Sympathetic Nucleation of Ferrite

Configurations of ferrite crystals have been found in a plain carbon steel which appear to have resulted from the nucleation of new ferrite crystals at the interphase boundaries of previously formed crystals despite the high carbon concentrations which necessarily develop at these boundaries. This phenomenon has been termed sympathetic nucleation. An attempt has been made to reconcile the occurrence of sympathetic nucleation with current nucleation theory.     

7N01铝合金板材表面的深灰色条纹和“气泡”缺陷原因分析

我公司生产的7N01铝合金板材表面上曾发现有深灰色条纹和"气泡"缺陷,通过对该缺陷进行宏观组织和显微组织的观察及分析得知:板材缺陷处存在大量密集的化合物初晶,此化合物初晶导致板材表面出现深灰色条纹和"气泡"。     

Magnetocrystalline anisotropy,magnetization curves,and domain structure of FeB single crystals

Single crystals of an orthorhombic compound FeB have been synthesized. Based on the data of magnetic measurements and X-ray diffraction analysis, it has been shown that two mutually perpendicular preferred magnetization axes exist in the orthorhombic single crystals of FeB: the easy axis (EA) corresponds to the crystallographic axis [010], and the hard axis (HA), to the [100] axis. The function of the energy of magnetocrystalline anisotropy (MCA) of the orthorhombic magnets has been analyzed for extrema. Orientations of the EAs and HAs have been determined. It has been established that in the orthorhombic magnets there is always realized a single type of MCA: two preferred mutually perpendicular axes always exist in the crystals, one of which is an EA, and the other is an HA. Expressions for the anisotropy fields of orthorhombic magnets have been obtained. The constants of MCA of the orthorhombic compound FeB have been calculated to be K ₁^* ≈ 4 × 10⁵ J/m³ and K ₂^* 7×10⁴ J/m³. The domain structure on the planes (100), (010), and (001) of the FeB single crystals has been studied. It has been shown that the main volume of the sample is occupied by stripe domains ∼40 μm wide with the walls oriented along (100) crystallographic planes. It has been found that the structure of closure domains on the plane (010) of the FeB single crystals has some specific features, namely, there exists a preferred direction in the structure for the orientation of the boundaries of the main domains, and the closure domains have the shape of regular rhombs. A model of the domain structure of FeB single crystals is suggested.     

Stoichiometry control and mechanical properties of NiAl single crystals

Stoichiometric NiAl crystals have been prepared by a modified Bridgman method. Chemical analysis methods have been elaborated for accurate composition analyses with a total error of 0.1 at.% Ni. The NiAl samples exhibit high room-temperature ductility in the as-grown state.     

Layer-by-layer magnetization reversal of nanophase crystals of a cobalt-platinum alloy after annealing under tensile loading

Behavior of magnetic domain structure in the course of magnetization reversal of CoPt crystals with optimum hysteresis properties after annealing under tensile stresses has been studied. Magnetic heterogeneities, which were periodically distributed in {100} and {110} planes have been revealed. An electron-microscopic investigation of the structure of the above CoPt crystals has been performed to show that the crystals are in a nanophase stressed-strained state. A connection between the magnetization-reversal mechanism and characteristic properties of the nanophase state of the crystals is discussed. An important role of magnetoelastic energy in the complicated quasi-periodic distribution of magnetization of the CoPt crystals investigated is emphasized.     

Magnetic and structural phase transitions in the monochalcogenides of uranium

A model of simultaneous magnetic and structural first-order transitions in crystals with strong cubic magnetic anisotropy has been constructed on the basis of a combination of the magnetic modified 8-state Potts model [1] and theoretical models of structural phase transitions in cubic crystals [2]. The magnetic heat capacity and specific volume, as well as the temperature dependence of the rhombohedron angle, have been calculated in a wide temperature range. The calculation of the temperature evolution of high-temperature diffuse magnetic neutron scattering has been performed to show that upon the passage through the Curie point it is converted into magnetic Bragg peaks.     

