反应合成法制备Ag/SnO2复合材料中Ag6O2/SnO2低指数界面研究

利用Ag/SnO2复合材料界面高分辨透射电镜分析结果,运用第一性原理对复合材料界面结合进行模拟计算.结果表明,反应合成后Ag6O2(101)面与SnO2(110)面存在晶格匹配,结合能,布居分布和态密度均表明这两个自由表面相结合与实验现象吻合,电子差分密度进一步证实未分解的Ag6O2向Sn提供富氧环境,利于纳米SnO2颗粒生成,最后分析界面表层原子的弛豫状态.     

Fe/TiN界面稳定性的第一性原理计算

采用基于第一性原理法,对低指数面的Fe与Ti N复合材料界面的结合能、态密度以及电荷密度等进行计算,采用界面粘附功评价了该界面的润湿性和结合强度。结果表明:当以Ti N(100)中的N原子直接与Fe(100)面的Fe原子直接结合时,界面结合能最大,润湿性较好,形成最稳定的结合界面。当以Ti N(111)中的Ti原子直接与Fe(100)面的Fe原子直接结合时,界面结合能最小,是整个界面构型的薄弱环节。     

旋转摩擦挤压制备MWCNTs/Al复合材料的界面微观结构

采用旋转摩擦挤压法制备多壁碳纳米管增强铝基(MWCNTs/Al)复合材料,通过高分辨透射电镜观察MWCNTs/Al复合材料的界面结构,并对界面反应进行研究。结果表明:在MWCNTs/Al复合材料中Al-C之间发生界面反应,两者之间的反应产物为Al4C3,其晶面间距为0.827nm,为(003)晶面;Al基体的(111)晶面与MWCNTs的(002)晶面及Al4C3的(003)晶面的界面结合良好,界面存在MWCNTs(002)∥Al4C3(003)的晶体学位相关系。     

分子动力学理论在铝铜合金凝固形核分析中的应用

将分子动力学理论应用于Al-2%Cu铝合金平衡凝固形核过程的分析中,使用分子动力学理论计算了Al-2%Cu合金平衡凝固形核处的结合能与态密度,通过对结合能、态密度以及实验结果进行比较,最终得出合金的最稳定结合结构为面心立方结构的置换固溶体及少量间隙固溶体。分子动力学理论计算结果与透射电镜分析结果相一致,充分表明了将分子动力学理论应用于金属凝固形核的分析当中是完全可行的。     

NiCrAlFe精密电阻合金中的L12有序结构研究

有序结构的形成是决定NiCrAlFe精密电阻合金电学性能的关键因素。本文利用第一性原理赝势平面波方法,计算了合金处于无序固溶体结构和形成L12型有序结构时的结合能、态密度、晶格常数等参数,并利用高分辨透射电子显微镜（HRTEM）对合金进行了结构表征,还测试了固溶态和时效态的电阻率。从结合能来看,该合金形成L12有序结构时比无序固溶体更加稳定;态密度以及部分态密度计算结果则表明,在L12有序结构中,Ni、Cr、Al、Fe会强烈成键而使得整个合金体系变得稳定;HRTEM分析结果证明固溶态合金经过和时效处理后出现了L12有序结构,而且该有序结构的晶格常数与计算值基本一致。对比无序固溶体与L12型有序结构费米能级处的态密度值发现,当形成L12有序结构时合金的导电能力较无序固溶体下降,电阻率升高,与实际测试结果吻合。     

锂辉石表面环烷酸吸附行为的量子化学

采用量子化学计算、红外光谱分析研究了环烷酸在锂辉石表面的吸附行为。通过计算表面能选取锂辉石(110)面为最佳解理面,并构建了无虚频的稳定环烷酸分子模型,运用分子动力学模拟得到环烷酸与锂辉石(110)面的最佳吸附构型。对最优吸附构型进行了量子化学计算,研究了其结构、电荷分布、差分电荷密度以及态密度等。结果表明:锂辉石(110)面吸附环烷酸分子后表面原子都向锂辉石内部弛豫,环烷酸吸附后的构型发生明显的变化,其羰基氧原子负电性得到增强,非羰基原子的负电性得到削弱,环烷酸与锂辉石的作用是通过羰基氧原子实现的。环烷酸与锂辉石吸附后,锂辉石(110)面的电子云重新分配,氧原子的电荷云密度增强并向周围区域发散开来,环烷酸整体态密度峰左移且费米能级附近的态密度峰由价带变为导带,体系趋向于稳定存在。红外光谱分析进一步表明:环烷酸在锂辉石表面吸附是物理吸附作用。     

Ag-Ni复合材料界面的第一性原理研究

采用第一性原理方法分析了Ag(110)、(211)与Ni(110)、(211)的界面结合情况。通过对界面结合能、电荷布居以及界面处的电子结构等研究分析发现,在Ag与Ni界面的结合形式中,以Ag(110)/Ni(211)的界面结合能最高,界面处的电子杂化最为剧烈,其界面结合也是最稳定的     

