Flexible Lead-Free BiFeO3/PDMS-Based Nanogenerator as Piezoelectric Energy Harvester

Highly Sensitive and Fast Responding Flexible Force Sensors Using ZnO/ZnMgO Coaxial Nanotubes on Graphene Layers for Breath Sensing

The authors report the fabrication of highly sensitive, rapidly responding flexible force sensors using ZnO/ZnMgO coaxial nanotubes grown on graphene layers and their applications in sleep apnea monitoring. Flexible force sensors are fabricated by forming Schottky contacts to the nanotube array, followed by the mechanical release of the entire structure from the host substrate. The electrical characteristics of ZnO and ZnO/ZnMgO nanotube-based sensors are thoroughly investigated and compared. Importantly, in force sensor applications, the ZnO/ZnMgO coaxial structure results in significantly higher sensitivity and a faster response time when compared to the bare ZnO nanotube. The origin of the improved performance is thoroughly discussed. Furthermore, wireless breath sensing is demonstrated using the ZnO/ZnMgO pressure sensors with custom electronics, demonstrating the feasibility of the sensor technology for health monitoring and the potential diagnosis of sleep apnea.

High-performance piezoelectric energy harvesting in amorphous perovskite thin films deposited directly on a plastic substrate

Most reported thin-film piezoelectric energy harvesters have been based on cantilever-type crystalline ferroelectric oxide thin films deposited on rigid substrates, which utilize vibrational input sources. Herein, we introduce flexible amorphous thin-film energy harvesters based on perovskite CaCu3Ti4O12 (CCTO) thin films on a plastic substrate for highly competitive electromechanical energy harvesting. The room-temperature sputtering of CCTO thin films enable the use of plastic substrates to secure reliable flexibility, which has not been available thus far. Surprisingly, the resultant amorphous nature of the films results in an output voltage and power density of ~38.7 V and ~2.8 × 106 μW cm-3, respectively, which break the previously reported record for typical polycrystalline ferroelectric oxide thin-film cantilevers. The origin of this excellent electromechanical energy conversion is systematically explored as being related to the localized permanent dipoles of TiO6 octahedra and lowered dielectric constant in the amorphous state, depending on the stoichiometry and defect states. This is the leading example of a high-performance flexible piezoelectric energy harvester based on perovskite oxides not requiring a complex process for transferring films onto a plastic substrate.

Hybrid Triboelectric-Electromagnetic-Piezoelectric Wind Energy Harvester toward Wide-Scale IoT Self-Powered Sensing

Wind energy is the most promising alternative to fossil fuels as a clean, nonpolluting, and renewable source of energy. However, how to achieve stable and efficient harvesting of wind energy has been a major challenge. Here, a triboelectric-electromagnetic-piezoelectric hybrid wind energy harvester (TEP-WEH) based on the cantilever is proposed. The TEP-WEH achieves a power density of 62.79 mW (m3 rpm)-1 at a 3 m s-1 wind speed, attributable to a rational and optimized structural design. In addition, owing to the soft contact strategy of the TENG module, the TEP-WEH provides excellent durability and drivability. The harvester is demonstrated to successfully and continuously light a commercial lighting bulb rated at 5 W and provide an energy supply for self-powered sensing. This work provides an efficient solution for wind energy harvesting and wide-scale self-powered IoT sensing.

Dynamic ion exchange engineering bismuth ferrite-derived Bi2O2CO3 for rapid piezo-photocatalytic degradation of tetracycline

Piezoelectric materials can generate the built-in electric field under ultrasound assistance, which is beneficial to the separation of the photogenerated electron-hole pairs in photocatalysis. Meanwhile, the ultrasound stress usually leads to accelerate electron transfer and enhance catalytic activity. Thus, piezo-photocatalysis technique is believed to be one of the effective techniques for organic pollutant degradation. In this work, a binary piezoelectric integrated piezo-photocatalytic Z-Scheme heterojunction with bismuth ferrite (BFO) and bismuth oxycarbonate (Bi2O2CO3, BOC) based on the in situ production of Bi2O2CO3 on Bi25FeO40 surface in dichloromethane, where Bi25FeO40 was employed as piezoelectric materials and Bi source, CO2 dissolved in dichloromethane was used as carbon source. Under 60 min ultrasound and visible light irradiation, the optimal BFO/BOC presented a higher piezo-photocatalytic tetracycline (TC) degradation rate (95 %) than Bi25FeO40 (30 %) and Bi2O2CO3 (17 %). Moreover, the optimal BFO/BOC illustrated higher piezo-photocatalytic TC degradation rate under ultrasound and visible light irradiation than that under visible light condition and ultrasound condition, respectively. These results strongly demonstrated the synergistically piezo-photocatalytic degradation of TC by BFO and BOC. This work not only provides a novel piezo-photocatalyst for pollutant degradation, but also provides a novel method to prepare Bi2O2CO3-based piezo-photocatalytic composite catalyst.

3D-Printed piezoelectric nanogenerator with aligned graphitic carbon nitrate nanosheets for enhancing piezoelectric performance

Carbon-based materials are attracting increasing attention in the field of electronic devices because of their nontoxicity, availability, low cost, and easy synthesis. In this study, we fabricated a printed piezoelectric nanogenerator (PENG) based on a Polyvinylidene fluoride (PVDF) and graphitic carbon nitrate (g-C3N4) composite. Piezoelectric films with different weight percentages (0, 5, 7.5, 10, and 15 wt%) of g-C3N4 nanosheets (CNNSs) were fabricated. The PVDF/CNNS with 7.5% CNNS exhibited higher performance. We observed that the printing process aligned all CNNS along the x-axis, which improved stress management and eventually improved the performance of the fabricated device. The fabricated device exhibited better performance without pooling and generated a peak-to-peak voltage of 6.65 V with a current of 0.195 µA, corresponding to a power density of 4.86 µW/cm2. The device generated a voltage of up to 18.8 V with footsteps.

