YSZ基片上Tl-2212超导薄膜的制备及其特性的研究

本文报道了在(001)掺钇氧化锆(YSZ)基片上生长高质量CeO2缓冲层和Tl-2212超导薄膜的制备方法,以及不同厚度的超导薄膜对其特性的影响.XRD和SEM测试表明,在经过合适条件退火的基片和CeO2缓冲层上,所生长的Tl-2212薄膜具有致密的晶体结构、优良的面内和面外取向.最佳样品的临界转变温度(Tc)和临界电流密度为(Jc)可以分别达到107.5 K和 4.24 MA/cm2(77 K,0 T).实验结果表明,采用该工艺所制备的不同厚度Tl-2212超导薄膜的主要指标能满足开发多种超导器件的要求.     

热分解工艺对溶胶-凝胶法制备Tl-2212超导薄膜特性的影响

研究了在铝酸镧(LAO)基片上TBCCO凝胶膜的热分解条件对Tl2Ba2 CaCu2O8(Tl-2212)薄膜的结晶质量、表面形貌、组分比例的影响.SEM和XRD研究表明,凝胶膜经过适当条件热分解后,可以制作出具有致密的晶体结构、高度c轴取向的外延Tl-2212超导薄膜,其薄膜具有较好的电学性能.其临界温度Tc可达106 K,临界电流密度Jc可达0.83 MA/cm2 (77 K,0T).     

CeO_2缓冲层热处理对Tl-2212薄膜超导特性的影响

本文采用原子力显微镜(AFM)和XRD研究了生长在蓝宝石(11-02)基片上的CeO_2缓冲层在不同的退火温度和退火时间下表面形貌和相结构的变化,以及对Tl-2212薄膜超导特性的影响.AFM和XRD研究表明,CeO_2薄膜在流动氧环境中退火,表面形貌发生显著的变化;CeO_2薄膜在最佳条件下退火后,可获得原子级光滑表面,结晶质量明显提高.实验结果表明,缓冲层的结晶质量和表面粗糙度与Tl-2212薄膜的超导特性密切相关.在经过最佳条件退火后的CeO_2缓冲层上制备了厚度为500 nm无裂纹的Tl-2212超导薄膜,其临界转变温度(T_c)达到107 K,液氮温度下临界电流密度(J_c)为3.9 MA/cm~2(77 K,0 T),微波表面电阻(R_s)约为281 μΩ(77 K,10 GHz).     

Tl-1223高温超导薄膜在蓝宝石单晶基片上的生长和性能研究

本文报道了采用射频磁控溅射法和快速升温烧结法在R面取向的蓝宝石单晶基片上生长CeO₂缓冲层和Tl-1223超导薄膜，研究了缓冲层生长情况和先驱膜后退火条件对超导薄膜结晶情况和超导特性的影响。AFM和XRD表征结果显示，蓝宝石基片经过退火后其表面形成具有光滑平台的台阶结构，同时基片的晶体质量得到了改善；本文所制备的CeO₂缓冲层和Tl-1223超导薄膜具有较好的c轴生长取向，而且两者呈现良好的ab面内织构。SEM表征结果显示，生长良好的Tl-1223超导薄膜呈层状结构，表面光滑平整、结构致密。在液氮环境下，测得所制备Tl-1223超导薄膜的临界转变温度T_c约为111 K,临界电流密度J_c(77 K,0 T)约为1.3 MA/cm²。     

Pechini法合成Bi2Sr2CaCu2O8+δ超导薄膜的研究

采用Pechini法在STO(100)单晶基底上制备Bi2Sr2CaCu2O8+δ(Bi2212)超导薄膜.重点研究了金属离子比例与预处理温度对Bi2212薄膜相组成及表面形貌的影响.结果表明,适当增加初始计量中Ca的摩尔比,有利于纯相的形成.预处理温度不仅影响样品的表面形貌,同时对相纯度的影响也很显著.较佳条件下,1108 K温度下热处理10 min可制备具有c轴外延取向的纯Bi2212相薄膜.     

单晶MgO基片超精密加工技术研究

单晶MgO具有良好的物理化学性能及光学性能,是性能优异的薄膜基片及光学零件材料,广泛应用于高温超导、航空航天、光电技术等领域.用作薄膜生长的基片必须具有高精度超光滑无损伤的表面,而单晶MgO是典型的硬脆难加工材料,这对MgO晶体的超精密加工技术提出了很高的要求.本文介绍了单晶MgO的特性及其应用领域,针对高温超导薄膜制备对MgO基片的要求,讨论了现有的MgO基片加工工艺存在的问题,分析了几种可用于MgO基片超精密加工的先进工艺技术的特点和应用研究现状.     

