LixNayCoO2的制备和热电性质

用固相反应方法，成功地合成了具有交互生长结构的Li_xNa_yCoO₂单相多晶系列样品. 热电势测量表明，该系统的室温热电势比Na_xCoO₂体系约高出60μV/K. 基于空穴载流子具有O2p特征，提出Li_xNa_yCoO₂中额外的热电势来源于氧空穴的占位熵. 关键词： xNa_yCoO₂')" href="#">Li_xNa_yCoO₂ 热电势 热电材料     

Reduced anti-ferromagnetism promoted by Zn 3d substitution at CuO2 planar sites of Cu0.5Tl0.5Ba2Ca3Cu4O12−δ superconductors

The role of charge carriers in ZnO₂/CuO₂ planes of Cu_0.5Tl_0.5Ba₂Ca₃Cu_4−yZn_yO_12−δ material in bringing about superconductivity has been explained. Due to suppression of anti-ferromagnetic order with Zn 3d¹⁰ (S=0) substitution at Cu 3d⁹ sites in the inner CuO₂ planes of Cu_0.5Tl_0.5Ba₂Ca₃Cu₄O_12−δ superconductor, the distribution of charge carriers becomes homogeneous and optimum, which is evident from the enhanced superconductivity parameters. The decreased c-axis length with the increase of Zn doping improves interlayer coupling and hence the three dimensional (3D) conductivity in the unit cell is enhanced. Also the softening of phonon modes with the increased Zn doping indicates that the electron–phonon interaction has an essential role in the mechanism of high-T_c superconductivity in these compounds.     

Superconductivity in the hole-doped oxy-arsenide RE1−xSrxFeAsO (RE = La, Pr)

Bulk superconductivity was observed in the FeAs-based RE_1−xSr_xFeAsO (RE = La, Pr) when the di-valence element Sr was substituted to the site of the tri-valence element La and Pr. The maximum superconducting transition temperatures T_c for the two systems are 26 K and 16.3 K, respectively. The doping dependence of the electrical properties and structure of these two systems were investigated systematically. A roughly monotonic increase of T_c and the lattice constants (a-axis and c-axis) with Sr concentration and a saturation behavior in the high doping levels were found. We confirmed that conduction in this type of materials is dominated by hole-like charge carriers by the Hall effect measurements. Also the resistive measurements revealed possible higher upper critical field in these systems comparing with the electron-doped ones.     

Electrical transport in La1−x Ca x MnO3 thin films at low temperatures

We report here the low-temperature resistivity of the chemical solution deposited La_1−x Ca _x MnO₃ (x=0.2, 0.3 and 0.33) thin films on LaAlO₃ substrates. The films were post-annealed in atmosphere at 850°C. The low temperature resistivity data has been studied in order to understand the nature of low-temperature conduction processes. The data showed T ² dependence from 60 K to 120 K consistent with the single magnon scattering process. The deviation from this quadratic temperature dependence at low temperatures is attributed to the collapse of the minority spin band. The two-magnon and electron-phonon processes contribute to scattering of carriers in the temperature range above 120 K.     

Ce4+离子在Ca2SnO4一维结构基质中的电荷迁移光谱研究

利用高温固相反应法制备了Ca₂Sn_1-xCe_xO₄和Ca_2-ySr_ySn_1-xCe_xO₄一维结构发光体. XPS结果显示 Ca₂SnO₄拥有两种结合能分别为5277 eV和5293 关键词： 2Sn_1-xCe_xO₄')" href="#">Ca₂Sn_1-xCe_xO₄ 2-ySr_ySn_1-xCe_xO₄')" href="#">Ca_2-ySr_ySn_1-xCe_xO₄ 一维结构 电荷迁移光谱     

碲镉汞焦平面光伏器件的实时γ辐照效应研究

对碲镉汞长波和中波焦平面光伏器件进行了实时γ射线辐照效应研究,通过辐照过程中实时测试器件的电流-电压特性,发现随着辐照剂量的增加,中波器件比长波器件表现出更好的抗辐照能力.对于长波器件,随着辐照剂量的增大,能够反映器件性能的零偏电阻逐渐降低;对于中波器件,零偏电阻随着辐照剂量的增加无固定变化趋势,辐照效应主要表现在电阻-电压曲线随着辐照剂量增加出现越来越明显的扰动.根据光伏器件的暗电流机理,对长波器件的电阻-电压曲线进行数值拟合,发现辐照引起少子产生-复合寿命逐渐降低,缺陷密度逐渐增大,主要影响的电流机理 关键词： γ辐照 辐照效应 光伏器件 碲镉汞     

