Preparation and acoustic properties of high-temperature acoustic emission sensor based on La_(3)Ga_(5)SiO_(14) crystal

With the rapid development of modern industries,the high-temperature piezoelectric sensors that can work in extreme environments are in great demand.In this work,langasite(La_(3)Ga_(5)SiO_(14),LGS),as a high-temperature piezoelectric crystal with stable electro-elastic performance,is used as core element,and air and porous Al_(2)O_(3) are selected as backing layers respectively to prepare two kinds of high-temperature acoustic emission(AE)sensors.The detection sensitivities at 25–500℃ are analyzed by the ball falling test and Hsu–Nielsen experiment.Under the condition of 25–500℃,the received amplitude signals by both sensors are maintained above 90 dB stimulated by the ZrO_(2) ceramic ball dropping.In the Hsu–Nielsen experiment,as the temperature rising from 25℃ to 500℃,the signal amplitude of sensor with air backing layer decays from 447 mV to 365 mV,while the signal amplitude varies from 270 mV to 203 mV for the sensor with porous Al_(2)O_(3) backing layer.Signiffcantly,compared with the bandwidth of the air-backing sensor(37–183 kHz),the sensor with porous Al_(2)O_(3) backing layer broadens bandwidth to 28–273 kHz.These results show that both these AE sensors have strong and stable response ability to AE signals at high-temperature of 500℃.Therefore,piezoelectric AE sensor based on LGS has great potential application in the ffeld of high-temperature structural health monitoring.

Ferroelectric and piezoelectric properties of lead-free Li_(0.06)(K_(0.5)Na_(0.5))_(0.94)NbO_(3) thin films

Lead-free(K_(0.5)Na_(0.5))NbO_(3)(KNN)and Li_(0.06)(K_(0.5)Na_(0.5))_(0.94)NbO_(3)(LKNN)thin films were fabricated by a sol-gel method.The effects of Li substitution on crystal structure,microstructure and electrical properties of KNN film were systematically studied.Li doping can enhance the ferroelectric and piezoelectric properties of KNN film.Compared with pure KNN film,the LKNN film possesses larger remanent polarization(P_(r)~9.3μC/cm^(2))and saturated polarization(P_(s)~41.2μC/cm^(2))and lower leakage current density(~10^(−5)A/cm^(2)at 200 kV/cm).Meanwhile,a typical butterfly shaped piezoelectric response curve is obtained in the LKNN film with a high piezoelectric coefficient(d_(33)~105 pm/V).Excellent fatigue resistance(~10^(9)switching cycles)and aging resistance(~180 days)demonstrate the long-term working stability of LKNN film.These findings indicate that KNN-based lead-free piezoelectric films have a broad application prospect in microelectromechanical systems(MEMS).

Flexible lead-free BFO-based dielectric capacitor with large energy density,superior thermal stability,and reliable bending endurance

As an essential energy-stored device,the inorganic dielectric film capacitor plays an irreplaceable role in high-energy pulse power technology area.In this work,propelled by the challenge of overcoming the bottlenecks of inflexibility and inferior energy storage density of the pure BiFeO3 films,the mica with high bendability and thermal stability is adopted as substrate,and the relaxor ferroelectric(Sr_(0.7)Bi_(0.2))TiO_(3) is introduced to form solid solution to introduce relaxor behavior.The subsequently fabricated 0.3Bi(Fe_(0.95)Mn_(0.05))O_(3)-0.7(Sr_(0.7)Bi_(0.2))TiO_(3)(BFMO-SBT)thin film capacitor exhibits a high recoverable energy storage density(W_(rec)=61 J cm^(-3))and a high efficiency(η=75%)combined with a fast discharging rate(23.5 μs)due to the large polarization difference(ΔP=59.4 μC cm^(-2)),high breakdown strength(E_(b)=3000 kV cm^(-1)),and the strong relaxor dispersion(γ=1.78).Of particular importance is the capacitor presents excellent stability of energy storage performance,including a wide working temperature window of -50-200℃,fatigue endurance of 108 cycles,and frequency range of 500 Hz-20 kHz.Furthermore,there are no obviously deteriorations on energy storage capability under various bending states and after 104 times of mechanical bending cycles.All these results indicate that BFMO-SBT on mica film capacitor has potential application in the future flexible electronics.

