圆对称环域Josephson隧道结的静态特性(Ⅰ)——准衍射现象和自场效应

本文研究了圆对称环域Josephson隧道结的静态特性。在环带宽度较窄的情形下,不计入自场,并考虑到外磁场在结区内的非均匀性,解析地得到了l_m与外磁场的l_H的关系。与典型的小结衍射图形所不同的是所有极小都不为零,表现出准衍射图形特征。在环带宽度较宽的情形下,对自场方程进行了数值计算,得到其与一般一维结不同的结特性。 关键词：     

Electronic structures and thermodynamic stabilities of aluminum-based deuterides from first principles calculations

The alanates (complex aluminohydrides) have relatively high gravimetric hydrogen densities and are among the most promising solid-state hydrogen-storage materials. In this work, the electronic structures and the formation enthalpies of seven typical aluminum-based deuterides have been calculated by the plane-wave pseudopotential method, these being AlD₃, LiAlD₄, Li₃AlD₆, BaAlD₅, Ba₂AlD₇, LiMg(AlD₄)₃ and LiMgAlD₆. The results show that all these compounds are large band gap insulators at 0 K with estimated band gaps from 2.31 eV in AlD₃ to 4.96 eV in LiMg(AlD₄)₃. The band gaps are reduced when the coordination of Al varies from 4 to 6. Two peaks present in the valence bands are the common characteristics of aluminum-based deuterides containing AlD₄ subunits while three peaks are the common characteristics of those containing AlD₆ subunits. The electronic structures of these compounds are determined mainly by aluminum deuteride complexes (AlD₄ or AlD₆) and their mutual interactions. The predicted formation enthalpies are presented for the studied aluminum-based deuterides.     

Raman spectra of As4S4 polymorphs: Structural implications for amorphous As2S3 films

Raman-scattering spectra of α-As₄S₄ and β-As₄S₄ have been determined at 300 and 10 K. Although similar in overall aspect, the spectral signatures of the two polymorphs are clearly distinct. We have made a careful comparison of these first-order crystal line spectra to the sharp features reported in the Raman spectra of freshly-deposited films of amorphous As₂S₃. Prior proposals for the presence of As₄S₄ molecules in the unannealed films are supported by these comparisons, but recent contentions that actual microcrystals of β-As₄S₄ are present in the as-deposited material are clearly contradicted by the absence of any of the lattice-phonon lines which are prominent in the crystals at frequencies below 70 cm^-1.     

Wigner and Weyl functions for <Emphasis Type="Italic">p</Emphasis>-adic quantum mechanics

A quantum system with positions in Z_p and momenta in Q_p/Z_p is studied. The displacement operators and also the displaced parity operators in the Z_p × Q_p/Z_p phase space of this system, are studied. The Weyl functions (which are intimately related to the displacement operators) and the Wigner functions (which are intimately related to the displaced parity operators) are discussed.     

First-principles calculations of the structural,elastic, electronic and optical properties of Si2P2O and Ge2P2O at high pressures

The structures of Si₂P₂O and Ge₂P₂O with the space group Cmc21 are derived. The structural, mechanical, elastic anisotropy, electronic and optoelectronic properties are calculated by first principles calculations based on density functional theory (DFT) with generalized gradient approximation (GGA) at high pressure for Si₂P₂O and Ge₂P₂O. By using the elastic stability criteria, it is shown that their structures are all stable. The phonon dispersion spectra are researched throughout the Brillouin zone as implemented in the CASTEP code, which indicates that the optimized structures are stable dynamically. The brittle/ductile behaviors are assessed in the pressures from 0 GPa to 50 GPa. Our calculations present that the performances of them become ductile with pressure rise. Moreover, the anisotropies of them are discussed by the Young's moduli at different pressure, and the results indicate that the anisotropies of them are obvious. The direct band structures of Ge₂P₂O and the indirect band gap of Si₂P₂O show that Si₂P₂O and Ge₂P₂O present semiconducting character at 0 GPa and 50 GPa. The band structures of Si₂P₂O are changed obviously with the increase of pressure. The total DOS originate mainly from O ‘s’ states, O ‘p’ states, P ‘s’ states and P ‘p’ states and M ‘p’ states (M=Si, Ge). The trends of DOS for Si₂P₂O and Ge₂P₂O display many similarities, and the change of DOS is obviously affected by the pressure for Si₂P₂O. The optoelectronic properties of them are researched. The calculated static dielectric constants, ɛ₁(0), are 3.2 at 0 GPa and 6.4 at 50 GPa for Si₂P₂O, and the values of Ge₂P₂O are 10.2 and 9.2 at 0 GPa and 50 GPa.     

