Sr位Nd掺杂对SrBi$lt;sub$gt;2$lt;/sub$gt;Nb$lt;sub$gt;2$lt;/sub$gt;O$lt;sub$gt;9$lt;/sub$gt;性能的影响及机理研究

采用传统固相法制备了（Sr_1-3x/2A_x/2Nd_x）Bi₂Nb₂O₉（x=0,0.05,0.1和0.2）陶瓷,并系统研究了Nd离子取代Sr离子对SrBi₂Nb₂O₉性能的影响及其作用机理.研究结果表明：Sr_1-3x/2A_x/2Nd_xBi₂Nb₂O₉的介电常数和介电损耗随温度变化的行为具有明显的离子松弛极化特征.Nd³⁺对Sr²⁺的部分取代,导致Sr_1-3x/2A_x/2Nd_xBi₂Nb₂O₉剩余极化强度P_r稍有下降,但其压电系数d₃₃却有所增加,根据铁电热力学理论,这是Nd³⁺对Sr²⁺取代导致材料介电常数增大所致.Sr_1-3x/2A_x/2Nd_xBi₂Nb₂O₉的居里温度（T_C）没有随Nd含量的增加而变化,拉曼光谱技术分析表明这是其NbO₆八面体畸变程度没有发生变化所致.Nd³⁺取代Sr²⁺提高了材料的介电常数ε_r、压电系数d₃₃、机电耦合系数K_p,同时降低了机械品质因数Q_m,但是谐振频率温度系数C值没有改变. 关键词： 压电陶瓷 介电性能 压电性能 拉曼光谱     

Na1/2Bi1/2TiO3体系的电子结构与极化特性

采用自洽场离散变分X_α计算方法,研究了ABO₃型钙钛矿结构无铅压电陶瓷Na_1/2Bi_1/2TiO₃体系的电子结构,分析了A,B位元素取代对Na_1/2Bi_1/2TiO₃压电陶瓷极化性能的影响.结果表明:NBT体系压电陶瓷材料存在自发极化,B位离子位移使铁电性增强,Ba,Sr与Mn离子A,B位复合取代可降低矫顽场、提高自发极化强度,从而提高材料的铁电性能,并通过实验对此结论进行了验证.     

0.7Pb(Mg1/3 Nb2/3)O3-0.3PbTiO3单晶/环氧树脂1-3型复合材料的压电性能研究

模拟了0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3(PMN-0.3PT)单晶1-3型压电复合材料的性能与单品体积分数的关系,得出性能最优时压电相的体积分数为64%,在这一体积分数下,采用切割-填充法,并使用了不同类型的环氧树脂填充制备复合材料.系统地研究了聚合物相对复合材料性能的影响,研究表明,减小聚合物相的刚度系数c和密度ρ有利于提高复合材料的性能,且聚合物相与压电相的结合强度对性能的影响非常明显,制备的PMN-0.3 PT单晶1-3型复合材料的厚度伸缩机电耦合系数k1高达90.1%,压电系数d33大于1000 pC/N,机械品质因数Qm为10.39,声阻抗Z也大大降低,性能明显优于传统的Pb(Zrx,Ti1-x)O3(PZT)陶瓷及其1-3复合材料,在压电换能器和传感器中显示出广阔的前景.     