Numerical analysis of the short-circuit current density in GaInAsSb thermophotovoltaic diodes

In this paper, a simulation and analysis on the short-circuit current density (J_sc) of the P-GaSb window/P-Ga_xIn_1−xAs_1−ySb_y emitter/N-Ga_xIn_1−xAs_1−ySb_y base/N-GaSb substrate structure is performed. The simulations are carried out with a fixed spectral control filter at a radiator temperature (T_rad) of 950 °C, diode temperature (T_dio) of 27 °C and diode bandgap (E_g) of 0.5 eV. The radiation photons are injected from the front P-side. Expressions for minority carrier mobility and absorption coefficient of Ga_xIn_1−xAs_1−ySb_y semiconductors are derived from Caughey–Thomas and Adachi’s model, respectively. The P-Ga_xIn_1−xAs_1−ySb_y emitter with a much longer diffusion length is adopted as the main optical absorption region and the N-Ga_xIn_1−xAs_1−ySb_y base region contribute little to J_sc. The effect of P-GaSb window and P-Ga_xIn_1−xAs_1−ySb_y emitter region parameters on J_sc is mainly analyzed. Dependence of J_sc on thickness and carrier concentration of the window are analyzed; these two parameters need to be properly selected to improve J_sc. Contributions from the main carrier recombination mechanisms in the emitter region are considered; J_sc can be improved by suppressing the carrier recombination rate. Dependence of J_sc on the carrier concentration and layer thickness of the emitter P-region are also analyzed; these two parameters have strong effect on J_sc. Moreover, adding a back surface reflector (BSR) to the diode can improve J_sc. The simulated results are compared with the available experimental data and are found to be in good agreement. These theoretical simulations help us to better understand the electro-optical behavior of Ga_xIn_1−xAs_1−ySb_y TPV diode and can be utilized for performance enhancement through optimization of the device structure.     

Simulation of temperature-dependent material parameters and device performances for GaInAsSb thermophotovoltaic cell

Temperature-dependent material parameters and device performances of Ga_xIn_1−xAs_1−ySb_y TPV cells applied in low temperature (800–1200 °C) radiators are simulated using the PC-1D. As is well known, the optimum bandgap (E_g) decreases towards lower radiator temperatures. So far, the lowest achievable E_g of Ga_xIn_1−xAs_1−ySb_y at 300 K is 0.5 eV. We mainly considering the Ga_0.8In_0.2As_0.18Sb_0.82 (E_g = 0.5 eV) TPV cell. The effects of doping concentration and recombination mechanisms of the emitter layer on photovoltaic conversion efficiencies (η_cel) are analyzed in detail, and η_cel can be improved by optimizing doping concentration and suppressing carrier recombination. The effects of GaSb window layer on η_cel are also presented. It shows the type-II energy-band alignment GaSb(window)/GaInAsSb(emitter) heterostructure affect η_cel mainly through V_oc. For the first time, the effects of operating temperatures on device performances are analyzed based on temperature-dependent material parameters, and the temperature coefficients of the device performances are presented.     

Structural studies and T c dependence in La2−x Dy x Ca y Ba2Cu4+y O z type mixed oxide superconductors

A new series of mixed oxide superconductors with the stoichiometric composition La_2−x Dy _x Ca _y Ba₂Cu_4+y O _z (x=0.0 − 0.5, y=2x) has been studied for structural and superconductiong properties. Our earlier studies on La_2−x (Y/Er) _x Ca _y Ba₂Cu_4+y O _z series, show a strong dependence of T _c on hole concentration (p _sh). In the present work, the results of the analysis of the neutron diffraction measurements at room temprerature on x=0.3 and 0.5 samples are reported. It is interesting to know that Ca substitutes for both La and Ba site with concomitant displacement of La onto Ba site. Superconductivity studies show that maximum T _c is obtained for x=0.5, y=1.0 sample (T _c ∼ 75 K), for La_1.5Dy_0.5Ca₁Ba₂Cu₅O _z (La-2125).     

