Piezoelectric Coefficient Research Articles

Narrow-Bandgap Tellurium-Based Chiral Hybrid Perovskite Single Crystals with Rashba-Dresselhaus Effect and Piezoelectricity.

Chiral hybrid perovskites have aroused great interest due to their unique versatile properties. However, designing chiral perovskites with narrow bandgaps is challenging, with their electronic properties such as the Rashba-Dresselhaus effect and piezoelectricity remaining unclear. Herein, single crystals of zero-dimensional (0D) tellurium-based chiral hybrid perovskite, (R-/S-α-PEA)2TeI6 and (R-/S-α-PEA)2TeBr6 (PEA = phenylethylammonium), with sizes of over 5 mm are grown by seed-crystal-assisted solution-temperature-lowering. The optical bandgaps are about 1.60 and 2.18 eV for the iodide and bromide analogues, respectively, which are the lowest among various chiral lead-free hybrid perovskites with the same halide ions in the X-site to the best of our knowledge. First-principles calculations reveal that (R-/S-α-PEA)2TeBr6 shows a larger Rashba-Dresselhaus spin-splitting than (R-/S-α-PEA)2TeI6, probably thanks to the greater distortion of [TeBr6] octahedra. Moreover, the piezoelectric coefficients d33 of (R-/S-α-PEA)2TeI6 and (R-/S-α-PEA)2TeBr6 are about 2.6 and 1.8 pC N-1, respectively. This work deepens the understanding of physical properties of 0D tellurium-based chiral perovskites with potential multifunctionality, including spintronic and piezoelectric performances.

London Dispersion Effects on the Structure and Properties of Nonlinear Optical BiB3O6 Crystal.

α-BiB3O6 (BiBO) is an important nonlinear optical (NLO) material with high efficiency for applications in harmonic generations and quantum technology. Owing to its low symmetry and cooperative Bi3+ lone pair arrangement, it has also exceptional large piezoelectric and electro-optic coefficients and strong anisotropies on other material characteristics. Previous theoretical calculations on its physical (mainly optical) properties often gave confusing results. It is found here that London dispersion (LD) tends to stabilize structures with closer pack entities like lone pair heavy ion Bi3+ with large polarizabilities, which is ignored in most previous density functional theory (DFT) calculations. Present study shows that without considering the LD effect, the structure of α-BiB3O6 (BiBO) was predicted with an over-estimated (by over 10 %) unique b-axis while underestimates a and overestimates c in a less amount. Consequently it is not possible to use the calculated structure to obtain meaningful properties of this important material. By applying a modified post-DFT LD correction based on linear combination of atomic orbitals (LCAO) and B3LYP functional, the experimental structure is well reproduced with the theoretical optimized one. Many important material property tensors of BiBO crystal are calculated in unprecedented precisions, including: dielectric constants (static and in THz range), elastic and elasto-optic constants, piezoelectric constants, refractive indices, NLO and electro-optic (EO) coefficients. Among them, theoretical calculation of the refractive indices in the THz range by diagonalizing the clamped-ion dielectric constants was firstly achieved at least for BiBO crystal. The calculation also confirms that BiBO has an exceptional large piezoelectric constant d22=40 pC/N and largest free EO coefficients , , on the order of 10 pm/V among borate crystals. The calculation also reveals that the large free EO coefficients are largely originated from the piezoelectric induced photo-elastic effect and for practical high speed applications only the clamped-ion EO coefficients take effect. The clamped ion EO coefficient of =-4.17 pm/V, =-2.61 pm/V are obtained for the first time and may be consulted if one seeks to design BiBO crystal as a high-speed EO modulator. Furthermore, full tensor matrix of the elasto-optic constants was obtained on the first time. Together with the calculated elastic constants, it can help to design acoustic optic modulating devices with preferable figure of merits 10 times that of traditional quartz crystal.

