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Bi0.95Ba0.05Fe0.95Zr0.05O3 (BBFZO) nanoparticles were synthesized by a sol–gel technique to develop a filler material with lower leakage current and oxygen vacancies compared to the host BiFeO3. In this work, we report the enhanced dielectric, ferroelectric, energy storage and energy harvesting performance of BBFZO incorporated PVDF composites. 15 wt% BBFZO loaded PVDF (15BBFZO) exhibited improved polarity (F(EA) = 77.42%) compared to neat PVDF (F(EA) = 37.01%). At an applied field of ∼14 kV cm−1 (1 Hz), this film (15BBFZO) exhibited a maximum energy storage density of 151.18 μJ cm−3 (at 1 Hz). Upon repeated human finger tapping, an average open circuit peak to peak a.c. voltage (VOC) ∼ 20 V was obtained from 15BBFZO. A comprehensive study of frequency dependent D–E loops and an extensive study of the effect of electrical poling on the output performance of the developed composite films have been performed. An improvement of the dipolar polarization was established through a frequency dependent D–E loop study of unpoled and poled 15BBFZO and from other experiments. After poling the energy storage density and VOC of 15BBFZO were 154.66 μJ cm−3 (at 1 Hz) and ∼30 V, respectively. After rectification this output electrical signal was able to charge a 10 μF commercial capacitor up to ∼5.5 V. After poling, the energy storage efficiency (η) of 15BBFZO also improved from 52.49% to 67.85% (at 1 Hz). The frequency dependence of the storage efficiency for all the samples has also been extensively investigated here. At 1 kHz, η improved to 93.30% for poled 15BBFZO.

Ferroelectric materials have attracted significant interest due to their wide potential in energy harvesting, sensing, storage, and catalytic applications. For monolithic and dense ferroelectric materials, their performance figures of merit for energy harvesting and sensing are limited by their high relative permittivity, and their low surface area can limit piezo- or pyro-catalytic applications. As a result, the introduction of porosity into dense ferroelectric materials can enhance performance for a variety of piezoelectric and pyroelectric applications. In this review, the piezoelectric, pyroelectric, ferroelectric and mechanical properties of porous ferroelectrics are presented, and the fabrication processes to create porous ferroelectric materials are classified and discussed. Simulations of the poling process and resulting piezo- and pyro-electric properties are also described to understand the underlying science of these fascinating porous materials and develop new approaches towards materials design. Applications of porous ferroelectric materials in specific fields are then summarized. Finally, conclusions and future perspectives for porous ferroelectric materials are provided. This journal is

Piezoelectric Poly (vinylidene fluoride) (PVDF) films with high flexibility are a suitable and promising replacement for rigid ceramic piezoelectric materials. However, for this purpose, enhancing piezoelectric properties and adopting an industrial fabrication method are of great importance. In this study, 5–9 µm thick PVDF films were fabricated by a nozzle-less ultrasonic spray coating (USC) system, followed by an annealing process at 100 °C. By applying proper spraying parameters, we could obtain highly uniform films with large d33 values (48 pm/V) and 56% crystallinity. Results show that the uniformity of the films plays an important role in the final piezoelectric properties. Thus, ultrasonic spray coating method can be used for fabrication of large-scale piezoelectric films with no need for poling or stretching processes.

Local structural correlations in a novel ferroelectric solid solution [$x\mathrm{Bi}({\mathrm{Ni}}_{0.5}{\mathrm{Hf}}_{0.5}){\mathrm{O}}_{3}\text{\ensuremath{-}}(1\ensuremath{-}x){\mathrm{PbTiO}}_{3}$ at $x=0.39$] have been drawn out through atomistic modeling against neutron pair distribution functions and complementary Raman scattering measurements. By examining polar displacements of different cations from the refined structural models, we reveal the distributions of cation-specific dipolar fluctuations at the key composition where the maximum piezoelectric response was recorded. It becomes clear that the unusual structural modifications observed after the poling are simply a manifestation driven by the varying extent of the dipolar fluctuations and not a structural transformation caused by adaptive cationic displacements. Moreover, in addition to strong dipolar flexibility under an electric field, both poled and unpoled ceramics exhibit orientation-independent polarized Raman scattering, which is more typical of a dipolar glass with a responsive and polarizable matrix than a polycrystalline material composed of ferroelectric domains. Therefore, compared to other analogous $x\mathrm{Bi}(\mathrm{Me}){\mathrm{O}}_{3}\text{\ensuremath{-}}(1\ensuremath{-}x){\mathrm{PbTiO}}_{3}$ systems, the current material is a unique case where chemical substitution has led to a highly polarizable ionic-covalent matrix that seems to be the key ingredient to generate giant piezoelectricity at a composition beyond the morphotropic phase boundary.