室温电化学法制备白钨矿SrWO4晶态膜的生长特性研究

采用恒电流电化学技术直接在金属钨片上制备了具有白钨矿结构的钨酸锶(SrWO4)晶态薄膜,通过SEM和EDX测试分析方法,研究了薄膜在不同的生长阶段(包括薄膜从最初成核并开始生长,到薄膜布满整个基片,即薄膜生长结束)的生长特性.研究结果表明,SrWO4晶核和晶粒优先选择在基片的缺陷处堆砌生长,在薄膜生长的初期,一定数量的WO4负离子配位多面体沉积在基片上并形成具有白钨矿结构的骨架,继而Sr2+对该骨架进行填充,由此形成晶核和晶粒;随着沉积时间的延长,晶粒密度不断增大,晶核和晶粒也不断长大,并沿着c轴生长的方向开始分叉,晶粒越大分叉越多;最终,当SrWO4薄膜生长过程结束时,团簇生长的花菜状晶粒布满整个基片,形成致密的薄膜.该研究结果对晶态薄膜电化学制备生长机制的认识、以及采用电化学方法制备晶态薄膜的工艺调控都具有重要意义.     

直流磁控溅射工艺对ZnO薄膜结构影响的研究

ZnO是一种新型的Ⅱ-Ⅵ族直接带隙化合物材料,是一种很有潜力的短波长光电器件材料.当ZnO薄膜具有良好的c轴取向和晶格结构时,可得到优良的光电性能比如紫外光受激发射.本实验用XRD和SEM研究了工艺条件如基片温度、氩氧比及退火工艺对ZnO薄膜结构特性的影响.结果表明在基片温度250℃、氩氧比为1∶4的条件下,可得到结晶质量良好的ZnO薄膜;通过退火可以使薄膜应力得到驰豫,降低缺陷浓度,改善薄膜的结构特性.本实验采用直流磁控溅射的方法,最终在(100)硅衬底基片上制备出了高c轴取向、晶粒尺寸约70nm的ZnO薄膜.     

溶剂热法制备Al掺杂ZnO薄膜的机理研究

采用溶剂热法在玻璃衬底上制备Al掺杂的ZnO薄膜,研究了溶剂热过程中升温、恒温和降温三个阶段分别对薄膜物相和形貌的影响,探讨了薄膜的生长机理.结果表明,升温阶段只是形核过程,基片仅在升温阶段与前驱液接触不能形成薄膜;基片在升温-恒温阶段与前驱液接触可制备(002)择优取向的薄膜;恒温阶段既有成核过程又有晶体生长过程,基片仅在恒温阶段与前驱液接触可以制备薄膜;降温阶段薄膜继续生长.     

溅射功率对ZnO∶Si透明导电薄膜性能的影响

采用直流磁控溅射法在室温玻璃基片上制备出了掺硅氧化锌(ZnO∶ Si)透明导电薄膜.研究了溅射功率对ZnO∶ Si薄膜结构、形貌、光学及电学性能的影响.结果表明,溅射功率对ZnO∶ Si薄膜的生长速率、结晶质量及电学性能有很大影响,而对其光学性能影响不大.实验制备的ZnO∶Si薄膜为六方纤锌矿结构的多晶薄膜,且具有垂直于基片方向的c轴择优取向.当溅射功率从45 W增加到105 W时,薄膜的晶化程度提高、晶粒尺寸增大,薄膜的电阻率减小;当溅射功率为105 W时,薄膜的电阻率达到最小值3.83×10-4 Ω·cm,其可见光透过率为94.41;.实验制备的ZnO∶ Si薄膜可以用作薄膜太阳能电池和液晶显示器的透明电极.     

Relationship of Morphological Types of Dynamic Forms of Crystals

Crystallography Reports - The relationship of morphological spectra (sets of data on the morphological types of real polyhedral crystals and their probabilities under current physicochemical...     

Development of Pauling's concepts of geometric characteristics of atoms

The evolution of the geometric characteristics introduced by Pauling and their dependence on the specific features of the structure and chemical bonds have been considered. The values of the covalent and van der Waals radii are given as well as their relationships and mutual transitions.     