Advanced 3D-printed PVDF/BT piezoelectric energy harvester with a bio-inspired 3D structure for a self-powered smart mouse

Piezoelectric polymers such as poly(vinylidene fluoride) (PVDF) exhibit remarkable flexibility, lightweight, durability, and biocompatibility compared to their ceramic counterparts. This unique characteristic makes them highly suitable for harvesting mechanical vibrations. However, conventional manufacturing methods mainly result in two-dimensional (2D) piezoelectric energy harvester (PEHs) structures. This confines the internal stress and, as a result, limits their potential voltage output. This study introduces an innovative bio-inspired three-dimensional (3D) structure crafted through fused deposition modeling (FDM). Barium titanate (BT) nanoparticles were added as piezoelectric fillers to improve the performance of the PEH. The obtained nanocomposite was poled under optimal poling conditions, achieving a β-phase fraction of 95,72 %, a piezoelectric charge coefficient (d33) of 28 pC/N, and a permittivity of 24.2 at 100 Hz. A parametric study was performed through numerical analysis, resulting in an effective and optimized structural configuration. The combined excellent piezoelectric properties of the nanocomposite with the optimized structure enabled the PEH to generate an open-circuit voltage of 30.8 V, enabling it to charge a commercial 1 μF capacitor to 25 V in just 260 s. The bioinspired PEH demonstrates its practical application by powering an innovative device known as the "smart mouse," showcasing its utility and potential in real-world applications.

Acoustic Loss in LiNb1−xTaxO3 at Temperatures up to 900 °C

Lithium niobate‐lithium tantalate solid solutions are new piezoelectric crystals that enable to combine the advantages of their edge compounds with respect to the high thermal stability of lithium tantalate and the high Curie temperature of lithium niobate. This study aims to determine of the acoustic losses of bulk resonators with varying Nb/Ta ratios and their correlation with charge transport at temperatures up to 900 °C and at reduced oxygen partial pressures. Techniques such as resonant piezoelectric spectroscopy and contactless resonant ringdown spectroscopy are used to determine the acoustic losses. Further, the electrical conductivity is determined by impedance spectroscopy. A one‐dimensional physical model for vibrating plates is fitted to the data to extract key parameters such as piezoelectric coefficients and elastic modulus as a function of temperature. Noncontacting determination of loss excludes the impact of metal electrodes and reveals up to 300 °C values in the order of Akhiezer‐type losses. Resonators operated at 2 MHz show a rapid loss increase above about 450 °C, which is attributed to the piezoelectric/carrier relaxation. The latter follows from atomistic models using the key parameters mentioned and the electrical conductivity. The modeling includes variation of the resonance frequency and suggests higher resonance frequencies to lower the acoustic loss.

Optimizing electromechanical properties of KNN-based piezoelectric ceramics through regulation of lattice distortion

With the rapid development of broadband transducers, there is an increasing demand for enhanced electromechanical properties in lead-free piezoelectric ceramics. In this study, the strategies to enhance the electrical properties of ceramics were explored by doping BaZrO3 into 0.96(K0.48Na0.52)Nb0.96Sb0.04O3-0.04(Bi0.5Ag0.5)ZrO3 ceramics, inducing lattice distortion (c/a) and regulating the phase structure. The ceramics doped with 1.5 mol% BaZrO3 demonstrate excellent electrical performance, with a piezoelectric coefficient (d33) of 545 pC/N, a relative dielectric constant (εr) of 4126, and an electromechanical coupling factor (kp) of 54.1 %. The reduced c/a ratio and rhombohedral-orthorhombic-tetragonal phase structure reduce the polarization energy barrier and promote the ordered arrangement of ferroelectric dipoles, thereby enhancing the comprehensive performance of the ceramics. Lastly, the electrical impedance of ceramics is studied in detail and reveals the main conduction mechanism in the microscopic region. This research provides new insights into optimizing the electrical properties of ceramics through microstructural manipulation and demonstrates the potential application of KNN-based ceramics in high performance piezoelectric transducers.

Large piezoelectricity in two-dimensional doped β-Ga2O3

2D piezoelectric materials that can realize the mutual conversion of mechanical and electrical energy play an important role in nanoelectromechanical devices. As a new generation of ultra-wide band gap semiconductor, the monoclinic β-Ga2O3 has received extensive attention and research. In this paper, the inversion center of 2D β-Ga2O3 was broken by a metal atom substitutional doping. The values of out-of-plane (in-plane) piezoelectric coefficient d31/d33 (d11) for Cu-doped and Al-doped β-Ga2O3 reach −4.04 (3.95) pm/V and −2.91 (0.37) pm/V, respectively. Although they are both two-dimensional structures, the results fall within the same order of magnitude as those of the commonly used bulk piezoelectric materials such as α-quartz (d11 = 2.3 pm/V), AlN (d33 = 5.1 pm/V), and GaN (d33 = 3.1 pm/V). Our research shows a great potential application of doped β-Ga2O3 in micro and nano-electromechanical devices such as sensitive sensors, smart wearables, and micro energy converters.