高居里温度铋层状结构钛钽酸铋(Bi_3TiTaO_9)的压电、介电和铁电特性

随着现代信息技术的飞速发展,压电材料的应用范围进一步拓展,使用的温度环境越来越严苛,在一些极端环境下对压电材料的服役性能提出了新的挑战.因此研究具有高居里温度同时具有较强压电性能的压电材料,是迫切需要解决的问题.本文利用普通陶瓷工艺制备了高居里温度铋层状结构钛钽酸铋Bi_3TiTaO_9+x wt.%CeO_2(x=0—0.8,简写为BTT-10xCe)压电陶瓷,研究了钛钽酸铋陶瓷的压电、介电和铁电特性.压电特性研究表明,稀土Ce离子的引入可以提高BTT陶瓷的压电性能, BTT-6Ce (x=0.6)陶瓷具有最大的压电系数d33～16.2 pC/N,约为纯的BTT陶瓷压电系数(d33～4.2 pC/N)的4倍.介电特性研究显示, BTT和BTT-6Ce (x=0.6)陶瓷均具有高的居里温度, T_C分别为890℃和879℃,同时稀土Ce离子的引入降低了BTT陶瓷的高温介电损耗tand.铁电特性研究表明,稀土Ce离子的引入提高了BTT陶瓷的极化强度.在180℃温度下和110 kV/cm的电场驱动下, BTT和BTT-6Ce (x=0.6)陶瓷的矫顽场Ec分别为53.8 kV/cm和57.5 kV/cm,剩余极化强度Pr分别为3.4μC/cm~2和5.4μC/cm~2.退火实验显示:稀土Ce离子组分优化的BTT压电陶瓷经800℃的高温退火后,仍具有优异的压电性能温度稳定性.研究结果表明, BTT-6Ce (x=0.6)陶瓷兼具高的居里温度T_c约为879℃和强的压电性能d33约为16.2 pC/N、较好的压电性能温度稳定性,是一类压电性能优异的高温压电陶瓷.     

La4/3(Sr1-xBax)5/3Mn2O7的电输运性质研究

本文主要介绍用溶胶-凝胶法制备的Ba离子掺杂的双层钙钛矿锰基氧化物La4/3(Sr1-xBax)5/3Mn2O7(00.4范围内,低温电阻值随烧结温度增加而减小.出现这种反常行为的结果可能是由于随着Sr逐步被Ba离子取代而引起的失配效应造成结构相分离所致.     

烧结温度对ZnO掺杂的KNN陶瓷微结构和压电性能的影响

以Zn O为烧结助剂,采用固相合成法制备了(K0.5Na0.5)Nb O3(缩写为KNN)压电陶瓷,研究了烧结温度对Zn O掺杂KNN陶瓷致密性、微结构以及压电性能的影响。结果表明:随着烧结温度的升高,KNN陶瓷的压电常数d33、密度?和机电耦合系数Kp均先升高后降低,在1100oC时达到最大值;而试样的介电常数则随烧结温度的升高而增大。烧结温度过高(达到1120oC),将会引起Na、K的大量挥发和晶粒异常生长,使得其结构变疏松。当Zn O含量为0.5wt%、烧结温度为1100oC时,KNN陶瓷的密度达到了4.43g/cm3;其压电学性能达到最优:d33=113p C/N,tan?(1k Hz)=5.31%,Kp=0.35。     

钙钛矿锰氧化物(La_(1-x)Eu_x)_(4/3)Sr_(5/3)Mn_2O_7(x=0,0.15)的磁性和电性研究

通过传统固相反应法制备了钙钛矿锰氧化物(La1-xEux)4/3Sr5/3Mn2O7(x=0,0.15)多晶样品,并且对其磁性和电性进行了研究.磁性测量表明:随着温度的降低,样品经历了一个复杂的转变过程,在温度为T*时经历二维短程铁磁有序转变,在温度为TC时进入三维长程铁磁态.随着Eu的掺杂,T*和TC减小,并且样品(La0.85Eu0.15)4/3Sr5/3Mn2O7在低温区表现出自旋玻璃行为.电性质测量表明:在母体La4/3Sr5/3Mn2O7中La位掺杂Eu后电阻率明显变大,金属绝缘转变温度TMI降低,磁电阻峰值增大.这些影响归因于较小的Eu3+离子替代La3+离子导致平均离子半径减小,晶格发生畸变.此外,较小的Eu3+离子优先占据层间岩盐层的R-site,使La3+,Sr3+,Eu3+离子在(La0.85Eu0.15)4/3Sr5/3Mn2O7中的分布更加有序,所以x=0.15的样品的ρ-T曲线只有一个峰.     

