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Abstract The development of high-performance lead-free K0.5Na0.5NbO3-based piezoceramics for replacing commercial lead-containing counterparts is crucial for achieving environmentally sustainable society. Although the proposed new phase boundaries (NPB) can effectively improve the piezoelectricity of KNN-based ceramics, the difficulty of achieving saturated poling and the underlying multiscale structures resolution of their complex microstructures are urgent issues. Here, we employ a medium entropy strategy to design NPB and utilize texture engineering to induce crystal orientation. The developed K0.5Na0.5NbO3-based ceramics enjoys both prominent piezoelectric performance and satisfactory Curie temperature, thus exhibiting an ultrahigh energy harvesting performance as well as excellent transducer performance, which is highly competitive in both lead-free and lead-based piezoceramics. Comprehensive structural analysis have ascertained that the field-induced efficient multiscale polarization configurations irreversible transitions greatly encourages high saturated poling. This study demonstrates a strategy for designing high-performance piezoceramics and establishes a close correlation between the piezoelectricty and the underlying multiscale structures.

The inferior temperature stability of piezoelectric response is the main drawback of KNN-based ceramics. Here, the Ba-doped 0.97(K0.48Na0.52)(Nb0.96Sb0.04)O3-0.03Bax(Bi0.5Ag0.5)1-xZrO3 (abbreviated as KNNS-BxBAZ) textured ceramics were prepared by the template grain growth (TGG) method. Excellent comprehensive properties (d33=(406 ± 15) pC/N, TC = 274 °C, strain is 0.17%) were achieved in KNNS-BxBAZ textured ceramics with x = 0.2. Meanwhile, its piezoelectric and strain properties also show superior temperature stability (d33 maintained within ±20% change in a wide temperature range from 25 °C to 200 °C and strain variation was less than 5% in the temperature range from room temperature to 165 °C). The high O-T phase transition temperature (TO-T is 110 °C) induced by incorporating Ba ions accounts for the enhanced temperature stability of piezoelectric properties. In addition, the crystal texture always maintains the contribution of piezoelectric anisotropy to the piezoelectric properties during elevated temperature, which significantly improved the temperature stability of piezoelectric properties. This work provides an effective strategy for simultaneously achieving high piezoelectric response and excellent temperature stability in KNN-based ceramics.

Bismuth ferrite–based ferroelectric ceramics are considered strong competitors in high–temperature piezoelectric applications that benefits from their high depolarization temperature (Td), but problems of large conductivity and low piezoelectric coefficient (d33) should be tackled. BiFeO3PbTiO3–x(Sr0.7Bi0.2□0.1)TiO3 (BF–PT–xSBT) ternary system are designed in this work that successfully resolves this tough paradox. Rietveld refinements show that this system exhibits multiphase coexistence with complex structural transition among rhombohedral, tetragonal and pseudocubic phase. Interestingly, a high Td ∼320 °C and d33 ∼ 236 pC/N are synergistically optimized in x=0.20 composition near pseudo–phase boundary, which are indicated by multi–scale techniques (phase structure, dielectric analysis etc.). What's more, dual electrostrain peaks appear at separate phase boundaries for x=0.20 and 0.66 compositions with distinct piezo/ferroelectric properties. Rayleigh law and piezoelectric force microscopy analysis clarify that the optimal electrostrain performance for both critical compositions are dominated by intrinsic (x=0.20) and extrinsic (x=0.66) contributions, respectively. This work not only provides a new BF–PT–xSBT system with a high Td and superior d33 that are promising candidates in high–temperature actuator and sensor applications, but also presents a possibility of multiphase–coexistence established exotic macroscopic performances.