Magnetism, ferroelectricity, and piezoelectricity in bulk α-CrOOH and its monolayer

Multifunctional materials with magnetic, piezoelectric, and ferroelectric properties have a wide range of applications. This study investigates the properties of bulk α-CrOOH and its monolayer using density functional theory. The findings reveal that bulk α-CrOOH exhibits a weak interlayer antiferromagnetism, but has a ferroelectric polarization of 28.45 µC/cm2 and piezoelectric strain constants d33 of 21.69 pm/V, which are comparable to those of the multiferroic material BiFeO3. The monolayer of α-CrOOH is a low-temperature ferromagnetic semiconductor that exhibits robust piezoelectricity. This is because of the intrinsic mirror symmetry breaking in the z-direction, resulting in large out-of-plane piezoelectric coefficients of e31 = 31.914 pC/m and d31 = 0.22 pm/V. These intriguing electric and magnetic properties make polarized bulk and monolayer α-CrOOH potential candidates for piezoelectric and ferroelectric device applications.

Enhancing the piezocatalytic performance of C3N5 through boron/oxygen doping for effective degradation of chlortetracycline

Utilizing sustainable energy in the environment to treat pollutants is an important research direction in the field of modern environmental governance. In this paper, a series of B-C3N5-O piezoelectric materials were prepared that have excellent piezoelectric properties. The test results of the quasi-static d33 measuring instrument showed that the piezoelectric coefficient of B-C3N5-O-2 is 1.429 times that of C3N5. Under ultrasound conditions, the removal rate of chlortetracycline by B-C3N5-O-2 after 80 min was 91.2 %, 4.48 times that of C3N5. The electron paramagnetic resonance test results showed that hydroxyl radicals and superoxide radicals played an important role in chlortetracycline degradation. The density functional theory calculation results showed that boron/oxygen doping reduces the band gap to 2.041 eV, thereby promoting electron migration in the material. In addition, possible degradation mechanisms and pathways were proposed. This work provided an effective method for treating organic pollutants in water and had broad application prospects.

Boosting piezoelectric response and electric-field induced strain in PMN-PT relaxor ferroelectrics

High-performance piezoelectric materials are essential for diverse electromechanical devices, from actuators to sensors and transducers. Here, we synthesized Ce2O3-doped Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (xCe-PMNT29) solid solutions via conventional solid-state methods. In the x = 2.5 % modified composition, we achieved a notable electrostrain-hysteresis trade-off, enhancing electrostrain (0.2 %), equivalent piezoelectric coefficient d33* (1701 pm V–1 at 3 kV cm–1), and reducing strain hysteresis to 8.1 %. Additionally, direct high-temperature piezoelectric characterizations revealed real-time variations in piezoelectric coefficient (d33) and the actual depolarization temperature, with d33 reaching 859 pC N−1 at 53 °C and planar electromechanical coupling coefficient (kp) exceeding 70 % within 30−85 °C. Leveraging x-ray diffraction (XRD) and piezoelectric force microscopy (PFM), we elucidated synergistic effects between complex nanodomains and local structural heterogeneity, enhancing piezoelectric activity. This study presents a promising approach for improving electromechanical performance and electrostrain in ferroelectrics, with significant potential for practical piezoelectric applications.

Investigation of the impact of planar microelectrodes on macrophage-mediated mesenchymal stem cell osteogenesis.

Osseointegration commences with foreign body inflammation upon implant placement, where macrophages play a crucial role in the immune response. Subsequently, during the intermediate and late stages of osseointegration, mesenchymal stem cells (MSCs) migrate and initiate their osteogenic functions, while macrophages support MSCs in osteogenesis. The utilization of ferroelectric P(VDF-TrFE) covered ITO planar microelectrodes facilitated the simulation of various surface charge to investigate their effects on MSCs' osteogenic differentiation and macrophage polarization and the results indicated a parabolic increase in the promotional effect of both with the rise in piezoelectric coefficient. Furthermore, the surface charge with a piezoelectric coefficient of -18 exhibited the strongest influence on the promotion of M1 polarization of macrophages and the promotion of MSCs' osteogenic differentiation. The impact of macrophage polarization and MSC osteogenesis following the interaction of macrophages affected by surface charge and MSC was ultimately investigated. It was observed that macrophages affected by the surface charge of -18 piezoelectric coefficient still exerted the most profound induced osteogenic effect, validating the essential role of M1-type macrophages in the osteogenic differentiation of MSCs.

