{110}〈111〉,{112}〈111〉和{123}〈111〉多滑移的屈服应力状态

在系统分析了bcc金属{110}〈111〉,{112}〈111〉和{123}〈111〉多滑移时的单晶屈服面(SCYS)的基础上,导出了临界剪切应力(CRSS)相等情况下完备的单晶混合屈服应力状态,求出了相应的活化滑移系及5个独立活化滑移系的组合数,并将所有可能的屈服顶点按晶体结构的对称性加以分类和列表.     

微碳深冲钢板的再结晶与{111}织构的形成过程

采用试验和微观组织分析的方法,研究了冷轧微碳深冲钢板的再结晶组织和织构的特点以及AlN相析出对{111}织构形成过程的影响.研究结果表明,{111}织构从再结晶的形核阶段就已经开始形成,而且在其形成和初始长大过程中吞噬了非{111}织构组分.退火时采用慢速升温有利于AlN相充分析出和长大,促进了{111}织构的形成,从而抑制了非{111}织构组分,提高了微碳深冲钢板的成形性能.     

A new method of {111} trace analysis

A new method of determining the orientation of grains of cubic lattice from {111} traces on a single surface is presented. The method is considerably simpler than other available methods and, because it is analytical, provides orientations as accurately as the trace data will permit.     

｛123｝〈111〉多滑移的屈服顶点

从Ｔｙｌｏｒ－Ｂｉｓｈｏｐ－Ｈｉｌｌ理论出发，系统分析和计算了ｂｃｃ金属在｛１２３｝〈１１１〉滑移系上滑移的单晶屈服面，发现共有３３８种应力状态，并将它们按晶体结构的对称性加以分类。结果表明，所有的屈服顶点共可分为１４组，它们分别活化５，６或８个滑移系，依赖于结晶学上不等价的滑移系组。     

Ferroelectric domains in pressureless-sintered barium titanate

Ferroelectric domains in pressureless-sintered BaTiO₃ ceramics have been studied using scanning and transmission electron microscopy. Both the 90°- and 180°-type exhibiting the characteristic features of herringbones, square-nets, and “water-mark”, respectively, are observed in polished sections. Most of the domains identified in thin foils are the conventional 90° a–a type. Unconventional 90° a–a domain boundaries lying on {111} are also identified from the CO₂-laser-sintered samples, but they have vanished after several minutes of electron beam irradiation. Both the wedge-shape and overlapped “microtwin” domains exhibit the characteristic δ-fringes. The displacement vector R of 〈101〉 is thought to have derived from a small lattice translation introduced by the rotation of the polarization vector across the domain boundaries. Lattice-fringe images of the 90° domain boundaries suggest that the lattice distortion has occurred to accommodate the strain generated by the c→t-BaTiO₃ phase transition. The strain thus induced is manifested by dot contrast appearing on the 90° domain walls as revealed by transmission electron microscopy. The distribution of dots suggests that the strains are taken up inhomogeneously both along and across the domain boundaries by the crystal lattices.     

Control of {111| twin formation and abnormal grain growth in BaTiO3

To investigate the experimental conditions for {111| twin formation and abnormal grain growth in BaTiO₃, various powder compacts with and without excess TiO₂ were sintered either in an oxidizing atmosphere (air) or in a reducing atmosphere (95N₂-5H₂). In all the samples sintered in 95N₂-5H₂, no twins formed and no abnormal grain growth occurred. On the other hand, when the samples with excess TiO₂ were sintered in air, abnormal grain growth occurred and all the abnormal grains contained {111| twins. X-ray diffraction analysis showed that, during sintering, the excess TiO₂ formed a Ba₆Ti₁₇O₄₀ phase with the space group A2/ a in air and a Ba₆Ti₁₇O_40-x phase with the space group C in 95N₂-5H₂. These results show that the {111| twins form and the abnormal grain growth occurs only when the powder compact contains excess TiO₂ to form a Ba₆ Ti₁₇O₄₀ phase and is sintered in an oxidizing atmosphere. The results may also suggest that the Ba₆Ti₁₇O₄₀ phase acts as the nucleation site of {111| twins. The suggestion has been further confirmed via a TEM observation.     

