Microstructure and electrical properties of 3-0 type composite of Na0.5Bi2.5Nb2O9-based bismuth-layered piezoceramics

The microstructure and electrical properties of 3-0 type composite of Na_0.5Bi_2.5Nb₂O₉-based bismuth layered piezoceramics modified by Al₂O₃ addition are investigated. The darker and plate-like grains, locating at the grain boundaries, are confirmed to be pure α-Al₂O₃ by high resolution transmission electron microscope, not a Bi₂AlNbO₇ pyrochlore phase. This 3-0 type Na_0.5Bi_2.5Nb₂O₉-Al₂O₃ composite piezoceramics have a large piezoelectric constant d₃₃ of 15.2pC/N with good temperature stability up to 600 °C, and good ferroelectric properties with a relatively large remnant polarization of ~11.6 μC/cm². These demonstrate that designing a 3-0 type composite structure would be an effective approach to tailor the microstructure and improve the electrical properties of bismuth layered piezoceremics for their potential applications at temperature up to 600 °C.     

压电石英晶片扭转效应理论研究与验证

从各向异性弹性理论和麦克斯韦电磁理论出发,较系统地探讨了圆形压电石英晶片扭转效应理论,得出了扭转应力场与非线性极化电场分布规律,并采用有限元法求得了极化电荷电场在压电片内的分布。根据理论分析,用分割电极法有效地在压电片表面布置了检测电极,理论与试验结果均表明电极检测的极化电荷量与外转矩成线性关系,理论与试验基本符合。这些研究为新型转矩传感器与测力仪的开发奠定了必要的理论基础。     

Effect of BiFeO3 additions on the dielectric and piezoelectric properties of (K0.44Na0.52Li0.04)(Nb0.84Ta0.1Sb0.06)O3 ceramics

(1 − x) (K_0.44Na_0.52Li_0.04)(Nb_0.84Ta_0.1Sb_0.06)O₃ − x BiFeO₃ (x = 0, 0.002, 0.004, 0.006, 0.008, 0.01) lead-free piezoelectric ceramics were prepared by the conventional ceramic processing. The compositional dependence of the phase structure and the electrical properties of the ceramics were studied. A morphotropic phase boundary between the orthorhombic and tetragonal phases was identified in the composition range of 0.004 < x < 0.006. The ceramics near the morphotropic phase boundary exhibit a strong compositional dependence and enhanced piezoelectric properties. The ceramics with 0.6 mol.% BiFeO₃ exhibit good electrical properties (d₃₃ ∼ 246 pC/N, k_p ∼ 43%, T_c ∼ 285 °C, ?_r ∼ 1871, and tan δ ∼ 1.96%). These results show that the (1 − x) (K_0.44Na_0.52Li_0.04)(Nb_0.84Ta_0.1Sb_0.06)O₃ − x BiFeO₃ ceramic is a promising lead-free piezoelectric material for applications in different devices.     

Effect of an interphase layer on the electroelastic stresses within a three-phase elliptic inclusion

Electroelastic stresses induced by electromechanical loadings and lattice mismatch between components and surrounding materials are found to significantly influence the electronic performance of devices and, in some cases, are identified as a major cause of failure and degradation. To reduce electromechanical failure an effective method is to apply an intermediate layer, with appropriate geometry and material properties, between the components of dissimilar piezoelectric materials. In this paper, the effect of an intermediate layer on the electroelastic stresses within an elliptical inhomogeneity is examined within the framework of linear piezoelectricity. Exact closed-form solutions are obtained for the electroelastic stresses in the inclusion, the interphase layer and the matrix, respectively, under remote mechanical antiplane shear and inplane electric field, by means of the complex variable method. It is shown that the electroelastic stresses depend on only two complex coefficients. Simple formulae and numerical examples are used to illustrate the effects of the interphase layer on the electroelastic stresses within the inclusion, and the dependency of this effect on the aspect ratio of the elliptical inclusion.     

Effects of K4CuNb8O23 on the structure and electrical properties of lead-free 0.94(Na0.5K0.5)NbO3–0.06LiNbO3 ceramics

Dense K₄CuNb₈O₂₃-modified (K_0.5Na_0.5)_0.94Li_0.06NbO₃ ceramics were prepared by normal sintering. The effects of K₄CuNb₈O₂₃ on the phase structure, microstructure and electrical properties of the ceramics were studied. Results showed that K₄CuNb₈O₂₃ induced a perovskite structure transition from coexistence of orthorhombic and tetragonal phases to orthorhombic symmetry. The addition of K₄CuNb₈O₂₃ promoted the sintering of (K_0.5Na_0.5)_0.94Li_0.06NbO₃ ceramics and simultaneously caused the grain growth. Moreover, K₄CuNb₈O₂₃-doping changed the (K_0.5Na_0.5)_0.94Li_0.06NbO₃ to “hard” ceramics and significantly enhanced the mechanical quality factor Q_m. It was found that the (K_0.5Na_0.5)_0.94Li_0.06NbO₃ ceramics doped with 0.60 mol% K₄CuNb₈O₂₃ exhibited a high mechanical quality factor (Q_m  983) as well as relatively large d₃₃ (136 pC/N) and k_p (35.9%), suggesting that this material is a promising candidate for lead-free piezoelectric ceramics for high-frequency applications.     

