Formation mechanism of barium titanate nanocrystals under hydrothermal conditions

Growth units and the crystallization habit of BaTiO₃ nanocrystals have been investigated. It has been proposed that the growth units of BaTiO₃ were surface hydroxylated Ti(OH)₆²⁻ octahedra. The relationship between crystal morphology and the variation of the current intensity in the solution has been obtained through the measurement of the OH⁻ in the solution and the hydrothermal experiment with superimposed direct electric field. Based on the computation of the stability energy of the growth units, the relationship between the crystallized morphology of crystallites and the most favorable growth units under different conditions has been derived. It has been found that there is structure similarity between anatase (TiO₂) and BaTiO₃ from the crystal chemistry viewpoint, so they are soluble in each other, which can serve as a reasonable explanation for the abnormal phenomenon of the retention of cubic substable phase at room temperature. Project supported by the National Natural Science Foundation of China.     

Template Effect on Structure and Morphology of Ni(OH)2 Powders Prepared by Hydro-chemical Method

Ｐｒｏｐｅｒｔｉｅｓｏｆｐｏｗｄｅｒｓａｒｅｃｌｏｓｅｌｙｒｅｌａｔｅｄｔｏｔｈｅｉｒｓｔｒｕｃｔｕｒｅｓａｎｄｍｏｒｐｈｏｌｏｇｉｅｓ ,ｍａｉｎｌｙｉｎｃｌｕｄｉｎｇｐａｒｔｉｃｌｅｓｉｚｅ,ｓｈａｐｅａｎｄｃｒｙｓｔａｌｌｉｎｉｔｙｏｆｐｏｗｄｅｒｓ[1].Ｆｏｒｐｏｗｄｅｒｓｐｒｅｐａｒｅｄｂｙｈｙｄｒｏ ｃｈｅｍｉｃａｌｍｅｔｈｏｄ ,ｓｔｒｕｃｔｕｒａｌａｎｄｍｏｒ ｐｈｏｌｏｇｉｃａｌｃｏｎｔｒｏｌｏｆｐｏｗｄｅｒｓｗｅｒｅｃｏｎｖｅｎｔｉｏｎａｌｌｙｒｅａｌｉｚｅｄｂｙｔｈｅａｄｊｕｓｔｍ…     

Template effect on structure and morphology of Ni(OH)2 powders prepared by hydro-chemical method

The template effect controlling the structure and morphology of ultrafine particles was described. Ni(OH)₂ powders were prepared by NH₃ coordination-precipitation method. The effects of SO ₄ ²⁻ , NO ₃ ⁻ , Cl⁻, NH₃, pH value on Ni(OH)₂ structure and morphology were investigated experimentally, explained with the theoretical model that the growth units were the polyhedral structure of coordination anions. The results showed that the structure and morphology of Ni(OH)₂ were effectively controlled by the growth units, the dimensions and the linking patterns of the growth units vary with the changes of physical and chemical conditions in the aqueous solution. Foundation item: The National Natural Science Foundation of China(No.59774018) Biography of the first author: LIU Zhi-hong, professor, born in 1963, majoring in hydrometallurgical technology and control of structure and morphology of powders.     

Growth units and forming mechanism of KDP crystals

Ｔｈｅｐｒｏｃｅｓｓｏｆｃｒｙｓｔａｌｇｒｏｗｔｈｉｓｇｅｎｅｒａｌｌｙｄｉｖｉｄｅｄｉｎｔｏ3ｓｔｅｐｓｉｎｓｕｃｃｅｓｓｉｏｎ,(ｉ)ｔｈｅｄｉｓｓｏｌｕｔｉｏｎｏｆｓｏｌｕｔｅ,(ｉｉ)ｔｈｅｆｏｒｍａｔｉｏｎｏｆｇｒｏｗｔｈｕｎｉｔｓ,ａｎｄ(ｉｉｉ)ｔｈｅｔｒａｎｓｐｏｒｔａｔｉｏｎａｎｄｃｏｍｂｉｎａｔｉｏｎｏｆｇｒｏｗｔｈｕｎｉｔｓｏｎｔｈｅｇｒｏｗｔｈｉｎｔｅｒｆａｃｅｓ.Ｔｈｅｅｘｉｓｔｉｎｇｆｏｒｍｓｏｆｇｒｏｗｔｈｕｎｉｔｓａｒｅｕｎｄｅｒｈｏｔｄｉｓｃｕｓｓｉｏｎｎｏｗ,ｗｈｉｌｅｔ…     

