Temperature-dependent ferroelastic switching of soft lead zirconate titanate

The longitudinal strain and polarization of a soft polycrystalline ferroelectric ceramic (lead zirconate titanate, PZT) were measured under uniaxial compressive stress at elevated temperatures utilizing a novel testing fixture. Ferroelectric ceramics have not previously been characterized under these conditions due to experimental complexity. In addition to nonlinear macroscopic constitutive behavior, the linear elastic moduli have been measured throughout the loading cycle, allowing for the determination of the relative contributions from the linear and nonlinear ferroelastic behavior as a function of stress and temperature. Experimental results show a strong temperature dependence of ferroelastic switching. The ferroelastic properties of unpoled and poled materials for temperatures up to the Curie point are contrasted with the spontaneous strain, elucidating the role of tetragonality in ferroelastic switching. When thermal changes are considered, marked changes in the maximum strain are observed.     

Ferroelastic domain switching fatigue in lead zirconate titanate ceramics

The influence of the frequency and amplitude of cyclic mechanical loading on soft, tetragonal lead zirconate titanate (PZT) ceramics was investigated via neutron diffraction. Intensity change in the {2 0 0} reflections provided quantitative measurements of domain switching behavior, domain texture and the strain resulting from domain switching. The results are explained using a viscoelasticity model. It was found that the magnitude of applied stress affects the level of strain accumulated, while its frequency affects the time taken for the strain to reach saturation. Furthermore, markedly different behaviors are exhibited by poled and unpoled samples. For samples loaded under identical conditions, the frequency effect is more pronounced in unpoled samples and the accumulated ferroelastic strain is greater in poled samples.     

Frequency effects on fatigue crack growth and crack tip domain-switching behavior in a lead zirconate titanate ceramic

The microstructural origins of the effect of frequency on the electrical fatigue behavior of pre-cracked soft ferroelectric Pb(Zr_0.48Ti_0.52)O₃ is investigated by means of a high spatial resolution hard X-ray synchrotron source. It is found that there is a strong link between the frequency of the applied bipolar field, domain-switching behavior in terms of ferroelastic reorientation of the domains around the crack tip and the resultant crack growth. The crack growth is accentuated under increased ferroelastic switching and, in particular, found to be more pronounced under low-frequency loading. The concept of domain wall viscoelasticity is applied to explain why lower frequencies accelerate crack growth under a bipolar electric field.     

TEM study of superstructure in a perovskite lead lanthanum zirconate stannate titanate ceramic

The superstructure of an antiferroelectric Pb_0.97La_0.02(Zr_0.66Sn_0.25Ti_0.09)O₃ phase, whose composition is near the morphotropic-phase boundary, was characterized. Systematic selected-area diffraction revealed that there were two kinds of superlattice reflections in the pseudocubic reciprocal lattice, i.e. superlattice reflections (h, k, l all odd), and one-dimensional incommensurate superlattice reflections, where g denotes the vectors of fundamental or superlattice reflections. Convergent-beam electron diffraction disclosed that the average structure of the phase was rhombohedral with space group of . Based on the rhombohedral reciprocal lattice, the reflections were no longer superlattice but fundamental reflections, and the reciprocal vector of the one-dimensional incommensurate reflections was re-expressed as

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, where h, k, l are integers and (−h + k + l) = 3n. In the light of the average structure and the reflection condition, the superspace Bravais class of the phase with one-dimensional incommensurate structure was determined to be in a (3 + 1)-dimensional space. In addition, the origins of the superlattice reflections were also examined and discussed.     

Dynamic processes of domain switching in lead zirconate titanate under cyclic mechanical loading by in situ neutron diffraction

The performance of ferroelectric ceramics is governed by the ability of domains to switch. A decrease in the switching ability can lead to degradation of the materials and failure of ferroelectric devices. In this work the dynamic properties of domain reorientation are studied. In situ time-of-flight neutron diffraction is used to probe the evolution of ferroelastic domain texture under mechanical cyclic loading in bulk lead zirconate titanate ceramics. The high sensitivity of neutron diffraction to lattice strain is exploited to precisely analyze the change of domain texture and strain through a full-pattern Rietveld method. These results are then used to construct a viscoelastic model, which explains the correlation between macroscopic phenomena (i.e. creep and recovered deformation) and microscopic dynamic behavior (i.e. ferroelastic switching, lattice strain).     