It is shown for the first time that the vacuum poling of soda-lime silicate glass and the subsequent processing of the glass in a melt containing silver ions results in the formation of silver nanoparticles buried in the subanodic region of the glass at a depth of 800–1700 nm. We associate the formation of nanoparticles with the transfer of electrons from negatively charged non-bridging oxygen atoms to silver ions, their reduction as well as their clustering. The nanoparticles do not form in the ion-depleted area just beneath the glass surface, which indicates the absence of a spatial charge (negatively charged oxygen atoms) in this region of the vacuum-poled glass. In consequence, the neutralization of the glass via switching of non-bridging oxygen bonds to bridging ones, which leads to the release of oxygen, should occur in parallel with the shift of calcium, magnesium, and sodium ions into the depth of the glass.

More than one century ago, piezoelectricity and ferroelectricity were discovered using Rochelle salt crystals. Today, modern societies are invited to switch to a resilient and circular economic model. In this context, this work proposes a method to manufacture piezoelectric devices made from agro-resources such as tartaric acid and polylactide, thereby significantly reducing the energy budget without requiring any sophisticated equipment. These piezoelectric devices are manufactured by liquid-phase epitaxy-grown Rochelle salt (RS) crystals in a 3D-printed poly(Lactic acid) (PLA) matrix, which is an artificial squared mesh which mimics anatomy of natural wood. This composite material can easily be produced in any fablab with renewable materials and at low processing temperatures, which reduces the total energy consumed. Manufactured biodegradable samples are fully recyclable and have good piezoelectric properties without any poling step. The measured piezoelectric coefficients of manufactured samples are higher than many piezoelectric polymers such as PVDF-TrFE.

Glass fiber reinforced epoxy nanocomposites are synthesized with different weight percentages of MgO nanofillers to improve their mechanical and electrical properties, especially for aerospace and high voltage insulation applications. Static contact angle studies have shown that 3 wt% MgO nanofiller added specimen has a higher contact angle, indicating a better surface profile. Marginal increment in real relative permittivity and dielectric loss tangent have been observed with the inclusion of MgO nanofillers. Pulsed Electro Acoustic (PEA) method was adopted for space charge measurement, which has shown hetero-charge accumulation in all the tested specimens. The amount of accumulated space charge density during poling period is lower and its decay rate during depoling is higher in 3 wt% MgO added specimen. Reduction in initial surface potential and increment in its lst decay rate was noticed after incorporation of MgO nanofillers. 3 wt% specimen has reflected a higher surface potential decay rate with reduced trap depth in comparison with other samples. Dynamic Mechanical Analysis (DMA) studies have shown increased storage modulus with a slight reduction in tan δ value after the inclusion of MgO nanofillers. In addition, the glass transition temperature and the activation energy of 3 wt% specimen were found to be higher compared to other specimens.

This work presents a new process to print piezoelectric polymer-based sensors through additive manufacturing via three-dimensional (3D) printing technology. 3D printing has become an efficient method to fabricate devices with complex geometric structures and embedded functionalities. The motivation of this research was to explore a path towards fully 3D printed multifunctional thin and flexible sensing devices. The 3D printed methods used were Fused Deposition Modelling and Direct Ink Writing. A fully 3D printed sensor consisting of a (2.54 cm × 2.54 cm) poly(vinylidene fluoride) (PVdF) film with thickness in the range of ∼250 μm to 350 μm was sandwiched between two fast-drying silver paint printed electrodes with thickness ranging from ∼10 μm to 50 μm. The arithmetic average roughness, Ra, of typical printed PVdF profiles with and without printed silver electrodes was ∼12.9 μm and ∼7.3 μm, respectively. Silver electrodes were printed to facilitate contact poling and to collect charges generated due to piezoelectricity. The average piezoelectric activity of printed unpoled films was 7.13 pC/N. The polarization in the printed PVdF films was realized by conventional contact poling at elevated temperatures (100, 110, 120 and 130 °C, respectively) with step increased electric fields, which were varied from 0.4 MV/m to 14 MV/m at 1 MV/m increments. To perform contact poling, PVdF films were immersed in mineral oil and a controlled voltage was applied to electrodes on one side while electrodes on the opposite side were grounded. The extrusion process during 3D printing and the subsequent contact poling process enabled the phase transition from the thermally stable α-phase to the piezoelectric active β-phase and the rearranging of the dipole alignments. The efficiency of poling was evaluated through measurement of the average value of the charge generated by six poled PVdF films in response to mechanical input increasing from 0.29 N to 1.91 N with ∼0.27 N increments. The highest average piezoelectric activity obtained was 59.2 pC/N, and a single device of 96.44 pC/N, at step increased poling voltages up to 3.5 kV under a fixed temperature 120 °C. The results demonstrate that by increasing the poling voltages and time, a higher piezoelectric activity (about 8 times compared to unpoled films) was achieved, indicating improvement of the β-phase content. This study provides a new method for continuous and direct printing of piezoelectric devices from PVdF polymeric filament. This technology opens a new path towards fully 3D printed free-form structured functional materials for sensing applications.