异形BaTiO3晶粒的制备与表征

为了获得片状BaTiO3陶瓷模板,在KF-NaF-BaTiO3伪三元体系中采用凝固法制备了异形BaTiO3晶粒粉体,表征了该粉体的结构和形貌.研究结果表明：不同原料配比制得的BaTiO3晶粒的大小、形态和相的纯度有显著的区别;以97.8（3KF-NaF）-2.2BaTiO3原料配比制备的粉体中BaTiO3含量高,BaTiO3晶粒形态大多呈片状,晶粒尺寸分布均匀.     

钛酸钡分子核磁共振的量子化学研究

用量子化学从头计算方法，在RHF／LANL2DZ的水平上对单个BaTiO3分子进行了基态构型优化。在此基础上进行了两种规范变换方法（GIAO和CSGT）的RHF／LANL2DZ的NMR屏蔽张量计算，得到与BaTiO3jjj wsg NMR实验研究相符合的结果。     

高温溶液中KTP晶体生长机制的研究

采用激光Ｒａｍａｎ光谱，研究了ＫＴＰ－Ｋ_２Ｏ－Ｐ_２Ｏ_５和ＫＴＰ－Ｋ_２Ｏ－Ｐ_２Ｏ_５－ＷＯ_３两种不同溶液的淬冷玻璃体，这些玻璃体部分地记录了相应溶液的溶质与溶剂间相互作用的信息，溶液中ＴｉＯ_６、ＰＯ_４、ＷＯ_４等阴离子基团形成了不同类型的溶剂合物。随后，以籽晶称重法测定了ＫＴＰ晶体在这两种不同溶液体系中的生长质量速度与溶液过饱和度之间的关系。实验结果表明，ＫＴＰ晶体生长机制与原子化的ＢＣＦ生长理论的面扩散或体扩散的线性定律与抛物线定律相吻合。     

应力对LaAlO3/BaTiO3超晶格结构及性能的影响

采用激光脉冲分子束外延技术,在(100)取向SrTiO3或Nb:SrTiO3单晶基片上成功外延生长不同结构的LaAlO3/BaTiO3超晶格。利用高能电子衍射技术和X射线衍射技术对LaAlO3/BaTiO3超晶格的生长过程和微结构进行了表征。发现由于LaAlO3和BaTiO3晶格常数的不匹配,在LaAlO3/BaTiO3超晶格中存在应变,该应变又对超晶格的铁电性能具有很大的影响。而不同的结构存在的应变不同,非对称结构的LaAlO3/BaTiO3超晶格的应变随每个周期中LaAlO3层厚度的增加、BaTiO3层厚度的减少而增大,其剩余极化强度不仅未减少,反而增加。     

Preparation and characterization of nanometer-sized barium titanate powder by complex-precursor method

A new complex-precursor method was proposed to prepare nanometer-sized BaTiO3 powder. Firstly,Ti2O（O2）2（ta）24-complex ions were prepared by the reaction of H2O2,Ti^4＋ and ta^3-（ta=[C6H6O6N]^3-） with a desirable amount of surface active agent,and then the Ba2[Ti2O（O2）2（ta）2]·2H2O precursor was obtained by reaction between [Ti2O（O2）2（ta）2]^4-and Ba^2＋. Finally,the precursor was annealed at 800 ℃ for 2 h to obtain BaTiO3 powder. The morphology,the particle size distribution,the purity and the molar ratio of Ba to Ti of BaTiO3 powder were investigated systematically by TEM,XRD,IR,Raman and chemical analysis,respectively. The results show that the BaTiO3 powders with the grain size of about 40 nm have a tetragonal crystalline structure at room temperature and a spherical morphology.     

