液相包裹法制备BaTiO3微粉合成机理研究

以Ｈ２ＴｉＯ３微粉为活性固相基体，Ｂａ（ＣＯＯＨ）２溶液为包裹相，采用液相包裹－界面反应的方法，进行制备ＢａＴｉＯ３微粉及其合成机理研究，提出了一套较完善且简便、适合于大生产的新的ＢａＴｉＯ３微粉制备技术与方法，初步揭示了液相包裹法制备ＢａＴｉＯ３微粉的反应过程及机理。通过这一方法，可以得到更为纯净、高分散、形貌更趋于球形的ＢａＴｉＯ３微粉。     

液相法制备BaTiO3基PTCR粉体的研究

采用高分子网络凝胶法和液相包裹法相结合的液相法合成了BaTiO3基PTCR陶瓷粉体．首先用高分子网络凝胶法在较低温度下制备施主掺杂的BaTiO3基陶瓷粉体,利用DSC、TG、XRD,TEM等技术表征了凝胶中间体和由此得到的氧化物粉末的物理和化学性能,结果表明,在700℃下煅烧2h可获得单相的(Ba,Sr)TiO3粉体,粉体的平均粒径d50为1．155μm．然后利用液相包裹法添加受主杂质和助烧剂,考察了所制备BaTiO3基PTCR陶瓷粉体的烧结性能及陶瓷制品的PTC特性,获得了室温阻值为17．5Ω,升阻比达10^4,阻温系数约为12％的PTCR．     

用Sol─Gel法制备PZT铁电陶瓷及薄膜

用Ｓｏｌ－Ｇｅｌ法制备了Ｐｂ（Ｚｒ＿（０．５）Ｔｉ＿（０．５））Ｏ＿３（ＰＺＴ）铁电陶瓷与薄膜，观察了它们的结晶情况并测定了它们的电学性能。利用Ｓｏｌ－Ｇｅｌ法，可降低ＰＺＴ陶瓷粉料的预烧温度约２００℃，所得陶瓷致密，晶粒均匀；具有较好的介电性能。ＰＺＴ陶瓷显示弥散相变特征。ＰＺＴ薄膜的晶化受基底影响很大。基底晶格越完整，与ＰＺＴ薄膜的晶格失配率越小，ＰＺＴ薄膜的晶化就越好。采用ＰｂＴｉＯ＿３过渡层促进ＰＺＴ薄膜在镀铂硅片上晶化。ＰｂＴｉＯ＿３过渡层与ＰＺＴ薄膜构成串联电路。其表现电学性能与相应的ＰＺＴ体材料相近。     

Al2O3微粉的表面改性及表征

以α—Al2O3微粉为基体，Y(NO3)3溶液为包裹相，采用液相包裹法进行加钇颗粒表面改性。获得了表面均匀包裹Y2O3的α—Al2O3粉体。将此粉体与Al合金复合制备复合材料，复合材料组织更加均匀，对材料进行力学性能测试，结果表明：改性粉体对Al合金增强效果明显增加，抗拉强度提高27．2％，屈服强度提高33．1％，延伸率提高10．3％。     

水热法制备PZT纳米晶体微粉结构与热效应的分析

本文报道了水热条件下制备的ＰＺＴ纳米晶体微粉结构和热效应分析的研究结果，认为ＰＺＴ纳米晶粒尺寸为１２～１４ｎｍ，ＰＺＴ纳米晶体微粉粒度１３０ｎｍ左右，产生最显著的热效应和热失重时的温度分别为８１１．２６℃和９２４．７１℃，用传统固相法制备的ＰＺＴ微粉产生最显著的热效应和热失重时的温度分别为１２４３．４７℃和１２１３．２９℃，这对有效地降低ＰＺＴ陶瓷材料的烧结温度和有效防止ＰｂＯ的挥发有重要意义。     

