铁电陶瓷中电畴翻转研究进展

电畴为铁电陶瓷固有的独特微观组织特征之一,铁电陶瓷的许多性能均与其密切有关.综述了铁电陶瓷中的电畴结构,系统介绍了电场、机械作用引起的电畴翻转,概述了电畴翻转对铁电陶瓷断裂韧性的影响及其研究进展.     

Variations in predicting domain switching of ferroelectric ceramics

In this article, a set of equivalent variational formulations for computing the driving forces for domain switching in ferroelectric materials is presented. It is proven that these formulations allow the free adoption of any couple of mechanical and electric fields as independent variables while obtaining consistent results. In addition, explicit expressions are provided for each formulation which allows for the study of the phase transformation process under different constraints.     

Numerical analysis of ferroelectric/ferroelastic domain switching in ferroelectric ceramics

A numerical approach predicting the behavior of ferroelectric ceramics under electric field and mechanical loading is proposed in this paper. In the model, macroscopic properties of ferroelectric ceramics are determined by microscopic structures. Ferroelectric ceramics are seen to be composed of many domains with different orientations, and domain switching is the source of the nonlinear constitutive behavior of the ferroelectric ceramics. Numerical calculations based on the model were carried out, and the computational results are compared with the experimental results, which shows the two sets of results consist with each other. The calculation approach can provide a guidance for the ceramics component design.     

Electric fatigue of (BaPb)TiO3 ferroelectric ceramics

The electric fatigue of (BaPb)TiO₃ ferroelectric ceramics was studied in present experiments. The results show that the resistance of the ferroelectric ceramics increases with the fatigue cycles, and the resistivity change increases with the Curie temperature. The SEM observations reveal that microcracks occurred inside the ceramics; electrode ions were transported into the ceramics; segregation of the ceramic element took place and sometimes new phases occurred near the electrode during electric fatigue.     

Electrical properties of Gd-modified Pb(SnTi)O3 ferroelectric ceramics

The Polycrystalline samples of (Pb_1−x Gd _x )(Sn_0.45Ti_0.55)_1−x/4O₃ (PGST) (x = 0, 0.05, 0.07, 0.1) were prepared using a standard mixed-oxide method. The XRD and SEM studies of the samples reveal that PGST samples have tetragonal symmetry with uniform grain distribution. Measurements of dielectric constant, dielectric loss and ac electrical conductivity were made in a wide temperature (300–650 K) and frequency (100 Hz to 1 MHz) range. These materials undergo a ferroelectric–paraelectric phase transition at 569, 582, 598, and 603 K for x = 0, 0.05, 0.07, 0.1, respectively. The ferroelectric property of some samples at room temperature was confirmed through the study of hysteresis loops. The Cole–Cole plots (ε′′ vs. ε′) at 125 and 150 °C form semicircular arcs with the center lying underneath the abscissa, deviated from the ideal Debye relaxation model to some extent. In all the compounds, the slope of ln σ_ac ~ 1/T shows a distinct variation for temperature below 450, 450 K to T _c and for T > T _c. The room temperature ac conductivity at 10 kHz lies in the range of 10⁻⁵–10⁻⁶ (Ω⁻¹ m⁻¹).     

Effect of starting raw materials on the dielectric, ferroelectric and electro-shape-memory properties of Mn3+ doped (Pb40Sr60)TiO3 ceramics

The effect of starting raw materials on the dielectric, ferroelectric and electro-shape-memory properties of 0.5 mol% Mn³⁺ doped (Pb₄₀Sr₆₀)TiO₃ ceramics was systematically studied. SEM observation showed that the ceramics fabricated from Pb₃O₄, SrCO₃, TiO₂ and MnCO₃ possessed the most homogeneous microstructure and the largest grain size. As the macroscopic consequence, such ceramics exhibited large dielectric property and well-developed double hysteresis loop. More interestingly, it showed large digital-like recoverable electrostrain of 0.11 % under the electric field of 3 kV/mm, which can rival the widely used linear piezoelectricity of the hard PZT ceramics. Defect distribution within the large and homogenous grains was analyzed to explore the microscopic origin of the simultaneous domain switching behavior and the digital-like strain properties. Such feature indicated the importance of material processing on the on/off-characterized electromechanical applications.     

Preparation and dielectric properties of Pb(Zn1/3Nb2/3)O3-based ferroelectric ceramics

The sintering behavior of mechanochemically prepared 0.9Pb(Zn_1/3Nb_2/3)O₃-0.1ABO₃ (ABO₃ = BaBiO₃, BaMnO₃, BaTiO₃) powders is studied. PbO and Bi₂O₃ are shown to volatilize at relatively low temperatures owing to partial reduction of these oxides during the mechanochemical synthesis. Dense (97% of theoretical density) ceramics are obtained under mild sintering conditions, and their dielectric properties are studied at different frequencies. The observed variations of their dielectric permittivity and loss tangent with frequency are typical of relaxor ferroelectrics, but the ceramics have a reduced dielectric permittivity, which is attributable to nanostructuring.     

