In Situ Monitoring of Thermally Cycled Metal Matrix Composites by Neutron Diffraction and Laser Extensometry

A novel stroboscopic neutron diffraction data collection system has beendeveloped. In combination with scanning laser extensometry this has beenused to investigate the thermal cycling behaviour of SiC short fibrereinforced Al matrix composites. Three-dimensional unit cell finite elementmodels have been produced, incorporating matrix deformation both by creepand plasticity. Comparison of the experimental results with modelpredictions has allowed conclusions to be drawn about the deformationprocesses which dominate at different parts of the thermal cycle.     

微透镜列阵衍射效应所致的串扰

本文分析了微透镜列阵衍射效应的影响因素,推导出了微透镜焦平面上光强分布的解析表达式,对菲涅尔数评价衍射效应的物理含义给予了合理的解释.并利用ZEMAX软件对微透镜列阵进行仿真,基于惠更斯子波直接积分的算法计算得到了微透镜列阵焦平面上的光场强度分布.通过比较不同条件下所得到的计算结果,验证了以菲涅尔数作为微透镜列阵衍射效应评价依据的的合理性,同时验证了以菲涅尔数判断焦斑间串扰的可行性.     

In situ monitoring of thermally cycled metal matrix composites by neutron diffraction and laser extensometry

A novel stroboscopic neutron diffraction data collection system has been developed. In combination with scanning laser extensometry this has been used to investigate the thermal cycling behaviour of SiC short fibre reinforced Al matrix composites. Three-dimensional unit cell finite element models have been produced, incorporating matrix deformation both by creep and plasticity. Comparison of the experimental results with model predictions has allowed conclusions to be drawn about the deformation processes which dominate at different parts of the thermal cycle.     

Influence of Charge Doping on Thermal Diffusivity of Double Perovskite Sr2FeMoO6 Studied by Mirage Effect

Effects of charge doping on thermal diffusivity have been investigated in double perovskite ferromagnetic Sr_2–x La _x FeMoO₆ (0 x 0.4) by means of the mirage effect at 300 K ( the critical temperature T _c 420 K). Substitution of the La³⁺ ions for the Sr²⁺ ions significantly increases the value of the thermal diffusivity from 0.39 cm² · s^–1 at x = 0 to 0.54 cm² · s^–1 at x = 0.4. The increased thermal diffusivity is ascribed to the extra itinerant electrons on the Mo4d band.     

Improved Thermal Stability and Film Uniformity of Halide Perovskite by Confinement Effect brought by Polymer Chains of Polyvinyl Pyrrolidone

Polyvinyl pyrrolidone (PVP) is doped to PbI₂ and organic salt during two-step growth of halideperovskite. It is observed that PVP molecules can interact with both PbI₂ and organic salt, reduce the aggregation and crystallization of the two, and then slow down the coarsening rate of perovskite. As doping concentration increases from 0 to 1 mM in organic salt, average crystallite size of perovskite decreases monotonously from 90 to 34 nm; Surface fluctuation reduces from 259.9 to 179.8 nm at first, and then increases; Similarly, surface roughness decreases from 45.55 to 26.64 nm at first, and then rises. Accordingly, a kind of “confinement effect” is resolved to crystallite growth and surface fluctuation/roughness, which helps to build compact and uniform perovskite film. Density of trap states (t-DOS) is cut down by ≈60% at moderate doping  (0.2 mM). Due to the “confinement effect”, power conversion efficiency of perovskite solar cells is improved from 19.46 (±2.80) % to 21.50 (±0.99) %, and further improved to 24.11% after surface modification. Meanwhile, “confinement effect” strengthens crystallite/grain boundaries and improves thermal stability of both film and device. T₈₀ of device increases to 120 h, compared to 50 h for reference ones.     

PVP对溶胶凝胶法制备负热膨胀ZrW_2O_8粉体形貌及性能的影响

以PVP为添加剂,采用溶胶凝胶法制备ZrW_2O_8粉体,研究添加剂对粉体形貌的影响及其负热膨胀特性。对其前驱体进行热重-差热分析(TG-DSC),以X射线粉末衍射(XRD),扫描电子显微镜(SEM)对产物结构及形貌进行表征。结果表明所得粉体为单一立方α-ZrW_2O_8相。加入PVP后,可以有效地改变粉体的形貌,随着加入量的增大,粉体的形貌从无规则的团聚体转变为长棒状、扇形及短棒颗粒。原位X射线粉末衍射分析表明,所得ZrW_2O_8粉体具有良好的负热膨胀特性。     

Large Enhancement of 2D Electron Gases Mobility Induced by Interfacial Localized Electron Screening Effect

The interactions between delocalized and localized charges play important roles in correlated electron systems. Here, using a combination of transport measurements, spectroscopic ellipsometry (SE), and X‐ray absorption spectroscopy (XAS) supported by theoretical calculations, we reveal the important role of interfacial localized charges and their screening effects in determining the mobility of (La_0.3Sr_0.7)(Al_0.65Ta_0.35)O₃/SrTiO₃ (LSAT/SrTiO₃) interfaces. When the LSAT layer thickness reaches the critical value of 5 uc, the insulating interface abruptly becomes conducting, accompanied by the appearance of a new midgap state. This midgap state emerges at ≈1 eV below the Ti t_2g band and shows a strong character of Ti 3d_xy – O 2p hybridization. Increasing the LSAT layer from 5 to 18 uc, the number of localized charges increases, resulting in an enhanced screening effect and higher mobile electron mobility. This observation contradicts the traditional semiconductor interface where the localized charges always suppress the carrier mobility. These results demonstrate a new strategy to probe localized charges and mobile electrons in correlated electronic systems and highlight the important role of screening effects from localized charges in improving the mobile electron mobility at complex oxide interfaces.