Mg<Subscript>2</Subscript>(OH)<Subscript>2</Subscript>CO<Subscript>3</Subscript>·3H<Subscript>2</Subscript>O whiskers growth mechanism

From the perspective of growth units, the growth mechanism of Mg₂(OH)₂CO₃·3H₂O whisker is investigated in this paper. Results show that the growth morphology of Mg₂(OH)₂CO₃·3H₂O whisker is consistent with the model of anion coordination polyhedron growth units. The growth solution Raman shift of Mg₂(OH)₂CO₃·3H₂O was monitored using Raman spectroscopy. The growth units are [Mg-(OH)₄]^2- and H₂CO₃. The growth process of Mg₂(OH)₂CO₃·3H₂O whisker is as follows: growth unit [Mg-(OH)₄]^2- first incorporates into the larger dimension [Mg-(OH)₄] _n ^2- , then the [Mg-(OH)₄] _n ^2- combines with H₂CO₃ into a linear skeleton Mg₂(OH)₂CO₃ in the same line. Mg₂(OH)₂CO₃ combines with H₂O by hydrogen bonds and ultimately transforms into Mg₂(OH)₂CO₃·3H₂O whisker. Magnesium carbonate whiskers have a layered structure, each of which is made of magnesium, carbon, oxygen, with H₂O in between each layer. When skeletons are superimposed within the same plane as a parallelepiped one, they grow into solid cuboid-shaped whiskers. When the parallelepiped skeletons planes combine with each other through the cascading links, they grow into hollow cylindrical whiskers.     

碱性环境下二维纳米AlOOH聚集体形态及“生长基元”运动

通过构建酸性水热环境条件下的AlOOH"生长基元"模型,揭示了酸性环境下晶体一维成长的机理。构建碱性水热条件下的"生长基元"模型,从原子层面揭示AlOOH发生二维片状定向生长的机理。重点分析pH=10,13条件下的纳米AlOOH的"聚集体"特点以及生长基元运动方式。用实验样品直接验证所构建模型的合理性。并通过X衍射结果佐证不同pH条件下的聚集体形态的存在,并验证了纳米AlOOH的Al 3+双聚体[Al3(OH)4(OH2)9]5+﹑[Al3(OH)5(OH2)8]4+﹑[Al3(OH)6(OH2)7]3+的存在。     

Coalescence of the crystallites under hydrothermal conditions (II) —— The morphology and stability energy calculation of cuprite

The coalescence of crystallite under hydrothermal conditions was discussed in our previous paper[1]. When the solute concentration exceeds the supersaturation, the nucleation and growth process take place. The initial crystallites are only several nanometers. They have high surface-to-volume ratio, high index surfaces, and therefore have high surface energy. As the hydrothermal reactions proceed in the alkaline medium, the crystallite surfaces are apt to absorb polar solvate ions such as OH-,…     

铁电和铁磁微分回线谱分析

利用费米统计公式证明了微分铁电或铁磁回线可分解为一至两个高斯或洛仑兹线型之和 .对TGS ,BaTiO3 单晶 ,和硅钢片 ,锰锌铁氧体的测量证明理论与实验完全符合 .用微分回线代替回线来表征材料性质更具有实用和理论上的意义 .     

Adsorption property of citrate dispersant on BaTiO3 particles in aqueous solution

Dispersion behavior of ultra fine BaTiO3 particles in the aqueous solution of ammonium citrate （NH4-CA） or citric acid lanthanum chelate （NH4-La-CA） was investigated. The dispersion property was characterized with sedimentation value. It is easier to obtain well dispersed slurry with NH4La-CA than NH4-CA. In an attempt to better understand the role of citric acid radical, simulation of the dispersant adsorption on BaTiO3 particle was performed with universal force field （UFF）. It is demonstrated that the interaction between citric acid radical and BaTiO3 particle surface is a weak chemical adsorption. Trivalent citric acid radical is adsorbed on BaTiO3 particle surface with maximal adsorption energy. And, larger molecules of NH4-La-CA formed by adding La^3＋ lead to better dispersion property than NHn-CA.     

