Discharge characteristics of pre-polarized doped lead zirconate titanate under impact at room and high temperature

Piezoelectric materials have more and more applications in modern smart fuzes due to their multiple uses such as energy storage and sensing. The electrical output characteristics of piezoelectric ceramics under high temperature and high overload environments are critical to the reliability of the device. In this paper, the mechanical and electrical response of pre-polarized doped lead zirconate titanate (PZT-5H) under impact at room temperature to 250°C, that is, above the Curie temperature, was investigated through a split-Hopkinson pressure bar experiment with an additional electrical output measurement system. The depolarization effect caused by temperature and the mechanical load was analyzed. A thermoviscoelastic constitutive model considering temperature and the strain rate was built based on the experimental data. The model can successfully predict the mechanical and electrical response of PZT-5H under impact at different temperatures. The discharge characteristics of PZT-5H under impact in the cooling stage after high-temperature depolarization were also investigated, and the apparent flexoelectric coefficient of the PZT after complete depolarization was calculated. The research results show that the dynamic piezoelectric coefficient of PZT-5H has a nonlinear relationship with temperature. During the high-temperature cooling process, PZT has a shock-induced polarization under the impact, and the output voltage is less than the polarized piezoelectric ceramic but higher than the flexural polarization at the same temperature. After complete depolarization, the apparent flexoelectric coefficient of PZT-5H is 127 μC/m.     

Effects of uniaxial prestress on the ferroelectric hysteretic response of soft PZT

This paper deals with the influence of preload stress on the ferroelectric hysteretic behavior of piezoelectric ceramics. The polarization and strain versus electric field hysteresis loops were measured for soft lead zirconate titanate (PZT) piezoceramic material under various uniaxial compressive stress preloads of up to −400 MPa. The investigation revealed that the superimposed compression load reduced the remnant polarization, decreased the coercive field, and also had a significant impact on the dielectric and piezoelectric properties. With increasing mechanical load, dielectric hysteresis and butterfly hysteresis became less and less pronounced, as the compressive stress prevented full alignment of the domains and induced mechanical depolarization. The slopes of the polarization and strain curves at zero electric field were measured to evaluate the dependence of permittivity and piezoelectric coefficients on the prestress. The experimental results were interpreted in terms of the non-180° domain switching process under combined electromechanical loading.     

Discharge characteristics of fractured soft piezoelectric ceramics under repeated impact

Pb_1·0[Zr_0·49Ti_0·46(Li_0·25Sb_0.75)_0.05]O₃(PZT-5H) is easy to break under overload. To explore the electrical output characteristics of fractured PZTs when they are subjected to repeated impact, experiments were performed by using SHPB loading and testing system. The results show that the irregularity of internal defects for PZT has different breaking strengths. The breaking strength of PZT-5H in experiments varies from 30 MPa to 50 MPa. The electric displacement and stress can meet the classical piezoelectric equation without considering the influence of fracture on discharge, but the dynamic and quasi-static piezoelectric constants d₃₃ are quite different. With the increase of stress rising rate, d₃₃ increases gradually. Under different impact velocities, the relationship between electric displacement and stress peak is nonlinear; Whether it is electrical short-circuit or open-circuit, the influence of fracture on the electrical output is limited. The influence of crack caused by overload on discharge can be ignored when the electrode material does not be damaged.     

Electromechanical properties of [0 0 1]-textured Mn–PMN–PZT ceramics under uniaxial pressure

Dielectric, ferroelectric, and piezoelectric properties of both random and textured Mn–PMN–PZT ceramics were characterized under uniaxial stress. Textured ceramics exhibit a large piezoelectric response under uniaxial pressure; the bias field piezoelectric constant is higher than 700 pC/N when pressure is below 50 MPa. Moreover, textured ceramics also show better depolarization resistance under uniaxial stress fields; overall, 30% of the origin performance will remain when stress approaches 200 MPa, but for random ceramics, it is only 10%. The ferroelectricity of both random and textured ceramics is suppressed by uniaxial compression. E_c, P_r, E_i, and dissipation energy all decrease with increasing uniaxial stress. In addition, phase-field simulation was used to better understand the polarization-changing effects on piezoelectric and dielectric performance. The uniaxial stress causes polarization rotation and increases the angle between polarization and the electric field, which is an important factor leading to the increase of the dielectric constant.     