AgxCu50-xZr50非晶态合金及其晶化

采用高频熔炼后的真空单辊急冷技术制备了Ag_xCu_50-xZr₅₀金属玻璃,发现在x<12的范围内都可得到完全的非晶态。测量了x=2,4,6和10的Ag_xCu_50-xZr₅₀金属玻璃的玻璃转变温度和晶化温度,并采用Kissinger方法测定了晶化激活能E_a。发现在金属玻璃Ag_xCu_50-xZr_{50关键词：}     

Analysis of the exchange magnetic structure in Pb<Subscript>3</Subscript>Mn<Subscript>7</Subscript>O<Subscript>15</Subscript>

The indirect-coupling model is used to analyze the exchange magnetic structure of Pb₃Mn₇O₁₅ in the hexagonal setting. The ratios of manganese ions Mn⁴⁺/Mn³⁺ in each nonequivalent position are determined. Pb₃(Mn_0.95Ge_0.05)₇O₁₅ and Pb₃(Mn_0.95Ga_0.05)₇O₁₅ single crystals are grown by the solution–melt method in order to test the validity of the proposed model. The structural and magnetic properties of the single crystals are studied. The magnetic properties of the grown single crystals are compared with those of nominally pure Pb₃Mn₇O₁₅.     

Na5, Na6和Na7团簇光学吸收谱的理论研究

以含时密度泛函理论为基础，结合从头赝势方法运用含时局域密度近似计算了Na₅，Na₆和Na₇团簇的动力学极化强度，并通过傅里叶变换得出了团簇的光学吸收谱.研究表明，计算结果可以较好地再现实验谱，而且Na₆和Na₇团簇的结果和组态相互作用的结果符合较好.二维结构和三维结构的Na₆团簇的计算结果表明，只有二维结构可出现低于2 eV以下的峰，而且二维结构光谱的计算结果与实验结果符合较好. 关键词： 光吸收谱 Na团簇 含时局域密度近似     

类花状ZnO-CoFe2 O4 复合纳米管束的制备及其电磁波吸收特性

在90 ℃水溶液中采用两步晶体生长法制备出类花状ZnO-CoFe₂O₄复合纳米管束.ZnO纳米管束的管壁厚度大约为60 nm,管的直径大约为350 nm,CoFe₂O₄纳米颗粒连续包覆在ZnO纳米管束的表面,CoFe₂O₄纳米颗粒尺寸小于40 nm, 壳层厚度随着CoFe₂O₄在ZnO-CoFe₂O_{4 关键词： 类花状 2}O₄')" href="#">ZnO-CoFe₂O₄ 纳米管束 微波吸收剂     

Tb0.3Dy0.7Fe2合金的本构参数辨识方法研究

建立了一种简便的、适用于磁畴模型应用的Tb_0.3Dy_0.7Fe₂ 合金本构参数辨识方法. 针对Tb_0.3Dy_0.7Fe₂合金磁畴模型中本构参数不明确且直接实验测试困难的问题, 提出了一种数值计算与实验测试相结合的参数辨识方法. 采用坐标变换与绘制自由能等势曲线相结合的方法, 简化了载荷作用下Tb_0.3Dy_0.7Fe₂ 合金内磁畴角度偏转的数值计算, 研究了合金磁畴角度偏转模型的参数依赖性. 在此基础上, 结合简单的实验测试, 建立了Tb_0.3Dy_0.7Fe₂合金各向异性常数K₁ 和K₂、能量分布因子ω、晶轴取向分布的辨识及修正方法. 该方法能够简单、快速地完成Tb_0.3Dy_0.7Fe₂ 合金磁畴模型中本构参数的辨识, 对完善磁致伸缩材料磁畴偏转的数值计算模型非常有意义. 理论分析可为类磁致伸缩材料磁机耦合模型的建立、完善, 以及材料本构参数的辨识、获取提供参考.     

