Linked-Cluster Expansion of the Ising Model

The linked-cluster expansion technique for the high-temperature expansion of spin modes is reviewed. A new algorithm for the computation of three-point and higher Green's functions is presented. Series are computed for all components of two-point Green's functions for a generalized 3D Ising model, to 25th order on the bcc lattice and to 23rd order on the sc lattice. Series for zero-momentum four-, six-, and eight-point functions are computed to 21st, 19th, and 17th order respectively on the bcc lattice.     

Synthese,Kristallstruktur und Eigenschaften eines neuen Sialons – SrSiAl2O3N2

Synthesis, Crystal Structure, and Properties of a New Sialon – SrSiAl₂O₃N₂ The sialon SrSiAl₂O₃N₂ was obtained as a coarsly crystalline solid by reaction of silicon diimide, aluminum nitride, and strontium carbonate under N₂ atmosphere in a high-frequency furnace at 1650 °C. According to the single-crystal structure determination the title compound is isotypic with LnSi₃N₅ (Ln = La, Ce, Nd, Pr). SrSiAl₂O₃N₂ (P2₁2₁2₁, a = 491.98(6), b = 789.73(7), c = 1134.94(18) pm, Z = 4, R1 = 0.0439, wR2 = 0.0939). In the solid a three-dimensional network structure of corner sharing SiON₃, AlO₃N, and AlO₂N₂ tetrahedra occurs. Lattice energetic calculations using the MAPLE concept confirm an unequivocally correct crystallographic differentiation between N and O as well as Al and Si atoms, respectively (Al–O: 167.4(5)–170.6(6); Al–N: 175.4(6)–179.4(6); Si–O: 171.2(6); SiN: 176.7(6)–179.6(6) pm). The Sr²⁺ ions are located in the voids of the (SiAl₂O₃N₂)^2– framework (Sr–O: 250.4(6)–304.2(6); Sr–N: 287.4(6) 318.2(6) pm).     

All-Impurities Scavenging,Safe Separators with Functional Metal-Organic-Frameworks for High-Energy-Density Li-Ion Battery

Li-ion batteries (LIBs) have wide applications owing to their high-energy density and stable cycle characteristics. Nevertheless, with the rapid expansion of electric vehicle market, issues such as explosion of LIBs and the need to secure a longer driving distance have emerged. In this work, functional metal–organic frameworks (MOFs) are introduced as a separator in LIBs, in which a highly heat-resistant polymer separator is fabricated through electrospinning. The MOFs can scavenge impurities (including gas, water, and hydrofluoric acid) that positively affect battery performance and safety. The multi-functional separator suppresses salt decomposition when a nickel-rich cathode is operated at high voltage and high temperature through it. This delays the deterioration of the cathode interface and results in a superb cycle stability with 75% retention even in the presence of 500 ppm of water in the electrolytes. In addition, the pouch cell is manufactured by enlarging the separator, and the degree of electrode swelling due to gas generation and interface degradation in the pouch state is alleviated to 50% or less. These findings highlight the necessity of scavenging impurities to maintain excellent performance and provides the development direction of functional separators in LIBs.     

Nitrogen-Rich Rigid Polybenzimidazole With Phosphoric Acid Shows Promising Electrochemical Activity and Stability for High-Temperature Proton Exchange Membrane Fuel Cells

Polybenzimidazoles (PBIs) are the most promising binders for the catalyst layer (CL) in high-temperature proton exchange membrane fuel cells (HT-PEMFC). However, traditional commercial PBIs are not applied in binders because they do not enhance the electrochemical performance and because the related solvents are not environmentally friendly. In addition, proton transfer channels in PBIs are not investigated at the microscopic and atomic scales to date. In this study, a nitrogen-rich rigid PBI binder containing pyridine, diazofluorene, and partially grafted nitrile (PBPBI-3CN) is prepared with a functionalized structure, good thermal stability, and good solubility in an environmentally friendly solvent. A membrane electrode assembly (MEA) is fabricated with the PBPBI-3CN binder, providing a high peak power density, low resistance, and good stability. The protonation, hydrogen bond networks, and platform for proton transfer are confirmed in the CLs. The protonation of PBPBI-3CN occurs in two steps. First, some phosphoric acid (PA) molecules bind to nitrogen-containing acidophilic groups via preliminary protonation; second, multiple PA molecules then interact with nitrogen-containing acidophilic groups via further protonation. With protonation as the foundation, a sufficient amount of PA molecules form a hydrogen bond network, and proton transfer channels are established.     