Ferroelectrets are typical cellular polymer foams that exhibit high flexibility and an excellent matching to air. Recently, biodegradable cellular polylactic acid (PLA) ferroelectrets have been introduced, exhibiting a large longitudinal piezoelectric coefficient. In this work, we present a combination of a PLA film and a printed PLA backplate using fused deposition modeling to build a ferroelectret air-coupled ultrasonic transducer. The ultrasonic transducer consists of three main components all made from PLA: the film presenting the vibrating plate, the printed backplate with well-defined groves, and the printed holder. The PLA film and the printed backplate build together the ferroelectret with artificial air voids. The printed holder clamps the film on the backplate and fixes the ferroelectret together. After poling, the trapped surface charge density serves as electrical bias as well as a mechanical pre-stress due to the permanent electrostatic forces. The resulting sound pressure is measured with a calibrated microphone (Type 4138, Bruel & Kjaer) at 30 cm distance. The sound pressure of the transducer is measured at the resonance frequency for different applied AC voltages (from 30 to 70 Vrms). The biodegradable ultrasonic transducer exhibits a large bandwidth of approximately 45 kHz and fractional bandwidth of 70 %. The resulting sound pressure at the resonance frequency can be increased from 98 dB up to 106 dB for driving voltages from 30 to 70 Vrms. respectively.

In ultrasonic transducers, there is a problem that the couplant to match the acoustic impedance and the backing material to absorb unnecessary vibration have low durability at high temperature. We have developed an ultrasonic transducer that does not require a couplant or backing material by using a sol-gel composite method. Although the Curie temperature of PT is around 490°C, when the poling voltage and the polarity of the applied electric field during measurement are matched, high temperature durability is achieved and clear ultrasonic waveforms can be measured even at 600°C. The polarity of the poling voltage and the applied electric field during measurement was matched.

The paper reports on our latest developments on fabrication of fine scale 1–3 piezocomposites for application as high frequency ultrasonic transducers using soft mold process. In previous work we showed that operating frequencies can be increased to frequencies of at least 40 MHz by modifying piezoceramic pillar size and layout within 1–3 piezocomposites. Especially circular pillars with hexagonal arrangement turned out to be beneficial to reduce influence of spurious modes. The current investigation focuses on the improvement of piezoelectric properties of 20 MHz ultrasonic transducers to enhance ultrasonic performance. During experimental verification process parameters like PZT powder as well as sintering and poling conditions were systematically varied to optimize dielectric and electromechanical properties, in particular thickness mode coupling factor k t . The results show that sintering temperature and polarization field strength are the most crucial parameters to influence coupling factor. By modifying fabrication process coupling factor could be increased to values of up to k t = 0.6. Best results were achieved by using calcined and pre-sintered PZT powder in combination with relatively low sintering temperatures ϑ s = 1060–1110 °C and high electric fields during poling $E$ pol ≥ 9 V /µm.

Potassium titanyl phosphate (KTP) is a nonlinear optical material with applications in high-power frequency conversion or quasi-phase matching in submicron period domain grids. A prerequisite for these applications is a precise control and understanding of the poling mechanisms to enable the fabrication of high-grade domain grids. In contrast to the widely used material lithium niobate, the domain growth in KTP is less studied, because many standard methods, such as selective etching or polarization microscopy, provides less insight or are not applicable on non-polar surfaces, respectively. In this work, we present results of confocal Raman-spectroscopy of the ferroelectric domain structure in KTP. This analytical method allows for the visualization of domain grids of the non-polar KTP y-face and therefore more insight into the domain-growth and -structure in KTP, which can be used for improved domain fabrication.

