontaneous polarization, and loss tangent are investigated theoretically in the vicinity of T c . We have expressed the equation of Dyson and decoupled the correlation function with the consideration of Zuberav's statistical article and two-time temperature-dependent Green's function approach to deduce the theoretical derivation of the above ferroelectric parameter. The thermal variations of the order parameters S x and S z that characterize the first-order phase transition phenomenon are also introduced. A comparison of the theoretical findings has been made with the experimental findings reported by earlier authors. Good agreement is observed for the above-mentioned ferroelectric properties in CsH2AsO4, RbH2AsO4, and KH2AsO4 crystals. [ABSTRACT FROM AUTHOR]

The molecular properties of a biphenyl benzoate based ferroelectric liquid crystal compound were estimated using DFT/6-31G method. Non Linear Optical properties of the compound have been estimated by calculating its polarizability and hyperpolarizability. Frontier molecular orbital (FMO), Molecular electrostatic potential (MEP) and Infrared (IR) spectra have been simulated. Global parameter and a few thermodynamic parameters have also been calculated. The phase sequence has been confirmed by polarizing optical microscopy. The spontaneous polarization and rotational viscosity of the compound have been measured. From results the efficacy of the compound in NLO or electro optical applications have been inferred. [ABSTRACT FROM AUTHOR]

An efficient carrier injection at the electrode/organic semiconductor interface of organic light‐emitting diodes (OLEDs) is challenging. It is well‐known that an electric dipole at the electrode/semiconductor interface improves the carrier injection from the electrode because of a vacuum‐level shift. In this study, poly (vinylidene fluoride‐trifluoroethylene) [P(VDF/TrFE)] is used as a polar polymer with spontaneous polarization. P(VDF/TrFE) is spin‐coated on an indium tin oxide (ITO) electrode surface as a hole injection layer for OLEDs. The P(VDF/TrFE) layer enhances the hole injection from the ITO electrode by causing a vacuum‐level shift. As a result, the device driving voltage can be lowered. In addition, annealing temperature dependence is observed. To investigate the origin of the hole injection effect, the P(VDF/TrFE)‐layered ITO surface and the thin film structure of the P(VDF/TrFE) layer are measured. The P(VDF/TrFE) layers at different annealing temperatures show no difference in surface properties but show significant differences in the thin film structure. The hole injection of OLEDs is significantly enhanced because of the structural change in ultrathin P(VDF/TrFE) layer. [ABSTRACT FROM AUTHOR]

The results of calculations of electric fields, potentials, and trajectories of photoelectrons calculations of single-channel dual-spectral thermal imager, implemented in the IIT architecture are presented. The values of the optimal potentials on the control electrodes (microchannel plate, reading electrode, and photocathode) that form a picture of the images of objects and ensure the correct reading of the potential relief from the surface of the sensor-converter pyroelectric film of the image thermal receiver under discussion are determined. [ABSTRACT FROM AUTHOR]

An innovative design of thermal imaging is considered. The results of analysis and calculations of the characteristics of a thermal image receiver (3–15 μm), made in the electron-optical converter architecture, are presented. The spatial dependences of the spontaneous polarization the electric field strengths and the electric potentials on the surface of pyroelectric film are calculated. The characteristics of thermal-field-induced polarization of various pyroelectric films are obtained. The temperature dependences of various pyroelectric films polarizations are calculated by the COMSOL Multiphysics software package based on the finite element method. The possible influences of the piezoelectric effect to the images of the distribution of electric potentials of pyroelectric films are taken into account. The estimates of the values of the main characteristics of the image intensifier tube architecture are obtained. [ABSTRACT FROM AUTHOR]

Pyroelectric materials in the field of photoelectrochemical (PEC) water splitting still face the problems of difficult low spontaneous polarization intensity and excessive carrier recombination. Based on the above problems, we altered the interaction between S−Nb−S in the [NbO]6−x‐xS structure, and the constructed [NbO]6−x‐xS structure achieved the regulation of charge density change and spontaneous polarization. The results show that under the stimulation of light and temperature fluctuations, the current density of the NS‐4 photoanode is as high as 0.574 mA/cm2 at 1.23 VRHE, which is about 1.59 times higher than the pure NaNbO3 current density value, and the NS −4 photoanode achieves IPCE value of 16.08 %. The first‐principles density‐functional theory calculations (DFT) reveal the principle of the [NbO]6−x‐xS structure for the suppression function of the carrier recombination and the improvement function of the pyroelectric effect. The analysis shows that the S‐doping leads to the weakening of S−Nb−S interactions in the [NbO]6−x‐xS structure, which improves the pyroelectric effect and suppresses the photo/pyro‐generated carrier recombination, and effectively enhances the performance of the pyro‐photo‐electric synergistic water splitting system. This work promotes the development of pyroelectric materials in the field of photoelectrochemical water splitting. [ABSTRACT FROM AUTHOR]