光电功能晶体材料研究进展

光电功能晶体,包括激光晶体、非线性光学晶体、电光晶体、介电体超晶格、闪烁晶体和PMN-PT驰豫电单晶等,在高技术发展中具有不可替代的重要作用。近年来,我国在这些重要晶体材料的生长、基础研究和应用方面都获得了很大成绩。综述了光电功能晶体材料研究和应用的部分进展。在此基础上,提出进一步发展晶体理论,扩大理论的应用范围,注重晶体生长基本理论研究,发展新的晶体生长方法和技术,加强晶体生长设备研制,加强晶体从原料到加工、后处理、检测及镀膜等全过程的结合等建议,以全面提高我国光电功能晶体研究发展及其产业化水平。     

片层取向对Ti—49at%AlPST晶体断裂机制的影响

用ＳＥＭ原位拉伸技术研究了Ｔｉ－４９ａｔ％ＡｌＰＳＴ晶体的断裂过程,研究表明：裂纹萌发和扩展路径强烈依赖于ＰＳＴ晶体的片层取向;不同取向ＰＳＴ晶体具有不同的断裂机制及断口形貌。     

循环变形铜单晶体的滞后回线形状变化与驻留滑移带的萌生

本文系统测量并总结了不同类型双滑移取向铜单体循环变形中滞后回线性形状参数ＶＨ随循环周次Ｎ的变化关系,结果表明,与单滑移晶体不同晶体取向双滑移晶体的滞后回线形状变化趋势有显著的影响,ＶＨ与驻留滑移带（ＰＳＢ）的形成有无明业对应关系与该取向单晶体的循环应力－应变（ＣＳＳ）曲线有无平台区或准平台区出现密切相关,ＶＨ随Ｎ的变化关系反映了晶体在循环变形中的微观组织结构的不同变化,通过ＶＨ确定了不同类型双滑移     

Hydrogen-sorption properties of magnesium and its intermetallics with Ca7Ge-Type structure

The statistical theory of the hydrogenation of magnesium and its alloys Mg₆ M′M″(with M′ = Mg, Ti, V, Nb, Zr; M″ = Mg, Al, Zn) has been developed. The energies of crystals have been calculated, and equations for their thermodynamic equilibrium state have been found. Equations for determining the P-T-c diagram have been obtained. Curves that determine the temperature dependences of the concentration of hydrogen desorbed from crystals were studied. The maximum hydrogen-desorption temperature and its dependence on interatomic-interaction energy parameters and the activity of hydrogen atoms were estimated. Isopleths of hydrogen solubility were calculated for different concentrations of hydrogen. The level of the curves for different coefficients of activity and slope for different hydrogen contents were found. Isotherms of hydrogen solubility in crystals were studied. The possibility of achieving the sorption hysteresis effect was clarified, and the length and width of the hysteresis loop at different temperatures were estimated. The aforementioned functional dependences were plotted. The calculated data were compared with experimental results available in the literature. The theoretical and experimental data agree qualitatively.     

Growth and X-ray structure of single crystals of 1,3,5-tris[(6,7-dimethyl-3-phenyl)quinoxaline-2-yl] benzene

Single crystals of 1,3,5-tris[(6,7-dimethyl-3-phenyl)quinoxaline-2-yl] benzene (Me-TPQ) have been grown from the vapour phase under high-vacuum conditions. Me-TPQ belongs to the class of star-shaped tris(phenylquinoxalines) which form usually amorphous glasses. Thermal analysis indicated however, that the title compound possesses a crystal phase. The structure of Me-TPQ crystals has been determined by single crystal X-ray diffraction measurements. Two unit cells have been detected, monoclinic and orthorhombic. We report, here, the crystal structure of the latter, which might be of interest for non-linear optics applications.     

Velocities of elastic waves and the elasticity moduli of nickel-base superalloys and of the 60N21 alloy

Measurements of velocities of elastic waves have been performed in polycrystalline samples of an intermetallic compound Ni₃Al, this intermetallic compound alloyed with niobium or cobalt, superalloys ZhS36 and VKNA-4U, and the 60N21 alloy. Elasticity moduli have been calculated, namely, Young’s modulus, shear modulus, bulk modulus, and the Poisson ratio. The results obtained are compared with those calculated from the tensor of the elasticity moduli obtained for single crystals. The calculations have been performed in the Voigt and Reuss approximations.     

Effects of N and/or S Doping on Structure and Photocatalytic Properties of BiOBr Crystals

The Bi OBr crystals doped with N and/or S have been prepared by a facile and rapid solvothermal method using urea and/or thiourea as doped resource.The morphologies and structures of the as-prepared samples were characterized by SEM,TEM,XRD,XPS and PL spectrum.Their electronic structures have been investigated and discussed using first principles based on the density functional theory.The photocatalytic properties of the products can be adjusted by the content and species of dopants.     