Performance study of a valveless piezoelectric pump with built-in semi-arc bluffbody antique tower channel

According to the bluffbody bypass effect, the irregular bluffbody can be used to improve the valveless piezoelectric pump. This paper designs a semi-arc bluffbody based on the bluffbody bypassing principle to alleviate the phenomenon of fluid backflow. The fluid passes through the shape of the antique tower to further enhance pumping efficiency. A positive fluid flow mechanism in the pump cavity is theoretically derived. The simulation of the velocity and pressure distribution in the tower-shaped channel of the pump cavity leads to the conclusion that the forward flow has better performance than the reverse flow, and the correctness of the theory is also verified. Experiments further proved that the volume of fluid in the forward direction was reduced by 10.8% when compared to the reverse direction. The study of the height of different semi-arc bluffbody and the angle of the tower trough shows that as the height and angle increase, the flow rate grows first and then reduces. The maximum flow rate is 243.83 ml/min when the bluffbody height is 4 mm and the channel angle is 20° (220 V, 85 Hz).

A high performance lead-free flexible piezoelectric nanogenerator based on AlFeO3nanorods interspersed in PDMS matrix for biomechanical energy scavenging to sustainably power electronics

Since lead-based piezoelectric nanogenerators (PENGs) possess serious health risks, environmental problems, proper disposal issues, and biocompatibility concerns, this work presents the fabrication of a flexible piezoelectric nanogenerator utilizing lead-free orthorhombic AlFeO₃nanorods for biomechanical energy scavenging to sustainably power electronics. Hydrothermal technique is used to synthesize the AlFeO₃nanorods and the PENG was fabricated on Indium tin oxide (ITO) coated Polyethylene terephthalate (PET) flexible film with AlFeO₃nanorods interspersed in polydimethylsiloxane (PDMS). transmission electron microscopy proved that the AlFeO₃nanoparticles are of nanorods shape. Through x-ray Diffraction, it is validated that AlFeO₃nanorods have orthorhombic phase and crystalline structure. A high piezoelectric charge coefficient (d₃₃) of 400 pm V^-1is obtained from the piezoelectric force microscopy of AlFeO₃nanorods. With optimized concentration of AlFeO₃in the polymer matrix, an open circuit voltage (V_OC) of 30.5 V, current density (J_C) of 0.7888±0.0001μA cm^-2and an instantaneous power density of 240.6 mW m^-2are obtained under the application of a force of 1.25 kgf. To investigate the nanogenerator's practical utility, the PENG is used for lighting multiple LEDs, charging of a capacitor and as a pedometer via biomechanical energy harvesting. Hence, it can be employed for developing various self-powered wearable electronics such as flexible skin, artificial cutaneous sensors, etc.

Piezoelectric Nanogenerators Based On BaTiO3/PDMS Composites for High-Frequency Applications

A series of highly flexible and environmentally friendly composites based on polydimethylsiloxane (PDMS) filled with 200 nm size ferroelectric BaTiO₃ (BTO) particles at different concentrations (from 7 to 23 vol %) have been fabricated by a simple dispersion method. The dielectric, piezoelectric, and ultrasonic properties have been studied. The ferroelectric state of BTO was confirmed by differential scanning calorimetry and ultrasonic spectroscopy. The addition of BTO into PDMS strongly affects the dielectric properties of the composites. At low temperatures close to 160 K, the PDMS matrix exhibits a dielectric anomaly related to a dynamic glass transition, which shifts to higher temperatures as the BTO content increases due to the strong interaction between polymer chains and nanoparticles. Ultrasonic measurements demonstrate the appearance of a piezoelectric voltage signal on a thin plate of the composite with the highest available filler concentration (23 vol %) under longitudinal stress applied by a 10 MHz ultrasonic wave. As a result, at room temperature, the detected signal is characterized by output voltage and specific stored energy values of 10 mV and 367.3 MeV/m², respectively, followed by a further increase with cooling to 35 mV at 150 K. The proposed BTO/PDMS composite system is thus a potential candidate for nanogenerators, namely, a simple, flexible, and lead-free device converting high-frequency (10 MHz) mechanical vibrations into electrical voltage.

Edge-Based Two-Dimensional α-In2Se3-MoS2 Ferroelectric Field Effect Device

Heterostructures based on two-dimensional materials offer the possibility to achieve synergistic functionalities, which otherwise remain secluded by their individual counterparts. Herein, ferroelectric polarization switching in α-In₂Se₃ has been utilized to engineer multilevel nonvolatile conduction states in a partially overlapping α-In₂Se₃-MoS₂-based ferroelectric semiconducting field effect device. In particular, we demonstrate how the intercoupled ferroelectric nature of α-In₂Se₃ allows to nonvolatilely switch between n-i and n-i-n type junction configurations based on a novel edge state actuation mechanism, paving the way for subnanometric scale nonvolatile device miniaturization. Furthermore, the induced asymmetric polarization enables enhanced photogenerated carriers' separation, resulting in an extremely high photoresponse of ∼1275 A/W in the visible range and strong nonvolatile modulation of the bright A- and B- excitonic emission channels in the overlaying MoS₂ monolayer. Our results show significant potential to harness the switchable polarization in partially overlapping α-In₂Se₃-MoS₂ based FeFETs to engineer multimodal, nonvolatile nanoscale electronic and optoelectronic devices.

Preparation of a SiO2 @Carbon Sphere/SiO2 -CNF Multilayer Self-standing Anode Prepared via an Alternate Electrospraying - Electrospinning Technique

The development of flexible lithium-ion batteries (FLIBs) is restrained by traditional rigidity anodes. Carbon nanofiber (CNF) is a promising anode material owing to its high specific surface and superior ion transportation capability. However, the low amount of active material loaded on the CNFs and the poor stability during long cycling restrain their applications. Herein, a SiO₂ @carbon sphere/SiO₂ -CNF self-standing anode was prepared via alternate electrospraying-electrospinning. The SiO₂ content of the anode was increased through the electrospraying SiO₂ @carbon spheres layers, and the electrospun SiO₂ -CNFs as robust layers enhanced the stability of the anode. The self-standing anode exhibited 633 mA h g^-1 in the initial cycle and maintained a 70% Coulomb efficiency for 1000 cycles at a current density of 100 mA g^-1 , which could be applied in FLIB and other electrochemical storage devices.

