Improvement in piezoelectric performance of the lead-free BiFeO_(3)-BaTiO_(3) ceramics by synergistic approach

High-piezoelectric properties in lead-free materials have been the pursuit for both industry and scientific research.In this work,the synergistic approaches of phase/domain engineering and novel poling method are adopted for the improvement of piezoelectric performance.The strategically designed lead-free donor-doped BiFeO_(3)-x BaTiO_(3) ceramics at the crystal structure morphotropic phase boundary(MPB)between the rhombohedral and tetragonal phases exhibited a high Curie temperature(T C≥450°C).Furthermore,si-multaneously enhanced static piezoelectric constant(d_(33))of 436±5 pC/N and thermally stable dynamic piezoelectric constant(d_(33)^(∗))of 550±10 pm/V were achieved.The high piezoelectric performance is col-lectively attributed to the crystal structure MPB,thermal quenching effect,local structure heterogeneity induced by donor doping,mesoscale nanodomains,and novel poling method inside a magnetic field.The temperature-insensitive and high piezoelectric performance of the current work is superior to the other lead-free piezoceramics.The synergistic approach for the improvement of piezoelectricity provides a path for the development of lead-free ceramics for high-temperature commercial applications.

Core-shell structure and domain engineering in Bi_(0.5)Na_(0.5)TiO_(3)-based ceramics with enhanced dielectric and energy storage performance

Coreeshell structured Bi_(0.5)Na_(0.5)TiO_(3)eKTaO_(3)þx%(in mass)Li_(2)CO_(3)ceramics were fabricated in this study.Increasing x from 0 to 2 leads to the decrease of sintering temperature from 1175℃to 1020℃.The limited diffusion of Ta5þresults in chemical heterogeneities and coreeshell microstructures.The Ta5þ-depleted cores show the nanodomains(~10 nm),while the Ta^(5+)-rich shells display the polar nanoregions(1e2 nm).From x¼0 to 1,the appearance of cores with nanodomains contributes to the increase of dielectric constant and maximum polarization,while the further addition of Li2CO3 suppresses the dielectric and polarization responses due to the reduced grain sizes and polarization coupling.The enhanced dielectric relaxation and existence of core-shell microstructure with different polarization levels help to optimize the dielectric temperature stability.The x¼2 ceramics exhibit a stable high dielectric constant~1400 over a wide temperature range of 20e520℃.More encouragingly,the ultrafine grain size and coreeshell microstructure in the x¼2 ceramics greatly benefit the improvement of breakdown strength.Combined with the delayed polarization saturation and high ergodicity,a high recoverable energy density of~5.07 J/cm3 is obtained under 44 kV/mm,with a high efficiency of~85.17%.

Phase and domain engineering strategy for enhancement of piezoelectricity in the lead-free BiFeO_(3)-BaTiO_(3)ceramics

Lead-free BiFeO_(3)-BaTiO_(3)ceramics attract widespread attention over the last two decades due to their high Curie temperature(TC)and excellent piezoelectric performance.Here,in the Nd-modified 0.67BiFeO_(3)-0.33BaTiO_(3)ceramics,an excellent piezoelectric constant(d33)of 325 pC/N was achieved by applying a novel poling method(AC-biasþDC-bias)with a high TC of 455℃.In addition,an ultrahigh normalized piezoelectric strain(d33*¼Smax/Emax)of 808 pm/V was obtained at the normal/typical and relaxor-ferroelectrics phase boundary simultaneously with good thermal stability(Dd33*(T)z 20%)in the temperature range of 25e125℃.The piezoelectric force microscopy results show the domain miniaturization from micro to nanoscale/polar nano-regions due to local structure heterogeneity caused by Nd doping.The mechanism for the giant piezoelectric strain is attributed to the thermal quenching,nano-domains,and reverse switching of the short-range order to the long-range order under the applied electric field.The strategic design of domain engineering and a proposed model for the high piezoelectricity is successfully supported by the phenomenological relation and Gibbs free energy profile.In this work,a new lead-free single-element modified BiFeO_(3)-BaTiO_(3)ceramics was developed by applying a synergistic approach of domain engineering and phase boundary for the high-temperature piezoelectric performance.

