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1.
The Ag-Pd internal electrode of multilayer piezoelectric ceramics needs to be sintered below 1000°C, and lead wires and components need to be welded with lead-free solder at 260°C. PNN–PMW–PZT–xSr piezoelectric ceramics with high Curie temperature (Tc > 260°C) were synthesized at a low sintering temperature (960°C) to meet the requirements of multilayer piezoelectric devices. The relationship between structures (phase, domain, and microstructures) and electrical properties (piezo/ferroelectric properties, and dielectric relaxation) in the Sr2+ substituted ceramics was investigated. Rietveld refinement and Raman spectra show that Sr2+ substitution can cause the phase change and increase the force constant of [BO6] octahedron. The piezoelectric response increases with increasing the content of the tetragonal phase (CTP) in the rhombohedral-tetragonal (R-T) coexisted ceramics. The ceramics with 0.6 mol% Sr2+ substitution have minimum activation energy for domain wall movement (Ea) of 0.0362 eV which favors the formation of nanometer-sized domains, and possess excellent electrical properties (d33 = 623 pC/N, d33* =783 pm/V, Tc =295°C). The higher the CTP, the lower the Ea. The lower Ea favors the rotation of polarization direction and extension, and is beneficial to the generation of the nanometer-size domains, resulting in high piezoelectric properties.  相似文献   
2.
The swelling behavior in micro-extrusion has a significant effect on the dimensional and shape accuracy of microproducts. In this study, the effect of characteristic scale, defined as the gap of die land in an annular micro-extrusion die, on the extrudate swelling behavior of viscoelastic melt is analyzed through numerical simulations and micro-extrusion experiments. The results show that the swelling behavior displays an obvious dependence on the characteristic scale. An increase in the characteristic scale reduces the swell ratio and retards the process to reach the equilibrium state. In contrast, a decrease in the characteristic scale results in a larger magnitude of change in velocity field and faster relaxation development of stress field. The location of the maximum velocity layer for the laminar flow gradually deviates from the geometric center of channel toward the wall of mandrel with the increase in the characteristic scale. Moreover, an increase in the flow rate results in a larger swell ratio for a constant characteristic scale. The elastic effect plays a more dominant role than the viscous effect in determining the viscoelastic swell behavior. It is imperative to consider the complicated swelling behavior and remarkable viscoelastic effect simultaneously in micro-extrusion process.  相似文献   
3.
目的 在YT15硬质合金刀片上制备出具有疏水特性的织构表面.方法 在静态的无水乙醇环境中,利用光纤激光打标机,在YT15硬质合金刀片上制备织构,制备好的织构表面不做任何改性处理.根据织构表面形貌、织构表面化学成分,分析加工环境及激光参数对织构表面润湿性的影响.结果 无水乙醇辅助激光制备的织构表面表现出了疏水特性,疏水角的大小受激光参数影响.激光功率增大,织构表面接触角随之增大,功率为12~20 W时,接触角为112.5°~126.9°;激光扫描速度增加,织构表面接触角随之减小,扫描速度为0.5~2.5 mm/s时,接触角为118.3°~125.7°.当加工次数为1,激光频率为200 kHz,扫描速度为1 mm/s,功率为20 W时,织构表面的接触角最大,为126.9°.结论 无水乙醇环境中,采用激光技术在YT15刀片上制备出了新型的环形凸起微纳织构.与无织构表面相比,织构表面C原子明显增加,表现出了疏水特性.织构表面接触角的大小与织构形貌有关,环形凸起织构密度越大,接触角越大.环形凸起织构的密度受激光参数影响.织构形貌及表面化学成分决定了表面的润湿特性.  相似文献   
4.
The morphotropic composition of the lead-free solid solution between Na0.5Bi0.5TiO3 and BaTiO3 (0.94 Na0.5Bi0.5TiO3-0.06 BaTiO3 or NBT-6BT) is of particular interest for the next generation of high-temperature capacitors but remains plagued by the diversity of dielectric properties reported in the literature. In order to explain the apparent inconsistencies among the reported dielectric properties of NBT-6BT, we examine the influence of stoichiometry, phase separation, and metallization method. We show that the nominal stoichiometry has a crucial effect, since increasing the nominal Na/Bi ratio increases conductivity and dielectric losses (tan δ). It also increases the real part of the permittivity (ε’) and the frequency dispersion of both ε’ and tan δ, thereby altering the shape of the evolution with temperature of the dielectric properties. Moreover it increases the depolarization temperature (Td) and decreases the temperature of maximum permittivity (Tm). Phase separation also occurs during the synthesis of NBT-6BT as Na evaporation leads to the formation of secondary Ba-containing phases. We report that these phases can have a positive impact on the dielectric properties: a moderate volume fraction (2.5 to 3.0%) and average grain surface (0.9 to 3.0 µm2) of these secondary Ba-containing phases increase the relative permittivity, decrease the dielectric losses, and increase the insulation resistance. We also show that the metallization method impacts the dielectric properties and therefore may contribute to the differences between various reports. The dielectric properties of NBT-6BT samples are measured during successive heating/cooling cycles and reveal that the permittivity value is lower during the first heating when silver paste, even cured, is used. These three components contribute to explaining the diversity of the reported dielectric properties of NBT-6BT.  相似文献   
5.