Influence of the prestressed layer on spherical transducer in sound radiation performance

To improve the acoustic radiation performance of the spherical transducer,a prestressed layer is formed in the transducer through fiber winding.The influence of the prestressed layer on the transducer is studied from the effects of the radial prestress(Tr)and acoustic impedance,respectively.First,a theoretical estimation of Tr is established with a thin shell approximation of the prestressed layer.Then,the acoustic impedance is measured to evaluate the efficiency of sound energy transmission within the prestressed layer.Further,the ideal effects of Tr on the sound radiation performances of the transducer are analyzed through finite element analysis(FEA).Finally,four spherical transducers are fabricated and tested to investigate their dependence of actual properties on the prestressed layer.The results show that with the growth of Tr,the acoustic impedance of the prestressed layer grows,mitigating the enormous impedance mismatch between the piezoelectric ceramic and water,while increasing attenuation of the acoustic energy,resulting in a peak value of the maximum transmitting voltage response(TVRmax)at 1.18 MPa.The maximum drive voltage increases with Tr,leading to a steady growth of the maximum transmitting sound level(SLmax),with a noticeable ascend of 3.9 dB at a 3.44 MPa Tr.This is a strong credibility that the prestressed layer could improve the sound radiation perfor­mance of the spherical transducer.

Stable self-polarization in lead-free Bi(Fe_(0.93)Mn_(0.05)Ti_(0.02))O_(3)thick films

The BiFeO3-based film is one of the most promising candidates for lead-free piezoelectric film devices.In this work,the 1μm-thick Bi(Fe_(0.93)Mn_(0.05)Ti_(0.02))O_(3)(BFMT)films are grown on the ITO/glass substrate using a sol-gel method combined with spin-coating and layer-by-layer annealing technique.These films display a large saturated polarization of 95μC/cm^(2),and a rema­nent polarization of 70μC/cm^(2).Especially,the films are self-poled caused by an internal bias field,giving rise to asymmetric polarization-electric field(P-E)loops with a positive shift along the x-axis.A stable self-polarization state is maintained during the applied electric field increasing to 1500 kV/cm and then decreasing back.The weak dependence of P-E loops on frequency(1-50 kHz)and temperature(25-125°C)indicate that the internal bias field can be stable within a certain frequency and tempera­ture range.These results demonstrate that the self-polarized BFMT thick films can be integrated into devices without any poling process,with promising applications in micro-electro-mechanical systems.

Achieving both large piezoelectric constant and low dielectric loss in BiScO_(3)-PbTiO_(3)-Bi(Mn_(2/3)Sb_(1/3))O_(3)high-temperature piezoelectric ceramics

BiScO_(3)-PbTiO_(3)binary ceramics own both high Curie temperature and prominent piezoelectric properties,while the high dielectric loss needs to be reduced substantially for practical application especially at high temperatures.In this work,a ternary perovskite system of(1-x-y)BiScO3-yPbTiO3-xBi(Mn_(2/3)Sb_(1/3))O_(3)(BS-yPT-xBMS)with x=0.005,y=0.630-0.645 and x=0.015,y=0.625-0.640 was prepared by the traditional solid-state reaction method.The phase structure,microstructure,dielectric/piezoelec­tric/ferroelectric properties were studied.Among BS-yPT-xBMS ceramic series,the BS-0.630PT-0.015BMS at morphotropic phase boundary possesses the reduced dielectric loss factor(tanδ=1.20%)and increased mechanical quality factor(Qm=84),and maintains a high Curie temperature(TC=410°C)and excellent piezoelectric properties(d_(33)=330 pC/N)simultaneously.Of particular importance,at elevated temperature of 200°C,the value of tanδis only increased to 1.59%.All these properties indicate that the BS-0.630PT-0.015BMS ceramic has great potential for application in high-temperature piezoelectric devices.

Ultrahigh energy harvesting properties in Ag decorated potassium-sodium niobite particle-polymer composite

Composite-type piezoelectric nanogenerator(PENG)can potentially provide power to the flexible electronics devices by harvesting the mechanical energy.The electricity output of the PENG is not entirely excavated until now because the polarization dipoles are not sufficiently aligned during the high-voltage poling process.In this study,some Ag particles are attached on the(K_(0.4425)Na_(0.52)Li_(0.0375))(Nb_(0.86)Ta_(0.06)Sb_(0.08))O_(3)(KNN)piezoelectric particles and then they are mixed with multi-walled carbon nanotubes and polydimethylsiloxane to fabricate the PENG device.The Ag particles can reduce the optimal poling electric field from 10 kV/mm down to 5 kV/mm.The PENG device with Ag particles poled at 5 kV/mm can generate the highest open-circuit voltage of 282 V,short-circuit voltage of 32.2 mA,and maximum instantaneous power of 3.5mW under the external mechanical stress of 10 kPa without timedependent degradation(only 27.9 V and 2.6 mA for the pure KNN-based PENG poled at 10 kV/mm).These are much better than previously reported composite-type PENG.The electrical energy generated from the PENG(20mm×40 mm)can light up 40 white light emitting diodes instantaneously without any storage unit during the stomping stage.