液相包覆制备Ce-TZP陶瓷的力学性能与稳定行为

采用XRD、SEM、TEM等分析手段对由液相包覆工艺制备的Ce—TZP陶瓷的微结构进行了研究，并和共沉淀粉体制备的Ce—TZP陶瓷进行了对比分析．力学性能表明，同共沉淀粉体制备的Ce—TZP陶瓷相比，由液相包覆工艺制备的Ce—TZP陶瓷虽硬度下降，但断裂韧性改善；液相添加少量Al2O3硬度随之增加、断裂韧性显著提高．电镜分析表明，液相包覆工艺制备的Ce—TZP陶瓷晶粒尺寸分布宽化，一部分晶粒尺寸较大但CeO2含量低、易发生马氏体相转变晶粒的存在是断裂韧性改善的主要原因．陶瓷体中单斜相大晶粒与四方相之间的残余应力、添加少量Al2O3在晶界上易形成薄的非晶包裹层，是增加可相变四方相数量，提高断裂韧性的其它机制。     

水热合成PZT热电体结晶粉末工艺及相关性能的研究

研究了水热合成ＰＺＴ热电体结晶粉末及相关性能，考察了合成温度、合成时间和促进剂对结晶性的影响。用ＸＲＤ、ＳＥＭ、ＥＰＭＡ和原子吸收光谱等测试手段分析了实验结果，表明这种结晶粉末的粒子粒径为０．１ｕｍ￣３ｕｍ，呈立方体状。用它制作的ＰＺＴ热电体陶瓷烧结温度１１６０℃左右，比传统的固相法降低６０℃左右，在烧结过程中ＰｂＯ的挥发速率比固相法小得多，有害杂质Ｋ＾＋离子的含量为０．００２％￣０．００６％。     

聚合物分解法合成BaSm 2Ti 4 O 12

以BaCO3、Sm（NO3）3及Ti（OC4H9）4为原料，采用柠檬酸盐前驱体法制备BaSm2 Ti4O12并与草酸盐共沉淀法制备BaSm2 Ti4O12粉体过程作了比较．结果发现，利用聚合物分解法，可以在1000℃的较低温度下得到单相结晶的BaSm2 Ti4O12，而草酸盐沉淀法则需要1300℃的高温才能合成纯的BaSm2 Ti4O12相．研究表明，这两种液相法所需合成温度相差很大，是由于不同的相演化过程及反应步骤所致．在共沉淀法中，当煅烧前驱体时，中间相Sm2 Ti2O7与BaTi4O9和BaTiO3反应生成BaSm2 Ti4O12相，其过程与固相法相类似．而在聚合物分解法中，前驱体在热分解过程中生成BaTi2O5相，导致了与固相过程完全不同的反应机制，促进了BaSm2 Ti4O12相的形成．     

用溶胶－凝法制备锆钛铅铁电薄膜

利用溶胶－凝胶法在镀铂硅片上制备了ＰＺＴ铁电薄膜。利用ＸＲＤ、ＳＥＭ和ＴＥＭ观察了ＰＺＴ薄膜的组成与形貌，测定ＰＺＴ薄膜的电学性能。为防止薄膜发生龟裂，在前体溶液中加入了干燥控制化学添加剂，并采用慢速变温的热处理过程。ＰｂＴｉＯ３过渡层保证了ＰＺＴ薄膜结晶完好。     

用溶胶—凝法制备锆钛铅铁电薄膜：1994年7月1日收到,8月20日修回

利用溶胶－凝胶法在镀铂硅片上制备了ＰＺＴ铁电薄膜，利用ＸＲＤ、ＳＥＭ和ＴＥＭ观察了ＰＺＴ薄膜的组成与形貌，测定了ＰＺＴ薄膜的电学性能。防防止薄膜发生龟裂，在前体溶液中加入了干燥控制化学添加剂，并采用慢速变温的热处理过程，ＰｂＴｉＯ３过渡层保证了ＰＺＴ薄膜晶完好。     

Direct precipitation of lead zirconate titanate by the hydrothermal method

Direct precipitation of fine powders of lead zirconate titanate (PZT) in the complete range of solid solution, is investigated under hydrothermal conditions, starting from lead oxide and titania/zirconia mixed gels. The perovskite phase is formed in the temperature range of 165 – 340°C. Sequence of the hydrothermal reactions is studied by identifying the intermediate phases. The initial formation of PbO: TiO₂ solid solution is followed by the reaction of the same with the remaining mixed gels giving rise to X-ray amorphous PZT phase. Further, through crystallite growth, the X-ray crystalline PZT is formed. This method can be extended for the preparation of PLZT powder as well. The resulting powders are sinterable to high density ceramics.     

