Formation mechanism of barium titanate nanocrystalis 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.     

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.     

TEM study of transformation units and the growth mechanism of bainite

Ｏｂｌａｃｋ[1]ｓｕｇｇｅｓｔｅｄｔｈａｔｔｈｅｂａｉｎｉｔｉｃｆｅｒｒｉｔｅｗａｓｃｏｎｓｔｉｔｕｔｅｄｂｙｓｕｂｕｎｉｔｓ.Ｔｈｅｅｘｉｓｔｅｎｃｅｏｆｓｕｂｕｎｉｔｓｗａｓｆｏｕｎｄａｎｄｔｈｅｓｕｂｕｎｉｔｓｗｅｒｅｔｈｏｕｇｈｔｔｏｂｅｔｒａｎｓｆｏｒｍａｔｉｏｎｕｎｉｔｓｏｆｂａｉｎｉｔｅ[2,3].Ｂｕｔｔｈｅｒｅｉｓｃｏｎｔｒｏｖｅｒｓｙａｂｏｕｔｔｈｅｎａｔｕｒｅｏｆｔｈｅｔｒａｎｓｆｏｒｍａｔｉｏｎｕｎｉｔｓ[4,5].Ｔｈｅｂａｉｎｉｔｉｃｌｅｄｇｅｇｒｏｗｔｈｍｅｃｈａｎｉｓｍｗａｓｐ…     

KDP晶体生长工艺研究

利用水溶法生长了KDP单晶体,系统论述了晶体生长装置和工艺各个过程.指出生长均匀、无缺陷KDP单晶体工艺过程中的注意的事项.实验表明晶体生长过程中溶液的纯度不高,会造成籽晶以外的溶液体系其他部位大量成核;pH值过高,生长的晶体会出现楔化现象,过低则影响生长速率,实验测得pH值为2.2;50℃的晶体退火温度能有效消除晶体内部的热应力,提高晶体的光学均匀性.同时籽晶的切向、温度控制的准确性等因素有效避免晶体生长过程中出现的生长层、晶面花纹等缺陷.     

Growth units model of anion coordination-polyhedra and its application to crystal growth

A crystal will exhibit various morphologies in different growth systems. This is known as the crystallization habit. Until now, most theories of crystal growth cannot guide optimization of the process of crystal growth well, because those theories deviate from and lose sight of the effect of external circumstance upon the process of crystal growth. For this reason, Zhong proposed the growth-units model of anion coordination-polyhedra in the early 1990s[1,2] to reduce the gap between the theory…     

The growth units and hydrothermal preparation of lead tungstate (PbWO4) crystallites

The crystal structure of lead tungstate (PbWO4) can be regarded as ordered combination of the tungsten oxide tetrahedrons (WO4) and lead ions (Pb2 ). According to the growth unit model, the growth units of lead tungstate are the aggregations of the tungsten oxide tetrahedrons and lead cations with various geometry configurations. It is suggested that the favorable growth units of lead tungstate crystal are pyramidal, tetragonal prism and quadrangular units corresponding to geometric orientations of the simple forms of the crystal. Under low restricted growth conditions, the growth form of lead tungstate crystallites is the aggregation of the geometric configurations of these favorable growth units. The above conclusions are completely confirmed by the experiment on hydrothermal preparation of lead tungstate crystallites.     

等离子体中双撕裂模线性增长率分析

在托卡马克等离子体中,撕裂不稳定存在已被人们广泛认识,针对双撕裂模线性增长情况,采用边界层法对其增长率进行了分析,并进行了数值模拟。     

Growth habit of polar crystal ZnO by solid-vapor method

Crystals of semiconductor ZnO were fabricated by means of solid-vapor growth method-carbon thermal reduction. Powder X-ray diffraction and field emission scanning electron microscope were used to characterize the phase and morphology of the samples. The results showed that the samples were wurtzite ZnO crystals and anisotropy of crystal growth relied on reaction temperature in solid-vapor process. The crystals synthesized at different temperatures were of short column-like shape, flat top hexagon pyramidal-...     

Formation of liquid inclusion induced light scatter in KDP (DKDP) crystals

We describe in this paper the formation of liquid inclusion induced light scatter in potassium dihydrogen phosphate (KDP) crystal and deuterated potassium dihydrogen phosphate (DKDP) crystals. The measurement has been done with an atomic force microscope (AFM). The mechanism of formation of liquid inclusion scatter has been proposed and the effect of super-saturation discussed.     

Coordination properties and structural units distribution of Q_T~i in calcium aluminosilicate melts from MD simulation

1　INTRODUCTIONCalciumaluminosilicatemelts ,whicharethemostimportantternarysystemformetallurgistandmineralogist ,havedisplayedcomplicatedmicrostruc tureandproperties.Intheliquidofbinarysystem ,suchasCaO SiO2 ,cationsare partitionedintotwotypes :networkformerSiandmodifierCa .Forcalci umaluminosilicateternarymelt ,Caisstillnetworkmodifier,andSinetworkformer ,butAlisam phiprotic,whichisdeterminedbythepairinterac tionswithoxygen[1] andlocalenvironment .There fore ,thecoordinationnumbersof…     

Coordination properties and structural units distribution of QiT in calcium aluminosilicate melts from MD simulation

The distribution of Al(j) and the structural units distribution of QiT in calcium aluminosilicate melts were studied by means of molecular dynamics simulation. The results show that provided there exists lower-field strength cation relative to Al3 , such as alkaline and alkaline earth metals, Al will be four-coordinated but not six-coordinated. Meanwhile, if there exist a large number of higher-field strength cations such as Si4 and little lower-field strength cation, six-coordinated aluminum will be formed. The relation of structural units distribution of QiT with chemical composition shift was also extracted, showing that as Ca2 exists, the distributions of QiSi, QiAl or QiT have the similar changing trend with the variation of component. Because of high-temperature effect, the Al-tetrahedral units in melts are greatly active and unstable and there exist dynamic transforming equilibria of Al(3)→←Al(4) and Al(5)→←Al(4). The three-coordinated oxygen and charge-compensated bridging oxygen are proposed to explain phe-nomena of the negative charge redundancy of AlO4 and location of network modifier with charge-compensated func-tion in aluminosilicate melts.     