Small organic molecules with a π-conjugated system that consists of only a few double or triple bonds can have significantly smaller optical excitation energies when equipped with donor and acceptor groups, which raises the quantum limits to the molecular polarizabilities. As a consequence, third-order nonlinear optical polarizabilities become orders of magnitude larger than those of molecules of similar size without donor-acceptor substitution. This enables strong third-order nonlinear optical effects (as high as 1000 times those of silica glass) in dense, amorphous monolithic assemblies. These properties, accompanied by the possibility of deposition from the vapor phase and of electric-field poling at higher temperatures, make the resulting materials competitive towards adding an active nonlinear optical or electro-optic functionality to state-of-the-art integrated photonics platforms.

We experimentally measure percent-level optical-to-multi-cycle terahertz conversion efficiencies by injecting a home-made wavelength- and duration-tunable two-line laser into periodically poled lithium niobate. We study the efficiency vs. the input laser peak fluence, pulse duration, crystal length and poling period at cryogenic temperature. Our work is a significant step towards high energy terahertz pulses for linear electron acceleration.

Hybrid organic electro-optic (OEO) devices consist of a layer of ordered organic chromophores confined between layers of metals or semiconductors, enabling optical fields to be tightly confined within the OEO material. The combination of tight confinement with the high electro-optic (EO) performance of state-of-the art OEO materials enables exceptional electro-optic switching performance in silicon-organic hybrid (SOH) and plasmonic-organic hybrid (POH) device architectures. Recent records in POH devices include bandwidths < 500 GHz and energy efficiency < 100 aJ/bit. However, optimization of device performance requires both understanding and improving the degree to which chromophores can be acentrically ordered near a metal or semiconductor interface. Applying bulk and/or isotropic models of OEO materials to nanophotonic device architectures often lead to overly optimistic translation of materials performance to device performance. Prior work has identified influences of high centrosymmetric order (birefringence), altered relations between acentric and centrosymmetric order (dimensionality), and surface electrostatics on chromophore ordering. We combine these models into a representation that can be used to understand the influences of these phenomena on device performance, how some prior OEO materials exhibited unusually high performance under confinement, how ordering close to surfaces may be improved, and implications for future electro-optic device design.

The charge carrier mobility in organic field-effect transistors (FETs) may be enhanced by a few orders of magnitude by an appropriate choice of the dielectric layer. Polymer ferroelectric dielectrics with their high dielectric constants are attractive for low-operating voltage FETs. However, due to the dynamic coupling of the charge carriers to the electronic polarization at the semiconductor-dielectric interface, polymer ferroelectric based organic FETs may result in low carrier mobilities. Selective electrical poling of the ferroelectric dielectric, poly(vinylidene fluoride trifluorethylene) (PVDF-TrFE), is seen to greatly improve the performance of small molecule and donor-acceptor copolymer based FETs [1]. A combination of vertical and lateral poling of the PVDF-TrFE layer, which reduces the gate leakage current as well as mitigates polarization fluctuation driven transport, yields carrier mobilities upwards of 1 cm2/Vs in TIPS-pentacene and 0.5 cm2/Vs in diketopyrrolopyrrole based FETs under ambient conditions [2]. Other strategies for improving the performance of FETs involve dissolving the ferroelectric polymer in high dipole moment solvents and adding thin polymer buffer layers. The incorporation of magnetic nanoparticles in non-ferroelectric dielectrics is yet another approach for enhancing the dielectric constant. Ferrite nanoparticles with biomimetic peptide nanostructures as gate dielectrics have ramifications in low-operating voltage organic FETs [3]. This work was supported by National Science Foundation under Grant No. ECCS-1707588 [1] Laudari et al. Adv. Mater. Interfaces 6, 1801787 (2019). [2] Laudari et al. ACS Appl. Mater. Interfaces 12, 26757 (2020). [3] Khanra et al. ACS Appl. Nano Mater 1, 1175 (2018).

Among lead-free ferroelectric materials, Barium Strontium Titanate (BST) has interesting ferroelectric, pyroelectric, piezoelectric, and energy-harvesting properties. This material can be advantageously solution-deposited. There is a need for homogeneous and dense films with optimized electrical properties. BST thin films are elaborated with a highly diluted precursor solution of less than 0.05 M. The electric properties are correlated with the morphology and structure of the films as a function of precursor solution dilution. The film growth is columnar with a tetragonal perovskite structure. As the dilution increases, the roughness of the top surface and of the columns decreases, facilitating grain coalescence. In addition, the permittivity of the grains and of the grain boundaries decreases. The highest dielectric strength (400 kV/cm) is obtained for the sample elaborated with the most diluted precursor solution of 0.008 M. For a given polarization, the necessary poling electric field decreases by a factor 2.3 as dilution increases by a factor 4. Finally, hysteresis loops are obtained with increasing saturation and remnant polarizations as the dilution increases. The saturation polarization is approximately doubled as the solution dilution is multiplied by four. To conclude, BST films elaborated with highly diluted solutions have enhanced ferroelectric properties.