形变参量和形变温度对微碳深冲钢板织构特征的影响

对生产试制的微碳深冲钢板的热轧、冷轧和退火试样的织构和金相组织进行了分析,描述了非{111}织构的工序演变过程,并与常规的{111}织构的演变过程进行了比较.研究表明,在非{111}织构的演变过程中,热轧终轧温度(FT)和冷轧压下率(CR)体现出对织构比较明显的影响规律.     

Abnormal grain growth in undoped strontium and barium titanate

Abnormal grain growth is a commonly observed phenomenon in perovskite materials. In order to study this phenomenon, grain growth experiments were conducted over a temperature range from 1425 to 1600 °C for the model system SrTiO₃ to analyse the nucleation of abnormal grains and to identify the growth mechanism involved for normal and abnormal grains. Grain boundaries of normal and abnormal grains were investigated in quenched samples by high-resolution transmission electron microscopy and by energy-dispersive spectroscopy in a scanning transmission electron microscope. No amorphous film was observed at the grain boundaries for either normal or abnormal grains. Non-stoichiometry at the grain boundaries was identified as a possible reason for the differences in growth speed. The results are compared to the nucleation and growth of abnormal grains in BaTiO₃.     

Preparation and characterization of barium titanate stannate solid solutions

BaSn_xTi_1−xO₃ (x = 0; 0.05; 0.1; 0.15; 0.2) solid solutions were prepared via conventional solid state reaction and sintered at 1300 °C for 4 h, resulting in dense single phase ceramics with homogeneous microstructures. Tetragonal symmetry for x ≤ 0.1, cubic for x = 0.2 and a superposition of tetragonal and cubic for x = 0.15 compositions were found by X-ray diffraction analysis. The temperature and frequency dependence of the complex dielectric constant and dc tunability were determined. A transformation from normal ferroelectric to relaxor with diffuse phase transition was observed with increasing the Sn concentration. All the investigated compositions show a relative tunability between 0.55 (for x = 0.2) and 0.74 (for x = 0.1), at a field amplitude of E = 20 kV/cm.     

Synthesis and dielectric properties of substituted barium titanate ceramics

Barium titanate is one of the most studied ferroelectric materials which has been used in various forms, e.g. bulk, thin and thick films, powder, in a number of applications. In order to achieve a material with desired properties, it is modified with suitable substituents. Most common substituents have been strontium, calcium and zirconium. Here, we report studies on lead and zirconium substituted barium titanate. The material series with compositional formula Ba_0.80Pb_0.20Ti_1?xZr_xO₃, with x varying from 0 to 0.1, was chosen for investigations. The material was synthesized by solid-state reaction method. Reacted powders compacted in the form of circular discs were sintered at 1300 °C. All the samples were subjected to X-ray diffraction (XRD) analysis and found to have single phase perovskite structure. Dielectric behavior was studied as a function of frequency and temperature. Curie temperature (T_c) was found to decrease with increasing x.     

粉末-凝胶法制备铌酸锶钡/钛酸锶钡陶瓷及其表征(英文)

钛酸锶钡(SrxBa1-xTiO3, BST)和铌酸锶钡(SrxBa1-xNb2O6, 0.25≤x≤0.75, SBN)是重要的铁电材料,具有优良的热电、介电和红外快速响应性能。使用廉价的 Nb2O5粉末,应用粉末-溶胶工艺合成铌酸锶钡/钛酸锶钡复相陶瓷(SBN/SBT)。XRD 结果表明:钨青铜相和钙钛矿相共存于体系之中。复相陶瓷形成过程中形成了 TiO2、BaNb2O6(BN)、SrNb2O6(SN)等中间相。干凝胶在800°C下预烧3h,X射线光电子能谱(XPS)分析表明,随着体系组分的变化,Ti元素只存在+4价的化合态,而Nb元素的价态和体系的组分有关。     

含有{111}织构的纳米孪晶多晶铜在拉伸变形过程中塑性各向异性机制的分子动力学模拟

基于分子动力学模拟,从主导滑移系的斯密特因子和位错机制两个方面系统研究含有{111}织构的纳米孪晶多晶铜在拉伸变形过程中的塑性各向异性机制.结果表明:主导滑移系的斯密特因子随着孪晶界倾角的改变而变化,但屈服应力或流动应力并不严格遵守斯密特定律.在拉伸变形过程中存在涉及不同位错机制的硬取向和软取向.硬取向的硬化机制在于塑...     