Wireless Self-Powered Optogenetic System for Long-Term Cardiac Neuromodulation to Improve Post-MI Cardiac Remodeling and Malignant Arrhythmia

Autonomic imbalance is an important characteristic of patients after myocardial infarction (MI) and adversely contributes to post-MI cardiac remodeling and ventricular arrhythmias (VAs). A previous study proved that optogenetic modulation could precisely inhibit cardiac sympathetic hyperactivity and prevent acute ischemia-induced VAs. Here, a wireless self-powered optogenetic modulation system is introduced, which achieves long-term precise cardiac neuromodulation in ambulatory canines. The wireless self-powered optical system based on a triboelectric nanogenerator is powered by energy harvested from body motion and realized the effective optical illumination that is required for optogenetic neuromodulation (ON). It is further demonstrated that long-term ON significantly mitigates MI-induced sympathetic remodeling and hyperactivity, and improves a variety of clinically relevant outcomes such as improves ventricular dysfunction, reduces infarct size, increases electrophysiological stability, and reduces susceptibility to VAs. These novel insights suggest that wireless ON holds translational potential for the clinical treatment of arrhythmia and other cardiovascular diseases related to sympathetic hyperactivity. Moreover, this innovative self-powered optical system may provide an opportunity to develop implantable/wearable and self-controllable devices for long-term optogenetic therapy.

Improvements in piezoelectric and energy harvesting properties with a slight change in depolarization temperature in modified BNKT ceramics by a simple technique

For many BNT-based ceramics, an attempt to increase the piezoelectric properties usually results in a decrease in depolarization temperature (T _d). This trend limits the applications of the materials. Many previous experiments have used different methods to enhance the piezoelectric properties and improve the T _d characteristic. In this study, we demonstrated a simple technique (thermal annealing) to enhance the piezoelectric properties with a very slight decrease in T _d by ∼2 °C for a modified BNKT ceramic (BNKT doped with ZnO). Other phase transition characteristic temperatures of the studied ceramics were also slightly changed. The optimum dielectric (ε _r = 651, tan δ = 0.0503, T _F-R = 167.38 °C, T _m = 305.41 °C, ε _max = 5551, T _B = 367.15 °C, T _d = 155.98 °C, and γ = 1.43), ferroelectric (P _max = 41.28 μC cm^-2, P _r = 35.85 μC cm^-2, E _c = 42.60 kV cm^-1 and R _sq = 1.42), piezoelectric (d ₃₃ = 198 pC N^-1, k _p = 0.598, and g ₃₃ = 34.35 × 10^-3 Vm N^-1), and energy harvesting (FoM = 6.80 pm² N^-1) were obtained for the 8 h annealed ceramic. Furthermore, higher energy harvesting properties (which were 32% higher than that of the unannealed ceramic) were obtained after employing this technique.

Flexible Lead-Free Piezoelectric Ba0.94Sr0.06Sn0.09Ti0.91O3/PDMS Composite for Self-Powered Human Motion Monitoring

Piezoelectric wearable electronics, which can sense external pressure, have attracted widespread attention. However, the enhancement of electromechanical coupling performance remains a great challenge. Here, a new solid solution of Ba_1-xSr_xSn_0.09Ti_0.91O₃ (x = 0.00~0.08) is prepared to explore potential high-performance, lead-free piezoelectric ceramics. The coexistence of the rhombohedral phase, orthorhombic phase and tetragonal phase is determined in a ceramic with x = 0.06, showing enhanced electrical performance with a piezoelectric coefficient of d₃₃~650 pC/N. Furthermore, Ba_0.94Sr_0.06Sn_0.09Ti_0.91O₃ (BSST) is co-blended with PDMS to prepare flexible piezoelectric nanogenerators (PENGs) and their performance is explored. The effects of inorganic particle concentration and distribution on the piezoelectric output of the composite are systematically analyzed by experimental tests and computational simulations. As a result, the optimal V_OC and I_SC of the PENG (40 wt%) can reach 3.05 V and 44.5 nA, respectively, at 138.89 kPa, and the optimal sensitivity of the device is up to 21.09 mV/kPa. Due to the flexibility of the device, the prepared PENG can be attached to the surface of human skin as a sensor to monitor vital movements of the neck, fingers, elbows, spine, knees and feet of people, thus warning of dangerous behavior or incorrect posture and providing support for sports rehabilitation.

Flexible Piezoelectric and Pyroelectric Nanogenerators Based on PAN/TMAB Nanocomposite Fiber Mats for Self-Power Multifunctional Sensors

Self-powered wearable electronics to convert mechanical and thermal energy into electrical energy are important for biomedical monitoring, which highly require good flexibility, comfortability, signal sensitivity, and accuracy. In this work, composite nanofiber mats of polyacrylonitrile (PAN) and trimethylamine borane (TMAB) were prepared by electrospinning, which exhibited excellent piezoelectric and pyroelectric abilities in harvesting mechanical and thermal energy. The PAN/TMAB-4 nanofiber mats not only generated a high voltage of up to 2.56 V and a high power of 0.19 μW upon shape deformation but also exhibited linear voltage response to thermal gradient. The hybrid piezoelectric and pyroelectric output signals were successfully integrated together and have been applied to precisely monitor human vital signs, including elbow bending angles, foot posture, and breathing status, in real time by attaching the flexible sensors to proper human body parts. Overall, good flexibility, bifunctional sensing ability, and self-power make PAN-/TMAB-type sensors very attractive in fabricating high-performance electronics for detecting motion, monitoring health, and making portable microelectronics.

Defect-Induced Self-Poling in a W18O49/PVDF Piezoelectric Energy Harvester

W₁₈O₄₉ nanostructures, previously used for electrocatalysis, energy storage, electrochromic, and gas sensing applications, are incorporated in poly(vinylidene fluoride) (PVDF) in this work for mechanical energy-harvesting applications. X-ray diffraction spectroscopy (XRD), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, differential scanning calorimetry (DSC), and the polarization-electric (P-E) field loop test prompts the addition of W₁₈O₄₉ nanorods in PVDF nucleates and stabilizes the piezoelectric polar γ-phase in the nanocomposite. Electrochemical experiments were employed for the first time to relate the event of the evolution of crystalline phases in PVDF to the transfer of electrons to the electrolyte from PVDF using the data from cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). High dielectric constant (ε') and low dielectric loss (ε″) values were obtained proportionately for different weight percentage additions of W₁₈O₄₉ nanorods in PVDF. DSC was employed to study the crystallization kinetics of γ-phase evolution. Piezoresponse force microscopy (PFM) was used to compare the piezoelectric responses from the PVDF nanocomposites. The W₁₈O₄₉/PVDF nanocomposite could generate a peak open circuit voltage of ∼6 V and a peak short circuit current of ∼700 nA. The W₁₈O₄₉/PVDF nanocomposite could light two commercial blue-light-emitting diodes (LEDs) with hand impulse imparting.