Cr、Ti掺杂Cu/石墨烯界面结合性能的第一性原理预测（英文）

基于密度泛函理论,对过渡金属Cr、Ti掺杂的Cu/石墨烯界面结合性能进行第一性原理预测,构建并对比一系列不同Cu/石墨烯界面的三明治和表面模型。计算结果表明,界面位相关系对界面结合强度影响不大。两种界面模型的计算结果均显示top-fcc配位模型是最稳定的界面结构,并具有较低的界面结合能。Cr掺杂倾向于偏析到界面上取代Cu,而Ti惨杂倾向于占据界面处的填隙位。虽然这两种元素的偏析趋势都较弱,其偏析可以显著提高界面的结合性能,从而强化界面。     

等径角挤扭法制备的SiC_p/Al复合材料界面、晶格畸变和位错密度（英文）

在523 K下,利用等径角挤扭变形工艺(ECAP-T)将纯Al和经氧化处理的Si C混合粉末固结成10%Si Cp/Al复合材料。采用透射电镜(TEM)和高分辨透射电镜(HRTEM)对所制备的复合材料界面进行观察,并对相应选区电子衍射花样(SAED)进行标定。利用能谱仪(EDS)对界面结合处进行元素含量测定,并对试样选区部分进行面分布扫描。采用X射线衍射仪(XRD)对不同变形道次(1,2和4道次)所制备的复合材料进行分析。研究结果表明,ECAP-T变形后,Al和Si C之间的界面相属于一种非晶态Si O2层,并含有少量从基体和增强颗粒扩散进入的元素(Al,Si和C);随着ECAP-T变形道次的增加,复合材料中Al晶粒的晶格应变不断增加,导致晶内位错密度增大,其典型晶面的布拉格衍射角逐渐减小,而晶面间距逐渐增大。     

金刚石单晶解理断裂的研究

本文通过实验观察和理论计算研究了金刚石单晶解理断裂现象.金刚石单晶晶面上实际的价电子密度并非简单的正比于原子密度.(110)晶面上原子分布不均匀.(110)晶面BQKJB区域内原子分布较少,原子密度低于其它晶面.(111)晶面的价电子键络分布均匀,且实际发生作用的价电子密度最大.计算和分析结果表明,金刚石单晶(111)晶面的有效价电子密度为46.212 nm-2,明显高于(110)晶面的38.542 nm-2,成为有效原子密排面.当金刚石受到外力作用时,(111)面间较弱的键相对更容易断裂,因而导致沿(111)面产生解理.这与实验观察结果相吻合.     

POSS在无铅焊点中界面反应能的分子动力学模拟

运用分子动力学模拟研究了环己烯POSS在无铅焊点锡(β-Sn)晶体的(100)、(110)、(001)面以及在Sn-Ag-Cu合金表面的界面反应,得到了各自的界面反应能大小.结果表明,环己烯POSS易与β-Sn的各主要晶面相结合,但在(110)面上具有最低的界面反应能,结合性能最好.在锡中加入银(Ag)和铜(Cu)提高了环己烯POSS在其表面的界面反应能,表明对结合性能产生了不利影响,但仍然具有较好的结合性能.此外,还计算了环己烯POSS的溶解度参数.对于理解POSS对于无铅焊点的增强作用以及应用POSS来开发焊料增强剂具有重要而实际的意义     

Study on Ag6O2/SnO2 Lower Index Interfaces in Ag/SnO2 Composites Prepared by Reactive SynthesisEI北大核心

Ag6O2/SnO2 interface bonding of Ag/SnO2 composites was simulated by HRTEM image analysis and first-principles calculations. Results show that there is lattice match between the interfaces of SnO2(1 (1) over bar0) and Ag6O2(101). According to cohesive energy, population and density of state (DOS), it is found the bonding of the two free interfaces is in good agreement with the experiment results. Furthermore, the electron density difference verifies the undecomposed Ag6O2 provided an oxygen-rich environment for Sn, which is favorable for SnO2 particle formation. At last the relaxation state of surface atoms in the interface was analyzed.     

Influence of misfit and interfacial binding energy on the shape of the oxide precipitates in metals: ; Interfaces between Mn3O4 precipitates and Pd studied with HRTEM