The influence of fabrication processing on domain structure and polarization switching in PZN-based ferroelectric ceramics

Lead zinc niobate (Pb(Zn_1/3Nb_2/3)O₃, PZN) based ceramics are prepared by using conventional mixing oxide and complex phase reaction-sintering ceramic techniques. From the results of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), it is clear that these two fabrication processing routes produce different microstructures and ferroelectric domains in the same Pb(Zn_1/3Nb_2/3)O₃–BaTiO₃–Pb(Zr_0.4Ti_0.6)O₃ composition. Furthermore, different phase transitions are observed for the temperature dependence of the dielectric permittivity that can be confirmed by differential scanning calorimetry (DSC). Different polarization switching characteristics are also examined by using high field-induced strain and ferroelectric hysteresis loop. It is suggested that the distribution of the inner stress and domain configuration should be related with the fabrication processing of ferroelectric ceramics.     

高度取向的(Pb0.5Sr0.5)TiO3/LaNiO3异质结构铁电薄膜性能

用sol-gel方法在Pt(111)/Ti/SiO2/Si(100)衬底上制备了具有LaN iO3(LNO)缓冲层的(Pb0.5Sr0.5)TiO3(PSrT50)/LNO/Pt异质结构铁电薄膜。X射线分析发现PSrT50薄膜在(100)方向高度取向,同时扫描电镜图像显示薄膜结构致密、表面平整。通过和直接在Pt上制备的、相同厚度的PSrT50薄膜比较,PSrT50/LNO/Pt结构薄膜在室温下具有更大的剩余极化(Pr=4.5μC/cm2)和更高的介电常数(rε=850)。同时,漏电流机理分析表明,PSrT50/LNO/Pt结构薄膜在低电场作用下呈现Pool-Frenkel发射效应,在高电场作用下则表现为空间电荷限制电流。     

Successive relaxor ferroelectric behavior in La modified (Ba,Sr)TiO3 borosilicate glass ceramics

In the present investigation, we are reporting the successive ferroelectric relaxor behavior of (Ba,Sr)TiO₃ borosilicate glass ceramics. The ferroelectric relaxor nature of the present glass ceramics is attributed to structural phase transition from the rhombohedral to orthorhombic to tetragonal to cubic. A very high value of dielectric constant was found to be 89,684 at 100 Hz in glass ceramic sample 64[(Ba_0.7Sr_0.3)TiO₃]–30[2SiO₂–B₂O₃]–5[K₂O]–1[La₂O₃], BST5K1L0.3S831 and such large value may be due to space charge polarization in glassy matrix. The various contribution in polarization processes are confirmed by impedance spectroscopic analysis.     

Effect of composition on rate dependence of ferroelastic/ferroelectric switching in perovskite ceramics

Abstract

The process of ferroelectric/ferroelastic switching is rate dependent as evidenced by the frequency dependence of the coercive field/stress in polarisation/strain–electric field/stress loops. The rate dependence of domain switching has been investigated in different compositions of ferroelectric/ferroelastic perovskites by studying their stress–strain hysteresis loops. Stress–strain loops were generated by applying a static compressive load and then superimposing cyclic compressive loads of different amplitudes and frequencies. The stress–strain loops were fitted using a Rayleigh type relationship, whose parameters characterise the intrinsic and extrinsic contributions to the strain. Using these parameters, the rate dependence of the extrinsic domain wall contribution was investigated.     

Effect of domain switching on kinking of a crack in a ferroelectric material

Summary Crack kinking induced by domain switching in a ferroelectric material under purely electric loading is investigated. Boundaries of domain switching zones for the asymptotic problem of a semi-infinite crack under the small scale conditions are determined based on the nonlinear electric theory. Stress intensity factors induced by the domain switching are numerically evaluated using the solution of the switching zone. Numerical results of the kink angle are obtained as a function of the ratio of the coercive electric field to the yield electric field for various polarization angles. Crack kinking in ferroelectric materials subjected to a cyclic electric field is also examined. The crack in the fully poled materials branches with different directions at application of the positive and negative electric fields, respectively. The electric fatigue crack is shown to have a forked crack pattern in the fully poled materials.     

Phase-transition temperatures and piezoelectric properties of (Bi1/2Na1/2)TiO3-(Bi1/2Li1/2)TiO3-(Bi1/2K1/2)TiO3 lead-free ferroelectric ceramics.

