退火温度对CuGa_(0.8)Ge_(0.2)Se_2薄膜结构及光学特性的影响

采用脉冲激光沉积法在SiO2衬底上制备了CuGa0.8Ge0.2Se2薄膜。采用X射线衍射和X射线能谱仪研究了退火温度对薄膜晶体结构和成分的影响,利用扫描电子显微镜表征了薄膜的表面形貌,采用紫外—可见分光光度计分析了薄膜的光学特性。结果表明,在CuGaSe2中掺杂Ⅳ族元素Ge,光子吸收能量分别为0.65和0.92 e V,禁带宽度为1.57 e V,能够形成中间带。并随着退火温度的升高,CuGa0.8Ge0.2Se2薄膜的光学带隙逐渐减小。     

大同南站清水混凝土双胞胎柱施工工艺

以大同南站高架厅清水混凝土支撑柱为研究对象,分析总结了清水混凝土双胞胎柱的深化设计方法、模板加固工艺、柱体接缝处理措施、预埋件安装方法以及混凝土浇筑的质量控制要点等。工程实施效果较好,可为类似的清水混凝土异形柱施工提供参考。     

Atomistic simulations of interactions between screw dislocation and twin boundaries in zirconium

Molecular statics was employed to simulate interaction between screw dislocation and twin boundaries (TB) in hexagonal close-packed zirconium. In the moving TB model, the interaction of a moving $\left\{10\overline{1}2\right\}$ TB with a static $1/3〈11\overline{2}0〉\left\{10\overline{1}0\right\}$ screw dislocation was investigated. Twinning dislocation (TD) nucleation and movement play an important role in the interaction. The screw dislocation passes through the moving TB and changes to a basal one with a wide core. In the moving dislocation model, a moving $1/3〈11\overline{2}0〉\left\{10\overline{1}0\right\}$ dislocation passes through the TB, converting into a basal one containing two partial dislocations and an extremely short stacking fault. If the TB changes to the $\left\{10\overline{1}1\right\}$ one, the moving $1/3〈11\overline{2}0〉\left\{10\overline{1}0\right\}$ prismatic screw dislocation can be absorbed by the static TB and dissociated into two TDs on the TB. Along with the stress–strain relationship, results reveal the complicated mechanisms of interactions between the dislocation and TBs.     

细化变质处理对铸造A356铝合金组织性能及共晶硅生长机制的影响

研究了采用新型Al-5Ti-1B-1RE中间合金和Al-10Sr中间合金对A356铝合金进行单一或复合细化变质处理后的组织、力学性能和共晶硅生长机制的影响。结果表明：单一细化变质处理中Al-5Ti-1B-1RE中间合金对A356铝合金中α-Al相有明显的细化作用,合金的强度和维氏硬度显著提高；Al-10Sr 中间合金对共晶硅有强的变质作用,合金的伸长率明显提高；而经复合细化变质处理后α-Al相形状和尺寸变得更均匀细小,晶界更清晰,共晶硅相几乎都转变成更弥散、更细小的纤维状,片层状共晶硅也几乎完全消失,共晶硅长度由铸态40-60 μm降低到1-2 μm之间,达到完全变质效果,其力学性能显著高于铸态、单一细化变质剂处理的A356铝合金。未细化变质的A356铝合金中的共晶Si的生长方式为典型的小平面台阶生长,复合细化变质处理的共晶硅以孪晶凹槽机制生长为主,小平面生长特征逐渐减弱直至消失。     

双模晶体相场研究六方四方相变过程晶界和位错演化

对于晶粒，晶界，应力和位错的交互作用的深入理解有助于优化材料组织和提升材料性能。本文采用双模晶体相场法研究六方相向正方相的转变。分别针对倾侧角为0°，15°，30°，和 45°，晶粒取向差为6°的六方相体系做了系统研究。六方晶粒长大、溶合、并形成共格晶界，位错组沿六方晶界均匀分布，并有两种取向。正方相在位错组处形核，并且其取向取决于位错组取向。每一种倾侧角的体系种均形成两个取向正方相的变体。针对倾侧角为0 °，15°，30°，和 45°的六方相体系生成的四方相相变体之间的取向差分别为30°, 30°, 10°, 和5°。不同取向的正方相晶粒长大熟化的方式有差异，位于有利取向的晶粒将会优先生长占据主导地位。以共格晶界形式长大的晶粒，晶界处有位错组生成以松弛晶粒长大的应力集中。     

Evaluating Schmid criterion for predicting preferential locations of persistent slip markings obtained after very high cycle fatigue for polycrystalline pure copper

Very high cycle fatigue carried out on pure copper polycrystals promotes early slip markings, labelled as slip markings of types II and III, localized close to grain or twin boundaries. In this work, we focus on whether Schmid criterion can predict the preferential sites of slip markings of types II and III and identify the active slip systems. Combining observations of slip markings and polycrystalline modeling, it is shown that considering pure cubic elastic behavior, maximum resolved shear stress as a criterion for type II slip markings preferential sites is 70% reliable criterion. Concerning slip markings of type III, the reliability falls to 30%. The role of cross slip is highlighted and a scenario rationalizing the stress amplitude conditions and sites to observe early slip markings of type II or III for copper polycrystals is proposed.     

Impedance spectroscopy studies on samarium and sodium substituted strontium bismuth titanate (SBTi)

Sr_1-x Sm_xNa_xBi₄Ti₄O₁₅ lead-free piezoelectric ceramics are prepared by solid-state sintering method using high energy Ball- Mill and ground for 10 h. The single phase of the compound is confirmed by X-ray Diffraction and highest intensity peak (1 1 0) is observed at 30°. Diffraction peaks shifted towards higher angles with an increasing concentration of Sm³⁺ and Na¹⁺ of SBT. Grains orientation and grain size are analyzed by Scanning Electron Microscope. Temperature and frequency dependent AC conductivity studies are carried out using impedance spectroscopy in the temperature range of 30 °C–650 °C using Wayn-Kerr LCR meter. At lower frequencies, conductivity is independent of frequency. The variation of Z″ with frequency shows peaks shifting towards higher frequencies with an increase of temperature. The resistance of grains (R_g), grain boundaries (R_gb) are calculated and it is found that grain resistance is greater than grain boundary resistance (R_g > R_gb). Relaxation times of grain and grain boundaries are calculated.     

An Investigation into the Thermal Boundary Resistance Associated with the Twin Boundary in Bismuth Telluride

The thermal boundary resistances (TBRs) of twin boundaries occurring at three different atomic layers (Te1, Bi, and Te2) of bismuth telluride (Bi₂Te₃) are investigated in use of the non-equilibrium molecular dynamics (NEMD) simulation method. The simulation results show that among all, the Te1-twin boundaries bring about a lowest interfacial energy corresponding to a most stable system, which explains why this type of twin boundaries is mostly often observed in the laboratory; the Te2-twin boundaries on the other hand possess a largest interfacial energy, resulting in a least stable system. The order in magnitude of the TBRs associated with these three types of twin boundaries is Te2-twin > Bi-twin > Te1-twin. Moreover, the TBR associated with a pair of twin boundaries separated by a distance of 4 unit cell (UC) is found to be about twice as large as that of a single twin boundary of the same type. It implies that the mutual coupling, which causes an increase in TBRs, may be ignored and the effect of twin boundaries may be counted individually as long as the separation distance is larger than 4 UC.