For glass-ceramics, how to realize the collaborative optimization of BDS and permittivity is the key to improve the energy storage density. In this work, ZrO2 is introduced into BPKNAS glass-ceramics as nucleating agent to promote crystal development of glass-ceramics and then achieve high permittivity. When 1.5 mol% ZrO2 is added, the glass-ceramics have the highest permittivity (∼128.59) and meanwhile possess high BDS (1948.90 kV/cm) due to the dense microstructure. Therefore, BPKNAS-1.5ZrO2 glass-ceramics has the highest theoretical energy storage density (21.62 J/cm3). Moreover, the permittivity variation of BPKNAS-1.5ZrO2 glass-ceramics is less than 6 % in the wide temperature range from −80 to 300 °C, showing excellent temperature stability. In addition, BPKNAS-1.5ZrO2 glass-ceramics possesses ultrahigh power density, which reaches up to 382.40 MW/cm3 in overdamped circuit. The above evidence shows that BPKNAS-1.5ZrO2 glass-ceramics with ultrahigh energy storage density and power density is very competitive in the field of energy storage applications.

Abstract Piezoelectric semiconductors have emerged as redox catalysts, and challenges include effective conversion of mechanical energy to piezoelectric polarization and achieving high catalytic activity. The catalytic activity can be enhanced by simultaneous irradiation of ultrasound and light, but the existing piezoelectric semiconductors have trouble absorbing visible light. A piezoelectric catalyst is designed and tested for the generation of hydrogen peroxide (H2O2). It is based on Nb‐doped tetragonal BaTiO3 (BaTiO3:Nb) and is sensitized by carbon quantum dots (CDs). The photosensitizer injects electrons into the conduction band of the semiconductor, while the piezoelectric polarization directed electrons to the semiconductor surface, allowing for a high‐rate generation of H2O2. The piezoelectric polarization field restricts the recombination of photoinduced electron–hole pairs. A production rate of 1360 µmol gcatalyst−1 h−1 of H2O2 is achieved under visible light and ultrasound co‐irradiation. Individual piezo‐ and photocatalysis yielded lower production rates. Furthermore, the CDs enhance the piezocatalytic activity of the BaTiO3:Nb. It is noted that moderating the piezoelectricity of BaTiO3:Nb via microstructure modulation influences the piezophotocatalytic activity. This work shows a new methodology for synthesizing H2O2 by using visible light and mechanical energy.

Three components of ferroelectric-dielectric composite ceramic 85Vol% Ba0.5Sr0.5TiO3 – 15Vol% MgO, 78Vol% Ba0.45Sr0.55TiO3 – 22Vol% Mg2TiO4 and 48Vol% Ba0.4Sr0.6TiO3 – 52Vol% BaWO4 were chosen and synthesized by solid-phase reaction. The ferroelectric-dielectric system with different mixing degree was obtained by controlling the milling time. The effects of phase distribution on dielectric properties of composite were reflected. The two-phase distribution of the composite was changed from the layered and columnar dominated structure to the spherical structure, with increasing milling time from 5 min, 30 min, 10 h to 24 h. Permittivity and tunability were increased obviously by the transform of phase distribution patterns. However, the quality factor Q values were strongly deteriorated with extending milling time. Different ball-milling times are used to reflect different phase distribution modes, and the dielectric properties of two-phase composite ceramics in different phase distribution modes are well verified.

Percolating composites with negative permittivity can be promising candidates for metamaterials. Herein, novel all-organic composite films containing of random coil polypyrrole (PPy) and poly(vinylidene fluoride) (PVDF) are fabricated via a solution casting method. The random coil PPy is prepared by oxidative template assembly approach for the first time. The experimental result indicates that the negative permittivity is easily adjusted through controlling the random coil PPy contents. Especially, the random coil PPy contents exceeded 7 wt% the negative permittivity appear attributed to the formation of 3D interconnected PPy network. This facile approach not only opens a new way to preparing negative permittivity of all-organic composite films, but also points out a route to facilitate the practical applications of metamaterials. Keywords: Polypyrrole, Composite films, Random coil, Negative permittivity