Polydimethylsiloxane/BaTiO3 Nanogenerators with a Surface-Assembled Mosaic Structure for Enhanced Piezoelectric Sensing

Incorporation of inorganic piezoelectric ceramic nanoparticles into a highly elastic polymer matrix is an effective method to develop self-powered sensors and energy harvesters. Herein, a piezoelectrically enhanced nanogenerator (NG) obtained by dispersing lead-free BaTiO₃ piezoelectric nanoparticles into elastic polydimethylsiloxane and further surface-modifying with a neoteric mosaic structure for self-powered sensing is proposed. The composites fabricated through this facile and low-cost approach exhibit enhanced voltage by a factor of 1.5 relative to those without modification and display improved mechanical properties with increased elongation at break (failure strain of 150%). The improved performance is mainly attributed to the embossed mosaic structure on the surface, which is theoretically verified by multiphysics simulation. The NGs exhibit highly sensitive and stable piezoelectric output under contact and noncontact working modes and can be applied to detect human vital signs, including bending of fingers and wrists, and various breathing activities, demonstrating wide applications in flexible and smart wearable electronics. The design of the neoteric mosaic structure could be extended to other composite-based NGs, offering significant advantages for the rational design of flexible electronics.

Development of a resonant piezohydraulic hybrid actuator

This paper proposes a piezohydraulic hybrid actuator driven by a resonant vibrator based on two rhombic micro-displacement amplifiers. The resonant piezohydraulic hybrid actuator consists of a resonant piezoelectric vibrator, a pump body, a manifold, a return valve, and an output cylinder. The vibration mode of the piezoelectric vibrator is simulated, and the working principle of the resonant piezohydraulic hybrid actuator is depicted. Then, the performance of the piezohydraulic hybrid actuator is experimentally investigated, and the effects of exciting frequency, exciting voltage, and bias pressure are analyzed. The results demonstrate that the hybrid actuator performs the best when the exciting frequency is near the resonant frequency; meanwhile, the higher the exciting voltage, the better the performance. Moreover, it indicates that a larger bias pressure will bring a larger reaction force to the vibrator and reduce the performance of the actuator system. The maximum blocked force and no-load velocity are 378 N and 4.8 mm/s, respectively, when the bias pressure is 1.5 MPa and the exciting voltage is 500 V_pp.

Enhanced Output Performance of a Flexible Piezoelectric Nanogenerator Realized by Lithium-Doped Zinc Oxide Nanowires Decorated on MXene

A flexible piezoelectric composite is composed of a polymer matrix and piezoelectric ceramic fillers to achieve good mechanical flexibility and processability. The overall piezoelectric performance of a composite is largely determined by the piezoelectric filler inside. Thus, different dispersion methods and additives that can promote the dispersion of piezoelectric ceramics and optimal composite structures have been actively investigated. However, relatively few attempts have been made to develop a filler that can effectively contribute to the performance enhancement of piezoelectric devices. In the present work, we introduce the fabrication and performance of the composite piezoelectric devices composed of Li-doped ZnO nanowires (Li: ZnO NWs) grown on the surface of MXene (Ti3C2) via the hydrothermal process. Through this approach, a semiconductor-metal hybrid structure is formed, increasing the overall permittivity. Moreover, the Ti3C2 layer can serve as a local ground in the composite so that the ferroelectric phase-transformed Li: ZnO NWs grown on its surface can be more effectively polarized during the poling process. In addition, the NW-covered surface of Ti3C2 prevents the aggregation of metallic Ti3C2 particles, promoting a more uniform electric field distribution during the poling process. As a result, the output performance of the piezoelectric nanogenerator (PENG) fabricated with a Li: ZnO NW/Ti3C2 composite was greatly improved compared to that of the devices fabricated with Li: ZnO NWs without the Ti3C2 platform. Specifically, the Li: ZnO NW/Ti3C2 composite piezoelectric nanogenerator (PENG) demonstrated a twofold higher output power density (∼9 μW/cm2) compared with the values obtained from the PENG devices based on Li: ZnO NWs. The approach introduced in this work can be easily adopted for an effective ferroelectric filler design to improve the output performance of the piezoelectric composite.

Ferroelectric Polymer Nanofibers Reminiscent of Morphotropic Phase Boundary Behavior for Improved Piezoelectric Energy Harvesting

Ferroelectric and piezoelectric polymers have attracted great attention from many research and engineering fields due to its mechanical robustness and flexibility as well as cost-effectiveness and easy processibility. Nevertheless, the electrical performance of piezoelectric polymers is very hard to reach that of piezoelectric ceramics basically and physically, even in the case of the representative ferroelectric polymer, poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)). Very recently, the concept for the morphotropic phase boundary (MPB), which has been exclusive in the field of high-performance piezoelectric ceramics, has been surprisingly confirmed in P(VDF-TrFE) piezoelectric copolymers by the groups. This study demonstrates the exceptional behaviors reminiscent of MPB and relaxor ferroelectrics in the feature of widely utilized electrospun P(VDF-TrFE) nanofibers. Consequently, an energy harvesting device that exceeds the performance limitation of the existing P(VDF-TrFE) materials is developed. Even the unpoled MPB-based P(VDF-TrFE) nanofibers show higher output than the electrically poled normal P(VDF-TrFE) nanofibers. This study is the first step toward the manufacture of a new generation of piezoelectric polymers with practical applications.

Design and modeling of a piezo-driven three-dimensional bridge-type amplification mechanism with input/output guiding constraint

Owing to the limited stroke of piezo stacks, compliant amplification mechanisms are widely employed to magnify the displacement of piezoelectric actuators for emerging applications in precision engineering. In this study, a three-dimensional (3D) bridge-type amplification mechanism composed of two serially connected bridge-type amplifiers with a novel constraint form has been developed. The parallel guiding beams mounted at the input and output ends significantly increase the lateral stiffness and minimize parasitic displacements for higher accuracy. Furthermore, a new theoretical model is established to predict the magnification behavior of the 3D amplifier that takes into account the displacement loss caused by the coupling of the two bridge-type amplifiers. The accuracy of this model and the mechanical performance of the developed amplifier are verified by conducting finite element simulations and experimental studies on the manufactured prototypes.