Piezocatalysis is a promising area of research that would enable new advances in environmental catalytic processes independent of energy sources such as light or electricity. To shed more light on this field, theoretical and experimental studies were conducted using poled and unpoled BF-KBT-PT ceramics as catalysts in order to investigate the effect that piezocatalyst size, piezocatalyst poling/unpoling and agitation mode have on the degradation of a dye, Rhodamine B (RhB), in water. While an apparently contradictory trend in the theoretical and experimental results was observed in relation to piezocatalyst size, poling indeed had a significant effect on the degradation of RhB, indicating that a complex combination of different phenomena such as ‘top-to-bottom’ electric potential difference due to ‘bulk’ piezoelectric polarisation, nanoscale piezoelectric response and sonocatalysis may result in the overall catalytic degradation of RhB. However, the greatest contribution to the degradation of the dye would come from sonochemistry, as ultrasound in absence of a catalyst already achieved a remarkable degradation of RhB. This study therefore demonstrates the complexity of piezocatalysis, and why other phenomena besides bulk piezoelectric polarisation of catalysts must be taken into account in piezocatalysis research.

The d33 coefficient = 28 pC/N of PVDF-TrFE piezoelectric films was achieved by the in situ polarization. Compared with traditional poling methods, the in situ polarization is performed with low poling voltage and short poling time, and it can ensure the PVDF-TrFE film with enhanced piezoelectric performances and uniform distribution among a large area of 200 mm2 × 200 mm2. The processing influence of drying, annealing, and poling on the crystalline properties and piezoelectric performances were investigated. Besides, the obtained PVDF-TrFE films present a good piezoelectric response to different extents of mechanical stimulations, which have great potential in energy harvesting applications.

A technique known as poling direction tuning is proposed to improve the material performance of piezoelectric based actuators. The piezoelectric material used in actuation applications of thin structures operates in d31 mode; hence, a method is devised to increase the value of piezoelectric coefficient, d31. Poling direction of the piezoelectric material is altered to activate d31, d33, and d15 modes, simultaneously. The performance of actuator is evaluated at different poling angle and poling angle for best performance is found. A simply supported plate with a layer of actuator piezoelectric material at the bottom is used for simulation studies. The computational technique used for calculating the time history of the structure is a finite-element method. The controlled shape using a fixed actuator voltage is calculated for different piezoelectric materials under consideration. Influence of poling angle on the shape control of the structure is scrutinized and is found to vary from material to material. A large enhancement due to poling tuning is seen in the properties of Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 (PMN-0.35PT), whereas other materials show very less improvement or even decay in the properties.

The present study proposes enhancement of harvested power and voltage by tuning the poling orientation in piezoelectric materials. The dependency of piezoelectric strain coefficients on performance is presented mathematically and to demonstrate the effect, a cantilever-based energy harvester having platinum substrate is considered with seven different materials. It is observed that PZT-2 shows an improvement of 598% in harvested power and 165% in voltage by poling tuning to 45°. Similar poling tuning helps PZT-7A to improve 325 and 106% in power and voltage generation, respectively. Huge improvement of 1425% in power and 290% for voltage is observed for PMN-0.35PT. PbTi03 shows a minimal improvement at poling angle of 30°. The performance of materials like Ba2NaNb5O15 and PVDF gets deteriorated with an increase in poling orientation. The peak values of power and voltage are observed at different poling angles for different piezoelectric materials. The least magnitudes of power and voltage generation occur at poling angle of 90° for any material system.

One century ago, ferroelectricity and then piezoelectricity were discovered using Rochelle salt crystals. Today, modern societies are invited to switch towards a resilient and circular economy model. In this context, this work proposes a method to manufacture piezoelectric devices made from agro-resources such as tartric acid and polylactide significantly reducing the energy budget without requiring any sophisticated equipement. These piezoelectric devices are manufactured by liquid phase epitaxy grown Rochelle salt (RS) crystals into a 3D printed poly(Lactic acid) (PLA) matrix being the artificial squared meshes which mimic the natural wood anatomy. This composite material can easily be produced in any fablab with renewable materials and at low processsing temperatures, reducing then the total energy consumed. Manufactured biodegradable samples are fully recyclable and have good piezoelectric properties without any pooling step. The measured piezoelectric coefficients of manufactured samples are higher than many piezoelectric polymers such as PVDF-TrFE.