Pyroelectric materials in the field of photoelectrochemical (PEC) water splitting still face the problems of difficult low spontaneous polarization intensity and excessive carrier recombination. Based on the above problems, we altered the interaction between S−Nb−S in the [NbO]6−x‐xS structure, and the constructed [NbO]6−x‐xS structure achieved the regulation of charge density change and spontaneous polarization. The results show that under the stimulation of light and temperature fluctuations, the current density of the NS‐4 photoanode is as high as 0.574 mA/cm2 at 1.23 VRHE, which is about 1.59 times higher than the pure NaNbO3 current density value, and the NS −4 photoanode achieves IPCE value of 16.08 %. The first‐principles density‐functional theory calculations (DFT) reveal the principle of the [NbO]6−x‐xS structure for the suppression function of the carrier recombination and the improvement function of the pyroelectric effect. The analysis shows that the S‐doping leads to the weakening of S−Nb−S interactions in the [NbO]6−x‐xS structure, which improves the pyroelectric effect and suppresses the photo/pyro‐generated carrier recombination, and effectively enhances the performance of the pyro‐photo‐electric synergistic water splitting system. This work promotes the development of pyroelectric materials in the field of photoelectrochemical water splitting. [ABSTRACT FROM AUTHOR]

Improving ferro-piezoelectric properties of niobate-based perovskites is highly desirable for developing eco-friendly high-performance sensors and actuators. Although electro-strain coupling is usually obtained by constructing multiphase boundaries via complex chemical compositions, defect engineering can also create opportunities for novel property and functionality advancements. In this work, a representative tetragonal niobate-based perovskite, i.e., KNbO3, is studied by using first-principles calculations. Two intrinsic types of Nb antisite defect complexes are selected to mimic alkali-deficiency induced excess Nb antisites in experiments. The formation energy, electronic profiles, polarization, and piezoelectric constants are systematically analyzed. It is shown that the structural distortion and chemical heterogeneity around the energetically favorable antisite pair defects, i.e., (NbK4·+KNb4′), lower the crystal symmetry of KNbO3 from tetragonal to triclinic phase, and facilitate polarization emergence and reorientation to substantially enhance intrinsic ferro-piezoelectricity (i.e., spontaneous polarization Ps of 68.2 μC/cm2 and piezoelectric strain constant d33 of 228.3 pC/N) without complicated doping and alloying.

The electric potential stimulation of biological structures in aqueous environments is well-known to be a result of the gating of voltage-gated ion channels. Such voltage-gated ion channels are ubiquitous in the membranes of a wide variety of cells and they play central roles in a wide variety of sensing mechanisms and neuronal functions in biological systems. Experimental studies of ion-channel gating are frequently conducted using path-clamp techniques by placing a cumbersome external electrode in the vicinity of the extracellular side of the ion channel. Recently, it has been demonstrated that laser-induced polarization of nanoscale quantum dots can produce voltage sufficient to gate voltage-gated ion channels. This study specifically focuses on a new method of gating voltage-gated ion channels using 2D structures made of materials exhibiting large naturally occurring spontaneous polarizations, thereby eliminating the need for an external electrode or an illuminating laser. The work presents the use of self-polarizing semiconductor flakes, namely, 2H-SiC, ZnO, and GaN, to produce electric potential that is sufficient to gate voltage-gated ion channels when existing in proximity to it.

Polarization field on diffusion thermopower Sd, of a two-dimensional electron gas (2DEG) formed at a wurtzite AlGaN/GaN heterojunction is investigated. The investigations of macroscopic polarization effect on diffusion thermopower over the wide range of temperature and barrier fluctuations bring out the role of spontaneous and piezoelectric polarization fields present in the heterostructure. The induced 2DEG charge density formed at the interface of AlGaN/GaN heterojunction due to in-built spontaneous and piezoelectric fields are assumed to be scattered by acoustic phonons via deformation and piezoelectric couplings, background and remote impurities via Coulomb interaction, interface roughness and interface charges. We find, the dominant contribution is from interface roughness scattering mechanism and that from acoustic phonons via deformation potential is negligible. Theoretical investigations of Sd show that, the effect of the spontaneous polarization is to reduce the diffusion thermopower significantly at practically relevant temperatures.