溶胶-凝胶法制备的高压电常数（Bi0.5Na0.5）1－xBaxTiO3系无铅压电陶瓷

测量了使用溶胶-凝胶工艺制备的(Bi0.5Na0.5)1-xBaxTiO3(x=0.00，0.04，0.06，0.08,0.12)系陶瓷的介电、压电、铁电和热释电性能.由于使用了溶胶-凝胶工艺制备的粉料，因此所有样品的压电性能都得到了较大提高.其中(Bi0.5Na0.5)0.94Ba0.06TiO.3系陶瓷具有该系列最大的压电常数，d33=173×10-12C/N，与传统工艺相比，d33提高了近40%.同时，在一定范围内，随Ba含量的增加，材料的剩余极化Pr和矫顽场Ec逐渐减小，退极化温度逐渐降低.对于(Bi0.5Na0.5)0.94Ba0.06TiO.3系陶瓷，剩余极化和矫顽场分别为25μC/cm2和28kV/cm，退极化温度约为80℃. 关键词： 溶胶-凝胶 压电常数 剩余极化 矫顽场     

Sb2O3的丰度对（1-x）La0.6Dy0.1Sr0.3MnO3/（x/2）（Sb2O3）电输运性质的影响

用固相反应法制备(1-x)La0.6Dy0.1Sr0.3MnO3/x/2(Sb2O3)(x=0.00,0.02,0.15)样品,通过X射线衍射(XRD)图谱,扫描电子显微镜(SEM)照片及SEM能谱(EDS),ρ～T曲线研究样品的结构及电输运性质.结果表明:Sb离子没有进入Mn位,Sb2O3包覆在La0.6Dy0.1Sr0.3MnO3颗粒表面,Sb2O3起助熔剂作用,使得复合样品的颗粒变大且大小相对均匀;复合样品的绝缘体-金属转变温度TP较纯的La0.6Dy0.1Sr0.3MnO3的TP提高20K左右,对x=0.15的样品电阻高峰值比纯的La0.6Dy0.1Sr0.3MnO3的峰值电阻率增大两个数量级,用自旋极化隧穿理论予以解释.     

A位等价与非等价取代对(K0.5Na0.5)NbO3陶瓷极化的影响

研究了在铌酸钾钠基陶瓷中,A位等价与非等价取代对陶瓷极化温度和极化电场的影响,结果表明:A位等价取代的陶瓷对极化温度和极化电场没有强烈依赖性,可以使极化足够充分,能有效提高铌酸钾钠基陶瓷的压电性能;相反,A位非等价取代的陶瓷对极化温度和极化电场敏感,容易击穿,极化不充分,限制了铌酸钾钠基陶瓷的压电性能. 关键词： 铌酸钾钠 极化 压电     

主成分回归法同时测定Cu2+、Pb2+、Hg2+和Cd2+

研究了用双硫腙光度法结合多元线性回归技术直接分析水相中有毒重金属离子的方法.结果表明,在β-环糊精和非离子表面活性剂Triton X-100的存在下,金属离子-双硫腙配位体系具有更高的灵敏度和稳定性.使用多元线性回归技术,可以在多种干扰金属离子共存的条件下,不经萃取和化学分离直接分析4种常见的有毒重金属离子.     

Relative equilibria of D2H + and H2D+

Relative equilibria of molecules are classical trajectories corresponding to steady rotations about stationary axes during which the shape of the molecule does not change. They can be used to explain and predict features of quantum spectra at high values of the total angular momentum J in much the same way that absolute equilibria are used at low J. This paper gives a classification of the symmetry types of relative equilibria of AB₂ molecules and computes the relative equilibria bifurcation diagrams and normal mode frequencies for D₂H⁺ and H₂D⁺. These are then fed into a harmonic quantization procedure to produce a number of predictions concerning the structures of energy level clusters and their rearrangements as J increases. In particular the formation of doublet pairs is predicted for H₂D⁺ from J ≈ 26.     

