CNTs/纳微米PZT/水泥压电复合材料的研究

研究制备了一种新型0-3 CNTs/纳微米PZT/水泥压电复合材料.该复合材料的基体相为硅酸盐水泥,压电活性相为锆钛酸铅(PZT)压电陶瓷,压电增强相为纳米碳管(CNTs).PZT采用溶胶-凝胶法合成,其粒径大多分布在几十至几百纳米之间.CNTs采用Fenton/UV法分散处理.研究了CNTs对该水泥基压电复合材料压电和介电性能的影响.CNTs可改善水泥基复合材料的导电性,使其可在室温中进行极化,提高了压电相的极化效率,从而显著提高复合材料的压电性能.0.9 vol;CNTs/70 vol;PZT/水泥复合材料的压电应变常数(d33)值可达到54.5 pC/N,显示出该类水泥基压电复合材料用作土木领域传感器的良好前景.     

纳微米PZT/水泥基压电复合材料的研究

采用溶胶-凝胶法合成了锆钛酸铅(PZT)纳微米粉体.XRD与SEM分析结果表明,经700 ℃煅烧的PZT粉体的平均晶粒尺寸约为26.4 nm,粉体团聚体的平均尺寸约为200 nm.采用干压成型-水化法制备了纳微米PZT/水泥基压电复合材料,研究了复合材料的压电及介电性能.SEM结果表明,PZT陶瓷相在基体中呈网状分布.PZT颗粒之间的良好连通性使复合材料具有优良的压电性能.     

面向水声换能器的压电单晶复合材料设计研究

压电单晶复合材料具有高压电常数、高机电耦合系数和高水声优值的优点,是制备下一代高性能水声换能器的关键材料.不同类型水声换能器对压电材料的性能要求不同,如何根据器件的具体应用需求,对压电单晶复合材料的结构和性能进行设计具有重要的意义.为了能够准确选取压电单晶复合材料中压电相与聚合物相两相材料特性、体积分数、宽高比等参数,本文提出了一种将解析模型与数值模型相结合的综合设计方法.实验结果证实,该方法可以准确高效地预测1-3型压电单晶复合材料的振动模态及宏观等效性能参数,实现以器件性能为指导的压电单晶复合材料设计.     

极化方法对PZT-4压电陶瓷性能的影响

Pb(Zr_1-xTi_x)O₃ (PZT)由于具有优异的综合性能而成为应用最广泛的压电陶瓷。之前研究工作证明了与直流极化(DCP)和交流极化(ACP)相比,采用交流极化和直流极化相结合的方法能进一步提高弛豫铁电单晶材料的压电性能。本工作报道了直流极化、交流极化和交流极化+直流极化后PZT-4压电陶瓷的介电性能和压电性能,探究了直流极化、交流极化和交流极化+直流极化的最佳极化条件。在最佳交流极化+直流极化条件下, PZT-4 压电陶瓷的压电常数(d₃₃)为350 pC/N,相比直流极化(305 pC/N)、交流极化(320 pC/N)分别提高了15%和9%。交流极化后的PZT-4陶瓷样品的应变值(0.08%)高于进行直流极化样品的(应变值0.05%),表明交流极化可以有效提高PZT-4陶瓷的应变值,但是交流极化后应变曲线的滞后增大不利于器件应用,交流极化对硬性压电陶瓷的影响还需要进一步探讨。     

B位取代PZT体系的电子结构与压电特性研究

采用自洽场离散变分Xα计算方法,分别计算了Pb(Zr1/2Ti1/2)O3(简称PZT)、Pb(Zn1/3Nb2/3)O3(简称PZN)、和Pb(Mn1/3Sb2/3)O3(简称PMS)体系的电子结构,研究了钙钛矿结构与烧绿石结构陶瓷的电子结构对压电性能的影响.结果表明,PZT铁电相较顺电相稳定,O的2p轨道与B位原子的最外层d轨道的杂化是铁电性的必要条件,杂化的强弱可表明铁电性的强弱;Mn1/3Sb2/3、Zn1/3Nb2/3取代(Zr, Ti)若生成四方钙态矿结构,体系总能量降低、轨道杂化增强,可以提高PZT体系的铁电性能,若生成立方烧绿石结构,由于B-O(//轴向)与B-O(⊥轴向)共价键强度差别太大,造成体系结构的不稳定,将导致铁电性的丧失.     