Dynamic fracture behavior of piezoelectric ceramics under impact: Force-electric response and electrical breakdown

The brittle fracture may occur in the application of piezoelectric ceramics, but the traditional research is still limited to the static fracture of the materials. Based on the improved Hopkinson pressure bar loading system and high-speed photography technology, the experimental study on the fracture behavior of piezoelectric ceramics under impact loading was carried out. The dynamic mechanical and electrical response of lead zirconate titanate (PZT) and the possible electric breakdown phenomenon were analyzed. The experimental results show that the output voltage is stable and the maximum output voltage is 889 V when the impact load does not cause the material to fracture. When the material breaks, its macroscopic output voltage fluctuates due to electric breakdown. Combined with the finite element simulation of the impact fracture process, the distribution characteristics of the stress field and electric field near the crack during the fracture process were analyzed. The results show that the sliding between grains formed the crack cavity parallel to the electric field during the impact process. Furthermore, based on the theory of dielectric breakdown, the possibility of electric breakdown in the initial defect and the elliptical cavity formed by the impact is analyzed.     

Ultrahigh-performance [001]-oriented porous PZT-5H single crystal grown by the solid state crystal growth method

Porous PZT-5H single crystals are grown by the solid state crystal growth (SSCG) method. The microstructure, phase structure and dielectric/piezoelectric properties are investigated for [001]-oriented porous PZT-5H single crystal. Evolution of phase structure with temperature is researched using in-situ temperature-dependent X-ray diffraction. The effect of pores on performance parameters is simulated using COMSOL Multiphysics® software. Ultrahigh piezoelectric coefficient d₃₃ of up to about 1700 pC/N and effective piezoelectric coefficient d₃₃* of up to about 3700 pm/V at 5 kV/cm are obtained. Moreover, the effective piezoelectric coefficient d₃₃* is stable around 1900 pm/V under 3 kV/cm and 5 kV/cm in the temperature range of 70–160 °C. Importantly, the sample possess an extremely large figure of merit g₃₃*d₃₃ (111 × 10⁻¹² m²/N), which is related to the presence of pores in the single crystal. This work expands the scope of PZT based single crystal and highlights their significant application possibilities in piezoelectric energy harvester, and actuator at high temperature.     

Preparation of PZT Microtubes by Slip Casting on Vermicelli,Followed by In Situ Polymerization

Slip casting of lead zirconate titanate (PZT) slurries of higher solids loading (48.8–51.6 vol%) prepared in a urea–formaldehyde (UF) monomer solution on vermicelli of ∼1000 μm diameter has been studied to prepare PZT microtubes with a higher wall thickness (200–960 μm) in a lower dipping time (0.5–4.0 min) to facilitate faster production and lower failure during drying and vermicelli burnout. Polymerization of the UF monomer by exposing the PZT slurry-coated vermicelli to HCl gas provides good strength and stability to the coating. The dielectric and piezoelectric properties of the microtubes compare well with the properties of PZT-5H ceramic compositions.     

Fatigue crack growth in ferroelectrics under electrical loading

Fatigue crack growth is investigated in the polycrystalline ferroelectrics PZT-5H and PLZT 8/65/35 under electrical loading. The fatigue cracks exhibit features such as bifurcation and tunnelling, followed by crack arrest. The nature of the resulting damage differs in the two materials: in PZT-5H a narrow zone of intergranular cracks propagates across the specimen, wedging the crack surfaces apart. In PLZT 8/65/35 a broad microcracked band spreads across the specimen. The rate of crack growth is found to correlate well with the amplitude of electric displacement.     

Flywheel-type tensile impact tester with a new load cell for polymer sheet and film

A new load cell for flywheel-type impact tensile testing was designed and fabricated for specimens of polymer sheet and film. The cell employs a piezoelectric ceramic oscillator (toric in shape) as a load sensor, which has a high natural frequency (1800 kHz) and high sensitivity (ca. 0.1 V/N without amplification). The time constant for the electric circuit was improved substantially by the introduction of a voltage follower using an operational amplifier with excellent performance (common mode voltage ±120 V and slew rate 100 V/μsec). The positioning of the load sensor and the shape of specimen clamps are important design features, especially the halved Morse-type taper pins in the structure of the specimen clamps. Signals of impact, passing through the piezoelectric oscillator and the voltage follower, are recorded by a transient time converter. The converter is equipped with a memorization system, an automatic pretrigger circuit, and a facility for reproduction under a slow time base, thus eliminating the need for troublesome photographing. For performance testing of the impact tester, oriented poly(ethylene terephthalate) sheets were used and good results were obtained.     

Directional properties of ordered 3‐3 piezocomposites fabricated by sacrificial template

Fabrication of piezoelectric composites with 3‐3 connectivity and their properties have attracted attention due to the application of these composites in acoustic transducers, medical imaging, and nondestructive testing. In this research, directional piezoelectric‐polymer composites with 3‐3 connectivity are prepared by a relatively simple fabrication process of dipping an ordered polymeric template (mesh) into lead zirconate titanate suspension followed by drying, pyrolysis, and sintering. The resulting porous ordered structures of lead zirconate titanate‐5A ranging from 18 to 32 vol% ceramic were subjected to polymer injection to form composites to be cut and polarized in different directions. In the composites, the effects of (i) polarization direction and (ii) active piezoelectric phase content on the dielectric and piezoelectric properties were investigated. The results showed that the dielectric constant and the piezoelectric properties are significantly dependent on the direction in composites of directional structure. In these composites, dielectric constant values were found to be higher in the direction parallel to ceramic ligaments. Moreover, the highest values for piezoelectric charge and voltage coefficient and figure of merit were found in the direction 45° to ceramic ligaments. In all composites, both dielectric constant and piezoelectric property values were proportional to the active piezoelectric phase content.     

