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The utilization of piezoelectric nanogenerator (PENG) based on halide perovskite materials has demonstrated significant promise for energy harvesting applications. However, the challenge of synthesizing halide perovskite materials with both high output performance and stability using a straightforward process persists as a substantial obstacle. Herein, we present the fabrication of CsPbI3 nanorods (NRs) exhibiting highly uniform orientation within polyvinylidene fluoride (PVDF) fibers through a simple texture engineering approach, marking the instance of enhancing PENG performance in this manner. The resultant composite fibers showcase a short-circuit current density (Isc) of 0.78 μA cm-2 and an open-circuit voltage (Voc) of 81 V, representing a 2.5 fold increase compared to the previously reported highest value achieved without the electric poling process. This outstanding output performance is ascribed to the orientation of CsPbI3 NRs facilitated by texture engineering and dipole poling via the self-polarization effect. Additionally, the PENG exhibits exceptional thermal and water stability, rendering it suitable for deployment in diverse and challenging environmental conditions. Our findings underscore the significant potential of textured CsPbI3 NRs composite fibers for powering low-power consumer electronics, including commercial LEDs and electronic watches. [ABSTRACT FROM AUTHOR]

The increasing need for wearable and portable electronics and the necessity to provide a continuous power supply to these electronics have shifted the focus of scientists toward harvesting energy from ambient sources. Harvesting energy from ambient sources, including solar, wind, and mechanical energies, is a solution to meet rising energy demands. Furthermore, adopting lightweight power source technologies is becoming more decisive in choosing renewable energy technologies to power novel electronic devices. In this regard, piezoelectric nanogenerators (PENGs) based on polymer composites that can convert discrete and low-frequency irregular mechanical energy from their surrounding environment into electricity have attracted keen attention and made considerable progress. This review highlights the latest advancements in this technology. First, the working mechanism of piezoelectricity and the different piezoelectric materials will be detailed. In particular, the focus will be on polymer composites filled with lead-free BaTiO3 piezoceramics to provide environmentally friendly technology. The next section will discuss the strategies adopted to enhance the performance of BaTiO3-based polymer composites. Finally, the potential applications of the developed PENGs will be presented, and the novel trends in the direction of the improvement of PENGs will be detailed. [ABSTRACT FROM AUTHOR]

BiFeO3 (BFO), Mn-doped-BFO (BFMO), Ti-doped-BFO (BFTO), and (Mn,Ti)-codoped-BFO (BFMTO) thin films are fabricated on the Pt/TiO2/SiO2/Si substrates via a sol–gel method combined with spin-coating and the subsequent layer-by-layer annealing technique. Compared with BFO film, the BFMTO film exhibits the lowest leakage current density (∼ 1 0 − 4 A/cm2@290 kV/cm). Notably, the polarization–electric field (P–E) loop of BFMTO film exhibits a positive displacement along the x-axis due to the existence of internal bias electric field, which is in agreement with the results of the PFM phase and amplitude curves. Especially, a very prominent inverse piezoelectric constant of d 3 3 ∼ 1 6 0 pm/V was obtained, which overcomes other related thin films. The internal bias electric field of BFMTO film can be caused by the different work functions of the thin film and the bottom electrode, accumulation of oxygen vacancies and the formation of defect dipoles. Besides, the internal bias electric field of BFMTO film has a good stability at the same electric field after experiencing the test cycle from low electric field to high electric field (400–1900 kV/cm). These results indicate that self-polarized BFMTO film can be integrated to devices without additional polarization process, and have a wide range of application in microelectromechanical systems. [ABSTRACT FROM AUTHOR]

Constructing π‐conjugated polymer structures through covalent bonds dominates the design of organic framework photocatalysts, which significantly depends on the selection of multiple donor‐acceptor building blocks to narrow the optical gap and increase the lifetimes of charge carriers. In this work, self‐bipolarized organic frameworks of single aromatic units are demonstrated as novel broad‐spectrum‐responsive photocatalysts for H2O2 production. The preparation of such photocatalysts is only to fix the aromatic units (such as 1,3,5‐triphenylbenzene) with alkane linkers in 3D space. Self‐bipolarized aromatic units can drive the H2O2 production from H2O and O2 under natural sunlight, wide pH ranges (3.0‐10.0) and natural water sources. Moreover, it can be extended to catalyze the oxidative coupling of amines. Experimental and theoretical investigation demonstrate that such a strategy obeys the mechanism of through‐space π‐conjugation, where the closely face‐to‐face overlapped aromatic rings permit the electron and energy transfer through the large‐area delocalization of the electron cloud under visible light irradiation. This work introduces a novel design concept for the development of organic photocatalysts, which will break the restriction of conventional through‐band π‐conjugation structure and will open a new way in the synthesis of organic photocatalysts. [ABSTRACT FROM AUTHOR]