Gadolinium (Gd) and Nickel (Ni) doped bismuth ferrite (BiFeO3) nanoparticles Bi0.925Gd.075Fe0.95Ni0.05O3 (BGFNO) with spontaneous polarization (2.5 μC/cm2) were mechano‐chemically synthesized and used to achieve high capacity retention in lithium sulfur (Li−S) batteries. The BGFNO particles were coupled with single walled carbon nanotubes (SWCNT)/sulfur (S) composite cathodes as well as coated on separator. The X‐ray diffraction of BGFNO@S/SWCNT cathodes show an orthorhombic structure with particle size distribution of 20–26 nm, while Raman spectra substantiate efficient coupling of BGFNO with S/SWCNT cathodes, in agreement with SEM images, showing the interconnected network of composites. The specific discharge capacity of S60BGFNO30SWCNT10 composite cathode @ 200 mA/g together with BGFNO coated separator gains maximum capacity up to 1611 mAh/g and retains up to 1294 mAh/g after 50th cycle with improved capacity retention of 80 % showing suppression of polysulfides formation. The coated separator controls transport of carrier ions and side reactions, however modified cathodes with BGFNO particles acts as trapping center for polysulfides to enhance the electrochemical performance of the cells. The Coulombic efficiency(CE) for BGFNO/S/SWCNT composites @ 100 mA/g attained >98 % and CE @ 200 mA/g it is attained > 80 to 90 % compared to S/SWCNT composites in terms of improved cycle stability and reaction kinetics. [ABSTRACT FROM AUTHOR]

SrCo0.2Zn0.2Fe11.6O18.8 hexaferrite was obtained by a "one-pot" green sol-gel synthesis method utilizing aqueous mandarin orange (Citrus reticulata) peel extract as an eco-friendly reactant. The research objective was to analyze the influence of cobalt and zinc co-doping and the synthesis process on the structure, morphology, magnetic, dielectric and ferroelectric properties of strontium hexaferrite in view of future applications. Structural and morphological characterization using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy coupled to energy dispersive X-ray spectrometry (SEM-EDX) confirmed the formation of a Co and Zn ion incorporated M-type magnetoplumbite with c/a lattice parameter ratio of 3.919 as crystallite nanoplatelets of 32 and 53 nm in thickness and width, respectively. The magnetic hysteresis loop of the synthesized powder recorded by a vibrating sample magnetometer (VSM) at room temperature confirmed its ferromagnetic nature with a coercive field (Hc) of 2539 Oe and a saturation magnetization (Ms) and remanent magnetization (Mr) of 44.6 emu/g and 21.4 emu/g, respectively. Room temperature ferroelectric loops measured at 100 Hz showed a maximal (Pmax) and a remanent (Pr) polarization of 195.4 and 31.0 nC/cm2, respectively. Both increased when the magnitude of the applied electrical field increased in the 1–24 kV/cm range. The dielectric constant decreased with the frequency increase, in accordance with the Maxwell–Wagner model, while the conductivity changed according to the Jonscher power law. The complex impedance was modeled with an equivalent circuit, enabling identification of the dominant contribution of grain boundary resistance (272.3 MΩ) and capacitance (7.16 pF). [ABSTRACT FROM AUTHOR]

Wurtzite aluminum nitride (AlN) crystal has a non-centrosymmetric crystal structure with only a single axis of symmetry. In an AlN crystal, the electronegativity difference between the Al atom and N atom leads to a distortion of electron cloud distribution outside the nucleus and a spontaneous polarization (SP) along the c-axis direction. The N-polar surface along the directions of [000-1] has higher surface energy than the Al-polar surface along the directions of [0001]. Due to the different atomic arrangement, Al atoms on the Al-polar surface bond with O and OH− in the environment to generate Al2O3·xH2O, which prevents the reaction from occurring inside the crystal. After the Al2O3·xH2O dissolve in an alkaline environment, N atoms have three dangling bonds exposed on the surface, which can also protect OH− from destroying the internal Al-N bonds, so the Al-polar surface is more stable than the N-polar surface.