Electro- and thermoreflectance of Bi2Te3 and Bi2Se3

Electroreflectance measurements in Bi₂Te₃ and Bi₂Se₃ with the electric field vector of the incident light both inclined and perpendicular to the C-axis have been made at room temperature. The structures found by other workers in the reflection measurements are observed in the present experiment, together with new structures at 0.91 eV, 1.18 eV, 1.78 eV, and 2.61 eV in Bi₂Se₃ which are not related to formerly observed transitions. From these measurements, the selection rules for direct optical transitions in Bi₂Te₃ and Bi₂Se₃ are studied. Thermoreflectance measurements are also made at both room and liquid-nitrogen temperatures. The positions of the peaks obtained in the present work are compared with the electroreflectance and reflection data.     

Kinetics of cation-distribution variation in magnesium-manganese ferrites

Results are presented of an X-ray and neutron-diffraction investigation of the cation distribution as a function of the quenching temperature and isothermal-tempering duration for the ferrites Mg_1.093Mn_0.123Fe_1,784O_3.953 and Mg_0.812Mn_0.289Ni_0.062Fe_1.837O_3.998. To describe the kinetics of the ion redistribution in tempering, equations are proposed which satisfactorily describe the experimental curves. The magnetic moment, Curie temperature, and coercive force are investigated as a function of quenching temperature. The experimental data obtained are satisfactorily accounted for by Néel's theory of ferromagnetism.     

Interface phonon-polaritons in quantum well systems of polar ternary mixed crystals

The interface phonon-polaritons in quantum well systems consisting of polar ternary mixed crystals are investi-gated. The numerical results of the interface phonon-polariton frequencies in the GaAs/AlxGa1-xAs, ZnSxSe1-x/ZnS, and ZnxCd1-xSe/ ZnSe quantum well systems are obtained and discussed. It is shown that there are six branches of interface phonon-polariton modes distributed in three bulk phonon-polariton forbidden bands in the systems. The electric fields of interface phonon-polaritons are also presented and show the interface locality of the modes. The effects of the ’two-mode’ and ’one-mode’ behaviours of the ternary mixed crystals on the interface phonon-polariton modes are shown in the dispersion curves.     

Thermal decay of photochromic color centers in CaF2, SrF2, and BaF2 crystals doped by La and Y impurities

The absorption spectra of photochromic centers in CaF₂, SrF₂, and BaF₂ crystals doped by La and Y impurities and thermal decay of the centers in the temperature range 80–600 K are investigated. Under low-temperature x-ray irradiation, ionized photochromic color (PC⁺) centers are generated in La- and Y-doped CaF₂ crystals and in a La-doped SrF₂ crystal. It is revealed that, upon heating of the CaF₂-LaF₃ crystal, PC⁺ centers are transformed into photochromic color (PC) centers. In the SrF₂-YF₃ crystal irradiated at room temperature, photochromic color centers are generated as well. All color centers decay at a temperature of approximately 600 K. After irradiation of the BaF₂-YF₃ crystal at a temperature of 80 K, absorption bands are observed at energies of 2.25 and 3.60 eV, which are related to neither PC centers nor PC⁺ centers.     

非晶态合金结构模型中势函数的局域和关联效应

Co₈₁P₁₉及Ni₆₄B₃₆非晶态合金的无规硬球密堆的初始位形,分别用Lenard-Jones势及Morse势进行了松弛。在Ni₆₄B₃₆的计算中,考虑了两种位移分数f=0.005及f=1情况。由计算数据可求得体系总能量,简约偏径向分布函数及角分布函数。文中讨论了势函数的局域性及关联性对二元非晶态合金中的化学短程序所造成的影响。 关键词：     