Ultra-Stable and Durable Piezoelectric Nanogenerator with All-Weather Service Capability Based on N Doped 4H-SiC Nanohole Arrays

Ultra-stable piezoelectric nanogenerator (PENG) driven by environmental actuation sources with all-weather service capability is highly desirable. Here, the PENG based on N doped 4H-SiC nanohole arrays (NHAs) is proposed to harvest ambient energy under low/high temperature and relative humidity (RH) conditions. Finite element method simulation of N doped 4H-SiC NHAs in compression mode is developed to evaluate the relationship between nanohole diameter and piezoelectric performance. The density of short circuit current of the assembled PENG reaches 313 nA cm^-2, which is 1.57 times the output of PENG based on N doped 4H-SiC nanowire arrays. The enhancement can be attributed to the existence of nanohole sidewalls in NHAs. All-weather service capability of the PENG is verified after being treated at -80/80 ℃ and 0%/100% RH for 50 days. The PENG is promising to be widely used in practice worldwide to harvest biomechanical energy and mechanical energy.

Prospects of Wireless Energy-Aware Sensors for Smart Factories in the Industry 4.0 Era

Advanced sensors are becoming essential for modern factories, as they contribute by gathering comprehensive data about machines, processes, and human-machine interaction. They play an important role in improving manufacturing performance, in-factory logistics, predictive maintenance, supply chains, and digitalization in general. Wireless sensors and wireless sensor networks (WSNs) provide, in this context, significant advantages as they are flexible and easily deployable. They have reduced installation and maintenance costs and contributed by reducing cables and preinstalled infrastructure, leading to improved reliability. WSNs can be retrofitted in machines to provide direct information from inside the processes. Recent developments have revealed exciting possibilities to enhance energy harvesting (EH) and wireless energy transmission, enabling a reliable use of wireless sensors in smart factories. This review provides an overview of the potential of energy aware WSNs for industrial applications and shows relevant techniques for realizing a sustainable energy supply based on energy harvesting and energy transfer. The focus is on high-performance converter solutions and improvement of frequency, bandwidth, hybridization of the converters, and the newest trends towards flexible converters. We report on possibilities to reduce the energy consumption in wireless communication on the node level and on the network level, enabling boosting network efficiency and operability. Based on the existing technologies, energy aware WSNs can nowadays be realized for many applications in smart factories. It can be expected that they will play a great role in the future as an enabler for digitalization in this decisive economic sector.

A Flexible Energy Harvester from an Organic Ferroelectric Ammonium Salt

Organic ferroelectrics due to their low cost, easy preparation, light weight, high flexibility and phase stability are gaining tremendous attention in the field of portable electronics. In this work, we report the synthesis, structure and ferroelectric behavior of a two-component ammonium salt 2, containing a bulky [Bn(4-BrBn)NMe₂ ]⁺ (Bn=benzyl and 4-BrBn=4-bromobenzyl) cation and tetrahedral (BF₄ )^- anion. The structural analysis revealed the presence of rich non-classical C-H⋅⋅⋅F and C-H⋅⋅⋅Br interactions in this molecule that were quantified by Hirshfeld surface analysis. The polarization (P) vs. electric field (E) hysteresis loop measurements on 2 gave a remnant polarization (P_r ) of 14.4 μC cm^-2 at room temperature. Flexible polymer composites with various (5, 10, 15 and 20) weight percentages (wt%) of 2 in thermoplastic polyurethane (TPU) were prepared and tested for mechanical energy harvesting applications. A notable peak-to-peak output voltage of 20 V, maximum current density of 1.1 μA cm^-2 and power density of 21.1 μW cm^-2 were recorded for the 15 wt% 2-TPU composite device. Furthermore, the voltage output generated from this device was utilized to rapidly charge a 100 μF capacitor, with stored energies and measured charges of 156 μJ and 121.6 μC, respectively.

Magnetorheological Elastomer-Based Self-Powered Triboelectric Nanosensor for Monitoring Magnetic Field

The adaptable monitoring of the ubiquitous magnetic field is of great importance not only for scientific research but also for industrial production. However, the current detecting techniques are unwieldly and lack essential mobility owing to the complex configuration and indispensability of the power source. Here, we have constructed a self-powered magnetic sensor based on a subtle triboelectric nanogenerator (TENG) that consists of a magnetorheological elastomer (MRE). This magnetic sensor relies on triboelectrification and electrostatic induction to produce electrical signals in response to the MRE's deformation induced by the variational magnetic field without using any external power sources. The fabricated magnetic sensor shows a fast response of 80ms and a desirable sensitivity of 31.6 mV/mT in a magnetic field range of 35-60 mT as well as preliminary vectorability enabled by the multichannel layout. Our work provides a new route for monitoring dynamic magnetic fields and paves a way for self-powered electric-magnetic coupled applications.

Flexible Perovskite CsPbBr3 Light Emitting Devices Integrated with GaP Nanowire Arrays in Highly Transparent and Durable Functionalized Silicones

The architecture of transparent contacts is of utmost importance for creation of efficient flexible light-emitting devices (LEDs) and other deformable electronic devices. We successfully combined the newly synthesized transparent and durable silicone rubbers and the semiconductor materials with original fabrication methods to design LEDs and demonstrate their significant flexibility. We developed electrodes based on a composite GaP nanowire-phenylethyl-functionalized silicone rubber membrane, improved with single-walled carbon nanotube films for a hybrid poly(ethylene oxide)-metal-halide perovskite (CsPbBr₃) flexible green LED. The proposed approach provides a novel platform for fabrication of flexible hybrid optoelectronic devices.

Enhanced dielectric, ferroelectric, energy storage and mechanical energy harvesting performance of ZnO-PVDF composites induced by MWCNTs as an additive third phase

The present work highlights an attempt of fabricating a nanocomposite by the addition of multi-walled carbon nanotubes (MWCNTs) as a third phase into flexible ZnO-poly(vinylidene fluoride) (ZnO-PVDF) composites. MWCNTs played a very important role in distributing ZnO fillers in the PVDF matrix more homogeneously and increased the connection capability. Enhancement of the piezoelectric phase, dielectric permittivity, ferroelectric polarization, energy storage density and mechanical energy harvesting performance of ZnO-PVDF composites after the addition of MWCNTs was confirmed from the respective characterization studies. The sensing capability was demonstrated by the generation of ∼22 V ac output voltage through the application of human finger tapping on 15 wt% ZnO and a 0.1 wt% MWCNT-loaded PVDF (15PZNT) based composite film. The rectified voltage from the fabricated 15PZNT film was used to charge a 10-μF capacitor up to ∼3 V which was used for the illumination of 30 commercial LEDs. The maximum power density from the film was found to be 21.41 μW cm^-2 at 4 MΩ load resistance. The effect of the addition of MWCNTs was also verified by simulation using COMSOL Multiphysics software.