Synthesis and growth mechanism of NbC–SiC micro/nanowire by carbothermal reduction

Abstract

NbC–SiC micro/nanowires (MNWs) with NbC content varying from 5 to 20 mol.-% were synthesised at 1600–1800°C via carbothermal reduction utilising silica sol, niobium pentoxide powder and carbon black as starting materials. The synthesis process and growth mechanism of NbC–SiC system were investigated. Results show that the morphology of the synthesised products mainly appears as curve shaped microwires or nanowires. The crystalline consists of both SiC and NbC phases which doped with each other by substitution and interstitial reactions in solid solution. NbC–SiC MNWs were developed by vapour–liquid–solid mechanism according to the existence of liquid droplet phase in the tip at reaction temperature. β-SiC twin crystal growing along [112] direction was formed in the stem, and NbC polycrystal was dissociated from Nb–Si liquid phase. The varied concentration of Nb and Si in the Nb–Si liquid phase could be a significant reason for the curved growth of NbC–SiC MNWs.     

A modified two-stage mixed oxide synthetic route to lead zirconate titanate powders

An approach to synthesis lead zirconate titanate [Pb(Zr_1−xTi_x)O₃; PZT] powders with a modified two-stage mixed oxide synthetic route has been developed. To ensure a single-phase perovskite formation, an intermediate phase of zirconium titanate (ZrTiO₄) was employed as starting precursor. The formation of perovskite phase in the calcined PZT powder has been investigated as a function of calcination temperature, soaking time and heating/cooling rates by differential thermal analysis (DTA) and X-ray diffraction (XRD) techniques. The morphology evolution was determined by scanning electron microscopy (SEM) technique. It has been found that the unreacted PbO and ZrTiO₄ phases tend to form together with PZT, with the latter appearing in both tetragonal and rhombohedral phases, depending on calcination conditions. It is seen that optimisation of calcination conditions can lead to a 100% yield of PZT in a tetragonal phase.     

PZT陶瓷粉体的水热合成

利用水热法合成了单相、立方体形貌且平均颗粒尺寸在1 μm的锆钛酸铅(PZT)陶瓷粉体. 研究了碱度、反应时间对最终产物的影响, 着重研究了不同碱度下Pb缺失的补偿问题. 结果表明: 碱度对最终PZT产物A位Pb离子的固溶程度有着重要的影响. 碱度越高, A位缺失的Pb离子就越多. 原料中适当的Pb过量能够有效补偿Pb离子的缺失, 碱度越高, 所需添加的Pb离子的过量程度也就越高. 但过多的Pb离子加入量会导致最终产物中出现第二相.     

Stability of the perovskite phase in PMN-PZN-PT ceramics

The thermal stability of ceramics based on PMN, PZN and their solid solutions PMN-PT, PZN-PT (PMN = PbMg_1/3Nb_2/3O₃, PZN = PbZn_1/3Nb_2/3O₃, PT = PbTiO₃) during sintering is investigated. The present work confirms that the incorporation of a limited excess of MgO in the starting materials is actually quite beneficial for the synthesis of a pure PMN perovskite phase, and that it prevents the formation of a secondary pyrochlore-type phase, after PbO loss during firing. An excess of ZnO is much less efficient for the stabilization of the PZN compound. Examination of the microstructural evolution as well as analysis of second phases in these materials and in their solid solutions formed with lead titanate by wavelength dispersive spectroscopy and/or energy dispersive X-ray spectroscopy techniques, allows a mechanism to be proposed for the stabilization of the PMN-based perovskite phases by an excess of MgO.     

