铌镁(锌)酸铅-钛酸铅弛豫铁电单晶研究进展

在最近十几年中,新型弛豫型铁电单晶铌镁酸铅-钛酸铅和铌锌酸铅-钛酸铅受到了广泛的关注。这是由于这种新型的弛豫型铁电单晶和传统的压电材料相比较,在准同型相界附近表现出良好的压电、介电与电致伸缩性能。文章介绍了铌镁(锌)酸铅-钛酸铅系列单晶的基本性质,国内外在该晶体制备及晶体性能相关领域的研究进展。     

偏铌酸铅压电陶瓷材料老化问题的探讨

对偏铌酸铅压电陶瓷的老化性能作了一些探讨,实验表明,掺杂改性后的偏铌酸铅显微结构发生了变化,晶界处有杂质分凝使得该材料老化性能好。     

添加剂对偏铌酸铅压电陶瓷烧结性能的影响

纯偏铌酸铅压电陶瓷虽然具有一系列的优良性能,但难以烧结,从而限制了它的应用,通过对纯偏铌酸铅的掺杂改性,使得该材料具有良好的烧结性能及机电性能.通过X射线结构分析和扫描电镜、透射电镜对材料进行了结构分析.     

湿化学法合成铌镁酸铅陶瓷微观结构

用湿化学法合成铌镁酸铅陶瓷，用Ｘ射线（ＸＲＤ），扫描电镜（ＳＥＭ）和透射电镜（ＴＥＭ）技术，研究陶瓷的微观结构，结果表明：湿化学法可合成纯钙钛矿相的铌镁酸铅陶瓷；陶瓷在８５０～９２０℃烧结，晶粒大小为１５０～２００ｎｍ，细小焦绿石相出现并分布在晶界上；过量ＰｂＯ相的形成有利于陶瓷的烧结。     

晶体畴反转过程中畴壁运动与极化电流特性研究

为了解晶体畴反转的动力学过程,利用马赫-曾德干涉实验系统,研究了外电场极化下掺镁铌酸锂和纯净铌酸锂晶体在畴反转过程中的畴壁运动和极化电流特性。实时记录了掺镁7 mol%、掺镁5 mol%铌酸锂和纯净铌酸锂晶体在畴反转过程中的畴壁特征和极化电流变化情况,发现离散的畴壁速度脉冲伴随着离散的极化电流脉冲,连续的畴壁速度脉冲对应着连续的极化电流脉冲。掺镁铌酸锂晶体正向反转和纯净铌酸锂反向反转的畴壁速度变化和极化电流变化比较尖锐,而掺镁铌酸锂晶体反向反转和纯净铌酸锂正向反转的畴壁速度变化和极化电流变化比较缓和。最后对实验现象进行了解释。     

对不同组份掺镁铌酸锂晶体紫外光致吸收的研究

研究了不同组份掺镁铌酸锂晶体的光致吸收现象.通过对不同组份掺镁铌酸锂晶体紫外光致吸收的动态暗衰减过程的测量,我们认为掺镁铌酸锂晶体中紫外光致吸收的浅能级缺陷中心是O-小极化子.     

共沉淀法合成铌镁酸铅──钛酸铅介电陶瓷粉末

通过共沉淀法合成铌镁酸铅－钛酸铅介电陶瓷粉末，经８００℃焙烧后，Ｘ射线衍射研究表明几乎为单一钙钛矿相；经１０００℃烧结的陶瓷片其密度达到理论值的９６．７７％，２０℃介电常数可达２０９４０。     

铌镁酸铅类钙钛矿结构铁电多晶体的制备技术

铌镁酸铅(PMN)类化合物是一类弱铁电特性的ABO_3型复合钙钛矿结构铁电弛豫体。利用在A/B位固溶外来离子(例如,Sr、Ba和Ti等)的原理,改变该类化合物基固溶体的电负性差值φ和加权结构容差因子t值,达到合成全钙钛矿结构相的目的。根据电负性差值理论和钙钛矿结构容差因子理论,本文提出了铌镁酸铅类化合物钙钛矿结构相稳定性优值参数M的新概念。基于M值定义和PZN基固熔体的实验数据,推算出钙钛矿结构相稳定性临介优值Mc=1.67,并用以设计和优选PMN和PZN基多晶体最佳配方,优化材料性能。同时研究了钙钛矿结构相合成程度与MnO_2添加量和Mg偏离化学计量比程度的关系。研制出性能稳定、特性优良的新材料。     