PMnS-PZN-PZT压电纤维的制备与铁电性能

采用固相法制备了0.8Pb(Mn1/3Sb2/3)0.05(Zr1/2Ti1/2)0.95O3–0.2Pb(Zn1/3Nb2/3)0.28(Zr1/2Ti1/2)0.72O3(PMnS–PZN–PZT)粉末,然后用塑性聚合物方法制备了PMnS–PZN–PZT压电纤维。研究了纤维夹持状态对其铁电性能的影响。结果表明:塑性聚合物法制备的PMnS–PZN–PZT压电纤维具有良好的铁电性能,压电纤维处于自由状态时,剩余极化强度和矫顽场分别为85.4μC/cm2和8.5kV/cm,但电滞回线很难饱和。将纤维采用环氧树脂固化后,剩余极化强度变成39.2μC/cm2,电滞回线呈饱和状态,说明夹持状态对纤维的铁电性能产生很大的影响。高压下压电纤维浇铸前后的漏电流测试结果表明,压电纤维浇铸后剩余极化强度变小主要与漏电流有关。     

Fabrication and function examination of PZT-based MEMS accelerometers

In this study, a hybrid sol-gel method was used to fabricate Pb(Zr_0.52Ti_0.48)_0.98Nb_0.02O₃ (PNZT) piezoelectric thick films. By preparing Pb(Zr_0.52Ti_0.48)_0.98Nb_0·02O₃ sol-gel solutions and mixing them with PZT-5A piezoelectric powders, therefore, the thickness of single layer coating can be increased and reduce the risk of film cracks. The proposed PNZT films have the dielectric constant of 1750, dielectric loss of 0.063, remnant polarization of 58 μC/cm², and d₃₃ of 133 p.m./V. Piezoelectric cantilever beam MEMS accelerometers were then designed, simulated and fabricated via photolithography methods on Si substrates. The sensitivity and natural frequency of the cantilever beam accelerometer are 16.8 mV/g and 200Hz, respectively. Finally, a cantilever beam accelerometer is successfully applied for the server hard-drive fault detection.     

Anisotropic growth kinetics and electric properties of PZT-5H single crystal by solid-state crystal growth method

The PZT-5H single crystal growth on [111]c-, [110]c-, and [001]c-oriented seed crystal by solid-state crystal growth (SSCG) method was investigated. The growth rate of PZT-5H single crystal strongly depends on seed crystal orientation and annealing time. The mean growth distance is 682, 620, and 93 μm for [111]c-, [110]c-, and [001]c-oriented PZT-5H single crystal grown at 1150°C for 8 h, respectively. The growth kinetics of SSCG-grown PZT-5H single crystal was discussed. It is found that the growth of single crystal is driven by the solubility difference between the matrix grains and single crystal growth front interface, arising from the local curvature and the crystallographic directions dependent solubility. The growth of [001]c-oriented PZT-5H single crystal was mainly contributed from the difference solubility arising from the local curvature of growth front interface, while the growth of [111]c- and [110]c-oriented PZT-5H single crystal was mainly contributed from the difference solubility between {111} and {110} plane of single crystal and matrix grains. The piezoelectric coefficient d₃₃ of up to 1028pC/N (about 50% larger than that of the same component ceramic) was obtained in a [110]c-oriented PZT-5H single crystal with a Curie temperature of about 230°C. The large field piezoelectric constants d₃₃* of up to 1160 pm/V (about 50% larger than that of the same component ceramic) at 15 kV/cm was also obtained in [110]c-oriented PZT-5H single crystal with a large strain of 0.18%. This work deepens our understanding on the growth kinetics of SSCG and pushes the way of growth of soft PZT single crystal by SSCG.     

New methodology for determining the dielectric constant of a piezoelectric material at the resonance frequency range

A new methodology is proposed to measure the dielectric constant and loss of a piezoelectric at the resonance frequency range based on the burst excitation method. Using a k₃₁ type soft PZT rectangular specimen, we investigated the “force” and “voltage” factors carefully under the short‐ and open‐circuit conditions of the burst method, in terms of the ratio of the ring‐down current and voltage with the plate end vibration velocity and the displacement, and their phase lags. We provide the obtained material properties, including loss parameters, in particular, dielectric properties at the resonance frequency range.     