密度泛函理论研究Scn，Yn和Lan(n=2—10)团簇的稳定性、电子性质和磁性

通过采用密度泛函理论对Sc₂,Y₂和La₂基本性质的计算,选择在较优理论水平下系统地研究了Sc_n, Y_n和La_n(n=2—10)团簇的几何结构、稳定性、电子性质和磁性及其随团簇尺寸的变化趋势.此同族三种团簇的稳定性由原子密堆集几何结构效应决定,幻数均表现出一致的结果.La_n团簇的能隙比 关键词： n')" href="#">Sc_n n和La_n团簇')" href="#">Y_n和La_n团簇 密度泛函理论 电子性质 磁矩     

SimCn （m+n≤7）团簇的密度泛函研究

使用密度泛函理论（DFT）的杂化密度泛函B3LYP方法在6-31G*基组水平上对Si_mC_n（m+n≤7）团簇各种可能的构型进行几何结构优化,预测了各团簇的最稳定结构. 并对最稳定结构的平均结合能（E_b）,二阶能量差分（Δ₂E）和能隙（E_g）等进行了理论研究. 结果表明,随着原子个数的增加,SiC二元团 关键词： mC_n （m+n≤7）团簇')" href="#">Si_mC_n （m+n≤7）团簇 密度泛函理论 结构与性质     

Influence of the sample orientation in Sn<Subscript>2</Subscript>P<Subscript>2</Subscript>S<Subscript>6</Subscript> crystals on the hydrostatic piezoelectric coefficients

The influence of the sample orientation on the effective value of the hydrostatic piezoelectric coefficients d _h ⁽ⁱ⁾ of Sn₂P₂S₆ crystals has been studied. The hydrostatic piezoelectric coefficients d _h ⁽¹⁾ and d′ _h ⁽³⁾ , were measured, d _h ⁽¹⁾ =(244±3) pC/N and d′ _h ⁽³⁾ =(92±1) pC/N. The hydrostatic piezoelectric coefficient d _h ⁽³⁾ for orthogonal axis system was calculated to be d _h ⁽³⁾ =(87±2) pC/N. The, optimal orientation of the sample has been found as (Xy l)−20°-cut. Maximal value of the effective hydrostatic piezoelectric coefficient d _h ⁽¹⁾ equals 260 pC/N. Double rotated samples were also studied. The orientation of the samples insensitive to the pressure has been found. The theoretical mean value of hydrostatic piezoelectric coefficient (d _h ) _mean corresponding to randomly oriented Sn₂P₂S₆ grains in a poled composite has been calculated to be (d _h ) _mean =136 pC/N.     

Synthesis and magnetic properties of Fe100-xMox alloy nanowire arrays

The Fe100-xMox(13≤x≤25) alloy nanowire arrays are synthesized by electrodeposition of Fe 2+ and Mo 2+ with different ionic ratios into the anodic aluminum oxide templates.The crystals of Fe100-xMox alloy nanowires gradually change from polycrystalline phase to amorphous phase with the increase of the Mo content and the nanowires are of amorphous structure when the Mo content reaches 25 at%,which are revealed by the X-ray diffraction and the selected area electron diffraction patterns.As the Mo content increases,the magnetic hysteresis loops of Fe100-xMox alloy nanowires in parallel to the nanowire axis are not rectangular and the slopes of magnetic hysteresis loops increase.Those results indicate that the magnetostatic interactions between nanowires and the magnetocrystalline anisotropy both have significant influences on the magnetization reversal process of the nanowire arrays.     

密度泛函理论研究MgnOn(n=2—8)团簇的结构和电子性质

采用密度泛函理论中的广义梯度近似对Mg_nO_n(n=2—8)团簇的几何构型进行优化,并对能量、频率和电子性质进行了计算.结果表明,当n=2,3时,团簇的最低能量结构是平面结构;当n≥4时, 团簇的最低能量结构可以看成是由Mg₂O₂和Mg₃O₃单元组成的三维结构.O—Mg—O的钝角和较多的电荷转移对团簇的稳定性 关键词： nO_n团簇')" href="#">Mg_nO_n团簇 几何结构 电子性质     

纳米结构CoxFe3-xO4多孔微球的磁性及交换偏置效应研究

用乙二醇为溶剂,用三氯化铁、二氯化钴和醋酸铵为起始反应试剂,通过溶剂热反应首次合成了纳米结构Co_xFe_3-xO₄多孔微球.用X射线衍射仪(XRD)、透射电子显微镜(TEM)和扫描电子显微镜(SEM)表征样品的结构和形貌,结果表明,所制备的单分散Co_xFe_3-xO₄多孔微球为立方多晶结构,其直径约300 nm,是由约30 关键词： xFe_3-xO₄')" href="#">Co_xFe_3-xO₄ 多孔微球 磁性 交换偏置效应     