共沉淀法合成铌镁酸铅—钛酸铅介是陶瓷粉末

通过共沉淀法合成铌镁酸铅－钛酸铅介电陶瓷粉末，经８００℃焙烧后，Ｘ射线衍射研究表明几乎为单一钙钛矿相；经１０００℃烧结的陶瓷片其密度达到理论值的９６．７７％，２０℃介电常数可达２０９４０。     

铌镁酸铅-钛酸铅单晶/压电双层结构材料中SH波的传播特性

将压电晶体板上、下表面的力学边界条件设为机械自由,其电学边界条件中分别考虑电学开路、电学短路和与空气介质相连的组合,基于铌镁酸铅-钛酸铅(PMN-PT)压电单晶的本构方程得到了频散方程,推导了反平面水平剪切(SH)波传播的一般解,分析了边界条件和压电双层晶体结构的层厚比对频散曲线的影响.结果表明,SH波的某些传播性能可以通过边界条件的处理和结构的设计来实现.     

The effects of transition metal in Sn-based pyrochlores on the methane catalytic combustion

Lanthanum stannate pyrochlores, La₂Sn₂O₇ and La₂SnMO₇ (M=Mn, Fe, Co, Ni, Cu), were successfully prepared by citric acid method and confirmed by XRD. TG and TPR characterizations showed that the introduction of transitional metals resulted in significant impacts on the structures and redox performances of prochlores. All the selected transitional metals could significantly improve their methane catalytic combustion performance. Among the doped pyrochlores, La₂SnCoO₇ pyrochlore possessed optimum activities at low temperatures, and Fe?doped pyrochlore showed highest reactivity for high temperature combustion and was proved to be promising materials for high temperature catalytic combustion. The reactivity differences of La₂SnMO₇ were reasonably attributed to the strong interactions between Sn and transitional metal.     

Spreading of human neutrophils on an ICAM-1-immobilized substrate under shear flow

Neutrophil (PMN) spreading on endothelium, mediated by the interactions between surface-bound β2 integrin and intercellular adhesion molecule-1 (ICAM-1) in the inflammatory cascade, is crucial for PMN post-adhesion and trans-migration in blood flow. The underlying mechanisms by which shear flow regulates PMN spreading dynamics are not well understood. Here, a parallel-plate flow chamber assay was applied to quantify the time course of PMN adhesion and spreading on an ICAM-1-immobilized substrate. Two types of shear flow, steady flows at shear stresses of 0.2, 0.5, and 1 dyne/cm2 and stepwise flows at 0, 1, and 10 dyne/cm2, were used to elucidate the impact of shear flow on cell adhesion and spreading. The number of adhered PMNs, the fraction of spreading PMNs and the projected area of spread PMNs were determined and were found to correlate with the distribution of surface-bound β2 integrin subunit (CD11a, CD11b, or CD18). The results indicate that PMN spreading on an ICAM-1 substrate is bi-directionally regulated under shear flow. CD11a, CD11b and CD18 subunits of β2 integrin contribute distinctly to PMN spreading on ICAM-1 substrates. This work provides new insights into understanding PMN spreading on the endothelium, mediated by β2 integrin and ICAM-1 under shear flow.     

N(Mg):N(Nb)为1:1时0.93PMN-0.07PT陶瓷的弛豫性能

在制备 ０．９３ＰＭＮ－０．０７ＰＴ（ＰＭＮＴ）陶瓷时,让 ＭｇＯ过剩使Ｎ（Ｍｇ）：Ｎ（Ｎｂ）（原子比）为１：１,它与ＰＭＮ的极性微区［Ｐｂ２ＭｇＮｂ］中Ｍｇ和Ｎｂ的原于比相同．测试结果表明：与以往的ＰＭＮ－ＰＴ材料（ＰＴ的原子百分数小于 ３５％）的情况不同,在ＸＲＤ图中可观测到的铁电四方相;代表极性的 Ｎｂ－Ｏ－Ｎｂ的键振动,在Ｒａｍａｎ谱中强至可以与低温时ＰＭＮ中存在长程相关的Ｎｂ－Ｏ－Ｎｂ键的振动相比较,这说明ＰＭＮＴ中的长程相关性增大．由于高铅缺位的钉扎、自由场的存在等的影响,在介电常数峰温的低温侧存在另一准弛豫铁电－准铁电性转变（ｑＲＦＥ－ｑｎＦＥ： ｔｒａｎｓｉｔｉｏｎ）．     