A simple measurement method for in-situ temperature-dependent piezoelectric coefficient d 33 of piezoelectric materials

Piezoelectric materials have been widely used in sensors, actuators, and transducers due to their positive and inverse piezoelectric effects, which can convert electrical and mechanical energy into one another. The most important parameter to evaluate the piezoelectric properties of materials is their piezoelectric coefficient (d 33). The value of d 33 varies with temperature. The measurement of temperature-dependent d 33 is a difficult task and at present, the equipment used to measure the temperature-dependent d 33 has many limitations. To overcome these limitations, the current study proposes an in situ temperature-dependent d 33 measuring method based on the inverse piezoelectric effect of piezoelectric materials. The newly developed measuring equipment contains a laser vibrometer, and automatic detection program including data processing. Moreover, the image is displayed on LabVIEW program. Compared with the quasi-static temperature-dependent d 33 measurement method, the KNN- based piezoelectric material demonstrated the reliability of this measurement method.

Doping effects and role conversion of CeO2 in 0.3PZN–0.7PZT ternary piezoelectric ceramics with enhanced electrical properties

In this work, the rare-earth doped ternary lead zirconate titanate ceramics with chemical formula of [0.3Pb(Zn1/3Nb2/3)O3–0.7Pb(Zr0.52Ti0.48)O3] + x wt% CeO2 (x=0–0.5, abbreviated as 0.3PZN–0.7PZT–xCe) were synthesized by a conventional solid-state reaction route, specific attentions was focused on the effects of CeO2 dopants on the structures and electrical properties of the 0.3PZN–0.7PZT ceramics, revealing the role conversion of CeO2 dopants with its doping amount (x). When less CeO2 (x≤0.2) is introduced into 0.3PZN–0.7PZT, the prepared ceramics are identified as the coexistence of rhombohedral and tetragonal phases, also involved with an increased grain size and a reduced atomic ratio of Pb/(Zr+Ti+Zn+Nb). The increased remanent polarization (Pr) and deceased coercive filed (Ec), as well as improved dielectric permittivity (εr) and piezoelectric coefficient (d33) demonstrate the donor substitution of Ce3+ for Pb2+ at the A-site of perovskite lattice. Conversely, the introduction of excessive CeO2 (x>0.2) causes a reversal evolution in the electrical properties of ceramics, suggesting that some of the introduced cerium element tends to become Ce4+, which equivalently substitutes for Zr4+ at the B-site. Additionally, the diffused phase transition (DPT) behaviors of the 0.3PZN–0.7PZT–xCe ceramics were investigated by the modified Curie–Weiss Law. The sample with x=0.2 shows reduced DPT character and optimized electrical properties, including TC=297 °C, εr=1400, d33=480 pC/N, tanδ=1.6%, kp=65%, d33×g33=16.32×10–12 m2/N, Pr=38.3 μC/cm2 and Ec=1.02 kV/mm. These enhanced electrical properties not only are contributed by the donor substitution effect of Ce3+, but also benefit from the optimized morphotropic phase boundary that is close to the tetragonal-rich side.

94‐3: 60 kHz Ultrasonic Actuators for Animal‐Friendly Haptic Displays

Enhanced piezoelectric coefficient (d33) and mechanical quality factor (Qm) are prerequisite for high performance of resonant piezoelectric applications (e.g., ultrasound haptic displays). We present high performance piezoelectric actuators with a resonant frequency above 60 kHz beyond audible ranges for animals. The ultrasonic actuators provide sufficient tactile feedback with a high vibration displacement, which is superior to that of many state‐of‐the‐art commercial actuators without any visible damages in plastic organic light‐emitting diode (POLED) displays. Furthermore, the actuators can be assembled into an ultrasound loudspeaker, which could facilitate the directional private sound for high‐end automotive applications.