Constructing π‐conjugated polymer structures through covalent bonds dominates the design of organic framework photocatalysts, which significantly depends on the selection of multiple donor‐acceptor building blocks to narrow the optical gap and increase the lifetimes of charge carriers. In this work, self‐bipolarized organic frameworks of single aromatic units are demonstrated as novel broad‐spectrum‐responsive photocatalysts for H2O2 production. The preparation of such photocatalysts is only to fix the aromatic units (such as 1,3,5‐triphenylbenzene) with alkane linkers in 3D space. Self‐bipolarized aromatic units can drive the H2O2 production from H2O and O2 under natural sunlight, wide pH ranges (3.0‐10.0) and natural water sources. Moreover, it can be extended to catalyze the oxidative coupling of amines. Experimental and theoretical investigation demonstrate that such a strategy obeys the mechanism of through‐space π‐conjugation, where the closely face‐to‐face overlapped aromatic rings permit the electron and energy transfer through the large‐area delocalization of the electron cloud under visible light irradiation. This work introduces a novel design concept for the development of organic photocatalysts, which will break the restriction of conventional through‐band π‐conjugation structure and will open a new way in the synthesis of organic photocatalysts. [ABSTRACT FROM AUTHOR]

BiFeO3 (BFO), Mn-doped-BFO (BFMO), Ti-doped-BFO (BFTO), and (Mn,Ti)-codoped-BFO (BFMTO) thin films are fabricated on the Pt/TiO2/SiO2/Si substrates via a sol–gel method combined with spin-coating and the subsequent layer-by-layer annealing technique. Compared with BFO film, the BFMTO film exhibits the lowest leakage current density ([Formula: see text][Formula: see text]A/cm2@290[Formula: see text]kV/cm). Notably, the polarization–electric field (P–E) loop of BFMTO film exhibits a positive displacement along the x-axis due to the existence of internal bias electric field, which is in agreement with the results of the PFM phase and amplitude curves. Especially, a very prominent inverse piezoelectric constant of [Formula: see text][Formula: see text]pm/V was obtained, which overcomes other related thin films. The internal bias electric field of BFMTO film can be caused by the different work functions of the thin film and the bottom electrode, accumulation of oxygen vacancies and the formation of defect dipoles. Besides, the internal bias electric field of BFMTO film has a good stability at the same electric field after experiencing the test cycle from low electric field to high electric field (400–1900[Formula: see text]kV/cm). These results indicate that self-polarized BFMTO film can be integrated to devices without additional polarization process, and have a wide range of application in microelectromechanical systems.

The values of the surface potentials of two sides of films of polyvinylidene fluoride, and its copolymers with tetrafluoroethylene and hexafluoropropylene, were measured by the Kelvin probe method. The microstructures of the chains in the surfaces on these sides were evaluated by ATR IR spectroscopy. It was found that the observed surface potentials differed in the studied films. Simultaneously, it was observed from the IR spectroscopy data that the microstructures of the chains on both sides of the films also differed. It is concluded that the formation of the surface potential in (self-polarized) ferroelectric polymers is controlled by the microstructure of the surface layer. The reasons for the formation of a different microstructure on both sides of the films are suggested on the basis of the general regularities of structure formation in flexible-chain crystallizing polymers. [ABSTRACT FROM AUTHOR]

In this work, we studied the pyroelectric activity of thin polycrystalline lithium niobate films fabricated by radio frequency magnetron sputtering and laser ablation, and thin polycrystalline lithium tantalate films fabricated by radio frequency magnetron sputtering. Using the dynamic method of studying the pyroelectric effect, it was found that all samples have self-polarization that occurs during the post-growth thermal annealing of the structure. An estimate of the pyroelectric coefficient showed that the values of the pyroelectric coefficient of lithium niobate and lithium tantalate thin films are several times lower than the values of the pyroelectric coefficient for bulk crystals of the corresponding materials. This may be due to the fact that the polarization vector of some grains lies in the film plane, as well as to the traps existing in the film volume and at the film/substrate interface, on which charge carriers recombine and do not participate in the generation of the pyroelectric current.

Piezoelectric nanogenerator (PENG) for practical application is constrained by low output and difficult polarization. In this work, a kind of flexible PENG with high output and self‐polarization is fabricated by constructing CsPbBr3–Ti3C2Tx heterojunctions in PVDF fiber. The polarized charges rapidly migrate to the electrodes from the Ti3C2Tx nanosheets by forming heterojunctions, achieving the maximum utilization of polarized charges and leading to enhanced piezoelectric output macroscopically. Optimally, PVDF/4wt%CsPbBr3/0.6wt%Ti3C2Tx‐PENG exhibits an excellent voltage output of 160 V under self‐polarization conditions, which is higher than other self‐polarized PENG previously. Further, the working principle and self‐polarization mechanism are uncovered by calculating the interfacial charge and electric field using first‐principles calculation. In addition, PVDF/4wt%CsPbBr3/0.6wt%Ti3C2Tx‐PENG exhibits better water and thermal stability attributed to the protection of PVDF. It is also evaluated in practice by harvesting the energy from human palm taps and successfully lighting up 150 LEDs and an electronic watch. This work presents a new idea of design for high‐performance self‐polarization PENG. [ABSTRACT FROM AUTHOR]