This work reports an n -type GaN/InGaN/GaN heterostructure vertical double-gate tunnel field-effect transistor (VTFET) using exhaustive calibrated simulation for the first time. Investigation has been done for the proposed structure by including a polarization layer of InGaN near the source-channel junction. From the analysis, it has been observed that after the introduction of polarization layer near the source-channel interface, drain current increases due to the increase in charge concentration (2DEG) near the interface due to inter-band tunneling. Value of 2DEG concentration achieved post introducing the polarization layer is 1 0 1 8 cm − 2 . The reported structure is optimized using parametric sweep optimization technique. Here, a detailed dc and analog/RF performance estimation has been done for the structure with heterostructure. In-depth sensitivity analysis has been done for the structure with the polarization layer. It is reported that the structure with HfO2 as the dielectric material with t ox of 2 nm and with gate metal work function of 5.8 eV gives the optimum performance at 300 K. Further, it demonstrates high cutoff frequency ( f t) and gain bandwidth product (GBW) as 1000 GHz and 300 GHz, respectively. Hence, the reported structure is a better alternative for high-power steep switching analog and RF applications. [ABSTRACT FROM AUTHOR]

High energy density and intrinsic safety are the central pursuits in developing rechargeable Zinc‐ion batteries (ZIBs). The capacity and stability of nickel cobalt oxide (NCO) cathode are unsatisfactory because of its semiconductor character. Herein, we propose a built‐in electric field (BEF) approach by synergizing cationic vacancies and ferroelectric spontaneous polarization on cathode side to facilitate electron adsorption and suppress zinc dendrite growth on the anode side. Concretely, NCO with cationic vacancies was constructed to expand lattice spacing for enhanced zinc‐ion storage. Heterojunction with BEF leads to the Heterojunction//Zn cell exhibiting a capacity of 170.3 mAh g−1 at 400 mA g−1 and delivering a competitive capacity retention of 83.3 % over 3000 cycles at 2 A g−1. We conclude the role of spontaneous polarization in suppressing zinc dendrite growth dynamics, which is conducive to developing high‐capacity and high‐safety batteries via tailoring defective materials with ferroelectric polarization on the cathode. [ABSTRACT FROM AUTHOR]

Tourmaline (TM) has received extensive interest in the purification field due to its unique spontaneous polarization. In this paper, the effects of three sizes of purified TM samples on the air filters were studied. The electrode performance of TM samples was investigated using piezoelectric and pyro‐electric experiments. The results show an electrode from the 0.074 mm separated TM had the superior property. Three types of TM powders with the highest B2O3% content were adhered to the filter to evaluate the filtration performance. Elbaite 0.074 mm with 9.34 B2O3% content had the optimal filtration efficiency when the pressure drop increased slightly. The Rietveld method was used to refine the samples X‐Ray diffraction patterns to obtain the crystal structure. The electrostatic adsorption caused by the TM spontaneous polarization contributes to improving the filtration property of the filter materials. [ABSTRACT FROM AUTHOR]

In this work, we searched for the optimal way to create ferroelectric nanostructured composite materials based on 4D-printed polyvinylidene fluoride polymer films. Method fused deposition modeling allow using polyvinylidene fluoride and its copolymers not only in microelectronics as pyroelectric and piezoelectric sensors, as well as creating dynamic memory elements, organic solar cells and used in robotics. At the first stage of the work, the authors were selected optimal extrusion parameters for the manufacture of a thread from powder and granules. The next stage of the work included the analysis and determination of printing parameters by the method of layer-by-layer filament deposition to obtain the best quality of polymer films. Using scanning electron microscopy, the existence of two phases, a polar β-phase and a nonpolar α-phase, is shown, where the crystalline phase is observed in the form of lamellar crystals chaotically oriented in the α-phase matrix. Pyroelectric measurements performed by the dynamic method showed the presence of a noticeable pyroelectric response in polyvinylidene fluoride films obtained using additive technologies, bypassing the orientation extraction stage. The calculation of the pyroelectric coefficient gives values corresponding to the values of the pyroelectric coefficient for polyvinylidene fluoride samples obtained by traditional methods.