Geometric and electronic structures of B12C6N6 fullerene

An electron deficient fullerene B₁₂C₆N₆ is studied by using ab initio calculations. The structure is generated by replacing N with C in the B₁₂N₁₂ cage to ensure only B–C and B–N bonds are formed. All the possible isomers are optimized and the low energy structures are determined. C and N atoms in the low energy isomers are inclined to segregate and form B₂C₂ and B₂N₂ squares. Natural bond analysis shows that the atomic orbitals of B, C and N in this cage hybrid approximately in sp^2.3 and then form B–C and B–N bonds. The 2p orbitals perpendicular to the cage surface are partially occupied and the molecular orbitals formed by these orbitals are highly delocalized. The natural charge on N is about −1.17 in both B₁₂N₁₂ and B₁₂C₆N₆, and the charge on C is −0.72 to −0.60. The molecular orbital compositions show that the B–N bonds are the same in B₁₂N₁₂ and B₁₂C₆N₆, and the B–C bonds possess stronger covalent character. The HOMO of B₁₂C₆N₆ is formed by 2p of B and C, and the LUMO is formed by 2p of C. The energy gap of C₂₄, B₁₂N₁₂ and B₁₂C₆N₆ is 2.52, 6.84 and 3.22 eV, respectively.     

Al2O3-Y2O3-ZrO2三相复合陶瓷的介电谱研究

采用传统的固相反应法,在1400–1500 ℃下烧结,制备得到Al₂O₃-Y₂O₃-ZrO₂三相复合陶瓷.样品的结构、形貌和电性能分别用X射线衍射(XRD)、扫描电子显微镜(SEM)及介电谱表征.XRD表明此三相复合体系无其他杂相,加入Y₂O₃及ZrO₂后使得Al₂O₃成瓷温度降低;SEM表明此体系晶粒直径为200–500 nm,并且样品随烧结温度的升高而变得更加致密,晶界更加清晰;介电损耗谱中出现峰值弛豫现象,根据Cole-Cole复阻抗谱得出其为非德拜弛豫. 关键词： 2O₃-Y₂O₃-ZrO₂三相陶瓷')" href="#">Al₂O₃-Y₂O₃-ZrO₂三相陶瓷 介电弛豫 阻抗谱 热导率     

Proton and deuteron magnetic resonance of methanes,silanes and GeH3D dissolved in nematic liquid crystals

The proton and deuteron magnetic resonance spectra of CH₄, CH₃D, CH₂D₂, CHD₃, CD₄, SiH₄, SiH₃D, SiH₂D₂, SiH₃D, SiD₄, GeH₃D, dissolved in nematic liquid crystals, are reported. It was found that these molecules, which are essentially tetrahedral, exhibit anisotropic interactions and are partially oriented in the nematic phase. This effect is presumably due to slight deformations induced by the anisotropic medium. Some of the aspects related to the interpretation of the results are discussed.     

Microwave absorption coefficients of atmospheric pollutants and constituents

Calculations of the transition frequencies and absorption coefficients of microwave rotational transitions are given for a number of atmospheric pollutants and constituents. New measurements of the absorption coefficients are made in the vicinity of 70 GHz. The apparatus used in these measurements is briefly described. The calculated absorption coefficients are compared with these measurements and with existing measurements at other frequencies where available. Transitions with frequencies up to about 200 GHz are considered for the molecules and radicals SO₂, O₃, H₂O, NO₂, H₂S, H₂CO, NH₃, CO, OCS, N₂O, NO, OH, O₂, SO. Also discussed are criteria for the selection of appropriate transitions for the development of high sensitivity monitors to be used in air pollution and combustion research.     

Structure, properties, and formation models of optical ceramics

The structure, properties, and formation mechanisms of Y₃Al₅O₁₂, Y₂O₃, and Lu₂O₃ laser ceramics are investigated. Their microhardness and fracture toughness are determined. It is shown that the change in mechanical properties is related both to the grain size and grain boundary structure. Processes of plastic deformation of crystals by mechanical twinning are considered. Mechanisms of formation and motion of twins in crystals with FCC structure are determined. It is shown that the realization of similar mechanisms in crystals with HCP structure results in the phase transformations. Models of the formation and motion of twin boundaries are proposed which result in pore healing when preparing monolithic samples of highly transparent ceramics.