Transmission electron microcopy (TEM) revealed Mn₃O₄ precipitates with two types of dominant shape in Pd–3 at.% Mn that was internally oxidized in air at 1000°C. One type is octahedrally shaped and bounded by {111} planes of the Mn₃O₄. These observations were compared with earlier observations in the Ag/Mn₃O₄ system and the octahedrons show a relatively larger truncation by (002) in Pd than in Ag. Further, the second type of precipitate shape, comprising about 1/3 of all of the precipitates in Pd, was not observed in Ag. It corresponds to a plate-like structure, showing an orientation relationship where the tetragonal axes of Mn₃O₄ are parallel to the cube axes of Pd, with the c-axis of Mn₃O₄ as habit plane normal. High-resolution TEM observations revealed the presence of a square misfit dislocation network with line direction 〈110〉 and Burgers vector 1/2〈110〉 at these interfaces with (002)Mn₃O₄6{200}Pd. The general conclusions of the present analysis are: (1) the anisotropy in interface energy for oxide precipitates in a metal matrix is substantial due to the ionic nature of the oxide, giving well-defined shapes associated with the Wulff construction; (2) the influence of misfit energy on the precipitate shape as bounded by semi-coherent interfaces is important only if sufficient anisotropy in mismatch is present and if the matrix is sufficiently stiff; and (3) the stronger coupling strength due to electronic binding effects across the interface in Pd compared with Ag is responsible for formation of the dislocation network structures at larger misfit.     

TEM Study on the Ag-BSCCO Interface of Silver-sheathed Bi-2223 Superconducting Tape

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原位合成TiB/Ti基复合材料增强体的生长机制

利用Ｔｉ与Ｂ之间的自蔓延高温合成反应,经非自耗电弧熔炼工艺制备了ＴｉＢ增强的钛基复合材料,借助Ｘ射线衍射（ＸＲＤ）,扫描电镜和透射电镜分析了复合材料的物相和增强体的形态,结果表明：只存在ＴｉＢ增强体和α－Ｔｉ。原位合成增强体ＴｉＢ的形貌与其Ｂ２７晶体结构密切相关,ＴｉＢ增强体容易沿（０１０）方向生长而生成柱状短纤维,其柱面由（１００）,（１０１）和（１０１）组成。     

Antiphase boundaries in GaP layers grown on (001) Si by chemical beam epitaxy

We have investigated the origin of contrast features observed in coalesced GaP islands, deposited by chemical beam epitaxy on (001) Si, by high resolution transmission electron microscopy and conventional dark field electron microscopy. Our results indicate that these features are antiphase boundaries (APBs) lying on {110} planes. Image simulations have been performed to show that APBs can only be seen under specific defocus conditions in high resolution lattice images. The observed contrast is attributed to the presence of Ga–Ga and P–P wrong bonds at APBs. A model is proposed to show that the coalescence of GaP islands on the same Si terrace may not produce APBs, and the formation of such boundaries may require the presence of monoatomic steps, separating the coalescing islands.     

Microstructural study of equiatomic PtTi martensite and the discovery of a new long-period structure

The martensitic phase in an equiatomic PtTi alloy was studied by electron microscopy, neutron and X-ray diffraction, and differential scanning calorimetry. The expected orthorhombic B19 structure with Type I twinning on {1 1 1} planes was found plus a new 33 long-period microtwin stacking based on this B19 structure, also including plate twinning. The measured microtwin volume fraction for the B19 is found to be larger than the value calculated from crystallographic theory, which can be explained by the fact that no martensite lattice parameters at the transformation temperature are known. An atomic model is suggested for the new long period structure in agreement with the electron diffraction and high resolution electron microscopy data.     

The crystallography of stress corrosion cracking in face centered cubic single crystals

The crystallography of transgranular stress corrosion cracking was studied for single crystals of α-brass (tested in 14 N NH₃), copper (tested in 1 M NaNO₂), and 304L austenitic stainless steel (tested in boiling 45 wt% MgCl₂). All fracture surfaces had characteristic flat parallel facets separated by crystallographic and/or fan-shaped steps. In α-brass and copper the facets consisted of {110} planes with the crystallographic steps following {111} planes. In 304L austenitic stainless steel cracking occurred primarily on the {100}, but secondary cracking on {110} was also found. Very smooth crystallographic-like steps were observed, generally following {100} planes. It is concluded that stress corrosion cracking in all systems tested occurred by cleavage. It is suggested that the stress corrosion cracks propagate on the lowest surface energy planes.     

Atomic-scale structure and chemistry of ceramic/metal interfaces—I. Atomic structure of {222} MgO/Cu (Ag) interfaces

Ceramic/metal (C/M) {222} MgO/Cu (Ag) heterophase interfaces, prepared by internal oxidation, are studied by scanning transmission electron microscopy (STEM). The observed spacing between misfit dislocations (1.45 nm) in a 〈110〉 projection is in agreement with the prediction of Bollmann's geometric O-lattice theory and experimental values in the literature for {222} MgO/Cu interfaces. It is concluded that the {222} MgO/Cu (Ag) interfaces are semicoherent and contain a trigonal network of pure edge misfit dislocations parallel to 〈110〉-type directions, with an (a/6)〈211〉-type Burgers vector. Misfit dislocations are also found in a standoff position at a distance of a single (111) spacing of the Cu (Ag) matrix. Extra intensity at the interface, in some angular dark-field images indicates silver segregation, in agreement with our atom-probe field-ion microscope results. On the metal side of the interface, extra intensity is observed in five atomic layers, which corresponds to a total silver enrichment of approximately 0.7 effective monolayers.