Van der Waals ferroelectric transistors:the all-round artificial synapses for high-precision neuromorphic computing

State number,operation power,dynamic range and conductance weight update linearity are key synaptic device performance metrics for high-accuracy and low-power-consumption neuromorphic com-puting in hardware.However,high linearity and low power consump-tion couldn’t be simultaneously achieved by most of the reported synaptic devices,which limits the performance of the hardware.This work demonstrates van der Waals(vdW)stacked ferroelectric field-effect transistors(FeFET)with single-crystalline ferroelectric nanoflakes.Ferroelectrics are of fine vdW interface and partial polar-ization switching of multi-domains under electric field pulses,which makes the FeFETs exhibit multi-state memory characteristics and ex-cellent synaptic plasticity.They also exhibit a desired linear conduc-tance weight update with 128 conductance states,a sufficiently high dynamic range of G_(max)/G_(min)>120,and a low power consumption of 10 fJ/spike using identical pulses.Based on such an all-round device,a two-layer artificial neural network was built to conduct Modified Na-tional Institute of Standards and Technology(MNIST)digital num-bers and electrocardiogram(ECG)pattern-recognition simulations,with the high accuracies reaching 97.6%and 92.4%,respectively.The remarkable performance demonstrates that vdW-FeFET is of obvious advantages in high-precision neuromorphic computing applications.

Optimized strain performance in <001>-textured Bi_(0.5)Na_(0.5)TiO_(3)-based ceramics with ergodic relaxor state and core-shell microstructure

Herein,a high strain of ~0.3% with a small hysteresis of 43% is achieved at a low electric field of 4 kV/mm in the highly <001>-textured 0.97(0.76Bi_(0.5)Na_(0.5)TiO_(3)-0.24SrTiO_(3))-0.03NaNbO_(3)(BNT-ST-0.03NN)ceramics with an ergodic relaxor(ER)state,leading to a large normalized strain(d_(33)^(*))of 720 pm/V.The introduction of NN templates into BNT-ST induces the grain orientation growth and enhances the ergodicity.The highly <001>-textured BNT-ST-0.03NN ceramics display a pure ergodic relaxor state with coexisted ferroelectric R3c and antiferroelectric P4bm polar nanoregions(PNRs)on nanoscale.Moreover,due to the incomplete interdiffusion between the NN template and BNT-ST matrix,the textured ceramics present a core-shell structure with the antiferroelectric NN core,and thus the BNT-based matrix owns more R3c PNRs relative to the homogeneous nontextured samples.The high <001> crystallographic texture and more R3c PNRs both facilitate the relaxor-to-ferroelectric transition,leading to the low-field-driven high strain,while the ergodic relaxor state ensures a small hysteresis.Furthermore,the d_(33)^(*)value remains high up to 518 pm/V at 100℃ with an ultra-low hysteresis of 6%.

Improved dielectric constant and energy density of P(VDF-HFP)composites using NBT-xST(x=0,0.10,0.26)whiskers

The high-performance energy-storage dielectric capacitors are increasingly important due to their wide applications in high power electronics.Here,we fabricated a novel P(VDF-HFP)-based capacitor with surface-modified NBT-xST(x?0,0.10,0.26)whiskers,denoted as Dop@NBT-xST/P(VDF-HFP).The influences of ST content,fillers’volume fraction and electric field on the dielectric properties and energy-storage performance of the composites were investigated systematically.The results show that the dielectric constant monotonously increased with the increase of ST content and fillers’volume fraction.The composite containing 10.0 vol%NBT-0.26STwhiskers possessed a dielectric constant of 39 at 1 kHz,which was 5.6 times higher than that of pure P(VDF-HFP).It was noticed that the D-E loops of the composites became thinner and thinner with the increase of ST content.Due to the reduced remnant polarization,the composite with 5.0 vol%NBT-0.26STwhiskers achieved a high energy density of 6.18 J/cm3 and energy efficiency of approximately 57%at a relatively low electric field of 200 kV/mm.This work indicated that NBT-0.26ST whisker is a kind of potential ceramic filler in fabricating the dielectric capacitor with high discharged energy density and energy efficiency.