Mechanism of electric fatigue crack growth in lead zirconate titanate

A series of experiments was performed with through-thickness cracks in ferroelectric double cantilever beam (DCB) specimens. Cyclic electric fields of different amplitudes were applied which resulted in cyclic crack propagation perpendicular to the electric field direction. Crack propagation was observed optically and three regimes were identified: a pop-in from a notch, steady-state crack growth and a decrease of the crack growth rate with increasing cycle number. Crack growth only occurred if the applied field exceeded the coercive field strength of the material. Furthermore, the crack extended during each field reversal and the crack growth rate increased with increasing field. Based on the experimental observations, a mechanistic understanding was developed and contrasted with a nonlinear finite element analysis which quantified the stress intensity in the DCB specimens. The driving forces for crack formation at the notch and subsequent fatigue crack growth were computed based on the distribution of residual stresses due to ferroelectric switching. The finite element results are in good agreement with the experimental observations and support the proposed mechanism.     

锆钛酸铅压电陶瓷的流延法制备及其性能

流延法工艺具有工艺便捷、尺寸可调、成膜质量好等优势。采用流延法制备PZT压电陶瓷,通过扫描电子显微镜观察压电陶瓷微观形貌,通过准静态d33测量仪测试压电陶瓷的压电应变常数d33。探究粉末粒径以及流延工艺参数包括刮刀高度、流延速度、热压压力等对PZT压电陶瓷性能的影响,获得的PZT压电陶瓷其压电应变常数d33最高可达454 pC/N,致密度最高可达97.68%。该方法适用于制备大尺寸压电器件。     

Influence of radial stress on the poling behaviour of lead zirconate titanate ceramics

The development of new piezoelectric materials is often hampered by high electrical conductivity or coercive fields, which make it virtually impossible to produce sufficient levels of electric polarization by application of an external electric field. As a remedy, we utilize a new poling method: stress-assisted poling, which is based on the simultaneous application of electrical field and mechanical stress. The method is demonstrated on a commercial ferroelectric (PZT PIC 151). The poling field E¹ where most domain switching occurs is reduced by about 40% if a radial compressive stress of about 90 MPa is applied to the sample. The piezoelectric coefficient d₃₃ is determined for different load magnitudes. Variations of both remnant and maximum polarization are determined with respect to the magnitude of compressive radial stress.     

Improving the fatigue endurance of lead zirconate titanate thin films through PbO interfacial modification

The effects of the modification of electrode/ceramic interfaces through a chemical solution deposition-derived PbO buffer layer on the fatigue endurance of lead zirconate titanate(PZT) thin films were investigated.The grain size and the surface roughness of the PZT films increased through PbO interfacial modification.Moreover,the PZT films with PbO interfacial modification had a better crystallographic structure and no evident secondary phases were observed.While the remanent polarization and dielectric constant were reduced,the fatigue endurance was improved.Based on the results,the mechanism for the fatigue endurance improvement was discussed.     

Influences of temperature and electric field on the bending strength of lead zirconate titanate ceramics

The present work studies the effects of temperature and a d.c. electric field on the bending strength of PZT-841 ceramics using three-point bending measurement. In the temperature range from 30°C to the Curie point T_c (≈272°C), the bending strength as a function of temperature exhibits a valley shape and the valley floors at a temperature around 225°C, revealing a 25% reduction in comparison with the bending strength at room temperature. Meanwhile, elastic compliance and damping factor exhibit peaks, respectively, at 225°C and 220°C, implying a strong correlation between bending strength and compliance. A positive or negative electric field larger than 3 kV/cm reduces the bending strength of PZT-841 ceramics significantly. For example, the bending strength under a positive field of 20 kV/cm is only one half of that without application of any electric field. The electric field is able to fracture mechanically sustained samples. Under a constant load of 70 MPa, the mean value of the critical electric field at fracture is 11.0 kV/cm. A 90°-domain wall kinetic model is herein proposed to understand the observed phenomena.     

Dielectric and piezoelectric properties of low-temperature sintered lead zirconate titanate ceramics with 0.78PbO-0.22CuO flux addition

Liquid phase sintering of lead zirconate titanate (abbreviated as PZT) ceramics with a 0.78 PbO-0.22 CuO (10:1 in weight ratio) flux was investigated. A small amount sintering flux consisting of a stoichiometrically mixed oxide of PbO-CuO with a eutectic composition successfully accelerated densification of the PZT ceramics far below the conventional sintering temperature. With the 3 wt% flux additions, full densifications of the PZT ceramics were achieved at temperatures as low as 825 °C. The results obtained in the crystal structure, microstructure, and electrical property analyses suggest that the Cu²⁺ impurity ion substitutes as an acceptor center for the perovskite B-site without forming isolated secondary phases. Defect associates of the Cu²⁺ impurities and charge compensating oxygen vacancies appear to affect dielectric and piezoelectric properties of the sintered PZT samples in both positive and negative ways by forming defect dipoles. When the Cu²⁺ content is small, slightly improved dielectric and piezoelectric performances were achieved, though ferroelectric relaxation was obviously developed at the higher Cu²⁺ contents. For the PZT samples sintered at 825 °C with 3 wt% flux addition, relative dielectric permittivity was 2200 and dielectric loss was less than 2%. Remnant polarization, coercive fields, and piezoelectric coefficient (d₃₃) were 32 μC/cm², 8.9 kV/cm and 373 pC/N, respectively.     