水热法KTP晶体形貌及成因

利用双圈接触测角仪、双圈反射测角仪、微分干涉显微镜等测试手段,对不同条件下水热法生长的KTP晶体的宏观形态及各族晶面的微观形貌特征进行了观察和描述.测试了水热法KTP晶体的成分、结构.水热法生长的KTP晶体的宏观形态与晶体生长溶液的过饱和度及籽晶的切向、形态、悬挂方式有关:低过饱和度时,晶体中易出现高指数晶面,随着溶液过饱和度的增大,高指数晶面逐渐消失.各族晶面的微观形貌主要受控于晶体的内部结构.     

Coalescence of the crystallites under hydrothermal conditions (II)

Cuprite (Cu₂O) particles are synthesized by hydrothermal method. Most crystalline particles have long column morphology. Particles which are regarded as assembling of the crystallites in definite directions are observed. The typical example is the particles formed by assembling six columns in three perpendicular directions. The cone surfaces are visible at the tops of the columns. The results revealed that the coalescence of the crystallites did happen under hydrothermal conditions in which the crystallite connected with other crystallite on certain structure compatible surfaces to form a crystalline particle with a special morphology. This phenomenon is called the second kind of coalescence. The Cu₂O structure unit is determined by its crystal structure. It is concluded that the tetragonal prism and three tetragonal prism-like growth units are the favorable units after stability energy calculation was performed on different kinds of growth units. It is believed that the first kind of coalescence exists commonly. The second kind of coalescence is unlikely to occur for all crystallites under hydrothermal conditions. The occurrence is dependent on the crystal structure.     

Effect of Al3+ on Tobermorite Crystallinity

The difference between the systems of CaO-SiO2,-H2O and CaO-SiO2-Al(OH)3,-H2O, was studied, especially the effect of Al3+on the crystallinity of tobermorite was focussed. As a result, in the system of CaO-SiO2-H2O, tobermorite formed early, however, withreaction time forward, tobermorite was replaced by xonotlite. So far as CaO-SiO2-Al(OH)3,-H2O was concemed, hydrothermal reactionwas cdried out under the same condition as CaO-SiO2-H2O to study the morphological changes of tobermorite crystals. It was found thatAl3+ accelefated the crystal growth of tobermorite to some extent and was in faVor ofplaty crystals. Moreovef, with the Al3+ content in-creasing in the starting material, the morphology of tobermorite did not change magnificently, but platy crystals became more and moreeminent. As soon as the Al2O3 content was over 15.6%, synthetic mineral greatly changed in smicthe and haled into hibschite differentfrom 1 .1 nm tobermorite. Obviously, xonotlite was not apt to form in the presence of Al3+.     

Growth habit of the basic oxysulfate magnesium whisker

The growth habit of the basic magnesium oxysulfate whisker was investigated based on the theoreticalmodelof anion coordination polyhedron growth units.It is found that typicalbasic magnesium oxysulfate whisker growth is consistent with anion tetrahedralcoordination incorporation rules.The growth units of basic magnesium oxysulfate whiskers are [Mg-(OH)_4]~(2-) and HSO_4~-.[Mg-(OH)_4]~(2-) is the favorable growth unit and whisker growth is in the direction of the [Mg-(OH)_4]~(2-) combination.A plurality of [Mg-(OH)_4]~(2-) s combine and become a larger dimensionalgrowth unit in a one-dimensionaldirection.Then HSO_4~- and larger dimensionalgrowth units connect as basic magnesium sulfate whiskers,according to the structuralcharacteristics of the basic magnesium sulfate whisker,which can guide the synthesis of magnesium hydroxide whisker.     

Effect of additive on synthesis of MnZn ferrite nanocrystal by hydrothermal crystallization

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The Synthesis and Electrorheological Properties of BaTiO_3-coated PMMA Microspheres

Coated-PMMA microspheres consisting of poly (methyl methacrylate)(PMMA) core and barium titanate (BaTiO3) shell were synthesized by the modified sol-gel processing and then adopted as an electrorheological (ER) materials. The structure and morphology of coated powders were characterized by SEM and FT-IR; the shear stress of the suspensions of coated-PMMA particles and pure PMMA particles in silicone oil with a 20 vol% were investigated. The results show that the BaTiO3 coated PMMA microspheres based suspension in silicone oil exhibited typical ER behavior and stronger ER effects.