Piezoelectric Materials for Energy Harvesting and Sensing Applications: Roadmap for Future Smart Materials

Piezoelectric materials are widely referred to as "smart" materials because they can transduce mechanical pressure acting on them to electrical signals and vice versa. They are extensively utilized in harvesting mechanical energy from vibrations, human motion, mechanical loads, etc., and converting them into electrical energy for low power devices. Piezoelectric transduction offers high scalability, simple device designs, and high-power densities compared to electro-magnetic/static and triboelectric transducers. This review aims to give a holistic overview of recent developments in piezoelectric nanostructured materials, polymers, polymer nanocomposites, and piezoelectric films for implementation in energy harvesting. The progress in fabrication techniques, morphology, piezoelectric properties, energy harvesting performance, and underpinning fundamental mechanisms for each class of materials, including polymer nanocomposites using conducting, non-conducting, and hybrid fillers are discussed. The emergent application horizon of piezoelectric energy harvesters particularly for wireless devices and self-powered sensors is highlighted, and the current challenges and future prospects are critically discussed.

Self-powered technology based on nanogenerators for biomedical applications

Biomedical electronic devices have enormous benefits for healthcare and quality of life. Still, the long-term working of those devices remains a great challenge due to the short life and large volume of conventional batteries. Since the nanogenerators (NGs) invention, they have been widely used to convert various ambient mechanical energy sources into electrical energy. The self-powered technology based on NGs is dedicated to harvesting ambient energy to supply electronic devices, which is an effective pathway to conquer the energy insufficiency of biomedical electronic devices. With the aid of this technology, it is expected to develop self-powered biomedical electronic devices with advanced features and distinctive functions. The goal of this review is to summarize the existing self-powered technologies based on NGs and then review the applications based on self-powered technologies in the biomedical field during their rapid development in recent years, including two main directions. The first is the NGs as independent sensors to converts biomechanical energy and heat energy into electrical signals to reflect health information. The second direction is to use the electrical energy produced by NGs to stimulate biological tissues or powering biomedical devices for achieving the purpose of medical application. Eventually, we have analyzed and discussed the remaining challenges and perspectives of the field. We believe that the self-powered technology based on NGs would advance the development of modern biomedical electronic devices.

Theoretical and experimental analyses of a legged piezoelectric bending actuator with shoe soles made of polyimide composites

Friction materials form a critical component of piezoelectric actuators, and wear of the material affects output and service life of the actuator. This paper examines the influence of polyimide (PI) composites when used as a friction material on the performance of a legged piezoelectric bending actuator. We design and manufacture demountable shoe soles, made of a novel PI-based friction material, for an actuator. A Coulomb friction model is also established to determine the behavior resulting from contact-induced friction between the surface and the actuator. Reciprocating wear tests involving an insulation rubber pad against phosphor bronze and PI composites as friction materials yielded average friction coefficients of 0.21 and 0.28, respectively. We also found that PI composites have higher wear resistance than phosphor bronze, with a specific wear rate of 1.36 × 10^-4 mm³/N m. The results of experiments and simulations indicate that the shoe soles made of PI composites reduced the actuator's driving frequency and vibrational amplitude, but they did not affect the principle of locomotion of the actuator. Furthermore, the operational stability of the actuator improved by 46.8% by using the demountable shoe soles made of PI composites, albeit at the cost of its velocity and load capacity. This work has guiding significance for the design and selection of friction materials for piezoelectric actuators.

Superflexible and Lead-Free Piezoelectric Nanogenerator as a Highly Sensitive Self-Powered Sensor for Human Motion Monitoring

For traditional piezoelectric sensors based on poled ceramics, a low curie temperature (T_c) is a fatal flaw due to the depolarization phenomenon. However, in this study, we find the low T_c would be a benefit for flexible piezoelectric sensors because small alterations of force trigger large changes in polarization. BaTi_0.88Sn_0.12O₃ (BTS) with high piezoelectric coefficient and low T_c close to human body temperature is taken as an example for materials of this kind. Continuous piezoelectric BTS films were deposited on the flexible glass fiber fabrics (GFF), self-powered sensors based on the ultra-thin, superflexible, and polarization-free BTS-GFF/PVDF composite piezoelectric films are used for human motion sensing. In the low force region (1-9 N), the sensors have the outstanding performance with voltage sensitivity of 1.23 V N^-1 and current sensitivity of 41.0 nA N^-1. The BTS-GFF/PVDF sensors can be used to detect the tiny forces of falling water drops, finger joint motion, tiny surface deformation, and fatigue driving with high sensitivity. This work provides a new paradigm for the preparation of superflexible, highly sensitive and wearable self-powered piezoelectric sensors, and this kind of sensors will have a broad application prospect in the fields of medical rehabilitation, human motion monitoring, and intelligent robot.

Elastic-Modulus-Dependent Macroscopic Supramolecular Assembly of Poly(dimethylsiloxane) for Understanding Fast Interfacial Adhesion

Macroscopic supramolecular assembly (MSA) is a new concept of supramolecular science with an emphasis on noncovalent interactions between macroscopic building blocks with sizes exceeding 10 μm. Owing to a similar noncovalently interactive nature with the phenomena of bioadhesion, self-healing, etc. and flexible features in tailoring and designing modular building blocks, MSA has been developed as a simplified model to interpret interfacial phenomena and a facile method to fabricate supramolecular materials. However, at this early stage, MSA has always been limited to hydrogel materials, which provide flowability for high molecular mobility to the interfacial binding. The extension to a wide range of materials for MSA is desired. Herein, we have developed a strategy of adjusting intrinsic properties (e.g., elastic modulus) of nonhydrogel materials to realize MSA, which could broaden the material choices of MSA. Using the widely used elastomer of poly(dimethylsiloxane) (PDMS) as building blocks, we have demonstrated the elastic-modulus-dependent MSA of PDMS based on the host/guest molecular recognition between supramolecular groups of β-cyclodextrin and adamantane. In the varied elastic modulus range of 0.38 to 3.84 MPa, we obtained the trend of the MSA probability decreasing from 100% at 0.38 MPa to 0% at 3.84 MPa. Meanwhile, in situ measurements of interactive forces between PDMS building blocks have supported the observed assembly phenomena. The underlying reasons are interpreted with the low-modulus flexible surfaces favoring for high molecular mobility to achieve interactions between multiple sites at the interface based on the theory of multivalency. Taken together, we have demonstrated the feasibility of directly adjusting the modulus of bulk materials to realize MSA of nonhydrogel materials, which may provide clues to the fast wet adhesion and new solutions to the additive manufacture of elastomer materials.