Stabilization of the orthorhombic phase of HfO2 with La allows very high polarization and endurance. However, these properties have not been confirmed yet in films having thickness of less than 10 nm. We have grown (111)-oriented La (2 at%) doped epitaxial HfO2 films on SrTiO3(001) and Si(001) substrates, and we report on the thickness dependence of their ferroelectric properties. Films of less than 7 nm have a high remanent polarization of about 30 µC cm-2 , show slight wakeup, endurance of at least 1010 cycles and retention of more than 10 years, both latest properties measured at the same poling voltage. La-doped HfO2 films even as thin as 4.5 nm also show robust ferroelectric properties., Financial support from the Spanish Ministry of Science and Innovation, through the Severo Ochoa FUNFUTURE (CEX2019- 000917-S), MAT2017-85232-R (AEI/FEDER, EU), PID2020- 112548RB-I00 (AEI/FEDER, EU), and PID2019-107727RB-I00 (AEI/FEDER, EU) projects, from CSIC through the i-LINK (LINKA20338) program, and from Generalitat de Catalunya (2017 SGR 1377) is acknowledged. Project supported by a 2020 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation. IF acknowledges Ramón y Cajal contract RYC-2017- 22531. TS is financially supported by China Scholarship Council (CSC), grant No. 201807000104. TS work has been done as a part of his Ph.D. program in Materials Science at Universitat Autònoma de Barcelona. RB and GSG acknowledge the financial support from the European Commission through the project TIPS (No. H2020-ICT-02-2014-1-644453), from the French national research agency (ANR) through the projects DIAMWAFEL (No. ANR-15-CE08-0034), and MITO (No. ANR-17- CE05-0018), and from CNRS through the MITI interdisciplinary programs (project NOTE). They are also grateful to the joint laboratory INL-RIBER, P. Regreny, C. Botella and J. B. Goure for the MBE technical support on the Nanolyon technological platform.

The polycrystalline (Bi1−xSrx)(Fe1−xTix)O3 (x = 0.0, 0.05, 0.10, and 0.20) thin films were grown on Pt(111)/TiO2/SiO2/Si(100) substrates using chemical solution deposition technique. X-ray diffraction pattern revealed that pure BiFeO3 film is crystallized in rhombohedrally distorted crystal structure. However, the patterns for doped samples displayed a mixed-phase (rhombohedral + tetragonal) structure. The Raman studies revealed the emergence of B mode related to the tetragonal phase along with the modes corresponding to the rhombohedral phase in doped systems. The photovoltaic studies displayed a large photovoltaic response for the parent compound with an open-circuit voltage of 0.47 V. However, it showed a decrease in the photovoltaic response with an increase in composition x. The composition-dependent photovoltaic response could be correlated to the evolution of tetragonal phase fractions and the polarization. Additionally, the poling-dependent photovoltaic studies revealed the dominant role played by the polarization in comparison with the interface Schottky effect. This work gives an improved understanding of the ferroelectric photovoltaic mechanism and, therefore, may offer guidelines to design and optimize photovoltaic materials.

Piezoelectric nanogenerators (PENGs), as a promising solution to harvest mechanical energy from ambient environment, have attracted much attention over the past decade. Here, the core-shell structured BaTiO3@Carbon (BT@C) nanoparticles (NPs) were synthesized by a simple surface-modifying method and then used to fabricate the efficient PENGs with poly[(vinylidene fluoride)-co-trifluoroethylene] (P(VDF-TrFE)). The carbon shell with the uniform thickness of 10-15 nm can increase the content of the polar β phase in P(VDF-TrFE) and significantly enhance the interfacial polarization between BT NPs and the polymer matrix during the poling process. Out of all compositions, the 15 wt % BT@C/P(VDF-TrFE) PENG exhibited the optimal piezoelectric performance with an output voltage of ∼17 V and a maximum power of 14.3 μW under bending-releasing mode. More importantly, the PENG can also efficiently harvest other types of mechanical energy from human activities and exhibits stable output after 1500 bending-releasing cycles. When the PENG was bent and beat by bicycle spokes, a peak voltage of 16 V was generated, which can light up 12 white LEDs directly and charge the commercial capacitors. Our research provides a new strategy to fabricate flexible and efficient PENGs from a nanoscale viewpoint; it can be hopefully applied in energy-harvesting systems and wearable electric sensors.