We report the control of self-polarization of monocrystalline Lead Zirconate Titanate thin films grown by Pulsed laser deposition by doping and bottom interface. Doped and undoped films grown on ScO2 terminated surface of polar PSO substrate have developed polarization oriented toward the substrate due to negative polarity (ScO−) of the substrate termination. For films grown on the strontium ruthenate (SRO) bottom electrode, only undoped and 1% Nb doped PZT films have developed upwards oriented self-polarization. The introduction of strontium ruthenate bottom electrode have made the work function difference between films and bottom electrode to be the dominant mechanism for self-polarization. [ABSTRACT FROM AUTHOR]

Colloidal metal nanoparticles in an electrolyte environment are not only electrically charged but also electrochemically active objects. They have the typical character of metal electrodes with ongoing charge transfer processes on the metal/liquid interface. This picture is valid for the equilibrium state and also during the formation, growth, aggregation or dissolution of nanoparticles. This behavior can be understood in analogy to macroscopic mixed-electrode systems with a free-floating potential, which is determined by the competition between anodic and cathodic partial processes. In contrast to macroscopic electrodes, the small size of nanoparticles is responsible for significant effects of low numbers of elementary charges and for self-polarization effects as they are known from molecular systems, for example. The electrical properties of nanoparticles can be estimated by basic electrochemical equations. Reconsidering these fundamentals, the assembly behavior, the formation of nonspherical assemblies of nanoparticles and the growth and the corrosion behavior of metal nanoparticles, as well as the formation of core/shell particles, branched structures and particle networks, can be understood. The consequences of electrochemical behavior, charging and self-polarization for particle growth, shape formation and particle/particle interaction are discussed.

Although charge excitation is an effective approach to achieve high charge density for triboelectric nanogenerators (TENGs), high output charge is limited by air‐breakdown. Due to capacitor structure, there are two ways to reduce the influence of air‐breakdown in TENG: decrease in thickness and increase in permittivity of dielectric film. Obviously, the increase in permittivity is more reliable in applications. Herein, a double‐layer TENG shared with one floating metal electrode is proposed, on which charge is injected by a self‐excitation circuit. An ultrafast self‐polarization effect is found in two barium titanate filled poly(vinylidene fluoride) composite films in the TENG by high electrical field produced from the floating electrode. According to comparison and analysis, the speed of polarization to saturation of dielectric composite films in self‐charge excitation approach is ≈3 times faster than that of external‐charge excitation. Optimization of various parameters is investigated to enhance the output performance of the TENG. A large output charge density of 1.67 mC m–2 is achieved in the atmosphere with 40% relative humidity due to self‐polarization effect of the dielectric composite film. This study provides insights into understanding the polarized behavior of molecules in dielectrics and further optimizing the output performance of TENGs in self‐charge excitation systems. [ABSTRACT FROM AUTHOR]

The effect of the external electric field on the ground state binding energy and self‐polarization of a hydrogenic donor impurity in quantum wells (QWs) made of different materials is calculated within the effective mass approximation using a variational scheme. The variations of binding energy and self‐polarization depending on well width, electric field, and impurity position have been studied in detail. For each QW made of different materials, it has been observed that the binding energy decreases with the increase of the electric field, whereas the self‐polarization increases. Also, it has been observed that InP/In1−xGaxP has higher binding energy values among the structures discussed. It is seen that material selection has a noticeable effect on self‐polarization and binding energy in QW‐based structures. [ABSTRACT FROM AUTHOR]

Multiple relaxation behaviors are promising for broad frequency band and strong electromagnetic wave (EMW) absorption based on polarization‐controlled electromagnetic (EM) attenuation. However, rational selection of materials and structure manipulation through tunable substitution or phase control are challenging toward optimization of EMW absorption. Herein, bi‐metallic organic frameworks (B‐MOFs) with various morphologies are employed as EMW absorbers. Remarkably, the polar units can be enhanced by introducing Ni‐metal nodes into the Cu‐coordinated MOFs, rendering the B‐MOFs with self‐polarized properties and consecutive multifrequency EMW absorption behaviors. The maximum reflection loss of acetylene black (ACET) filled NiCu‐MOFs can reach –40.54 dB together with a wide bandwidth (<‐10 dB) of 5.87 GHz at a thickness of 2.5 mm. As a counterpart of the Ni/Cu/C derivatives, significantly increased broad band absorption (6.93 GHz) and multifrequency absorbing and polarization characteristics are also maintained in bimetal coexisting carbonized architectures as prepared by calcination of CuNi‐MOFs. This work demonstrates that the performance of effective absorbing frequency band can be enhanced in multi‐metallic organic frameworks‐based architectures, and paves a novel avenue for developing broadband and strong EMW absorbers. [ABSTRACT FROM AUTHOR]

In this study, self-polarization (SP) for the first excited state in the finite quantum well is presented by taking into account the hydrostatic pressure and the external electric field. We calculated the SP of the first excited state by using the variational method under the effective mass approximation. These calculations were made for different values of the quantum well-width, hydrostatic pressure, external electric field and impurity positions. Our results indicate that the self-polarization of the first excited state in finite quantum well depends remarkably on the hydrostatic pressure, external electric field strength and impurity position. [ABSTRACT FROM AUTHOR]