压电纤维复合材料的静电场分析

采用有限元法分析了外电压作用于压电纤维复合材料时的静电场分布,讨论了静电场对元件极化和作动性能的影响,研究了电极区聚合物的介电常数和厚度尺寸,及其IDE宽度和周期对压电纤维复合材料静电场的影响,研究结果表明:增加电极区聚合物的导电性,压电纤维复合材料静电场可以得到显著提高,最大可以提高54倍;减小电极区聚合物的厚度,同样可以显著提高静电场,最大可以提高55倍.IDE参数对电场的均匀性区域大小和电场强度大小影响也比较大.     

3m点群晶体纵向压电性能的研究

本文详细地介绍了通过坐标变换研究晶体压电性能随空间变化的方法.在以前的工作基础上,对LiNbO3、LiTaO3和PZT60/40等3m点群晶体纵向压电系数d33及机电耦合系数k33在空间分布的共同规律进行了归纳总结,发现它们在空间中的分布具有明显的各向异性,并存在着一些特殊方向,沿这些方向,晶体的压电性能有较大幅度的提高.在此基础上,本文还根据不同文献中报道,对另一著名的3m点群晶体β-BaB2O4的压电系数数据进行了比较和分析.     

ZnO压电薄膜的制备与性能表征

采用射频磁控溅射法在硅(100)衬底上制备高质量的ZnO压电薄膜.利用X射线衍射仪(XRD)、原子力显微镜(AFM)、压电响应力显微镜(PFM)等仪器研究了薄膜成分,表面形貌和压电性质.结果表明:实验制备的ZnO薄膜具有很好的压电性质,c轴取向和表面粗糙度对薄膜压电特性有很大影响,高度c轴取向生长和表面粗糙度较小的ZnO薄膜表现出更好的压电性质.     

无铅压电陶瓷的研究进展

BaTiO3、Na0.5Bi0.5TiO3和K0.5N0.5NbO3三大体系无铅压电陶瓷因其优异的压电介电性能,尤其是以准同型相界(MPB)多晶型相界(PPB)附近优异的压电性能受到极为深入和广泛的研究.结合近几年相关文献报道,分析和评价了三大体系无铅压电陶瓷的组分设计和相界构建与性能调控的最新研究进展,讨论了离子或化合物掺杂改性、制备工艺以及压电性能与微观结构之间的关系等关键科学和技术问题.分析并展望了体系构建、新制备工艺以及相关理论在无铅压电陶瓷研究领域的研究前景.     

溶胶电泳沉积法制备PZT压电厚膜及其性能研究

采用溶胶-凝胶方法制备Pb(Zr0.52Ti0.48)O3(PZT)纳米粉末,将此粉末按一定比例加入到同成分PZT溶胶中,采用溶胶-电泳沉积技术在ITO玻璃衬底上制备PZT厚膜.采用X射线衍射分析、SEM及HP4294A阻抗分析仪等对PZT膜进行了微观结构和介电性能测试,研究了电泳电压、热处理温度及电泳时间对PZT膜结构及膜厚的影响,结果表明,在1V电压下进行电泳,600℃热处理20min,可以得到表面均匀平整的纯钙钛矿结构PZT膜,以(110)择优取向,通过控制电泳时间可有效控制膜的厚度.获得了膜厚为30μm、介电常数达到ε33T/ε0=781、介电损耗为tanδ=0.0083、剩余极化与矫顽电场强度分别为24.6μC/cm2与61.9kV/cm铁电性能较好的PZT膜材料.     

Modelling of mechanism of agglomeration of KCl crystallization

The article presents an analysis into agglomeration during KCl vacuum crystallization. The theoretical and experimental investigations into the mechanism of agglomeration during mass crystallization result in an extension of the growth phenomena within the known model equations. The basis for this is essentially constituted by the collision model concepts of the theory of floculation in disperse systems. The parameters derived from the microprocess analysis (energy dissipation, content of solids, growth rate of individual grains) lead to model equations which are confirmed by laboratory and test trials.     

Relationship of Morphological Types of Dynamic Forms of Crystals

Crystallography Reports - The relationship of morphological spectra (sets of data on the morphological types of real polyhedral crystals and their probabilities under current physicochemical...     