The phase-transition temperatures and piezoelectric properties of x(Bi(1/2)Na(1/2))TiO3-y(Bi(1/2)Li(1/2))TiO3-z(Bi(1/2)K(1/2))TiO3 [x + y + z = 1] (abbreviated as BNLKT100(y)-100(z)) ceramics were investigated. These ceramics were prepared using a conventional ceramic fabrication process. The phase-transition temperatures such as depolarization temperatures T(d), rhombohedraltetragonal phase transition temperature T(R-T), and dielectric-maximum temperature T(m) were determined using electrical measurements such as dielectric and piezoelectric properties. The X-ray powder diffraction patterns of BNLKT100(y)-100(z)) show the morphotropic phase boundary (MPB) between rhombohedral and tetragonal at approximately z = 0.20, and the piezoelectric properties show the maximum at the MPB. The electromechanical coupling factor k(33), piezoelectric constant d(33) and T(d) of BNLKT4-20 and BNLKT8-20 were 0.603, 176 pC/N, and 171 degrees C, and 0.590, 190 pC/N, and 115 degrees C, respectively. In addition, the relationship between d33 and Td of tetragonal side and rhombohedral side for BNLKT4-100z and BNLKT8-100z were presented. Considering both high Td and high d(33), the tetragonal side of BNLKT4-100z is thought to be the superior composition. The d(33) and T(d) of BNLKT4-28 were 135 pC/N and 218 degrees C, respectively. Moreover, this study revealed that the variation of T(d) is related to the variation of lattice distortion such as rhombohedrality 90-alpha and tetragonality c/a.     

Mechanochemical synthesis, phase composition, and properties of Pb(Zn1/3Nb2/3)O3-based ferroelectric ceramics

Pb-containing relaxor ferroelectric ceramics are prepared by mechanochemical ceramic processing. Mechanochemical reactions in binary and ternary mixtures of the PbO-ZnO-Nb₂O₅ system are studied by x-ray diffraction. Disordered compounds with the columbite, changbaiite, and pyrochlore structures are prepared. The perovskite and pyrochlore phases in 0.9Pb(Zn_1/3Nb_2/3)O₃ + 0.1ABO₃ morphotropic phase boundary materials are shown to be in mechanochemical equilibrium. Among the ABO₃ additives studied, BaMnO₃ is the most effective for stabilizing the perovskite structure. The mechanochemical synthesis path has a strong effect on the phase composition of the resulting material. Conventional synthesis through a columbite phase leads to the predominant formation of a pyrochlore phase. Firing conditions also have a profound effect on the phase composition of the ceramics, but the disordered perovskite phase retains cubic symmetry.     

铁电陶瓷的电畴及畴变观测研究进展

铁电陶瓷材料，特别是锆钛酸铅(PZT)在众多领域具有广泛的应用前景，影响其推广应用的主要因素是使用过程中外电、力场引起的材料性能的退化。观测铁电电畴及畴变的方法对研究其在外场下性能破坏机理、提高其使用的可靠性和预防其失效具有重要的理论和实际意义。本文比较了不同实验方法和测试技术的优缺点，对铁电陶瓷的电畴观测进行了综述，并简要总结了铁电陶瓷的畴变观测技术研究现状，指出了目前该领域研究中存在的问题。     

Pb(Zn1/3Nb2/3)O3-Ba(Zn1/3Nb2/3)O3铁电陶瓷结构与性能的研究

采用固相反应的方法系统地研究了BZN稳定PZN基陶瓷的相结构与介电性能.随着BZN含量的增加,PZN-BZN陶瓷中钙钛矿相的稳定性增强,居里温度近似呈线性下降,室温介电常数和介质损耗随也显著降低,最小值分别为380和0.002.为获得100%钙钛矿结构的PZN基陶瓷所需BZN的最小用量为8mol%～10mol%,当BZN的mol%超过15mol%时,PZN基陶瓷中钙钛矿相所占的百分比不再受烧结工艺的影响,基本保持100%.1kHz时Pb0.9Ba0.1Zn1/3Nb2/3O3陶瓷的最大介电常数Kmax=8680,tgδ=0.02,相应的居里温度Tm为24℃.     

Influence of synthesis methods on the dielectric properties of (Ba0.2Pb0.8)TiO3 ceramics

The dielectric properties of (Ba_0.2Pb_0.8)TiO₃ prepared by several methods related to dispersion have been studied. The sol-gel derived specimens without dispersion have lower density, and lower dielectric constant at the Curie temperature. The sol-gel specimens derived from a well-dispersed suspension with pH 11 and 13, and 2% PMMA show higher dielectric constant at the Curie temperature, and higher density, because the grains grow homogeneously in the well-dispersed system. The sol-gel derived specimens have a higher Curie temperature than that of calcined mixed oxides and molten salt synthesis derived specimens.