Definition: Colloidal metal nanoparticles in an electrolyte environment are not only electrically charged but also electrochemically active objects. They have the typical character of metal electrodes with ongoing charge transfer processes on the metal/liquid interface. This picture is valid for the equilibrium state and also during the formation, growth, aggregation or dissolution of nanoparticles. This behavior can be understood in analogy to macroscopic mixed-electrode systems with a free- floating potential, which is determined by the competition between anodic and cathodic partial processes. In contrast to macroscopic electrodes, the small size of nanoparticles is responsible for significant effects of low numbers of elementary charges and for self-polarization effects as they are known from molecular systems, for example. The electrical properties of nanoparticles can be estimated by basic electrochemical equations. Reconsidering these fundamentals, the assembly behavior, the formation of nonspherical assemblies of nanoparticles and the growth and the corrosion behavior of metal nanoparticles, as well as the formation of core/shell particles, branched structures and particle networks, can be understood. The consequences of electrochemical behavior, charging and self-polarization for particle growth, shape formation and particle/particle interaction are discussed. [ABSTRACT FROM AUTHOR]

Flexible pressure sensors based on PVDF and its copolymers have been extensively investigated due to their unique self-powered characteristics and high sensitivity. Herein, a new strategy of manipulation the interfacial binding energy between the organic and inorganic groups has been utilized to enhance the performance of the flexible piezoelectric pressure sensors. Four types of interfacial interactions of different binding energy have been designed in the polydopamine (PDA) decorated lead zirconate titanate (PZT) and P(VDF-TrFE) composites. The results based on first-principles calculations reveal that PDA acts as a binder between PZT and P(VDF-TrFE) due to the strong interaction between -NH 2 and -CF 2 - dipoles. The strong interaction results in enhanced self-polarization effect and enhanced piezoelectric effect, and the improved sensitivity of the pressure sensors. The β-phase content of P(VDF-TrFE) increases from 17% to 87% when the content of PZT@PDA nanoparticles reaches 15 wt%. PZT@PDA/P(VDF-TrFE) self-powered pressure sensor (SPPS) exhibits an output voltage of 44 V and a high sensitivity of 1.38 V/kPa with no significant performance degradation during 10,000 cycles of pressure application. Moreover, the SPPS shows an excellent self-powered ability with the highest short-circuit current of 8.6 μA and the peak power density of 15 μW/cm2. The SPPS demonstrates the extraordinary sensing performance in body motion sensing and hand gesture recognition. [Display omitted] • SPPSs have been fabricated by using PZT@PDA NPs/P(VDF-TrFE) flexible nanofiber. • High sensitivity of 1.38 V/kPa and 2.6 ms response time have been achieved in SPPSs. • SPPSs combined with external circuits to realize multi-channel gesture sensing. [ABSTRACT FROM AUTHOR]

Using the variational method within the effective-mass approximation, the effects of geometrical shape and impurity position on the ground-state self-polarization and binding energy of a donor impurity are theoretically studied for the infinite GaAs/AlAs tetragonal quantum dot. We have found that the ground-state self-polarization and binding energy depend on geometrical shape and impurity-AlAs layer distance. [ABSTRACT FROM AUTHOR]

Effects of the electric field and impurity position on the 2p-excited state self-polarization and binding energy of the electron-impurity in a spherical quantum dot are investigated as a function of the dot radius using variational approach. According to results, turning point of 2p-excited state binding energy changes with the electric field strength and position of impurity in the spherical quantum dot. Self-polarization and binding energy between the 1s-ground state and 2p-excited state of a hydrogenic donor impurity in SQD are presented as a function of the dot radius for different electric field value and impurity positions. Obtained numerical results show a good agreement with the literature. [ABSTRACT FROM AUTHOR]

The photovoltaic properties of ferroelectric films have been extensively studied due to their potential applications in the fields of photodetection, energy conversion harvesting and storage. However, the effect of the gradient distribution of oxygen vacancies on the photovoltaic properties remains unclear. Herein, we prepared BiFeO 3 (BFO) and two types of gradient calcium-doped BiFeO 3 (BiFeO 3 /Bi 0.95 Ca 0.05 FeO 2.975 /Bi 0.90 Ca 0.10 FeO 2.950 /Bi 0.85 Ca 0.15 FeO 2.925 : BCFO-1 and Bi 0.85 Ca 0.15 FeO 2.925 /Bi 0.90 Ca 0.10 FeO 2.950 /Bi 0.95 Ca 0.05 FeO 2.975 /BiFeO 3 : BCFO-2) films deposited on fluorine-doped tin oxide glass substrates. Piezoresponse force microscopy studies indicate the upward self-polarization phenomenon in BFO and BCFO-1 films, while the downward self-polarization phenomenon in BCFO-2 films. The J – V characteristic curves show rectifier behaviors for these films due to the configuration of oxygen vacancies. For photovoltaic response, the open circuit voltage of BCFO-1 films is more than 2 times higher than that of BFO films, and the short-circuit photocurrent densities of BCFO-1 and BCFO-2 films are increased by nearly 32 and 6 times, respectively. The direction and magnitude of photovoltaic response are possibly associated with the energy band modulation governed by self-polarization and the gradient distribution of oxygen vacancies. The work demonstrates the merits of gradient doping with lower valence cation towards enhanced photovoltaic properties with high stability for ferroelectric oxides. [ABSTRACT FROM AUTHOR]