New ternary compounds in the Lu-{Ru,Rh}-{Si,Ge} systems

Investigations made by powder X-ray diffraction on new ternary LuRuSi, Lu₂Ru₃Si₅, LuRu₂Si₂, LuRhSi, LuRh₂Si₂, LuRuGe, Lu₄Ru₇Ge₆, LuRhGe, Lu₄Rh₇Ge₆ and Lu₃Rh₄Ge₁₃ compounds are reported. The compounds LuRuSi (a=0.6823(1) nm, b=0.4188(1) nm, c=0.7151(1) nm), LuRhSi (a=0.6691(1) nm, b=0.4146(1) nm, c=0.7365(1) nm), LuRuGe (a=0.6871(1) nm, b=0.4259(1) nm, c=0.7305(1) nm) and LuRhGe (a=0.6736(1) nm, b=0.4216(1) nm, c=0.7493(1) nm) crystallize in the orthorhombic TiNiSi-type structure (space group Pnma). The Lu₂Ru₃Si₅ compound (a=1.0611(1) nm, c=0.5537(1) nm) crystallizes in the tetragonal Sc₂Fe₃Si₅-type structure (space group P4/mnc). The compounds LuRu₂Si₂ (a=0.4131(1) nm, c=0.9411(1) nm) and LuRh₂Si₂ (a=0.4005(1) nm, c=0.9830(2) nm) crystallize in the tetragonal CeGa₂Al₂-type structure (space group I4/mmm). The compounds Lu₄Ru₇Ge₆ (a=0.8239(1) nm) and Lu₄Rh₇Ge₆ (a=0.8244(1) nm) adopt the U₄Re₇Si₆-type structure (space group Im3m). The Lu₃Rh₄Ge₁₃ compound (a=0.8882(1) nm) belongs to the cubic Pr₃Rh₄Sn₁₃-type structure (space group Pm3n).     

Synthesis of anatase TiO_2 with exposed {001} and {101} facets and photocatalytic activity

Anatase titanium(Ⅳ) oxide(TiO_2) particles with exposed {001} and {101} facets were prepared by hydrothermal treatment of amorphous TiO_2 with H_2O_2-NH_3 solution. Crystal phase, shape, and size of TiO_2 particles are found to be greatly dependent on the ratio of H_2O_2-NH_3 solution. The prepared TiO_2 particles with specific exposed crystal faces show higher photocatalytic activity for acetaldehyde decomposition than commercial spherical TiO_2 particles. This result implies that recombination is prevented by spatial separation of redox sites in the particles because of selective migration of electrons and positive holes to specific exposed crystal faces and/or different reactivity of electrons and positive holes on the specific exposed crystal face.     

Preparation of IaA-type diamond crystals containing a high concentration of nitrogen by annealing {111}-oriented N-doped diamond crystals

In this study, we report the growth of gem-quality N-doped {111}-oriented diamond crystals by adding phosphorus nitride (P₃N₅) into the growth cell at 6.0 GPa pressure and 1550–1650 K temperature. The concentration of nitrogen (C_N) incorporated into the synthetic diamond crystals was found to be in the range of 476–2624 ppm, whereas the P impurity could only be detected in the graphite phase. The annealing treatment of the diamond crystals show that the aggregation rate of N atoms in the high-level N-doped diamond crystals is ~ 71 times of that in the conventional synthetic Ib-type diamonds. Therefore, the green color Ib-type diamond crystals containing a higher C_N were found to be good candidates for the preparation of IaA-type diamond crystals.