Piezoelectric catalysis is the catalytic action driven by the force-electrical conversion of piezoelectric materials. In this paper, the piezoelectric activity of K0.5Na0.5NbO3 (KNN) was thoroughly investigated by annealing KNN at a series of temperatures and poling KNN under different electric-fields. With the application of an ultrasonification, the degradation activity for the Rhodamine B (RhB) dye molecules of the poled KNN was 253% higher than that of unpoled samples. The piezocatalytic activity of the poled KNN was significantly improved, which stemmed from the orderly ferroelectric domain to effectively reduce the recombination rate of the carriers by the built-in electric field. In addition, the superior piezocatalytic activity was achieved at KNN materials with the average grain size of ~0.29 μm, and after 160 min of mechanical vibration, the degradation rate of RhB (~5 mg/L) was as high as 95.7%. The high mechanical catalytic degradation rate of KNN materials reveals a bright application prospects in vibration catalytic degradation of organic pollutants.

We use a strategy to reduce the driving electric field of the relaxor 0.72Bi1/2Na1/2TiO3–0.28SrTiO3 (BNT–28ST) by introducing ferroelectric plate–type Bi1/2(Na0.78K0.22)1/2TiO3 (BNKT) particles. Consequently, 10 vol.% BNKT added BNT–28ST/BNKT (relaxor/ferroelectric) composite has delivered large normalized strain (Smax/Emax = 650 pm/V) under relatively low applied field of 2.5 kV/mm with the reduction in the poling field value to 36% compared to that of pure BNT–28ST ceramics. We demonstrated that such behavior comes from the stress induced effect at the boundary of the ferroelectric and relaxor materials due to their different nature (relaxor/ferroelectric). The generation of stress is expected from the ferroelectric (BNKT) to the relaxor (BNT–28ST) at the boundary. Thereby, field–dependent stress at relaxor/ferroelectric phase boundary is monitored proposing the reduction of the poling field due to the strain coupling mechanism. Our findings provide a pathway for reducing the poling field in BNT–based incipient piezoelectric ceramics.

A phosphosilicate glass (PSG) nonlinear film is prepared on a fused silica plate using plasma- enhanced chemical vapour deposition (PECVD) and thermal poling. Under all poling conditions, t...

The local ferroelectric domain structure of interconnected PVDF nano-dots with applied DC voltages of ± 10 V to ± 100 V is evaluated using various Piezo force microscopy (PFM) methods such as conventional PFM and Dynamic contact electrostatic force microscopy (DC-EFM). The self-assembled PVDF nano-dots are fabricated by using a spin coater method with 2 wt% of PVDF-DMSO solution. The polar gamma phase is found to be induced by the microstructural confinement of PVDF monomers and also reveals a strong ferroelectric nature after poling at different DC bias voltages. Poling with altered directions of the voltages renders a 180° phase reversal of PVDF domains. The local domain study depicts that each nano-dot is functioning as a single domain and switches as a whole. The single nano-dot switching signifies the potential of using the nano-dots for organic ferroelectric memory devices.

Seven Indian copper coins of the Kushan Period (1st–3rd centuries C.E.) were studied by multi-analytical techniques like WD-XRF, XRD, and FESEM-EDX to understand coin composition and the metallurgical process of fabrication. Analytical results reveal a compositional gradient in the distribution of elements between the external surface and the inner core of the coins, and the coins show isolated patches of surface mineralization leading to the formation of copper oxides, magnesium silicate, and silica. The analysis also showed the probable use of sulfide ore of copper for smelting and poor workmanship for this hoard. The impurities like sulfur, iron, silica, etc. could not be removed due to low firing temperature and improper poling during smelting. Striations have formed in the coin interior, with grain boundaries showing micro-cracks due to stress like punching or hammering with the die. The coins under study are a single-phase copper with associated impurities of Si, Al, P, and Mg in all coins and black spots of copper sulfide in coin inner core.

Pb-free (Ba0.88Ca0.12)(Ti0.94Sn0.06)O3 piezoelectric nanopowder was synthesized by solid-state reaction method. Piezoelectric properties were improved by two different approaches by optimizing poli...