Particulate matter (PM) pollution in air is thought to be an important mortality risk factor globally. Most existing air filters face the extreme challenge of effectively removing PM0.3, which has the most penetration particle size (MPPS) of ≈0.3 µm yet is particularly harmful. Here, an innovative in situ electret electrospinning/netting technique that can manipulate both solution phase separation and crystal phase transition is reported to develop self‐polarized polyvinylidene fluoride nanofiber/net membranes with 2D networks and superior surface adhesion. By combining the true nanoscale diameter (≈21 nm), small pore size (≈0.26 µm), and highly electret surface (6.8 kV potential) of the 2D nanonets, the synergistic effect of sieving and adhesion for MPPS PM0.3 is achieved. Such double capture characteristic enables the high‐efficiency (≈99.998%) capture of PM0.3 while maintaining low air resistance (≈0.1% atmosphere pressure). Moreover, the nanofiber/net filters show integrated properties of superhydrophobicity, desirable transparency (91%), and long‐term stability. The synthesis of such attractive nanomaterials presents a promising attempt toward the development of high‐performance filtration/separation materials for numerous applications. [ABSTRACT FROM AUTHOR]

Electrolyte-gated organic field-effect transistors (EGOFETs) were fabricated using 6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS-Pentacene) as a p-type organic semiconductor. The devices were characterized as reference-less (RL) EGOFETs, and the self-polarization mechanism was studied. The fact that EGOFETs can exhibit field-effect behavior even without the gate electrode was demonstrated. This work provides useful guidelines for optimizing RL-EGOFET technology. [ABSTRACT FROM AUTHOR]

In this study, novel mixed matrix membranes (MMMs) composed of MoO 3 /Poly (vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) with distinctive piezo-photocatalytic properties were prepared. The membranes were made from dopes containing a high ratio of MoO 3 to P(VDF-TrFE) (2:1 wt%/wt%) through a modified solvent evaporation method. The addition of MoO 3 particles significantly impacted the crystallization and self-polarization of the P(VDF-TrFE) matrix, leading to a substantial increase in total crystallinity from 46.4% to 88.9% and a transformation from α to β phase. The flow-induced piezoelectric potential created an internal electric field, enhancing the spatial separation of photogenerated carriers through the piezoelectric effect. Controlled water flow further promoted the spatial separation of carriers. The developed MMMs demonstrated a high Rhodamine B degradation rate, reaching 83.1% within 45 minutes and over 99% within 90 minutes under natural light conditions. The MoO 3 /P(VDF-TrFE) MMMs exhibit promising piezo-photocatalytic attributes and hold potential for diverse applications due to their unique combination of piezoelectric and photocatalytic properties. [Display omitted] • The mixed matrix membranes(MMMs) with mass ratio of MoO 3 to P(VDF-TrFE) 2:1 were prepared by solvent evaporation method. • The addition of MoO 3 particles promoted the crystallization of piezoelectric phase and enhanced the piezoelectricity of MMMs. • Under the mechanical drive of water flow, the piezoelectric effect promotes the separation of MoO 3 photogenerated carrier. • MoO 3 /P(VDF-TrFE) MMMs showed good degradation of Rhodamine B under xenon lamp and natural light conditions. [ABSTRACT FROM AUTHOR]

Abstract Li x Bi 1- x Nb x Fe 1- x O 3 films with various Li+ and Nb5+ substitutions were fabricated onto LaNiO 3 -buffered Pt(111)/Ti/SiO 2 /Si substrates through sol-gel methods. Owing to the substitution by smaller Li+ and Nb5+ for larger Bi3+ and Fe3+ respectively, the phase structure of Li x Bi 1- x Nb x Fe 1- x O 3 films experiences a transition from rhombohedral phase (R phase, high symmetry) to tetragonal-like phase (T-like, low-symmetry) upon the chemical pressure with Li+ and Nb5+ substitution increases. Additionally, the dielectricity, ferroelectricity and leakage behaviors of substituted Li x Bi 1- x Nb x Fe 1- x O 3 films are also significantly improved. More importantly, the substituted Li x Bi 1- x Nb x Fe 1- x O 3 films show significantly enhanced piezoelectric responses, especially for the Li 0.05 Bi 0.95 Nb 0.05 Fe 0.95 O 3 film, whose d 33 with the value of 107.5 pm/V might be compared with some lead-based piezoelectric films. The enhanced piezoelectric response of the Li 0.05 Bi 0.95 Nb 0.05 Fe 0.95 O 3 film is contributed by synergistic effects of low-symmetry phase, improved ferroelectricity and downward self-polarization, where the electric field-triggered R-T phase transition and polarization vectors rotation can be easily took place upon small stimuli. Additionally, the reduction of leakage currents for substituted Li x Bi 1- x Nb x Fe 1- x O 3 films also help to improve their dielectric, ferroelectric and piezoelectric properties. [ABSTRACT FROM AUTHOR]