Velocities of Disappearance and Lifetime of Faces of Growing Crystals

The formulae for absolute R_disap and relative R velocities of disappearance and lifetime τ of faces of growing crystals have been derived for stationary growth. It was shown that the quantities are determined by the relative growth velocity R_A/R_critA of the vanishing face A with respect to the critical growth velocity R_critA and by the geometry of a crystal expressed by the trigonometric functions of interfacial angles β and γ formed between face A and the adjacent faces. R increases and τ decreases with the increase in R_A/R_critA to certain limiting values. The calculations have been verified and illustrated by the experimental results for triclinic potassium bichromate (KBC) crystals. Results enable ones to predict values of velocities of disappearance and lifetimes of undesirable, supplementary faces of any real crystal.     

Development of Pauling's concepts of geometric characteristics of atoms

The evolution of the geometric characteristics introduced by Pauling and their dependence on the specific features of the structure and chemical bonds have been considered. The values of the covalent and van der Waals radii are given as well as their relationships and mutual transitions.     

A review of measurement of thermophysical properties of silicon melt

Measurements of thermophysical properties of Si melt and supplementary study of X-ray scattering/diffraction by the authors' group were reviewed. The values obtained differed variously from those of literature. Density was 2–3% larger, surface tension 20–30% smaller, viscosity up to 40% larger, electrical conductivity 8% smaller, spectral emissivity more or less in good agreement with literature values, and thermal diffusivity a few percent larger. An anomalous density jump was found near the melting point. Surface tension and viscosity also showed anomaly. A strange time-dependent change of density was observed over 3 h after melting. X-ray analyses suggested a slight change in local atom ordering, but showed no sign of cluster formation. An addition of 0.1 at% gallium caused the density jump to disappear, while that of boron caused no change. An EXAFS study of the former melt indicated a strong interaction between Ga and Si atoms as if molecules of GaSi₃ existed. The implications of the measured properties are a possibility of soft-turbulence in an Si melt in a relatively large crucible, a more complicated manner of intake of oxygen depleted molten Si from the free surface region to underneath the growing crystal, and a relaxation of the melt after melting arising from trapped gas species.     

Dependence of the parameters of equations of viscous flow on chemical composition of silicate melts

The temperature dependence of viscosity of silicate melts is discussed in the framework of the Avramov–Milchev (AM) equation. The composition is described by means of two parameters: the molar fraction, x, and the “lubricant fraction”, l. The molar fraction is the sum of the molar parts x_i of all oxides dissolved in SiO₂, the molar fraction of the latter being 1 ? x. It is shown that, with sufficient precision, two of the parameters of the AM equation can be presented as unique functions of the molar fraction. On the other hand, x is not sufficient to determine properly the reference temperature T_r , at which viscosity is η_r = 10¹³ [dPa.s]. Therefore, additional parameter, “lubricant fraction” l, is introduced. For each of the components, l_i is a product of molar part x_i and a specific dimensionless coefficient 0 ≤ k_i ≤ 1 accounting for the specific contribution of this component to the increased mobility of the system. It is demonstrated that, for l > 0, the reference temperature is related to the “lubricant fraction” l through the reference temperature T_r,SiO2 of pure SiO₂.     

Comparative analysis of two methods of calculation of the orientation of domain walls in ferroelastics

Two types of domain-wall equations are analyzed: the equations derived by the Sapriel method and the equations obtained by interface matching of the thermal-expansion tensor. It is shown that, for W-type domain walls, these methods yield the same equations. For W′-type domain walls, the equations obtained by different methods coincide for proper ferroelastics and differ for improper ferroelastics.     

Generation of crystal structures of heteromolecular compounds by the method of discrete modeling of packings

Within the method of discrete modeling of packings, an algorithm of generation of possible crystal structures of heteromolecular compounds containing two or three molecules in the primitive unit cell, one of which has an arbitrary shape and the other (two others) has a shape close to spherical, is proposed. On the basis of this algorithm, a software package for personal computers is developed. This package has been approved for a number of compounds, investigated previously by X-ray diffraction analysis. The results of generation of structures of five compounds—four organic salts (with one or two spherical anions) and one solvate—are represented.