Synthesis of Si-C nanostructures by laser ablation of silicon target in n-heptane vapor

Controllable synthesis of Si-C nanostructures was realized in a laser ablation system by adopting solid silicon target and n-heptane vapor as starting materials. Ultrafine SiC nanocrystals and graphite-coated SiC nanocrystals were synthesized with the laser frequency of 1 Hz and 20 Hz, respectively. According to the real-time observation on the plasma evolvement, we proposed a formation mechanism of Si-C nanostructure related to vapor-phase reaction. Our method can be extended to other material systems for diverse novel nanostructures.     

新型钙钛矿型铁电陶瓷BSPT研究进展

(1-x)BiScO3-xPbTiO3(BSPT)是一种新型钙钛矿型结构的铁电体.BSPT体系在x=0.64附近有三方相和四方相的准同型相界(MPB).BSPT陶瓷的制备主要采用传统的电子陶瓷制备方法,包括常压法和高压法.BSPT陶瓷具有优良的介电和压电性能,居里温度Tc比Pb(Zr,Ti)O3(PZT)的高.综述了近年来对BSPT陶瓷的研究进展,重点介绍了邻近MPB的0.36BiScO3-0.64PbTiO3铁电陶瓷的性能.同时还介绍了掺杂对BSPT陶瓷的影响.     

Multi‐Step Crystallization of Self‐Organized Spiral Eutectics

A method for the solidification of metallic alloys involving spiral self‐organization is presented as a new strategy for producing large‐area chiral patterns with emergent structural and optical properties, with attention to the underlying mechanism and dynamics. This study reports the discovery of a new growth mode for metastable, two‐phase spiral patterns from a liquid metal. Crystallization proceeds via a non‐classical, two‐step pathway consisting of the initial formation of a polytetrahedral seed crystal, followed by ordering of two solid phases that nucleate heterogeneously on the seed and grow in a strongly coupled fashion. Crystallographic defects within the seed provide a template for spiral self‐organization. These observations demonstrate the ubiquity of defect‐mediated growth in multi‐phase materials and establish a pathway toward bottom‐up synthesis of chiral materials with an inter‐phase spacing comparable to the wavelength of infrared light. Given that liquids often possess polytetrahedral short‐range order, our results are applicable to many systems undergoing multi‐step crystallization.     

Factors influencing the piezoelectric behaviour of PZT and other “morphotropic phase boundary” ferroelectrics

Recent studies of the mechanism of piezoelectricity in PZT and related materials are reviewed and complemented by new analyses based on the Landau-Ginzburg-Devonshire theory of ferroelectricity. Particular attention is given to the nature of the morphotropic phase boundary between the tetragonal and rhombohedral perovskite phases and the accompanying peak in the piezoelectric coefficient. The importance of the changes in angular dependence of single crystal piezoelectric coefficients as a function of composition is highlighted together with the concept of field-induced rotation of the polarization in the (110) plane. It is shown that introducing the tendency to form monoclinic phases enhances this phenomenon. The model that the monoclinic phase in PZT is due to the condensation of local disorder in the polar cation displacements from the macroscopic tetragonal and rhombohedral phases is examined in some detail using statistical analyses of the Zr/Ti conformation. Whilst the concept of monoclinic nano-domains is not inconsistent with statistically random distributions, it is argued that some ordering of the B-site cations may be required to enable the transformation to a macroscopically observable phase. The implications of this model on the contribution of polarization rotation to piezoelectricity in PZT are discussed.     

纳米铌镁酸铅机械化学法低温快速合成

采用一种新型螺杆研磨机,以氧化物为原料,仅需3h的研磨,即可得到钙钛矿相结构的纳米铌镁酸铅(PMN)粉体.并研究了原料粉质量、研磨功率、研磨时间等不同因素对于合成的影响.通过对比分析发现,提高研磨功率,可以缩短合成时间、提高产物纯度、减小粉体粒径.通过原料交叉反应实验,确定剪切力机械化学法合成铌镁酸铅的反应机理为:MgO与Nb2O5反应生成MgNb2O6,然后与PbO反应获得铌镁酸铅.