Heterometallic fullerides of Fe and Cu groups with the composition K2MC60 (M=Fe+2, Fe+3, Co+2, Ni+2, Cu+1, Cu+2, Ag+1)

Heterometallic fullerides with composition K₂MC₆₀, synthesized by exchange chemical reaction of K₅C₆₀ or K₄C₆₀ with chlorides of metals Fe and Cu groups have been investigated by X-ray diffraction, magnetic resonance, Raman and Mössbauer spectroscopy. Magnetization and susceptibility measurements have also been carried out. Metal chlorides from Fe and Cu groups enable to cover the whole range of electronic configuration of metal from d⁵ to d¹⁰. Heterometallic fullerides with M=Cu⁺², Fe⁺², Fe⁺³ and Ni⁺² appeared to be superconductors with T_c=13.9–16.5 K. Ferromagnetism and superconductivity coexist in investigated fulleride K₂Fe⁺³C₆₀.     

Properties of Ca-doped Bi2+xSr2−xCuO6+δ

Specific-heat measurement is performed for Ca-substituted samples for Sr in Bi_2.1Sr_1.9?yCa_yCuO_6+δ. Specific heat anomaly associated with the superconducting transition is observed for the samples for y = 0.8, 0.95 and 1.0. The anomalies are consistent with the behavior of the magnetic measurement and suggest the bulk effect of the 80 K-class superconductivity.     

High pressure effect on the chemoselectivity of catalyzed [2+2] and [2+2+2] addition reactions involving acetylenic esters

Abstract

The chemoselectivity is changed by pressure in the catalyzed addition of propynoates to norbornadiene, but is not altered in the corresponding addition to norbornene.     

EPR study of Fe3+ and Mn2+ in CeO2 and ThO2

Attempts were made to grow CeO₂ and ThO₂ single crystals doped with transition metal ions. Only Fe³⁺ and Mn²⁺ could be detected by the EPR technique. The EPR spectrum of Fe³⁺ in CeO₂ exhibits the well-known fine structure in cubic fields. The parameters areg=2.0044(1) anda=15.6(1)·10^?4 cm^?1. The hyperfine constantA for⁵⁷Fe in hexahedral coordination was found to be 8.9(1)·10^?4 cm^?1. The EPR spectrum of Mn²⁺ in CeO₂ reveals two cubic Mn²⁺ centers. The parameters for center 1 areg=1.9999(1) andA=86.9(1)·10^?4 cm^?1 and for center 2g=1.9984(1) andA=87.0(1)·10^?4 cm^?1. Heating the Mn doped CeO₂ samples in hydrogen, the Mn²⁺ centers transform from cubic into trigonal centers with approximate values ofg=1.9988(2),A=84.5(6)·10^?4 cm^?1 andD=203(1)·10^?4 cm^?1. The two observed Mn²⁺ centers in ThO₂ exhibita priori axial symmetry with approximate values ofg=2.0006(2),A=88.9(4)·10^?4 cm^?1 andD=33(3)·10^?4 cm^?1.     

Efficiencies of third bodies in the reaction H + O2 + M = HO2 + M

Vibrational transition probabilities have been calculated by the Schwartz, Slawsky and Herzfeld method [3] for the deactivation of HO₂* in collision with H₂, O₂ and CO₂. The relative efficiencies of H₂, O₂ and CO₂ are compared with their third-body efficiencies found experimentally and it is concluded that the transfer of large vibrational quanta from HO₂* is unlikely to play an important part in determining the position of the second explosion limit of the H₂/O₂ reaction. This conclusion is at variance with the explanation put forward by Walsh [1] of the ‘anomalous’ third-body efficiencies of H₂O and CO₂ in this reaction.     

EPR study on Mn2+-Cu2+ and Ni2+-Cu2+ mixed pairs

An EPR study at X- and Q-band frequencies has been made on mixed metal pairs Mn²⁺-Cu²⁺ and Ni²⁺-Cu²⁺ obtained by doping the dimer complex C₅H₅NO CuCl₂ · H₂O. Available experimental data have been confirmed and extended, particularly as regards the characteristic directions of the various magnetic tensors. The qualitative behaviour of the spectra and the somewhat singular values of the magnetic parameters can be well-described on the basis of a theoretical model in which a very strong “cosine” interaction between the total electronic spins is assumed. From the model some interesting new aspects emerge, concerning the relations between pairs and single-ion EPR parameters.