A review of measurement of thermophysical properties of silicon melt

Measurements of thermophysical properties of Si melt and supplementary study of X-ray scattering/diffraction by the authors' group were reviewed. The values obtained differed variously from those of literature. Density was 2–3% larger, surface tension 20–30% smaller, viscosity up to 40% larger, electrical conductivity 8% smaller, spectral emissivity more or less in good agreement with literature values, and thermal diffusivity a few percent larger. An anomalous density jump was found near the melting point. Surface tension and viscosity also showed anomaly. A strange time-dependent change of density was observed over 3 h after melting. X-ray analyses suggested a slight change in local atom ordering, but showed no sign of cluster formation. An addition of 0.1 at% gallium caused the density jump to disappear, while that of boron caused no change. An EXAFS study of the former melt indicated a strong interaction between Ga and Si atoms as if molecules of GaSi₃ existed. The implications of the measured properties are a possibility of soft-turbulence in an Si melt in a relatively large crucible, a more complicated manner of intake of oxygen depleted molten Si from the free surface region to underneath the growing crystal, and a relaxation of the melt after melting arising from trapped gas species.     

Generation of crystal structures of heteromolecular compounds by the method of discrete modeling of packings

Within the method of discrete modeling of packings, an algorithm of generation of possible crystal structures of heteromolecular compounds containing two or three molecules in the primitive unit cell, one of which has an arbitrary shape and the other (two others) has a shape close to spherical, is proposed. On the basis of this algorithm, a software package for personal computers is developed. This package has been approved for a number of compounds, investigated previously by X-ray diffraction analysis. The results of generation of structures of five compounds—four organic salts (with one or two spherical anions) and one solvate—are represented.     

Investigation of the Mechanism of Influence of Stress Corrosion on the Development of Macroplastic Instabilities of Aluminum–Magnesium Alloy

Crystallography Reports - Macroscopic jumps of plastic deformation (few percent in amplitude) on creep curves of aluminum–magnesium alloy, caused by a local effect of concentrated solution of...     

Comparative analysis of two methods of calculation of the orientation of domain walls in ferroelastics

Two types of domain-wall equations are analyzed: the equations derived by the Sapriel method and the equations obtained by interface matching of the thermal-expansion tensor. It is shown that, for W-type domain walls, these methods yield the same equations. For W′-type domain walls, the equations obtained by different methods coincide for proper ferroelastics and differ for improper ferroelastics.     

Dependence of the parameters of equations of viscous flow on chemical composition of silicate melts

The temperature dependence of viscosity of silicate melts is discussed in the framework of the Avramov–Milchev (AM) equation. The composition is described by means of two parameters: the molar fraction, x, and the “lubricant fraction”, l. The molar fraction is the sum of the molar parts x_i of all oxides dissolved in SiO₂, the molar fraction of the latter being 1 ? x. It is shown that, with sufficient precision, two of the parameters of the AM equation can be presented as unique functions of the molar fraction. On the other hand, x is not sufficient to determine properly the reference temperature T_r , at which viscosity is η_r = 10¹³ [dPa.s]. Therefore, additional parameter, “lubricant fraction” l, is introduced. For each of the components, l_i is a product of molar part x_i and a specific dimensionless coefficient 0 ≤ k_i ≤ 1 accounting for the specific contribution of this component to the increased mobility of the system. It is demonstrated that, for l > 0, the reference temperature is related to the “lubricant fraction” l through the reference temperature T_r,SiO2 of pure SiO₂.     

Mechanism of thermal expansion of structural modifications of zinc pyrovanadate

Crystal chemical characteristics of the α and β modifications of Zn₂V₂O₇ are calculated based on in situ high-temperature X-ray measurements. The expansion of the structure is found to be strongly anisotropic up to the negative volumetric thermal expansion of the α-Zn₂V₂O₇ unit cell in the temperature range of 300–600°С, α _V =–17.94 × 10^–6 1/K. The transformations of the “hard” and “soft” sublattices with an increase temperature and at the phase transition are considered in detail. It is shown that the negative volumetric thermal expansion of α-Zn₂V₂O₇ is due to the degeneracy of the zigzag-like shape of zinc–oxygen columns at constant distances between their vertices.     

A SAXS study of kinetics of aggregation of silica sols

SAXS in situ experiments on the evolution of TMOS solutions during hydrolysis and polycondensation lead to power laws with scaling exponents ≈ 2. It is suggested that this could be the result of the polydispersity of the samples and that only an apparent fractal dimension can be obtained in this way. Kinetic studies tend to indicate that agglomeration in the sol is the result of a diffusion-controlled process.