Featured Application: Insight into the electrochemical nature of the growth of metal nanoparticles supports the development of new concepts and protocols for the production of non-spherical nanoparticles of high homogeneity, for control of particle geometry and for the development of new types of nanoparticles. The growth and aggregation behavior of metal nanoparticles can be modulated by surfactants and different other additives. Here the concept of how open-circuit mixed electrodes helps to understand the electrical aspects of nanoparticle growth and the consequences for the particle geometries is discussed. A key issue is the self-polarization effect of non-spherical metal nanoparticles, which causes a local decoupling of anodic and partial processes and asymmetry in the local rates of metal deposition. These asymmetries can contribute to deciding to the growth of particles with high aspect ratios. The interpretation of electrochemical reasons for particle growth and behavior is supported by experimental results of nanoparticle syntheses supported by microfluidics which can supply high yields of non-spherical nanoparticles and colloidal product solutions of high homogeneity. [ABSTRACT FROM AUTHOR]

The electronic structures of CdS quantum dot (QD) with dielectric mismatch are calculated. Poisson equation is solved analitically in case of point charge placed inside semiconductor sphere embeded in dielectric matrix in case of different values of the dielectric permittivity of QD and matrix. The validity of the effective mass approximation for the conduction band is assumed. Schrödinger equation for one electron is solved analitically. On the basis of the Poisson equation solution self potential is examined and used as perturbation to calculate the self-polarization effect.

Ferroelectric materials are used in actuators or sensors because of their non-volatile macroscopic electric polarization. GeTe is the simplest known diatomic ferroelectric endowed with exceedingly complex physics related to its crystalline, amorphous, thermoelectric, and—fairly recently discovered—topological properties, making the material potentially interesting for spintronics applications. Typically, ferroelectric materials possess random oriented domains that need poling to achieve macroscopic polarization. By using X-ray absorption fine structure spectroscopy complemented with anomalous diffraction and piezo-response force microscopy, we investigated the bulk ferroelectric structure of GeTe crystals and thin films. Both feature multi-domain structures in the form of oblique domains for films and domain colonies inside crystals. Despite these multi-domain structures which are expected to randomize the polarization direction, our experimental results show that at room temperature there is a preferential ferroelectric order remarkably consistent with theoretical predictions from ideal GeTe crystals. This robust self-poled state has high piezoelectricity and additional poling reveals persistent memory effects.

Abstract: Interfaces in oxides are found to possess different properties and can be engineered for modifying local structure and properties of nearby area. In this work, it is reported that the interfaces can be formed in Ba/Zr (BZ)‐doped (K,Na)NbO3 (KNN) thin films by cycles of chemical solution deposition using same precursor solution. In the films, a novel and special cross‐sectional structure is observed with periodic distribution of Ba‐rich and Zr‐rich layers. The Ba‐rich and Zr‐rich layers exhibit different strain, lattice parameters, and crystal structure, leading to an obvious effect on the general ferroelectric properties of the KNN‐based thin films. Moreover, the self‐polarization is also observed, which can be understood to originate from the formed built‐in field by layered distribution of Ba and Zr in the KNN‐BZ thin films. [ABSTRACT FROM AUTHOR]

In this study, we investigate the simultaneous effects of anisotropy and internuclear distance on the self-polarization of the D 2 + complex in quantum dots for different confinement sizes. Numerical calculations were carried out within the effective mass approach using the two-dimensional diagonalization method. The obtained results reveal that a change in the internuclear distance and anisotropy parameter regulates the effective confinement potential of the system. The variation in effective confinement potential plays an important role in the spatial elongation of the wave function, which determines the observed behavior of the self-polarization effect (S P E). The magnitude of the S P E in the prolate case has been found to be greater than that of the oblate case. The obtained results reveal that the S P E of the D 2 + complex can be arranged in quantum dots as desired by adjusting the internuclear distance and anisotropy of the system. • A singly ionized double donor complex (D 2 +) confined in a quantum dot. • We have demonstrated the existence of the tunability of the self-polarization effect of the D 2 + complex by adjusting the internuclear distance and the anisotropy of the quantum dot. • The magnitude of the self-polarization effect in the prolate case has been found to be greater than that of the oblate case. • The obtained results reveal that the self-polarization effect of the D 2 + complex can be arranged in quantum dots by adjusting the internuclear distance and anisotropy of the system. [ABSTRACT FROM AUTHOR]

The growth and aggregation behavior of metal nanoparticles can be modulated by surfactants and different other additives. Here the concept of how open-circuit mixed electrodes helps to understand the electrical aspects of nanoparticle growth and the consequences for the particle geometries is discussed. A key issue is the self-polarization effect of non-spherical metal nanoparticles, which causes a local decoupling of anodic and partial processes and asymmetry in the local rates of metal deposition. These asymmetries can contribute to deciding to the growth of particles with high aspect ratios. The interpretation of electrochemical reasons for particle growth and behavior is supported by experimental results of nanoparticle syntheses supported by microfluidics which can supply high yields of non-spherical nanoparticles and colloidal product solutions of high homogeneity.