Improved piezoelectric and photoluminescence properties in Ce-doped PSN-PMN-PT piezoelectric ceramics by multiscale coordination

The large piezoelectric coefficient (d33) and high mechanical quality factor (Qm) are essential for piezoelectric ceramics used in high-power devices. It is pity that the two parameters are usually opposite, with higher d33 corresponding to lower Qm. In order to well-balance the d33 and Qm, the rare-earth element Ce with multi-valence was introduced into the 0.06 Pb(Sc1/2Nb1/2)O3-0.61 Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 (xCe-PSN-PMN-PT) ceramics in this work. The structure, electrical properties and optical properties of ceramics were systematically analyzed. Optimal electrical performances (d33 = 719 pC/N, Qm = 256, and dielectric loss tanδ = 0.007) were obtained in 0.02Ce-PSN-PMN-PT ceramics. These excellent performances originate from the multiscale coordination effects among defect dipoles, local structural heterogeneity, domain structure, phase structure, and grain size. The xCe-PSN-PMN-PT ceramics exhibit excellent photoluminescence properties in the blue wavelength range. Our research provides a new paradigm for deep-sea electro-optical communication.

Ultrafast high-temperature sintering of potassium-sodium niobate: Processing and properties

Current regulations pushing for lead-free piezoelectric alternatives have highlighted potassium-sodium niobate (K0.5Na0.5NbO3, KNN) as a promising candidate. However, conventional sintering of KNN faces challenges like alkali element volatilization and inadequate densification. Ultrafast high-temperature sintering (UHS) offers a solution by rapidly heating ceramics, yielding fine microstructures, with minimal volatile element loss. Here, using a custom UHS equipment we produced undoped KNN ceramics, identifying optimal sintering conditions via a UHS processing map. UHS KNN ceramics sintered for ≤90 s achieved 91 % density, <2 µm average grain size, and no secondary phases. This study reports also the first dielectric, piezoelectric, and ferroelectric properties of UHS KNN ceramics. Differences between as-UHS and post-annealed ceramics were observed as well, with the latter exhibiting piezoelectric coefficients of ~80pC/N. This research enhances understanding of UHS applications and potential of KNN for lead-free piezoelectric uses.

The piezoelectric catalysis effect of tourmalines in the degradation of organic pollutants

The discovery of the piezoelectricity of tourmalines has been reported over three decades, but very few studies exploring the piezoelectric catalysis effect of tourmalines. Herein, the piezoelectric catalysis effect of iron-based and lithium-based tourmalines (Fe-TM and Li-TM) was studied through the degradation of Rhodamine B (RhB) and p-nitrophenol (PNP) in aqueous solution as model reaction in tourmaline/ultrasound system. In ultrasonic condition, the obvious degradation of RhB and PNP was observed and confirmed stemming from the piezoelectric catalysis effect of Fe-TM and Li-TM. Fe-TM was found to have higher surface voltage (560–590 mV) and a higher piezoelectric coefficient of 9.5 pC/N, compared to Li-TM (surface voltage: 410–450 mV; piezoelectric coefficient: 6.7 pC/N). Accordingly, high and stable piezoelectric catalysis activity was observed on Fe-TM in the degradation of RhB and PNP. Through annealing at 800 ℃ in air, Fe-TM can be converted from buergerite tourmaline into foitite tourmaline, and the piezoelectric catalysis activity was basically unchanged. In tourmaline/ultrasound system, the degradation of RhB and PNP was mainly initiated by •OH that be produced from the oxidation of water with the piezoelectric potential of tourmalines. The present work observes and confirms the piezoelectric catalysis effect of tourmalines, which could inspire the new applications and understanding of tourmalines.

Flexible, biodegradable ultrasonic wireless electrotherapy device based on highly self-aligned piezoelectric biofilms.

Biodegradable piezoelectric devices hold great promise in on-demand transient bioelectronics. Existing piezoelectric biomaterials, however, remain obstacles to the development of such devices due to difficulties in large-scale crystal orientation alignment and weak piezoelectricity. Here, we present a strategy for the synthesis of optimally orientated, self-aligned piezoelectric γ-glycine/polyvinyl alcohol (γ-glycine/PVA) films via an ultrasound-assisted process, guided by density functional theory. The first-principles calculations reveal that the negative piezoelectric effect of γ-glycine originates from the stretching and compression of glycine molecules induced by hydrogen bonding interactions. The synthetic γ-glycine/PVA films exhibit a piezoelectricity of 10.4 picocoulombs per newton and an ultrahigh piezoelectric voltage coefficient of 324 × 10-3 volt meters per newton. The biofilms are further developed into flexible, bioresorbable, wireless piezo-ultrasound electrotherapy devices, which are demonstrated to shorten wound healing by ~40% and self-degrade in preclinical wound models. These encouraging results offer reliable approaches for engineering piezoelectric biofilms and developing transient bioelectronics.