In this work, BiFeO3-SrTiO3 (BFO-STO) solid solutions have been studied with particular emphasis on the problems related to conventional solid state synthesis of BFO-based systems. This method results in the formation of Bi-rich phase on grain boundaries and inhomogeneities inside the grains, similar to the core-shell microstructure previously reported for several BFO-based ceramic systems. Highly homogeneous and dense BFO-STO ceramics were prepared by mechanochemical activation-assisted synthesis. The as-prepared (x)BFO-(1-x)STO ceramics with 0.7 ≥ x≥ 0.575 exhibited high remanent polarization (30–50 μC cm−2) and a maximum d33 value of 69 pC N-1 at x = 0.625. It is shown that the compositions in the close proximity of the pseudocubic phase (x ≤ 0.6), however, exhibit pronounced aging of d33 coefficient with time, which is most probably related to the low stability of the domain structure after poling. The results of this study could further promote the processing optimization and compositional design of the BFO-STO and other BFO-based systems.

Multiferroic materials exhibit both ferroelectricity and ferromagnetism, and their magnetoelectric effects can be modulated by both magnetic and electric fields. Thus, they exhibit great potential in next-generation data memory devices. In this study, we implemented an eight-state memory prototype based on room-temperature single-phase multiferroic Sr 3 Co 2 Fe 24 O 41 . Data were imported by a poling procedure with electric and magnetic fields and derived visa electric polarization, P m , or the magnetoelectric coefficient, α m . This memory prototype possesses the advantages of a single structure, being easy to integrate, having a high storage capacity and a high stability. In this research, we enriched the magnetoelectric coupling performance of multiferroic materials, which demonstrates their possibilities for applications in the memory field.

Driven by environmental concerns and governmental directives, a sustained research effort in the last decade and half has led to the development of lead-free alternatives which can potentially replace the commercial lead-based piezoceramics in niche applications. Na0.5Bi0.5TiO3 (NBT)-based lead-free piezoceramics have found acceptance as promising lead-free transducers in high power ultrasonic devices. An issue of concern however is the low depolarization temperature which limits the device's tolerance for temperature rise during operation. While several strategies have been reported to improve thermal depolarization in NBT-based piezoceramics, there is a lack of consensus regarding the most fundamental factor/mechanism which enhances the depolarization temperature. In this paper we unravel a coupled microstructural-structural mechanism which controls the thermal depolarization in NBT-based piezoceramics. First, we demonstrate the phenomenon of a considerable increase in the depolarization temperature, without significantly losing the piezoelectric property in unmodified NBT by increasing the grain size. We then establish a grain size controlled structural mechanism and demonstrate that the rise in depolarization temperature is primarily associated with the bigger grains allowing relatively large lattice distortion to develop in the poling stabilized long range ferroelectric phase. We reconfirmed the validity of this mechanism in the model morphotropic phase boundary (MPB) composition 0.94Na0.5Bi0.5TiO3-0.06BaTiO3. For the sake of generalization, we demonstrate that the same mechanism is operative in another lead-based relaxor-ferroelectric system 0.62PbTiO3-0.38Bi(Ni0.5Hf0.5)O3. Our study provides the fundamental structural basis for understanding thermal depolarization delay in relaxor ferroelectric based piezoceramics.

Purpose Previous studies have found an acute performance improvement with longer pole lengths in double poling (DP) at low-to-moderate speeds. We investigated the influence of pole lengths (PL) on O2-cost, 3D kinematics, and performance in DP at moderate-to-high speeds before (Pre) and after (Post) eight training sessions with long poles on a rollerski treadmill. Methods Seven male and four female skiers completed tests with two different PLs (84 and 90% of body height). Submaximal O2-cost (1º; 4.5 [females] or 6 m s−1 [males]) and a peak velocity test (1º; ∼ 7.3 m s−1) were assessed before and after a six week training period. The training sessions consisted of 50 min of low-moderate intensity training and 4 × 10 s maximal sprints with PL90%. Results On average for all tests, PL84% induced 1.0 ± 1.0% higher peak velocity compared to PL90% (mean ± CI) with no difference in vertical displacement of center of mass (COMz). From Pre to Post, peak velocity and cycle time were increased and the displacement of COMz were reduced similarly for both PLs. At moderate speed, PL90% induced less displacement of COMz with subsequent 1.1 ± 0.7% lower O2-cost compared to PL84%. From Pre to Post, the O2-cost and COMz were reduced similarly for both PLs. Conclusions Longer PL than skiers self-selected lengths reduce O2-cost at moderate speeds, but induced lower peak velocity. Eight sessions of training with PL90% did not influence the difference between PL84% and PL90% on O2-cost, kinematics or peak velocity.