Design and Optimization of Piezoelectric-Powered Portable UV-LED Water Disinfection System

Due to the environmental pollution threatening human life, clean water accessibility is one of the major global issues. In this context, in literature, there are many portable water disinfection systems utilizing ultraviolet (UV) radiation. UV water disinfection systems employ piezoelectric-based electric power along with UV light-emitting diode (LED) sources. This paper elaborates on the detailed design and parametric optimization of a portable UV disinfection system. The proposed system aims to generate piezoelectric harvesting-based electrical power simply by shaking, and the generated power is then used to supply UV-LEDs for water disinfection. To this end, overall system parameters along with a physical-mathematical model of mechanical, electrical and biochemical aspects of the system are fully developed. Moreover, the main design parameters of the developed model are derived for optimal operation of the system by employing Genetic Algorithm (GA). Finally, optimal design parameters were identified for three different cost scenarios. The model can further be improved for practical implementation and mass production of the system.

Anisotropic Triboelectric Nanogenerator Based on Ordered Electrospinning

As a new type of energy harvesting and conversion device, nanogenerator can collect various energies from daily life environment and convert it into electrical energy; it has great flexibility and can provide power for small independent systems. The triboelectric nanogenerator (TENG) is widely concerned because of their high output energy density. However, in the case of an open circuit, there will be static charge accumulation on the friction surface. The high voltage generated by the accumulation of charge on the surface will bring the risk of electrostatic discharge (ESD) to nearby circuits. To solve this problem, we have used the ordered polymer nanofibers obtained by electrospinning technology to form an anisotropic triboelectric nanogenerator with better tensile properties and mechanical strength than disordered electrospinning TENG. By adjusting the effective contact area, the voltage output in the longitudinal direction is one order of magnitude higher than the voltage output in the lateral direction. When not in use, the nanogenerator can be rotated 90°, so static charge accumulation and circuit burnout can be avoided, providing an easy method of preventing ESD in a wearable environment.

Frequency dependent energy storage and dielectric performance of Ba-Zr Co-doped BiFeO3 loaded PVDF based mechanical energy harvesters: effect of corona poling

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.

Enhancement of dielectric and electric-field-induced polarization of bismuth fluoride nanoparticles within the layered structure of carbon nitride

A single-pot, wet chemical method has been reported for the synthesis of bismuth fluoride nanoparticles (BF) and functionalized BF within the network of carbon nitride (BFCN). In BFCN, a structural transformation of BF, from cubic to pseudo-cubic (as evidenced by Rietveld refinement analysis), confirmed the contribution of carbon nitride (CN) on functionalization. The effect of functionalization of BF has been investigated through dielectric and field-induced polarization studies under different temperature and frequency conditions. Enhancement of dielectric constant values was noticed in BFCN as compared with BF system, in the order of 2.5 (30 °C) and 8.0 (100 °C) at 100 Hz. Fatigue-free maximum polarization values of 0.041 µC/cm2 and 0.054 µC/cm2, under the electric field of 5 kV/mm, were achieved for BF and BFCN samples, respectively, for 5 × 103 cycles.

Template-free fabrication of BiFeO3 nanorod arrays: multiferroic and photo-electrochemical performances

BiFeO₃ (BFO) has been widely investigated in many forms and morphologies because of its combined multiferroic and photovoltaic properties. However, direct growth of vertically aligned BFO nanorods on an underlying substrate has remained a challenge. In this work, we report template free growth of BiFeO₃ nanorod arrays on fluorine doped tin oxide coated glass substrate. This has been achieved by a two-step process, in which FeOOH nanorods are grown by chemical bath deposition and converted into BFO using bismuth (Bi) coating by physical vapour deposition (PVD). Both DC sputtering and thermal evaporation are attempted under PVD and the results suggest that Bi deposited by DC sputtering leads to well-defined BFO nanorods, which show superior performance in both multiferroic and photoelectrochemical studies. Piezoelectric force microscopy data shows the signature butterfly loop that confirms piezoelectric behaviour with a d ₃₃ value of 8 pmV^-1 in the BFO nanorods grown by DC sputtering. Further, the M-H hysteresis curve for the same samples reveals a remanent magnetization (M_r) value of 0.54 emu cc^-1 and antiferromagnetic nature at room temperature. Finally, a stable photocurrent density of 0.05 mA cm^-2 is achieved at 0.8 V vs Ag/AgCl under 1 Sun illumination. This work opens up new avenues for BFO in applications involving 1D nanostructures.

Progress in lead-free piezoelectric nanofiller materials and related composite nanogenerator devices

Current piezoelectric device systems need a significant reduction in size and weight so that electronic modules of increasing capacity and functionality can be incorporated into a great range of applications, particularly in energy device platforms. The key question for most applications is whether they can compete in the race of down-scaling and an easy integration with highly adaptable properties into various system technologies such as nano-electro-mechanical systems (NEMS). Piezoelectric NEMS have potential to offer access to a parameter space for sensing, actuating, and powering, which is inflential and intriguing. Fortunately, recent advances in modelling, synthesis, and characterization techniques are spurring unprecedented developments in a new field of piezoelectric nano-materials and devices. While the need for looking more closely at the piezoelectric nano-materials is driven by the relentless drive of miniaturization, there is an additional motivation: the piezoelectric materials, which are showing the largest electromechanical responses, are currently toxic lead (Pb)-based perovskite materials (such as the ubiquitous Pb(Zr,Ti)O3, PZT). This is important, as there is strong legislative and moral push to remove toxic lead compounds from commercial products. By far, the lack of viable alternatives has led to continuing exemptions to allow their temporary use in piezoelectric applications. However, the present exemption will expire soon, and the concurrent improvement of lead-free piezoelectric materials has led to the possibility that no new exemption will be granted. In this paper, the universal approaches and recent progresses in the field of lead-free piezoelectric nano-materials, initially focusing on hybrid composite materials as well as individual nanoparticles, and related energy harvesting devices are systematically elaborated. The paper begins with a short introduction to the properties of interest in various piezoelectric nanomaterials and a brief description of the current state-of-the-art for lead-free piezoelectric nanostructured materials. We then describe several key methodologies for the synthesis of nanostructure materials including nanoparticles, followed by the discussion on the critical current and emerging applications in detail.