The majority of the previously reported nanocomposites obtainable with higher energy density (>15 J cm−3) relies strongly on much higher breakdown strength (>4000 kV cm−1). The operation of capacitors in such higher applied electric field brings challenges because of the substantially increased the failure probability. In this study we explored the dispersibility and the orientation of fillers in nanocomposites as they play vital roles in the energy density. Based on the infinite element modulation results, an original design of 1–3 type composite structure was employed in the current study. This design adopts the one-dimensional (110)-oriented monodispersed barium strontium titanate Ba0.67Sr0.33TiO3 (BST) nanorod array as fillers embedded in the three-dimensional poly (−vinylidene fluoride) (PVDF) polymer matrix. With these originally designed BST/PVDF nanocomposites, we have demonstrated a significant enhancement of energy density at a lower applied electric field. For example, an energy density of 13.10 J cm−3 at electric field of 3400 kV cm−1 can be obtained, an enhancement of 3 times larger than that of bare PVDF. Moreover, the discharge efficiency is maintained at 69% at 3400 kV cm−1. The high performance of this originally designed nanacomposite demonstrated its potential application in the next generation energy storage devices.

Abstract Antiferroelectric ceramics with extraordinary energy‐storage density have gained exponentially soaring attention for their applications in pulsed power capacitors. Nevertheless, high energy dissipation is a deficiency of antiferroelectric materials. The modulation of Ba/La‐doped (Pb0.91BaxLa0.06−2x/3)(Zr0.6Sn0.4)O3 (x = 0.015, 0.03, 0.045, 0.06) antiferroelectric ceramics is aimed at increasing the energy efficiency and obtaining an ideal energy storage density. The traditional solid‐state reaction is exploited for ceramics fabrication and all prepared samples exhibit an ultralow electrical hysteresis due to the local structural heterogeneity, as verified by Raman spectroscopy. Of particular importance is the fact that the (Pb0.91Ba0.045La0.03)(Zr0.6Sn0.4)O3 ceramic possesses an excellent recoverable energy storage density (Wrec = 8.16 J cm−3) and a remarkable energy efficiency (η = 92.1%) simultaneously under an electric field of 340 kV cm−1. Moreover, the corresponding ceramic exhibits a superior discharge current density (CD = 1498.6 A cm−2), a high level of power density (PD = 202.3 MW cm−3), and a nanosecond‐level discharge period (53 ns). This provides a promising antiferroelectric material for fabricating ceramic capacitors with excellent energy storage and high power characteristics.

High-energy storage density, responsivity and efficiency, i.e. WR = 1.07 J/cm3, ξ = 119 J/(kV m2) and η = 92%, were simultaneously obtained in Mn-doped 0.62Bi0.5Na0.5TiO3-0.06BaTiO3-0.32(Sr0.7Bi0.2□0.1)TiO3 ergodic relaxor ceramics. Appropriate Mn doping was beneficial to enhance breakdown field strength. Moreover, temperature and different atmosphere-dependent impedance spectroscopy results indicated that oxygen vacancies were the conductivity mechanism for all samples. The valence state of Mn together with the conjugation between Mn ion and oxygen vacancies was confirmed by X-ray photoelectron spectra and electric paramagnetic resonance. The above results indicate that quasi-hysteresis-free loops with high-energy storage performances can be obtained by the induced defect complex. IMPACT STATEMENT High-energy storage density WR = 1.07 J/cm3, responsivity ξ = 119 J/(kV m2) and efficiency η = 92% were simultaneously obtained in quasi-hysteresis-free ceramics by introducing defect complex.

Increasing concern has been focused on the search for ecofriendly dielectric ceramics to meet the extensive demands of pulsed capacitors. Due to the advantages of high-energy storage density, efficiency, and excellent temperature stability, optimization of energy storage performance in dielectric ceramics has been a goal in the past decades. This review summarizes the recently reported progress in energy storage properties of typical perovskite-type lead-free ceramics. The advantages and shortcomings in the various kinds of ceramics are discussed. Finally, future prospects are presented to provide some guidelines for the exploration of new materials.