钆铋铁石榴石单晶生长及其磁光性能

采用助熔剂法并配以加速坩埚转动技术生长出钆铋铁石榴石（ＧｄＢｉＩＧ）单晶，在近红外区（０．９～１．７μｍ）测量了它的法拉第旋转谱和光吸收谱．从ＧｄＢｉＩＧ的磁光优值谱与ＹＩＧ的磁光优值谱比较表明，ＧｄＢＩＩＧ是一种优良的磁光晶体．     

论我国区域经济增长机制

区域经济增长机制是区域经济发展的源泉,包括动力机制、传递机制和协调机制。     

Hydrothermal preparation and formation mechanism of titanium dioxide microcrystallites

Hydrothermal preparation experiments of TiO_2 microcrystallites were carried out. The formation of TiO_2 microcrystallites of polymorpbic forms was related to the precursor types and the basicity or acidity of reaction mediums under hydrothermal conditions. Based on the "growth unit" model, the space lattice graphs of growth units responding to different polymorphs were established. The stable energy of growth unit was calculated for different basicity or acidity of reaction mediums. The formation of polymorphic TiO_2 microcrystallites under hydrothermal conditions was discussed based on the experimental results.     

金属硅化物熔体中不同形貌SiC晶体的生长

以过渡族金属硅化物为溶剂，采用自发熔渗法和溶液法来研究不同形貌SiC晶体在金属硅化物熔体中的生长情况.利用光学显微镜（OM）、扫描电镜（SEM）、体视显微镜等对熔渗试样和采用溶液法生长的单晶和晶须的形貌结构进行了观察和表征，利用X射线衍射仪（XRD）对采用溶液法生长的晶体和晶须进行了相组成和晶型的表征，并讨论了SiC晶须和SiC单晶的生长机理.结果表明，Fe5Si3、CoSi、Co4.5CrSi4.5、Ti2.3Si7.7等熔体适合生长SiC单晶，FeSi、FeSi2等熔体适合生长SiC晶须，而当Fe3Si熔体渗入SiC预制件后，仅有石墨相析出.     

Al掺杂四针状纳米ZnO生长机制分析

采用热物理法制备不同量Al掺杂的ZnO纳米材料,利用XRD分析掺杂前后试样的物相结构,并通过TEM鉴定粉体中的四针状纳米氧化锌（T-ZnO）结构。结果表明,Al掺杂纳米T-ZnO晶须的结晶过程是气液固（VLS）方式,晶须生长具有择优取向。透射电镜高分辨图像揭示凝固过程中晶须沿[0001]轴向生长,随着时间的延长,Zn原子首先形成核心部分并向外在晶须表面呈台阶状生长,从Al液中带走部分Al原子,进而促成纳米晶须的不断伸长且直径变大。     

Coordination properties and structural units distribution of Q^iT in calcium aluminosilicate melts from MD simulation

The distribution of AI(j) and the structural units distribution of Q^iT in calcium aluminosilicate melts were studied by means of molecular dynamics simulation. The results show that provided there exists lower-field strength cation relative to Al^3 , such as alkaline and alkaline earth metals, AI will be four-coordinated but not six-coordinated. Meanwhile, if there exist a large number of higher-field strength cations such as Si^4 and little lower-field strength cation, six-coordinated aluminum will be formed. The relation of structural units distribution of Q^iT with chemical composition shift was also extracted, showing that as Ca^2 exists, the distributions of Q^Si, QAl or QT have the similar changing trend with the variation of component. Because of high-temperature effect, the Al-tetrahedral units in melts are greatly active and unstable and there exist dynamic transforming equilibria of Al(3)←→AI(4) and Al(5)←→Al(4). The three-coordinated oxygen and charge-compensated bridging oxygen are proposed to explain phenomena of the negative charge redundancy of AIO4 and location of network modifier with charge-compensated function in aluminosilicate melts.     

生态安全格局视角下中国城市增长边界研究进展

[目的]新型城镇化不断加快,城市所占土地资源扩张程度越发迅速,传统粗放的城市增长过程中呈现出生态系统结构与功能的破坏、城市无序扩张等问题,怎样合理控制城市规模、优化城市生态安全格局已成为当前中国国土资源管理的重点工作之一.探索中国城市增长边界划定的效益及现行方法,讨论未来发展驱动力和城市增长边界协调优化方法可能的研究方...     

一个具有Robin自由边界的双曲肿瘤生长模型解的定性分析

研究了一个具有Robin自由边界的双曲肿瘤生长数学模型,该模型包含了一个描述营养物浓度变化的椭圆型方程,一个描述肿瘤半径的常微分方程和描述肿瘤细胞生长的两个双曲型偏微分方程.本文通过特征线方法结合Banach不动点定理证明了该模型整体解的存在性和唯一性.最后证明当KR=0时,有(limt→∞)R(t)=∞.