6.
A large-scale high-precision scan stage is important equipment in the industrial productions of micro-fabrication such as flat panel display (FPD) lithography systems. Designing controllers for multi-input multi-output (MIMO) systems is time-consuming and needs experience because of the interaction between each axis and many controller tuning parameters. The aim of this study is to develop a peak filter design method based on frequency response data to reduce repetitive disturbance. This data-based approach does not use the model and only uses the frequency response data of the controlled system and the disturbance spectrum calculated from the scanning error data (Contribution 1). The peak filter is designed by convex optimization and satisfies robust stability conditions for six-degree-of-freedom systems (Contribution 2). The control performance of the designed peak filter is experimentally demonstrated with an industrial MIMO large-scale high-precision scan stage in reducing the scanning error of the main stroke of the translation along the x-axis (Contribution 3).  相似文献   
7.
笔者提出一种高精度电池寿命损耗评估模型,该模型能充分挖掘厂家提供数据中的有效信息,从而建立起动态循环效率、放电深度(DOD)与实时荷电状态(SOC)应力等因素之间的映射关系。同时,针对采用更精细化的储能模型所引入的非线性项,提出一种基于滚动McCormick松弛方法的优化求解算法,该算法可将原本包含混合整数非线性规划问题转化为混合整数线性规划问题,从而实现优化问题的数值化求解。最后,通过算例证明所提出的精细化电池寿命模型与滚动McCormick求解算法的合理性和优越性。  相似文献   
8.
LiCuNb3O9 has been reported newly a colossal permittivity (CP) perovskite, in which the B-site NbO6 octahedra play a bridging role in the polaron hopping. However, how the A-site modification affects the origin of the polarons and further the CP behaviours remains unexplored. To this end, A-site Ca2+ was incorporated to form Li1-xCaxCuNb3O9, and the local states, dielectric relaxations and conduction behaviours were comprehensively studied. The substitution induces the polyvalent Cu cations, i.e. Cu+/Cu2+/Cu3+. Bond valence sum calculations imply that Cu2+ and Cu3+ are underbonded, and Cu+ is overbonded, while B-site Nb5+ shows slightly different with theoretical pentavalence. All the compositions exhibit a similarly room-temperature CP response, but present two dielectric relaxations, i.e. TR1:170–300 K and TR2:260–400 K. Comprehensive investigations on universal dielectric response and bulk dc conductivity indicate that the TR1 follows the variable-range-hopping where the electron hopping between the mixed Cu+/Cu2+, while TR2 contributes from the Cu3+ nearest neighbor hopping.  相似文献   
9.
Sr-modified Cu/Nb co-doped BaTiO3 ceramics were prepared using solid-state reactions and the structures and dielectric properties were studied. All the samples had single-phase perovskite structures with no detectable secondary phases. In the low-temperature range, the dielectric constant decreased as the Sr content increased in the high- and low-frequency ranges. Two dielectric constant plateaus accompanied by dielectric relaxation peaks were present in the loss curves, and the relaxation process deviated from the Arrhenius law at low temperatures. The dielectric constants of different plateaus were related to inhomogeneous structures such as grain interiors and grain boundaries. The polarization strength of the grain boundaries in the low-frequency range increased with the temperature and that of the grain interiors demonstrated paraelectric behaviour in high-temperature ranges. An analysis of the electric modulus spectra indicated a close relationship between the relaxation process and resistivity of the grains for high-frequency relaxation. The impedance spectra at high temperatures consist of three electrical responses, corresponding to the effects of grains, grain boundaries, and electrodes. The dielectric relaxation appeared in high temperature range was related to the electrical properties of the grain boundaries.  相似文献   
10.
在500、550和600 ℃及不同初始应力下对Ti-6.5Al-2Zr-1Mo-1V钛合金进行了应力松弛实验。基于经典的Maxwell指数衰减函数,得到了应力松弛极限。提出了利用松弛稳定系数(CS)和松弛速率系数(CR)来描述Ti-6.5Al-2Zr-1Mo-1V合金的松弛特性,有利于制定残余应力消减工艺。根据Norton和Arrhenius方程计算了应力指数。通过应力指数和显微组织分析,阐明了应力松弛机理。在不同初始应力下,500 ℃时,位错的攀移和扩散主导了应力松弛过程;550 ℃时,位错滑移在应力松弛过程中起主要作用;600 ℃时,位错滑移、边界滑移和晶粒旋转控制着松弛过程。  相似文献   
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