Controlling the domain evolution is critical both for optimizing ferroelectric properties and for designing functional electronic devices. Here we report an approach of using the Schottky barrier formed at the metal/ferroelectric interface to tailor the self-polarization states of a model ferroelectric thin film heterostructure system SrRuO 3 /(Bi,Sm)FeO 3 . Upon complementary investigations of the piezoresponse force microscopy, electric transport measurements, X-ray photoelectron/absorption spectra, and theoretical studies, we demonstrate that Sm doping changes the concentration and spatial distribution of oxygen vacancies with the tunable host Fermi level which modulates the SrRuO 3 /(Bi,Sm)FeO 3 Schottky barrier and the depolarization field, leading to the evolution of the system from a single domain of downward polarization to polydomain states. Accompanied by such modulation on self-polarization, we further tailor the symmetry of the resistive switching behaviors and achieve a colossal on/off ratio of ∼1.1 × 10 6 in the corresponding SrRuO 3 /BiFeO 3 /Pt ferroelectric diodes (FDs). In addition, the present FD also exhibits a fast operation speed of ∼30 ns with a potential for sub-nanosecond and an ultralow writing current density of ∼132 A/cm 2 . Our studies provide a way for engineering self-polarization and reveal its strong link to the device performance, facilitating FDs as a competitive memristor candidate used for neuromorphic computing.

In ferroelectric materials, significant piezoelectric response only occurs after poling by an external electric field applied along a certain crystallographic direction, and the piezoelectric effect generally disappears upon heating to the Curie temperature (T C ) where the poled state vanishes. This thermally induced depoling often restricts the temperature range for the applications of piezoelectric devices. It has been a challenge to develop materials that exhibit high piezoelectric performance that is not affected by electric poling, nor thermal depoling. Here we report an unusual piezoelectric effect found in Pb(Mg 1/3 Nb 2/3 )O 3 -PbSnO 3 -PbTiO 3 ternary ferroelectric crystals which exhibit a relatively high piezoelectricity (with the piezoelectric coefficient d 33 = 1350–1400 pC/N) without undergoing any poling process. Moreover, this high piezoelectric performance is retained after repeated thermal annealing at temperatures above T C , showing a piezoelectric memory effect. This uncommon piezoelectric effect is explained by a self-polarization mechanism based on the defect-dipoles formed in the crystals due to the presence of mixed valence states of Sn 2+/4+ . The defect-dipoles generate internal bias electric fields which, in turn, provide the stabilizing and restoring forces leading to preferred orientation states and the retention of spontaneous polarization. This mechanism offers a new perspective for designing novel piezoelectric materials with high performance and a wide temperature range of operation. [ABSTRACT FROM AUTHOR]

Spontaneously appearing macroscopic polarization (self-polarization) in ferroelectrics without an electrode or an external electric field would enable the freedom to design many ferroelectric heterostructures and devices. The (K0.5Na0.5)(Mn0.005Nb0.995)O3 (KNMN) thin film was grown on Nb:SrTiO3 single-crystal substrate and the resultant self-polarization behavior due to strain relaxation was investigated. The lattice mismatch and difference in TEC between the KNMN thin film and the Nb:SrTiO3 substrate creates a compressive strain. The compressive strain gradient may be the main cause for the observed downward self-polarization. The downward self-polarization of the KNMN thin film can be explained by the strong inhomogeneous compressive strain caused by strain relaxation. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) devices have become one of the most attractive clean energies due to its potential high efficiency and simplicity but it is very challenging to make a highly efficient and stable practical device. Up to date, BiVO 4 as the most promising ternary metal-oxide photoanode can only achieve a photocurrent of no more than 1.0 mA cm −2 , which is far below its theoretical value (7.5 mA cm −2 ), and is mainly caused by its high charge recombination from defects and sluggish water oxidation kinetics. Herein we fabricate a BiVO 4 /ferroelectric BiFeO 3 composite photoanode by a surface passivation approach to greatly enhance photocurrent by ~4.4 times plus ~400 mV negative shift of the onset potential than the plain BiVO 4 . BiVO 4 /BiFeO 3 also greatly decreases charge recombination rate from 17 s −1 to 0.6 s −1 in comparison to the plain BiVO 4 by ~28 times. The PEC performance of BiVO 4 /BiFeO 3 can also be manipulated based on the direction of self-polarization in BiFeO 3 . Moreover, BiVO 4 /BiFeO 3 shows much better stability than that of the BiVO 4 as well as BiVO 4 /Co-Pi. It is discovered that the PEC performance enhancement mechanism is attributed to the BiFeO 3 passivation for a bifunctional film as a buffer layer to significantly reduce charge recombination while as an efficient catalyst to boost charge separation/transfer. [ABSTRACT FROM AUTHOR]

Ytterbium (Yb 3+ ) assisted porous poly(vinylidene fluoride) (PVDF) composite film comprising flexible ferroelectretic nanogenerator (FTNG) is highlighted where traditional poling treatment is completely avoided. The piezoelectric output of FTNG is realized by the co-operative activity of self-polarized − / − -CH 2 / -CF 2 dipoles with porous electret-like structure in the composite film. Owing to extraordinary ferroelectric and dielectric properties, FTNG is acting as a highly efficient mechanical energy harvester. It is capable to capture several forms of abundant mechanical energy arising from human finger movements, machine vibrations and sound waves. As a proof of concept, under compressive deformation, FTNG is enable to instantly powers up several consumer electronics and thus provides a promising strategy for achieving self-powered electronic devices. [ABSTRACT FROM AUTHOR]

The article focuses on the study related to self-polarization of chemical compound Barium titanate (BaTiO3) and flexoelectric effect. Topics discussed includes persistency of ferroelectricity to a few unit cells by ferroelectric oxide thin films, piezoresponse force microscopy was performed to characterize the ferroelectric domain structure, and various factors responsible for the different self-poarlization of ferroelectric thin films.