通过掺杂V和F提高碳包覆的磷酸铁锂锂离子电池的电化学性能

在原位聚合合成方法的基础上,结合两步烧结过程制得LiFe_1-xV_x(PO₄)_(3-y)/₃F_y/C.V和F掺杂对碳包覆的磷酸铁锂材料的结构、形貌和电化学性能有影响.通过XRD、FTIR、SEM、充/放电测试和电化学阻抗谱对材料的结构、形貌和电化学性能进行了表征.结果表明,V和F的掺杂并没有破坏橄榄石结构中的LiFePO₄/C,但可以提高晶体结构的稳定,降低电荷的转移阻抗,提高锂离子扩散速度,改善了LiFePO₄/C材料的循环性能和高倍率性能.     

WnNim(n+m=8)团簇结构与电子性质的理论研究

采用密度泛函理论(DFT)中的B3LYP方法,在Lanl2dz基组水平上对W_nNi_m(n+m=8)团簇的各种可能构型进行了几何参数全优化,得到了它们的基态构型;并对基态构型的平均结合能、Wiberg键级(WBI)、磁学性质、NBO进行了分析,结果表明:团簇随着W原子数的增多,稳定性增强,n≥5时,结构中都含有纯钨团簇的结构基元;W-W键级高于W-Ni键和Ni-Ni键;W₅Ni₃,W₆Ni₂团簇发生了"磁矩猝灭"的现象;在W,Ni原子内部,轨道电荷发生了转移,产生了"轨道杂化"现象,W,Ni原子之间也发生了电荷转移形成了较强的化学键. 关键词： nNi_m(n+m=8)团簇')" href="#">W_nNi_m(n+m=8)团簇 几何结构 电子性质 密度泛函理论     

B位等价掺杂SrBi4Ti4O15铁电材料的性能研究

采用了传统的固相烧结工艺,制备了不同Zr和Hf掺杂量的SrBi₄Ti_4-xZr_xO₁₅（x=000,003, 006,010,020）和SrBi₄Ti_4－xHf_xO₁₅（x=000,0005, 0015,0030,0060）的陶瓷 关键词： 4Ti_4-xZr_xO₁₅')" href="#">SrBi₄Ti_4-xZr_xO₁₅ 4Ti_4－xHf_xO₁₅')" href="#">SrBi₄Ti_4－xHf_xO₁₅ 铁电性能 介电性能     

三明治结构Tan(B3N3H6)n+1 团簇的磁性和量子输运性质

利用密度泛函理论和非平衡格林函数方法, 本文对小尺寸团簇Ta_n(B₃N₃H₆)_n+1 (n ≤ 4)的磁性和量子输运性质进行了系统的研究. 计算结果表明, 此类体系采用三明治结构作为其基态并且具有较高的稳定性. 体系的磁矩随团簇尺寸的增大而线性增大. 当把Ta_n(B₃N₃H₆)_n+1团簇耦合到Au电极上时, 形成的Au-Ta_n(B₃N₃H₆)_n+1-Au体系在有限偏压下展示出了较强的自旋过滤能力, 因而可以被看做是一类新型的低维自旋过滤器.     

密度泛函理论研究Run和RunAu(n=1-12)团簇的结构和电子性质

采用密度泛函理论中的广义梯度近似(GGA) 对 Ru_n Au和Ru_n 团簇的几何构型进行优化,并对能量、频率、电子性质和磁性质进行了计算. 结果表明,Ru_n Au团簇的最低能量结构可以通过Au原子代替Ru_n+1团簇中的Ru原子生长而成.除了局域的结构畸变,Ru_n Au和Ru_n+1团簇具有相似的几何结构.二阶能量差分、电离势、亲和势和分裂能表明Ru₅, Ru₈, Ru₅Au, Ru₈Au 是稳定的团簇,Au的掺杂没有改变Ru_n 的相对稳定性.通过电子性质的分析发现,当Au原子掺杂在Ru_n 中,团簇的化学活性增加,且团簇的能隙主要由电子的配对效应决定;对于大多数团簇来说,Au原子掺杂提高了Ru_n Au的磁矩. 关键词： n Au和Ru_n 团簇')" href="#">Ru_n Au和Ru_n 团簇 几何结构 电子性质