Superlattice-like (SLL) phase-change film is considered to be a promising phase-change material because it provides more controllabilities for the optimization of multiple performances of phase-change films. However, the mechanism by which SLL structure affects the properties of phase-change films is not well-understood. Here, four SLL phase-change films [Ge8Sb92(15 nm)/Ge (x nm)]3 with different x are fabricated. Their behaviors of crystallization are investigated by measuring sheet resistance and coherent phonon spectroscopy, which show that the crystallization temperature (TC) of these films increases anomalously with x, rather than decreases as the interfacial effects model predicted. A new stress effect is proposed to explain the anomalous increase in TC with x. Raman spectroscopy reveals that Raman shifts of all phonon modes in SLL films deviate from their respective standard Raman shifts in stress-free crystalline films, confirming the presence of stress in SLL films. It is also shown that tensile and compressive stresses exist in Ge and Ge8Sb92 layers, respectively, which agrees with the lattice mismatch between the Ge and Ge8Sb92 constituent layers. It is also found that the stress reduces with increasing x. Such a thickness dependence of stress can be used to explain the increase in crystallization temperature of four SLL films with x according to stress-enhanced crystallization. Our results reveal a new mechanism to affect the crystallization behaviors of SLL phase-change films besides interfacial effect. Stress and interfacial effects actually coexist and compete in SLL films, which can be used to explain the reported anomalous change in crystallization temperature with the film thickness and cycle number of periods in SLL phase-change films.

Ceramic-polymer nanocomposites, consisting of surface hydroxylated cube-shaped Ba0.6Sr0.4TiO3 nanoparticles (BST–NPs) as fillers and poly(vinylidenefluoride) (PVDF) as matrix, have been fabricated by using a solution casting method. The nanocomposites exhibited increased dielectric constant and improved breakdown strength. Dielectric constants of the nanocomposite with surface hydroxylated BST–NPs (BST–NPs–OH) were higher as compared with those of their untreated BST–NPs composites. The sample with 40 vol % BST–NPs–OH had a dielectric constant of 36 (1 kHz). Different theoretical models have been employed to predict the dielectric constants of the nanocomposites, in order to compare with the experimental data. The BST–NPs–OH/PVDF composites also exhibited higher breakdown strength than their BST–NP/PVDF counterparts. A maximal energy density of 3.9 J/cm3 was achieved in the composite with 5 vol % BST–NPs–OH. This hydroxylation strategy could be used as a reference to develop ceramic-polymer composite materials with enhanced dielectric properties and energy storage densities.

The refractory transition metal nitride (TMN) film Hafnium nitride (HfNx) was successfully prepared on silicon-based substrates as bottom electrodes for resistive random access memory (RRAM) cells in Pt (top)/metal oxide/ HfNx (bottom) sandwich structure. The reproducible resistive switching (RS) characteristics of the memory cells were studied systematically for RRAM applications. The advantages of adopting HfNx instead of Pt as bottom electrode material were demonstrated, including the improvement of the low resistive state value, the RS endurance and the uniformity of RS parameters. The composition and chemical bonding states of the prepared HfNx was analyzed by X-ray photoelectron spectroscopy (XPS) technique. The nitrogen content in the HfNx and the Gibbs free energy of the corresponding metal oxide formation has great influences on the RS properties. The oxygen reservoir ability and diffusion barrier effect of the HfNx play a key role in the RS performance improvement of the RRAM devices.

High-performance lead-free piezoelectric thin films are urgently required for microelectromechanical systems. In this study, thin films based on the 0.8Bi0.5Na0.5TiO3-0.2(Sr0.7Bi0.20.1)TiO3 system were prepared on Pt(111)/TiOx/SiO2/Si substrates by a sol--gel method. The large lattice distortions were induced by introducing five rare-earth ions with different ionic radii (Er/Pr/Sm/Nd/La) to achieve the purpose of regulating the piezoelectric response of the thin films with the maximum inverse piezoelectric coefficient up to 425.9 pm/V. X-ray diffraction, Raman spectroscopy, Piezoresponse force microscope, and additional testing methods were used to observe the phase composition and microstructure of the thin films to investigate the effect of doping rare-earth elements with different ionic radii at the A-site on lattice distortion, and to summarize the transformation law. This study is significant for improving the piezoelectric properties of thin films and has crucial applications in microelectronic sensing. [ABSTRACT FROM AUTHOR]