Theoretical modeling of coexisting tetragonal and rhombohedral heterophase polydomain structures in lead zirconate titanate ferroelectric films near the morphotropic phase boundary

The coexistence of tetragonal and rhombohedral phases as elastic domains is studied in this paper for lead zirconate titanate (PZT) ferroelectric films near the morphotropic phase boundary (MPB). The volume fractions of the phases and different twin components are obtained as functions of misfit strain and film orientation. It is shown that the superior electromechanical properties of MPB-PZT films may be understood on the basis of a field-induced evolution of the heterophase polydomain structure.     

Comparative studies on structural and electrical properties of lead titanate synthesized by ceramic and co-precipitation method

Lead titanate, PbTiO₃ (PT), ceramic material is a useful piezoelectric material for high-temperature and high-frequency applications such as non-volatile memories, infrared sensors and capacitors. However, it is very difficult to obtain a pure-phase and dense PT as a result of a maximum c/a ratio. In this paper, we have reported a conformable PT ceramics with standard double sintering as well as chemical co-precipitation method were successfully synthesized by means of carefully controlled processing parameters, viz., pH value, sintering temperature, soaking time and heating/cooling rates. This novel method was developed to synthesize PbTiO₃ sample so as to gain better control on chemical homogeneity and stoichiometry. Moreover, relatively inexpensive laboratory grade (LR) lead nitrate [Pb(NO₃)₂] and titanium tetra-isopropoxide [Ti{OCH(CH₃)₂}₄] are used as starting materials. Single phase formation was confirmed through X-ray diffraction (XRD) analysis. The room temperature conductivity study was done by measuring AC conductivity in the frequency range from 100 Hz to 1 MHz and DC resistivity in the temperature range from room temperature to 800 K. Dielectric measurements were carried out at selected frequencies from room temperature to well above transition temperature (T_c). Discussion on comparison between both preparation methods was made on the basis of observed results from electrical properties.     

Electrical properties of a-axis aligned lanthanum-modified lead titanate thin films prepared using sol-gel process

The (100) epitaxial lanthanum-modified lead titanate (PLT) film was fabricated using sol-gel method on platinized MgO substrates. The substrate used was Pt(100)JTi(100)JMgO where Pt and Ti layers had been sputter-deposited at 600°C. We used the direct furnace insertion method and the crystallization temperature of 700°C in order to fabricate the epitaxial film. The phase of the film was examined using x-ray diffraction (XRD) and the film orientation was examined by pole figure and x-ray rocking curves. The epitaxial PLT thin film had higher dielectric constant and better ferroelectricity and fatigue resistance than the polycrystalline films. However, it shows higher leakage current than the polycrystalline film.     

Crack tip chemistry and electrochemistry of environmental cracks in AA 7050

The role of the crack environment in establishing environment-assisted crack (EAC) propagation in AA 7050 alloys is elucidated. A suite of mini-electrodes provided real-time in situ measurements of the crack potential, pH, and chloride concentration during stage II cracking in a chromate-chloride electrolyte under electrochemical control. For material aged to an EAC-susceptible condition, crack growth during an incubation period is characterized by tip polarization to near the applied electrode potential (E_App) and bulk-like chemistry near the crack tip. In contrast, establishment of high-rate crack growth coincided with the development of an acidic, high chloride concentration tip environment and tip depolarization. During steady state high rate crack growth, the tip potential was ∼−0.85V_SCE; near-tip potential gradients were ∼1 V/cm. Large ohmic potential drop within fast-growing cracks is indicative of net anodic current in the near tip region and increased mass transport resistance within the crack due to solid corrosion products and/or hydrogen bubble formation. Microinjection of a corrosion-inhibiting or corrosion-promoting solution at the tip suppresses or prompts, respectively, the transition from incubation to high-rate cracking, highlighting the intimate dependence of the crack growth kinetics on the local chemistry. The exceptional EAC resistance of over-aged AA 7050 is intrinsic; injection of an acidic aluminum chloride solution at the tip of a crack of this material while polarized to a high E_App failed to induce brittle crack advance.