Flexoelectric polarization, which is caused by symmetry breaking in a distortion of material, was investigated in liquid crystalline elastomers composed of wedge-shaped mesogens prepared by cross-linking under horseshoe-shaped deformation. X-ray diffractometry suggested that splay distortion along the depth direction was induced in the pseudo-isotropic phase. While almost no electric charge was observed in the smectic A phase, an electric charge caused by polarization due to the flexoelectric effect appeared and reached −1367 pC/mm2 in the pseudo-isotropic phase. We tentatively conclude that the macroscopic polarization due to the flexoelectric effect emerged and was fixed in the liquid crystalline elastomers by cross-linking under horseshoe-shaped deformation. [ABSTRACT FROM AUTHOR]

Abstract Ferroelectricity, characterized by the reversible switching of spontaneous polarization (Ps) under external electric field, exists in polar crystalline materials without a spatial‐inversion symmetry. On account of inherent Ps, ferroelectric materials show intriguing physical properties including piezoelectricity, pyroelectricity, second‐order optical nonlinearity, and electro‐optic effect. Such functions of ferroelectric materials have been widely used for practical applications. Recently, hybrid perovskites are emerging as a promising ferroelectric family that enables the combination and/or coupling of ferroelectricity, photoexcitation, and semiconductor behaviors. Due to the polarization deterioration caused by leakage current of photoexcited carriers, however, it is still a challenge to accomplish practical applications of ferroelectric semiconductors in the photoelectric field. In this review, the recent progress of ferroelectric system of perovskite‐type hybrids with different dimensions is summarized. Primarily, a brief description of crystallographic symmetry breaking which is a fundamental criterion to creating ferroelectricity, is illuminated. The combination and/or coupling of photoelectric properties with ferroelectric Ps is then presented. Finally, the further development tendency and possible application outlooks of this ferroelectric material system are prospected.

[Display omitted] • The phase transition stress engineering was used to motive the spontaneous polarization for CdS. • The photocurrent density of spontaneous polarization CdS is almost 6.2 times of H-CdS. • The residual stress caused by phase transition effectively enhanced the spontaneous polarization of CdS. • Spontaneous polarization generated a built-in electric field for promoting carrier separation and PEC performance. • Spontaneous polarization CdS is motived greater polarization potential due to phase transition residual stress. The built-in electric field caused by piezoelectric polarization has emerged as one of the most effective strategies for photoelectrochemical (PEC) water splitting, but is challenged by low piezoelectric polarization efficiency. Herein, we firstly introduce residual stress into CdS through phase transition stress engineering for improving the spontaneous polarization of CdS with a view to revealing the mechanism of the piezoelectric PEC (piezo-PEC) performance of CdS is advanced by the spontaneous polarization. The spontaneous polarization of CdS caused via phase transition residual stress generated built-in electric field to advance carriers separation. Moreover, the spontaneous polarization of CdS is motived a greater potential under external force than hexagonal wurtzite CdS due to the existence of phase transition residual stress, which effectively improves the piezo-PEC performance of CdS. The photocurrent density of miscibility of cubic sphalerite and hexagonal wurtzite CdS (M−CdS) is 0.61 mA/cm2 at 1.23 V vs RHE, which is almost 1.79 times of hexagonal wurtzite (H-CdS). In addition, the value of M−CdS photocurrent density is reached 2.12 mA/cm2 at 1.23 V vs RHE after ultrasound, which is almost 6.2 times of H-CdS. Our detail work proves that this strategy not only stimulates the piezo-PEC performance of CdS, but also can be extended to other hexagonal wurtzite semiconductor phase transition piezoelectric fields. [ABSTRACT FROM AUTHOR]

Polar crystals have attracted interest for the applications to polar materials with piezo‐ and pyroelectricity, and second harmonic generation. Despite their potential utility for flexible polar materials, a strategy for ordering polar helicenes has remained elusive. Here, we demonstrate the creation of polar crystals with unsymmetrically substituted aza[5]helicenes tuned by substituents. The unsymmetric aza[5]helicenes have been prepared through regioselective mono‐protiodesilylations. We disclose that triisopropylsilyl‐substituted derivatives show 1D chain columnar packings. In particular, enantiopure crystals showed spontaneous polarization. Optical and single‐crystal X‐ray diffraction experiments with other derivatives, as well as theoretical calculations, revealed that the presence of triisopropylsilyl or electron‐withdrawing aryl substituents is essential for forming the 1D chain columnar structure. Hirshfeld surface analyses further showed that CH‐π interactions between 1D chain columns regulate the polar assembly. Finally, we determined the polarizability of the nitro derivative by ab initio calculation to be 4.53 μC/cm2. This value corroborates the first example of a spontaneously polar crystal of helicenes. We believe that this study will contribute to the development of polar materials from organic molecules. [ABSTRACT FROM AUTHOR]

The features of ferroelectric materials and their applications are presented. State-of-the-art employment of characterization techniques, and the properties of ferroelectric materials are described. Classification of ferroelectric materials, phase transitions, and diffuse phase transition (DPT) have been discussed. Properties of ferroelectrics, polarization-field hysteresis, dielectric hysteresis, reversal of spontaneous polarization, and dielectric properties have been explained. Besides these, piezoelectric and pyroelectric properties of materials have also been demonstrated. The applications of ferroelectric thin films have been discussed with a specific focus on acousto-optic (AO) properties and their applications.