Effect of ZnO addition on the sintering and electrical properties of (Mn,W)-doped PZT-PMS-PZN ceramics

The effect of ZnO addition on the phase structure, microstructure and dielectric and piezoelectric properties of 0.2 wt.% MnO₂ and 0.6 wt.% WO₃-doped Pb(Zr_0.52Ti_0.48)O₃-Pb(Mn_1/3Sb_2/3)O₃-Pb(Zn_1/3Nb_2/3)O₃ (PZT-PMS-PZN) ceramics was investigated. X-ray diffraction shows that the phase structure of ceramics is transformed from rhombohedral to tetragonal with the increasing of ZnO addition. The bulk density significantly increases when ZnO is added and then it slightly decreases for ZnO addition above 0.2 wt.%. SEM micrographs show the grains of ceramics are uniform and well developed by adding 0.1 wt.% ZnO. The Curie temperature (T_c) of 270 °C is obtained at the 0.1 wt.% ZnO addition. Mechanical quality factor (Q_m), electromechanical coupling factor (K_p) and piezoelectric constant (d₃₃) increase firstly, and then decrease with the increasing of ZnO addition, while dielectric loss tan δ drops all the time. The Q_m, K_p, d₃₃, tan δ and T_c of the ceramics show the optimum values of 1899, 0.55, 300 (pC/N), 0.0063 and 270 °C, respectively, at the lower sintering temperature of 1120 °C and with 0.1 wt.% ZnO addition.     

Effect of CeO2 addition on structure and electrical properties of (Na0.5Bi0.5)0.93Ba0.07TiO3 ceramics prepared by citric method

(Na_0.5Bi_0.5)_0.93Ba_0.07TiO₃ ceramics added with 0–0.8 wt.% CeO₂ were prepared by a citrate method, and the influence of the CeO₂ addition on the structure and electrical properties was investigated. The specimens containing various amounts of CeO₂ show the coexistence of rhombohedral and tetragonal phases, with the relative content of the tetragonal phases gradually enhancing with increasing amount of CeO₂. Compared with (Na_0.5Bi_0.5)_0.93Ba_0.07TiO₃, the specimen added with a small amount of CeO₂ (≤0.2 wt.%) display a slightly improved electromechanical coupling factor (k_p) and piezoelectric constant (d₃₃) in conjunction with a reduced dielectric loss (tg δ) and an enhanced mechanical quality factor (Q_m), while higher CeO₂ amounts led to a rapid deterioration of the piezoelectric and ferroelectric properties. The variation of the electrical properties with the CeO₂ addition was tentatively interpreted with respect to doping effect, crystal-structural evolution and stability of ferroelectric domains.     

Influence of A-site nonstoichiometry on sintering, microstructure and electrical properties of (Bi0.5Na0.5)TiO3 ceramics

Lead-free (Bi_0.5Na_0.5)_1+xTiO₃ ceramics (x = −0.02, −0.01, −0.005, 0, 0.005 and 0.01) were prepared by ordinary sintering. The effect of A-site stoichiometry on the densification, microstructure, dielectric properties, high-temperature impedances, and piezoelectric properties was explored. It was found that the high conductivity of (Bi_0.5Na_0.5)TiO₃ (BNT) ceramics should be mainly attributed to the formation of A-site cation vacancies during sintering. Improved physical and electrical properties can be achieved in the sample with A-site cation excess. The control of the stoichiometry proves to be an effective way to improve BNT ceramics for possible application.     

Finite element model of efficient zig-zag theory for static analysis of hybrid piezoelectric beams

Finite element model is presented for the analysis of hybrid piezoelectric beams under static electromechanical load, using the one-dimensional (1D) coupled zig-zag theory developed recently by the authors. Two noded elements are used with cubic Hermite interpolation for deflection and electric potentials at the sub-layers and with linear interpolation for axial displacement and shear rotation. The expressions for the variationally consistent stiffness matrix and load vector are derived and evaluated in closed form using exact integration. The formulation is validated by comparison with the analytical solution for simply-supported beam. The finite element model is free of shear locking. The present zig-zag finite element results for cantilever beams are compared with the 2D finite element results using ABAQUS to establish the accuracy of the zig-zag theory for these boundary conditions.S. Kapuria is grateful to Department of Science and Technology, Government of India, for providing financial assistance for this work.