陶瓷体积分数对水泥基压电复合材料性能的影响

采用切割-填充法，以硫铝酸盐水泥为基体，铌镁锆钛酸铅（简称PMN）为压电功能体制备了1—3型硫铝酸盐水泥基压电复合材料。研究了压电陶瓷体积分数对1—3型水泥基压电复合材料的压电性能和介电性能的影响。结果表明：随着PMN体积分数增大，压电应变常数d33呈非线性增大，压电电压常数g33呈非线性减小。平面和厚度机电耦合系数Kp和Kt及介电常数εγ，随PMN体积分数的增大而增大，在低频段和高频段，其介电常数随频率的变化较平稳，表现出良好的介电频率稳定性。     

Zr含量对大功率0.125PMN 0.875PZT陶瓷压电性能的影响

采用二次合成法制备不同zr含量（x=0.46～0.52）的0.125 Pb(Mg_1/3Nb_2/3)O₃-0.875PbZr_xTi_1-xO₃（0.125PMN-0.875PZT）三元压电陶瓷。采用x线衍射仪（XRD）、阻抗分析仪等对陶瓷进行表征和性能测试,考察了Zr含量变化对陶瓷烧结相结构、体积密度、介电和压电性能的影响。结果表明:采用二次合成法,制备了纯钙钛矿相结构的陶瓷;当x=0.48～0.50时,0.125PMN-0.875PZT陶瓷处于四方一三方准同型相界（MPB）.在x=0.49时制备的0.125PMN-0.875PZT陶瓷性能最佳,体积密度为7.84 g/cm³,介电损耗低至0.76%,相对介电常数为2 130,压电常数为:320 pC/N,机电耦合系数达0.61,机械品质因数为76。     

过量PbO和过量MgO对PMN-PT陶瓷相结构及显微结构的影响

采用NaCl-KCl熔盐法制备了单一钙钛矿相结构的0．8PMN－0.2PT陶瓷,并详细研究了添加过量PbO和过量MgO对0．8PMN－0．2PT陶瓷样品的相结构和显微结构的影响,结果表明,过量PbO和过量MgO都能抑制和消除焦绿石相,提高陶瓷的致生,而且过量MgO的效果更好。     

纯钙钛矿相PMN-PT的改进铌铁矿法合成

以碱式碳酸镁代替氧化镁,在1 100℃×6 h条件下合成出纯的铌铁矿相,从而避免了第二步预烧过程中焦绿石相的形成。以碱式碳酸铅代替氧化铅,在650-1 150℃不同温度下预烧2 h后的XRD相组成分析表明:预烧粉体主相为钙钛矿相的PMN-PT,随预烧温度提高,PMN-PT固溶体不断形成,同时PbO发生四方相-正交相转变,但均未出现焦绿石相。因此,该工艺特别适合在需要过量PbO来实现低温烧结制备PMN-PT陶瓷的情况。     

WPAN及多网互通环境下通信网容量的分析

研究了WPAN及多网互通环境下通信网的容量，以电信网原始话务量模型为基础，归纳了通信网容量研究中的通用参数及基本公式，分析了公众电信网和移动通信网容量的影响因子，提出了改进方案与修正模型，给出了仿真分析．结果表明修正因子是多网互通环境下容量分析的重要参数，对分析wPAN接入各类通信网的容量影响具有理论意义和实用价值．     

Compression behavior of Sm）2Ti2O7-pyrochlore up to 50 GPa：single-crystal X-ray diffraction and density functional theory calculations

Single-crystal X-ray diffraction at pressures up to 50 GPa has been employed to study the compression behavior of Sm2Ti2O7-pyrochlore. In contrast to earlier reports, we observed no pressure-induced amorphization or pressure-induced anion disorder up to 50 GPa. The experimental study has been complemented by density functional theory-based calculations. A combination of the theoretical and experimental data yields a bulk modulus of 185 GPa, significantly higher than a value which had been reported earlier. In comparison to earlier work, the current study provides more reliable data due to the use of neon as a pressure medium, which provides a more hydrostatic pressure than the aluminum, which had been employed as a pressure medium in the earlier studies. An analysis of the compressibility of Al2B2O7 pyrochlores shows an approximately linear dependence of the bulk modulus on the unit cell volume.     

阀用电-机械转换器的应用研究

介绍了传统和新型两类电-机械转换器的作用、原理及特点,并对其性能进行了分析比较;着重阐述了超磁致伸缩电-机转换器(GIANT MAGNETOSTRICTIVE ACTUATOT,GMA),压电 PZT／电致PMN伸缩型电-机转换器,形状记忆合金(SHAPE MEMORY ALLOY,SMA)在流体控制元件中的应用现状。分析结果表明:超磁致伸缩型和电致PMN伸缩型电-机转换器具有应变大,结构简单,响应快和精度高等优点,它的出现为微流体元件的驱动提供了更新更有效的方法,具有良好的应用前景。