• Internal spontaneous polarization of BiVO 4 photocatalyst can be modulated in the presence of polyvinylpyrrolidone at various concentrations. • The polarization field can drive the electrons and holes to transfer along opposite directions. • The charge separation and interfacial migration can be promoted and thus enhance the photocatalytic performance. Photocatalytic performance can be improved by optimizing the morphology and surface texture of the photocatalyst or forming different p-n and/or n-n heterojunctions. Although the heterojunction system enhances photocatalytic property; however, an internal spontaneous polarization electric field may be much more effective due to the separation of electron-hole pairs when the polarization field forces them to move in different directions. The present study demonstrated this insight where the BiVO 4 synthesis condition and polarization field forces were controlled via homogeneous precipitation in the presence of polyvinylpyrrolidone (PVP). The as-synthesized BiVO 4 photocatalysts' structure and morphology were investigated using XRD, SEM, Raman, DRS, and PL. The result revealed that the increase of PVP concentration reformed the shaping to the truncated bipyramid-like shape and creates a spontaneous internal polarization that enhanced BiVO 4 photocatalytic performance. The photocatalytic activity of BiVO 4 was evaluated by monitoring the photocurrent enhancement using chronoamperometry, electrochemical impedance spectra and the photodegrading of methylene blue (MB) aqueous solution to harmless compounds in the presence of light. The spontaneous polarization between the different facets of BiVO 4 crystal enhances the e−/h+ separation during internal facets homojunction and leads to four times photocurrent enhancement and the MB photocatalytic degradation rate increased from 0.43 to 1.92 min−1. [Display omitted] [ABSTRACT FROM AUTHOR]

SrCo0.2Zn0.2Fe11.6O18.8 hexaferrite was obtained by a “one-pot” green sol-gel synthesis method utilizing aqueous mandarin orange (Citrus reticulata) peel extract as an eco-friendly reactant. The research objective was to analyze the influence of cobalt and zinc co-doping and the synthesis process on the structure, morphology, magnetic, dielectric and ferroelectric properties of strontium hexaferrite in view of future applications. Structural and morphological characterization using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy coupled to energy dispersive X-ray spectrometry (SEM-EDX) confirmed the formation of a Co and Zn ion incorporated M-type magnetoplumbite with c/a lattice parameter ratio of 3.919 as crystallite nanoplatelets of 32 and 53 nm in thickness and width, respectively. The magnetic hysteresis loop of the synthesized powder recorded by a vibrating sample magnetometer (VSM) at room temperature confirmed its ferromagnetic nature with a coercive field (Hc) of 2539 Oe and a saturation magnetization (Ms) and remanent magnetization (Mr) of 44.6 emu/g and 21.4 emu/g, respectively. Room temperature ferroelectric loops measured at 100 Hz showed a maximal (Pmax) and a remanent (Pr) polarization of 195.4 and 31.0 nC/cm2, respectively. Both increased when the magnitude of the applied electrical field increased in the 1–24 kV/cm range. The dielectric constant decreased with the frequency increase, in accordance with the Maxwell–Wagner model, while the conductivity changed according to the Jonscher power law. The complex impedance was modeled with an equivalent circuit, enabling identification of the dominant contribution of grain boundary resistance (272.3 MΩ) and capacitance (7.16 pF).

The authors studied the effect of the temperature of sodium niobate synthesis on the state of polarization in ceramic samples of pure sodium niobate and modified with lithium. A comparative study of the structure and pyroelectric properties of the obtained samples has been carried out. It is shown that the introduction of lithium as a modifier leads to a significant change in the structure in the depth of ceramic samples based on sodium niobate. If in the depth of the pure sodium niobate samples, as well as on the surface, there are individual grains, then the central part of the sodium niobate-lithium niobate ceramics is a continuous mass in which individual grains are not observed. In all samples, except for pure sodium niobate, which was synthesized by double synthesis (the first at 650°C, the second at 700°C), the existence of a polarization gradient along the thickness of the samples was established. The gradient is directed from the side corresponding to the positive end of the polarization vector to the side corresponding to the negative end of the polarization vector.

