Optimization of calcination temperature of lead-free BiFeO3–BaTiO3 high-temperature piezoceramics

0.7BiFeO₃-0.3BaTiO₃+1mol% MnO₂(0.7BFO-0.3BTO) ceramics were synthesized by conventional solid-state powder method under different calcination temperatures (T_cal) between 770 and 830 °C. The phase structure, microstructure, and ferroelectric and piezoelectric properties changed greatly depending on the applied T_cal. Benefitting from the formation of low defect levels and large grain size and an appropriate morphotropic phase boundary (MPB) with the rhombohedral-to-pseudocubic phase ratio = 49.1 : 50.9, BFO-BTO ceramics calcined at 785 °C showed the best ferroelectric, piezoelectric, and insulating properties (P_r = 23.1 μC/cm², E_C = 25.8 kV/cm, d₃₃ = 167.8 pC/N, k_p = 0.342%). Above T_cal = 800 °C, however, the ferroelectric and piezoelectric properties deteriorated because volatilization of Bi and reduction of Fe caused a poor insulating property and high degree of chemical inhomogeneity. Moreover, the ceramics calcined at 785 °C showed a high Curie temperature (T_C) of 509.2 °C and excellent thermal aging resistance of d₃₃ up to 450 °C, demonstrating great potential for use in high-temperature applications.     

Preparation of PZT Thick Films by an Interfacial Polymerization Method

Pb(Zr_0.53Ti_0.47)O₃ (PZT) films of 10 to 50 m in thickness were prepared by a new sol-gel process using an interfacial polymerization technique. The interfacial polymerization process is that an alkoxide precursor solution is poured on the surface of water in a container to form a gel film at the interface between the two immiscible liquids. The precursor solution was prepared by adding PZT alkoxide solution, PZT powders coated with Pb₅Ge₃O₁₁ (PG), and a surfactant into hexane solvent. After the polymerization at the interface, the gel films were gently placed on a silicon substrate by draining the water in the container. The gel films containing PZT powders were sintered at 950°C for 10 min to obtain crystallized PZT films. The remanent polarization of a PZT thick film was 33.1 C/cm². The piezoelectric d ₃₃ constant measured with a Mach-Zehnder interferometer was 225 pm/V and was independent of frequency from 0.2 to 3 kHz.     

Short-Term Damage of a Transversely Isotropic Piezoelectric Material with Complex Strain-Stress State

The microdamage of porous transversely isotropic piezoelectric materials under complex macrostress is studied. The microdamages are modeled by pores. The damage of a microvolume is defined by the generalized Huber-Mises failure criterion for a transversely isotropic medium. The ultimate strength is a random function of coordinates with exponential or Weibull distribution. The stress-strain state and effective properties of the material are determined from the stochastic equations of electroelasticity. The deformation and microdamage equations are closed by the porosity balance equations. Deformation curves are plotted for two values of macrostrain or macrostress and different values of electric intensity. The influence of electric intensity on the microdamage of piezoelectric materials is studied__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 3, pp. 79–92, March 2005.     

集成结构振动主动控制和抑制

采用一种新的压电板单元,建立了含有分布压电传感元件和执行元件的集成结构的有限元动力模型。研究了这种集成结构在常增益负速度反馈控制规律作用下,振动的主动控制与抑制的问题,并提出了集成结构振动主动控制和抑制的一般方法。最后,提供了数值示例,说明本文提出方法的有效性。     

Electromechanical response of 2-2 layered piezoelectric composites: A micromechanical model based on the asymptotic homogenization method

A micromechanical model based on the asymptotic homogenization technique has been developed to predict the complete elastic, dielectric and piezoelectric properties of a general 2-2 layered piezoelectric composite where the constituent phases are elastically anisotropic and piezoelectrically active. Two classes of layered piezoelectric composites (i.e. longitudinally and transversely layered) are considered in two widely different ceramic- and polymer-based systems and their effective properties are obtained in the limits of both large-volume (i.e. bulk) and small-volume (i.e. thin-film) systems. It is demonstrated that: (i) in the bulk, ceramic–ceramic layered composite system, the elastic, piezoelectric, and dielectric properties of the composites vary linearly with volume fraction of the second phase, while in the bulk ceramic–polymer layered composite system, the corresponding properties vary non-linearly with volume fraction of the second phase; (ii) in the prismatic (thin-film) layered piezoelectric composite system, the non-vanishing, effective elastic, piezoelectric and dielectric properties vary linearly with the volume fraction of the second phase for both the longitudinally and transversely layered composite structures in the ceramic–ceramic and the ceramic–polymer composite systems; (iii) the ceramic–polymer piezoelectric layered composites that incorporate a low density polymeric phase with lower acoustic impedance generally exhibit enhanced piezoelectric coupling constants and lowered acoustic impedance; (iv) the longitudinally layered composites exhibit higher piezoelectric coupling constants and lower acoustic impedance compared to that of the transversely layered composites; and (v) the best combination of properties for applications such as hydrophones (i.e. the highest piezoelectric coupling constants and the lowest acoustic impedance) is obtained in the ceramic–polymer, longitudinally layered, thin-film, piezoelectric composites.     

智能结构有限元动力模型的建立及主动振动控制和抑制

采用一种新的压电板单元，建立了含有分布压电传感元件和执行元件结构（智能结构）的有限元动力模型。利用两种反馈控制律，研究了智能结构振动控制与抑制的问题，并提出了智能结构主动振动控制和抑制的一种方法。最后，提供了数值示例，说明本文提出方法的应用。     

Simulation of butterfly loops in ferroelectric materials

Ferroelectric materials exhibit complex behaviour upon electric and mechanical loading. Their change of polarization and length is accompanied by hysteresis. The so-called butterfly loop characterizing the strain due to an applied electric field is striking. As these materials are used in technical applications as sensors, actuators, and non-volatile memory units, the ability to simulate these hysteretic phenomena is important. Here, a one-dimensional model is proposed that is capable of describing the qualitative behaviour of widely used perovskite-type ferroelectric materials.Received: 3 July 2003, Accepted: 10 July 2003     

Nonaxisymmetric Electroelastic Vibrations of a Hollow Cylinder with Radial Axis of Physicomechanical Symmetry

An approach is proposed to calculate the natural frequencies and modes of vibrations of cylindrically anisotropic piezoelectric cylinders. The frequency equation is derived, and the frequency spectrum is analyzed __________ Translated from Prikladnaya Mekhanika, Vol. 41, No. 7, pp. 68–72, July 2005.