Development of Sn-doped ZnO based ecofriendly piezoelectric nanogenerator for energy harvesting application

In this work, we have a demonstrated zinc oxide (ZnO) polymer-based ecofriendly piezoelectric nanogenerator (PENG) on a paper substrate for an energy harvesting application. The ZnO thin film is developed on the paper substrate, where different doping concentrations of Sn have been investigated systematically to validate the effect of doping towards enhancing the device performance. The piezoelectric potential of the fabricated device is evaluated by applying three different loads (4 N, 8 N, 22 N), where the source of the corresponding mechanical loads is based on the object of a musical drum stick. The results suggest that the pristine ZnO PENG device can generate a maximum output voltage and current of 2.15 V and 17 nA respectively. Moreover, the ZnO PENG device doped with 2.5% Sn achieved an even higher voltage (4.15 V) and current (36 nA) compared to pristine ZnO devices. In addition, the hydrothermal growth technique used to develop Sn-doped ZnO has the benefits of high scalability and low cost. Hence, the Sn-doped PENG device is a suitable candidate for energy harvesting applications operating in both uniform and non-uniform loading conditions.

Free-Standing PVDF/Reduced Graphene Oxide Film for All-Solid-State Flexible Supercapacitors towards Self-Powered Systems

The development of polymer-based devices has attracted much attention due to their miniaturization, flexibility, lightweight and sustainable power sources with high efficiency in the field of wearable/portable electronics, and energy system. In this work, we proposed a polyvinylidene fluoride (PVDF)-based composite matrix for both energy harvesting and energy storage applications. The physicochemical characterizations, such as X-ray diffraction, laser Raman, and field-emission scanning electron microscopy (FE-SEM) analyses, were performed for the electrospun PVDF/sodium niobate and PVDF/reduced graphene oxide composite film. The electrospun PVDF/sodium niobate nanofibrous mat has been utilized for the energy harvester which shows an open circuit voltage of 40 V (peak to peak) at an applied compressive force of 40 N. The PVDF/reduced graphene oxide composite film acts as the electrode for the symmetric supercapacitor (SSC) device fabrication and investigated for their supercapacitive properties. Finally, the self-charging system has been assembled using PVDF/sodium niobate (energy harvester), and PVDF/reduced graphene oxide SSC (energy storage) and the self-charging capability is investigated. The proposed self-charging system can create a pathway for the all-polymer based composite high-performance self-charging system.

Effect of particle size and morphology on the performance of BiFeO3–PDMS piezoelectric generators

The effect of the size and morphology of piezoelectric BiFeO₃ particles on the performance of BiFeO₃–PDMS composite generators is revealed.

Wrinkle Structured Network of Silver-Coated Carbon Nanotubes for Wearable Sensors

Soft-strain-based sensors are being increasingly used across various fields, including wearable sensing, behavior monitoring, and electrophysiological diagnostics. However, throughout all applications, the function of these sensors is limited because of high sensitivity, high-dynamic range, and low-power consumption. In this paper, we focus on improving the sensitivity and strain range of the soft-strain-based sensor through structure, surface, and sensitive unit treatment. Nanosilver (Ag)-coated hydroxyl-functionalized multi-walled carbon nanotubes (OH-f MWCNTs) were explored for highly acute sensing. With stretching and depositing methods, Ag@OH-f MWCNTs and polydimethylsiloxane (PDMS) are fabricated into a wrinkled and sandwich structure for a soft-strain-based sensor. The electronic properties were characterized in that the gauge factor (GF) = ΔR/R0 was 412.32, and the strain range was 42.2%. Moreover, our soft-strain-based sensor exhibits features including flexibility, ultra-lightweight and a highly comfortable experience in terms of wearability. Finally, some physiological and behavioral features can be sampled by testing the exceptional resistance change, including the detection of breath, as well as facial and hand movement recognition. The experiment exhibits its superiority in terms of being highly sensitive and having an extensive range of sensing.

Multiferroic ABO3 Transition Metal Oxides: a Rare Interaction of Ferroelectricity and Magnetism

This review article summarizes the development of different kinds of materials that evolved interest in all field of science particularly on new nano-materials which possess both electric and magnetic properties at the nanoscale. Materials of such kind possessing both magnetic and electric properties have tremendous applications and own an intensive research activity. These materials induce new properties which are particularly important in electronic and magnetic devices and even in the materials where magnetic property will change by electric field or vice versa. The discovery of such ferroic properties for scientific applications is the need of hour and spreads an exciting new area that has technical and commercial potential for the discovery of advanced materials. In recent studies, the actual path by which the multiferroic properties exist has been focused and new metal oxide compounds were discovered. The understanding of the structure of these compounds through research describes a wide range of applications and the challenges of these multiferroic materials that need to be explored. In this study, fundamental aspects and structural variations of ternary transition metal oxides have been covered which possess novel properties in storage devices such as hard disk platters and magnetic read heads.

Soft Piezoionic/Piezoelectric Nanocomposites Based on Ionogel/BaTiO3 Nanoparticles for Low Frequency and Directional Discriminative Pressure Sensing

We report on the fabrication and electro-mechanical characterization of a nanocomposite system exhibiting anisotropic electrical response under the application of tactile compressive stresses (5 kPa) at low frequencies (0.1-1 Hz). The nanocomposite is based on a chemically cross-linked gel incorporating a highly conductive ionic liquid and surface functionalized barium titanate (BaTiO₃) ferroelectric nanoparticles. The system was engineered to respond to mechanical stimulations by combining piezoionic and piezoelectric activity, generating electric charge due to a redistribution of the mobile ions across the polymer matrix and to the presence of the electrically polarized ceramic nanoparticles, respectively. The nanocomposite response was characterized in a quasi-static regime using a custom-designed apparatus. The results obtained showed that the combination of both piezo-effects led to output voltages up to 8 mV and anisotropy in the response. This allows to discriminate the sample orientation with respect to the load direction by monitoring the phase and amplitude modulation of the output signal. The integration of cluster-assembled gold electrodes produced by Supersonic Cluster Beam Deposition (SCBD) was also performed, enabling to enhance the charge transduction efficiency by a factor of 10, compared to the bare nanocomposite. This smart piezoionic/piezoelectric nanocomposite represents an interesting solution for the development of soft devices for discriminative touch sensing and objects localization in physically unstructured environments.