Abstract Although electrostatic actuators have a simple structure and are lightweight, their range of application is limited because a high applied voltage of more than several kilovolts is required for practical use. Since the force acting between the electrodes of an electrostatic actuator is determined by the electric charge accumulated at the electrode/dielectric interface, the focus is on spontaneous polarization of ferroelectrics to increase the charge. As the ferroelectric material, a nematic liquid crystal material with a spontaneous polarization of 5 µC cm−2 is used. It is demonstrated that a force of 1.3 N is generated at an applied electric field of 0.5 MV m−1. This force is 1200 times higher than that for standard paraelectric materials with a dielectric constant of ten. Further, the generated force responds linearly to the applied voltage, whereas it is proportional to the square of the applied voltage for paraelectric materials. The actuator function of this ferroelectric is examined using a double‐helical coil electrode fabricated using a 3D printer. It can be successfully operated at a voltage of several tens of volts. Under an electric field of 0.25 MV m−1, a remarkable contraction of 6.3 mm occurs, corresponding to 19% of the original length.

Heavy-metal-free ferroelectrics are sought as environmentally compatible alternatives to commonly used inorganic oxides. Here, we demonstrate direct evidence of the ferroelectric properties of a hybrid organic–inorganic material, dimethylglycinium-dimethylglycine chloride. At room temperature, the compound crystallizes in the polar space group P21 and exhibits a switchable spontaneous polarization of 1.9 μC cm−2. Ferroelectric properties are preserved in a wide temperature range up to about 401 K, where the crystal undergoes the transition to the paraelectric phase of the space group P21/c. The temperature-dependent single-crystal X-ray diffraction study and the calorimetric data indicate an order–disorder contribution to the transition mechanism, which is consistent with the critical slowing down of the dielectric relaxation observed near the Curie point. The spontaneous polarization results from ionic displacements that are induced by changes in the disordering of the dimeric cations. In the ferroelectric phase, the crystal exhibits remarkable piezoelectric activity. The electromechanical and elastic properties of the material were thoroughly characterized.

The ambient pressure cation disordered InVO3 bixbyite has been predicted to form a GdFeO3‐type perovskite phase under high pressure and high temperature. Contrary to the expectation, InVO3 was found to crystallize in the polar LiNbO3‐type structure with a calculated spontaneous polarization as large as 74 μC cm−2. Antiferromagnetic coupling of V3+ magnetic moments and a cooperative magnetic ground state below about 10 K coupled with a polar structure suggest an intriguing ground state of the novel LiNbO3‐type high‐pressure InVO3 structure. [ABSTRACT FROM AUTHOR]

This paper introduces a new method for adjusting the particle size of ZrO2 powder through the electric field effect of tourmaline. The 3 mol% yttria‐stabilized ZrO2 (3YSZ) powder was prepared by using ZrOCl2∙8H2O, YCl3∙6H2O, NaOH, and nano‐tourmaline powder as raw materials through direct precipitation. The powder was characterized with thermogravimetric‐differential scanning calorimeter, X‐ray diffraction, Brunauere‐Emmette‐Teller, Fourier transform infrared, scanning electron microscope, and transmission electron microscope, and the mechanism of tourmaline in the process of powder preparation was also discussed. Findings demonstrate that the electric field generated by spontaneous polarization of tourmaline can control the size of ZrO2 crystal grains, improve the dispersibility of the powder, and promote the stability of ZrO2 in the tetragonal phase. When the electric intensity of tourmaline is 9.02 × 106 V/m, and the addition amount is 2.5 vol%, tourmaline/3YSZ powders are mainly tetragonal phase, and the grain size is the smallest, with an average crystallite size of 19 nm. Then the mechanical properties of tourmaline/3YSZ ceramics were tested. Compared with 3YSZ ceramics without tourmaline, the flexural strength and fracture toughness were improved by 39.5% and 35.8%. [ABSTRACT FROM AUTHOR]

The features of ferroelectric materials and their applications are presented. State-of-the-art employment of characterization techniques, and the properties of ferroelectric materials are described. Classification of ferroelectric materials, phase transitions, and diffuse phase transition (DPT) have been discussed. Properties of ferroelectrics, polarization-field hysteresis, dielectric hysteresis, reversal of spontaneous polarization, and dielectric properties have been explained. Besides these, piezoelectric and pyroelectric properties of materials have also been demonstrated. The applications of ferroelectric thin films have been discussed with a specific focus on acousto-optic (AO) properties and their applications. [ABSTRACT FROM AUTHOR]