液固相复合-轧制铜包钢线的组织性能及界面冶金行为

以液固相复合-轧制工艺生产的铜包钢线为研究对象,研究了在特定工艺条件下铜／钢界面的组织组成及其界面区的冶金行为。经金相组织观察,铜、钢晶粒在界面处直接接触,界面呈极细微的凹凸不平的状态,经冷轧后,铜、钢晶粒在界面处互相咬合,且铜与钢的变形随着变形量的增大而趋于均匀。通过对界面区的成分进行能谱分析表明,Cu,Fe原子间发生了互扩散,形成了Fe／Cu的固溶体,其中Fe向Cu扩散量明显高于Cu向Fe的扩散量,测试界面结合强度表明,铜包钢线的初结合界面剪切强度可达80-95 MPa,轧制变形后该强度可提高3％-5％。     

液固相复合-轧制铜包钢线的组织性能及界面冶金行为

以液固相复合-轧制工艺生产的铜包钢线为研究对象,研究了在特定工艺条件下铜/钢界面的组织组成及其界面区的冶金行为.经金相组织观察,铜、钢晶粒在界面处直接接触,界面呈极细微的凹凸不平的状态,经冷轧后,铜、钢晶粒在界面处互相咬合,且铜与钢的变形随着变形量的增大而趋于均匀.通过对界面区的成分进行能谱分析表明,Cu,Fe原子间发生了互扩散,形成了Fe/Cu的固溶体,其中Fe向Cu扩散量明显高于Cu向Fe的扩散量,测试界面结合强度表明,铜包钢线的初结合界面剪切强度可达80～95 MPa,轧制变形后该强度可提高3%～5%.     

Effect of dimensions and anisotropy on the formation of domain structures of uniaxial single crystals

Distribution of magnetization in infinitely long single-crystal prisms of Co, Nd₂Fe₁₄B, and Ni₈₀Fe₂₀ with different cross sections has been calculated using the method of minimization of the free-energy functional and by solving the Landau-Lifshitz equation. It has been shown that in cobalt single crystals, domain structures of the Landau type arise. In Nd₂Fe₁₄B single crystals the domain structures have a stripe type; in Ni₈₀Fe₂₀ single crystals, the domain structure is in a single-domain state.     

Transport and optical property measurements in indium intercalated molybdenum diselenide single crystals grown by DVT technique

This paper describes the transport and optical property measurements in indium intercalated MoSe₂ single crystals. The crystals have been grown by a direct vapour transport (DVT) technique. Various transport properties, e.g. room temperature resistivity, high temperature resistivity (perpendicular to c-axis from room temperature to 423 K and parallel to c-axis from room temperature to 773 K), anisotropy ratio, low temperature resistivity (77 K to room temperature), Hall effect measurements, thermo-power measurements have been carried out and the results have been systematically presented. This study has clearly shown that indium intercalated molybdenum diselenide like the host crystal MoSe₂ are n-type semiconductors. Optical absorption studies of the grown crystals have been used to evaluate the energies of the direct band gaps in them. The variation of direct energy gap with amount of indium in In_xMoSe₂ has been adequately explained.     

Characterizing pathological imperfections in macromolecular crystals: lattice disorders and modulations

Macromolecular crystal structure determination can be complicated or brought to a halt by crystal imperfections. These issues motivated us to write up what we affectionately call ‘The Definitive Hitchhiker’s Guide to Pathological Macromolecular Crystals: Lattice Disorders and Modulations’. Perhaps the most challenging imperfections are lattice order–disorder phenomena and positional modulations. Many of these types of crystals have been solved, and progress has been made on the more challenging forms. Diagnostic tools and how to solve many of these problem crystal structures are reviewed. New avenues are provided for approaching the solution of incommensurately modulated crystals. There are a good number of case studies in the literature of lattice order–disorder phenomena and crystallographic modulations that make it timely to write a review. This review concludes with a projected pathway for solving incommensurately modulated crystals, personal views of future directions and needs of the crystallographic community.     

Optical floating zone method growth and photoluminescence property of MgNb2O6 crystal

MgNb₂O₆ single crystals are grown by the optical floating zone method. The as-grown crystals are dark brown and have dimensions of Ø 4-6 mm × L 87 mm, with the largest crystal domain being Ø 5 mm × L 32 mm. After being annealed, the crystals fade to light brown. The powder X-ray diffraction analysis shows that the crystals have a columbite-type MgNb₂O₆ structure. The crystal grows along the c-axis and the cleavage plane is the (0 1 0) plane. Transmission polarized light microscopy measurements show that the crystal is free of low-angle grain boundaries and inclusions. The crystals have been characterized by Raman scattering, which reveals the change of Nb-O band in annealed and non-annealed samples. The photoluminescence spectra exhibit a broad and strong blue emission band centered at 435 nm.     

难熔金属及其合金单晶的发展

主要介绍了难熔金属W，Mo，Ta，Nb及其合金单晶的制备技术，单晶的发展现状，并对单晶制备技术和单晶材料的发展方向提出了一些合理化建议。