LiNbO3 thin films were deposited on Al2O3 substrates by RF-magnetron sputtering with in-situ electric field to study the self-polarization effect. The films have been characterized crystallographically by x-ray diffraction, and morphologically by atomic force microscopy. The films contain crystallites of LiNbO3 with preferable orientation [012] along the normal to the Al2O3 substrate surface (012). Piezoresponse force microscopy was used to study vertical and lateral polarization direction in LiNbO3 thin films. The analysis of the histograms of vertical piezoresponse images allowed to reveal self-polarization effect in films. The local piezoelectric hysteresis performed on the nanometer scale indicates switching behavior of polarization for LiNbO3 thin film. [ABSTRACT FROM AUTHOR]

[Display omitted] • Development of electrode-free piezoelectric nanogenerator. • Polyvinylidene fluoride–hexafluoropropylene as matrix and carbon black as filler. • Electrode-free signal transmission via interface polarization effect. • CB particles as both inner electrode and piezoelectric enhancer. • Facile repair via re-spraying due to self-polarization-based preparation. Flexible piezoelectric nanogenerators (PENGs) with high sensitivity, easy deformability, anti-corrosion features, and facile fabrication are highly advantageous for biological tissue sensing/monitoring applications in complex environments. The large-scale and low-cost preparation of flexible piezoelectric polymers requires additional electrode layers for charge collection, compromising the flexibility and corrosion resistance of the PENGs while increasing their fabrication difficulty and cost. In this study, we developed an electrode-free PENG based on a composite film composed of polyvinylidene fluoride–hexafluoropropylene (PVDF-HFP) as the matrix, and carbon black (CB) as the filler. With an appropriate content of approximately 5 wt%, and under the interface polarization effect, the CB particles in the composite film acted as both the inner electrode and the piezoelectric enhancer, thus realizing a sensing functionality without the use of an additional electrode. The effects of the positions of CB particles in the PVDF matrix on the potential distribution, and the functions of CB polarization in the inner electrode and piezoelectric enhancer were simulated using COMSOL Multiphysics software. An excellent piezoelectric performance was achieved, including a current of 0.66 μA, voltage of 17.6 V, and charge of 4.7 nC. Further, electrode-free PENGs, with the multi-self-polarization PVDF-HFP matrix exhibit a promising application as sensors for effectively monitoring human activities and complex environments and can be effectively repaired (up to 80 %) via a facile spray-coating process. [ABSTRACT FROM AUTHOR]

Although utilizing charge excitation is an effective strategy to achieve high charge density for triboelectric nanogenerators (TENGs), the conductive pathways formed by water molecules in a high-humidity environment cause inevitable output charge decay and limit practical applications of TENGs. Herein, a self-polarization effect-based charge-excitation TENG (SP-CE-TENG) is proposed with high surface charge density (SCD), and the charge self-increase phenomenon of dielectric materials with different strong polar groups is investigated. It is found that the unique strong polarization characteristics of water molecules further promote the self-polarization process of dielectric materials with the increase in humidity. As a result, an ultra-high SCD of 2.88 mC m−2 is obtained in the atmosphere with 40% relative humidity (RH) using 7 µm homemade poly(vinylidene fluoride-trifluoroethylene) film. Meanwhile, the effective SCD of the SP-CE-TENG maintains more than 1.92 mC m−2 even at 90% RH, which is the highest charge density for TENGs in a high humidity environment. This work presents a practical approach to boosting the output charge density of TENGs, which is helpful for in-depth exploration of the polarization behaviors of polar molecules in a high-humidity environment. [Display omitted] • The self-polarization effect of polar materials with different strong polar groups was systematically studied. • Hydrogen bonds' unique strong polarization characteristics further promote dielectric materials' self-polarization process with increased humidity. • The surface charge density of SP-CE-TENG always maintains more than 1.92 mC m−2 even at 90% RH. [ABSTRACT FROM AUTHOR]

Submicron ferroelectric PZT films deposited on the Pt/TiO2/SiO2/Si substrate by RF magnetron sputtering and annealed at 530–570 °C consisted of spherulitic blocks with crosswise size of ~5-40 μm. The films composition corresponded to morphotropic phase boundary. The spherulite sizes, excess lead oxide content, the dielectric constant, self-polarization, and residual polarization changed with the increase of films annealing temperature. It is assumed that high values of self-polarization in thin films are determined by effective screening of the spontaneous polarization by conducting intergranular space occupied by the lead oxide. [ABSTRACT FROM PUBLISHER]