Synthesized oxynitride perovskites materials exhibited very interesting properties, in particular ferroelectricity, which allow their uses in various applications and qualify them as very promising candidates for multifunctional materials. This study highlights the use of first-principle calculations based on density functional theory to carry out investigations of spontaneous polarizations into two groups of perovskite-type oxynitrides. The first group is A3+B4+(O2N)7− where A3+ = Y, Sc, La, Lu and B4+ = Si, Ge, Sn while the second one is A2+B5+(O2N)7− where A2+ = Mg, Ca, Sr, Ba and B5+ = V, Nb, Ta. Therefore, we have computed the structural parameters, formation energy, tolerance factor, octahedral factor, bond ionicity, spontaneous polarization, and band gaps. As a result, we have deduced (1) that all studied oxynitride perovskites are distorted and can be synthesized, and are all insulators or semiconductors, some of which have narrow energy gaps. (2) Some perovskites exhibit high spontaneous polarization values that appear to be stimulated by the large displacements of B-cations away from their centrosymmetric positions, by the lower B-cation ionic radius, and the higher A-cation ionic radius of the tetragonal ABO2N perovskite structure. (3) Spontaneous polarization in oxynitride perovskites increases for higher electronegativity of B-cations and lower interatomic distance between the B-cation and the N-anion. It also noted that spontaneous polarization was more pronounced in the valence group A3+B4+(O2N)7− than that of A2+B5+(O2N)7−. [ABSTRACT FROM AUTHOR]

In this paper, the spontaneous polarization and the phase transition of order–disorder type H-bonded KH2PO4-type crystals are theoretically investigated. With the help of a modified (presently) model Hamiltonian, and by applying the double-time thermal-dependent statistical Green's function technique and Dyson's equation, various expressions are derived for KH2PO4-type crystals. In this (PLCM) model, the direct spin–spin interaction term, the four-body interaction term, extra spin–phonon interaction term, and the third-order and fourth-order lattice anharmonic interactions terms are considered. Theoretical expressions for the spontaneous polarization, Cochran's soft-mode frequency, energy shift and width, permittivity, and tangent delta (tanδ) are derived. Thermal variations for these quantities with temperature are found. The formulae for these quantities are derived by using Green's function method. Model values are fitted for a KH2PO4 crystal to obtain the variation with temperature. The results are compared with experimental variations reported by other workers (Kaminow and Damen, Phys Rev Lett 20(20):1105, 1968; Von and Bantle, Helv Phys Acta 17:298–318, 1944). A good agreement is observed. [ABSTRACT FROM AUTHOR]

The static bending and the flexoelectric effect induced in an anisotropic dielectric nano-plate are studied in the frame of the simplified strain gradient elasticity theory (SSGT). The Kirchhoff plate theory is considered for a simply supported nano-plate loaded by a uniformly distributed constant forces at its upper surface. The displacement and the induced spontaneous polarization are formulated such that the dimensions of the problem reduce to two dimensions only. The variational concept of the internal energy and the virtual work exerted by the external forces are used to obtain the governing equations as well as the boundary conditions. The choose of the cubic materials avoid the ambiguity between piezoelectricity and flexoelectricity, where all odd tensors are vanished. The finite Fourier transform is employed to obtain the analytical solution. The numerical calculations of the problem are presented with the help of the commercial software Maple. Some selected significant results are introduced through sets of figures with physical explanations. The results reveal that the flexoelectric effect at the surface of the clamped nanoplate should be considered and cannot be neglected. Moreover, the nanoscale dimension enhances the flexoelectric effect more than macroscale.

The CdS/Bi2S3 supported three-dimensional (3D) porous faveolate carbon structure (CdS/Bi2S3@C) composite photocatalyst was constructed. Bi2S3 nanoparticles are regarded as photothermal agents and pyroelectric materials to absorb near infrared light (NIR) and convert it into heat. 3D porous faveolate of carbon acts as incubator to reduce heat loss and optimize photothermal effects. There is a greater fluctuating temperature difference (ΔΤ) between photothermal effect of Bi2S3 and cold photocatalytic system. This enhances the pyroelectric effect that Bi2S3 undergoes spontaneous polarization and releases the surface charge. Therefore, the separation of electrons and holes in the CdS photocatalyst can be induced. The COMSOL simulation results show that, the higher pyroelectric potential producted by larger ΔΤ is more favorable to the photocatalytic process. The hydrogen evolution rate of CdS/Bi2S3@C photocatalyst can reach 5.88 ​mmol·g−1·h−1 with excellent cycle stability.