Determination of reversible and irreversible contributions to the polarization and strain response of soft PZT using the partial unloading method

Experimental work is aimed at systematically investigating the non-linear ferroelectric and ferroelastic behavior of a commercially available soft lead zirconate titanate (PZT) material. The fast partial unloading method is used to measure the material properties of unpoled soft PZT under pure electric field and of initially pre-poled soft PZT under compressive stress loading. In the first experiment using unpoled PZT, the evolution of piezoelectric constants and dielectric permittivity is determined as a function of electric field. It is found that the piezoelectric constants and dielectric permittivity depend on the electric field history. The results are used to separate the reversible strain and polarization from the irreversible ones caused by domain switching. In the second experiment using initially pre-poled PZT, it is found that the strain response is significantly dependent on the stress loading rate. The elastic moduli and piezoelectric coefficients are evaluated with respect to the compressive stress history. The measured longitudinal and transverse irreversible strains change significantly during both loading and unloading processes. An attempt is made to discuss the use of irreversible strain and irreversible polarization as internal variables for constitutive modeling. This investigation provides valuable information for modeling to predict the performance and for improving the reliability of piezoelectric devices.     

Mechanical response and crack propagation of oil well cement under dynamic and static loads

The dynamic mechanical properties and fracture mechanism of three types of oil well cement with different formulations were investigated using a Φ50?mm split Hopkinson pressure bar (SHPB) and quasi-static mechanical tests were conducted with a hydraulic universal testing machine. The stress-strain diagram, time-stress diagram, total energy absorption diagram, and the dynamic growth factor (DIF) under different strain rates were obtained. The crack propagation process of the oil well cement under dynamic loading is evaluated using high-speed photography to determine the fracture mechanism. The test results show that the strength of the cement increases under a dynamic impact. The compressive strength of the pure cement increases from 37?MPa to 184.80?MPa under static loading. However, the peak stress of the cement stone strengthened with cellulose fiber is lower under a dynamic load than a static load. Under dynamic loading, the absorption energy is higher for the pure cement stone than for the cement stone reinforced with whiskers and cellulose. Furthermore, the crack initiation, crack propagation, and fracture characteristics of the oil well cement are different under dynamic and static loads. Under a static load, the rupture of the cement is the result of the propagation of the tensile cracks. Under dynamic loading, there are fewer micro cracks on the cement surface and a composite fracture results from tensile and shear cracks.     

Measurement of Indentation Residual Stresses in Materials Susceptible to Slow Crack Growth

Knowledge of the size and distribution of the indentation residual stress field is important when interpreting slow crack growth data for indented ceramic materials. A technique based on compressively loading indentation cracks has been used to measure the wedging residual stresses at radial indentation cracks. The method also gives information on the fatigue limit and can be applied on any ceramic material susceptible to slow crack growth. Soda–lime glass specimens were indented and the resulting residual stresses, wedging the radial cracks, were measured as a function of indentation load. Calculations of K ₀, the fatigue limit, were made for both virgin indentation cracks and cracks aged until saturation. The magnitude of closing stress needed to prevent slow crack growth was found to depend linearly on the indentation load. For example, for indentation loads of 20 and 60 N, the corresponding closing stresses were 14 and 26 MPa, respectively.     

Thermodynamic Theory of Single-Crystal Lead Titanate with Consideration of Elastic Boundary Conditions

A phenomenological free-energy function including the effects of elastic boundary conditions was presented and used to investigate the single-domain, single-crystal properties of the ferroelectric perovskite, PbTiO₃. In particular, the effects of tensile and compressive hydrostatic stress on the spontaneous polarization, Curie point, dielectric susceptibility, and piezoelectric property coefficients were examined. The calculated shift of the Curie point with hydrostatic stress, along with the entropy and enthalpy of the ferroelectric-paraelectric phase transition, was found to be in good agreement with experimental measurements. The isothermal variation of the relative dielectric susceptibility and piezoelectric coefficients with hydrostatic stress exhibited the expected behavior near the ferroelectric-paraelectric phase transition.     

Poling of Lead Zirconate Titanate Ceramics and Flexible Piezoelectric Composites by the Corona Discharge Technique

In the conventional poling method, piezoelectric ceramics and composites are poled by applying a large dc voltage. Poling of composites having a polymer matrix with 0–3 connectivity is especially difficult because the electric field within the high-dielectricconstant grains is far smaller than in the low-dielectric-constant polymer matrix. Therefore, very large electric fields are required to pole these types of composites. However, large electric fields often cause dielectric breakdown of the samples. In this study for improved poling, the corona discharge technique was used to pole piezoelectric ceramics, fired PZT composites, and 0.5PbTiO₃· 0.5BiFeO₃ 0–3 polymer composites. An experimental setup for corona poling is described. The dielectric and piezoelectric properties of materials poled by the corona discharge technique were comparable to those obtained with the conventional poling method.