高温超导约瑟夫森结太赫兹混频系统

在小型脉冲管制冷机（工作温度约60 K）上搭建了高温超导约瑟夫森结太赫兹谐波混频系统,并采取了一系列措施增强结与太赫兹波的耦合。所采取的措施主要有：研究不同基片对结的影响并最终选择MgO做为双晶结基片,设计平面周期对数天线,同时使用一个超半球硅透镜和两个离轴抛物面反射镜组成准光学系统。最终成功在小型脉冲管制冷机中获得结对623 GHz太赫兹波的响应,并且成功进行24次谐波混频实验。     

Flux growth and characterizations of NdPO4 single crystals

Neodymium phosphate single crystals, NdPO₄, have been grown by a flux growth method using Li₂CO₃-2MoO₃ as a flux. The as-grown crystals were characterized by X-ray powder diffraction(XRPD), differential thermal analysis (DTA) and thermogravimetric analysis (TG) techniques. The results show that the as-grown crystals were well crystallized. The crystal was stable over the temperature range from 26 to 1200 °C in N₂. The specific heat of NdPO₄ crystal at room temperature was 0.41 J/g °C. The absorption and the fluorescence spectra of NdPO₄ crystal were also measured at room temperature.     

High-temperature electron mobilities in LPE-Grown GaP

We report measurements to 500°C of resistivity and Hall mobility in Sn-doped, n-type GaP grown by liquid phase epitaxy. Samples with room-temperature carrier densities between 1 × 10¹⁶ and 1 × 10¹⁸cm⁻³ were studied. Mobilities were in the range 100–180 cm²/V-sec at room temperature and in the range 27–35 cm²/V-sec at 400°C. Carrier densities increased by only about a factor of two with increasing temperature. Theoretical fits to the mobility data were made by considering contributions from intervalley, polar-optic, acoustic-deformation-potential, and ionlzed-impurity scattering mechanisms. Our results confirm the utility of GaP for high-temperature device applications and provide important information on electrical parameters needed for device modeling and design.     

Research progress on thermal protection materials and structures of hypersonic vehicles

Hypersonic vehicles represent future trends of military equipments and play an important role in future war. Thermal protection materials and structures, Which relate to the safety of hypersonic vehicles, are one of the most key techniques in design and manufacture of hypersonic vehicles. Among these materials and Structures, such as metallic temperature protection structure, the temperature ceramics and carbon/carbon composites are usually adopted in design. The recent progresses of research and applica- tion of ultra-high temperature materials in preparation, oxidation resistance, mechanical and physical characterization are summarized.     

新型精铸热锻模具钢高温磨损性能同其显微组织的相关性

研究了经不同热处理条件下的新型精铸热锻模具钢的组织同其高温磨损性能的相关性,对比分析了新型铸钢与H13锻钢的高温磨损性能,并探讨了其磨损机理.结果表明:新型精铸热锻模具钢的高温耐磨性能明显优于锻钢H13;在马氏体、贝氏体和马贝复相3种组织中,贝氏体和马贝复相的高温耐磨性能较好,马氏体相的高温耐磨性能最差;经过400～620℃回火处理的新型精铸热锻模具钢的硬度为42～43HRC,高温耐磨性能较好;当回火温度大于650℃或小于400℃时,新型精铸热锻模具钢的磨损率明显增大,耐磨性显著降低.     

Resonant States in High-Temperature Superconductors with Impurities

A microscopic theory of resonant states for the Zn-doped CuO₂ plane in the superconducting phase is formulated in the effective t–J model. In the model derived from the original p–d model, Zn impurities are considered as vacancies for the d states at Cu sites. In the superconducting phase, in addition to the local static perturbation induced by the vacancy, a dynamical perturbation appears that results in a frequency-dependent perturbation matrix. Using the T-matrix formalism for the Green's functions in terms of the Hubbard operators, we calculate the local density of electronic states with d, p, and s symmetries.