Ultra-high electrostrain in flux-grown (Bi0.5Na0.5)TiO3-0.06BaTiO3-0.03(K0.5Na0.5)NbO3 single crystals around the nonergodic/ergodic crossover region

In this study, we successfully grew large-sized single crystals (12 × 11 × 8 mm³) of 0.91Bi0.5Na0.5TiO3-0.06BaTiO3-0.03(K0.5Na0.5)NbO3 (BNT-6BT-3KNN) with a <100>c orientation using the flux growth method. This marks the first instance of achieving such crystals. The single crystals display double hysteresis loops, featuring a maximum polarization of ∼64.6 μC/cm2. Capitalizing on the nonergodic/ergodic boundary, the single crystals exhibit a substantial strain (Sm) of 0.91% at the maximum electric field of 20 kV/cm and an exceptionally high inverse piezoelectric coefficient d33* of 4550 pm/V. The creation of long-range domains from needle-like nanodomains and polar-nano regions under the application of an electric field was confirmed through bright-field transmission electron microscopy and piezoresponse force microscopy analyses. The phase diagram for BNT-6BT-3KNN single crystals was constructed by analyzing the temperature dependence of dielectric, ferroelectric, and electrostrain behaviors.

Nano PDA@Tur-Modified Piezoelectric Sensors for Enhanced Sensitivity and Energy Harvesting.

Tourmaline is known for its natural negative ion effect and far-infrared radiation function, which promote human blood circulation, relieve pain, regulate the endocrine system, and enhance immunity and other functions. These functions motivate the use of this material for enhanced sensitivity of wearable sensors. In this work, taking advantage of the unique multifunctions of tourmaline nanoparticles (Tur), highly boosted piezoelectricity was achieved by incorporating polydopamine (PDA)-modified Tur in PVDF. The PDA@Tur nanofillers not only effectively increased the β-phase content of PVDF but also played a major role in significantly enhancing piezoelectricity, wettability, elasticity, air permeability, and stability of the piezoelectric sensors. Especially, the maximum output voltage of the fiber membrane with 0.5 wt % PDA@Tur reached 31.0 V, being 4 times that of the output voltage of the pure PVDF fiber membrane. Meanwhile, the sensitivity reached 0.7011 V/kPa at 1-10 N, which was 3.6 times that of pure PVDF film (0.196 V/kPa). The power intensity reached 8 μW/cm2, being 5.55 times that of the pristine PVDF PENG (1.44 μW/cm2), and the piezoelectric coefficient from d33 m/PFM is 5.5 pC/N, higher than that of pristine PVDF PENG (3.1 pC/N). Output signal graphs corresponding to flapping, finger, knee, and elbow movements were detected. The response/recovery time of the sensor device was 24/19 ms. The piezoelectric nanogenerator (PENG) was capable of charging multiple capacitors to 2 V within a short time and lighting up 15 light-emitting diodes bulbs (LEDs) simultaneously with a single beat. In addition, a 4 × 4 row-column multiplexed sensor array was made of PENGs, which showed distinct responses to different stress areas in different sensor modules. This study demonstrated high-performance PDA@Tur PVDF-based PENG being capable of energy harvesting and sensing, providing a guideline for the design and buildup of wearable self-powered devices in healthcare and human-computer interaction.

Recent Advances in Ferroelectret Fabrication, Performance Optimization, and Applications.

The growing demand for wearable devices has sparked a significant interest in ferroelectret films. They possess flexibility and exceptional piezoelectric properties due to strong macroscopic dipoles formed by charges trapped at the interface of their internal cavities. This review of ferroelectrets focuses on the latest progress in fabrication techniques for high temperature resistant ferroelectrets with regular and engineered cavities, strategies for optimizing their piezoelectric performance, and novel applications. The charging mechanisms of bipolar and unipolar ferroelectrets with closed and open-cavity structures are explained first. Next, the preparation and piezoelectric behavior of ferroelectret films with closed, open, and regular cavity structures using various materials are discussed. Three widely used models for predicting the piezoelectric coefficients (d33) are outlined. Methods for enhancing the piezoelectric performance such as optimized cavity design, utilization of fabric electrodes, injection of additional ions, application of DC bias voltage, and synergy of foam structure and ferroelectric effect are illustrated. A variety of applications of ferroelectret films in acoustic devices, wearable monitors, pressure sensors, and energy harvesters are presented. Finally, the future development trends of ferroelectrets toward fabrication and performance optimization are summarized along with its potential for integration with intelligent systems and large-scale preparation.