Li_(2/3)H_(1/3)IO_3多晶的离子电导

文献[1]报道了在 LiIO3-HIO3 体系中存在一个新的化合物2LiIO3·HIO3(Li_(2/3_H_(1/3)IO_3).它与a-LiIO3晶格常数的差异引起了晶格畸变.通过电导的研究,可以揭示离子传导对结构参量的敏感特性,井对这种材料作为固体电解质应用作出估价.本文还研究了文献[2—4]报道的Li_(1-x)Mg_     

CdSexS1-x电子学结构及光学性质的第一性原理研究

CdSe是Ⅱ-Ⅵ族中重要的半导体材料,一定条件下可与CdS形成无限固溶体CdSexS1-x(0≤x≤1)。CdSexS1-x在薄膜太阳电池及光电器件等领域具有重要的应用,对CdSexS1-x的电子学结构和光学性质进行研究有助于进一步提高其在光电器件等方面的应用。基于第一性原理,采用平面波超软赝势方法,计算了CdSexS1-x的电子学结构及光学性质,并将计算结果与实验进行了对比。结果表明,CdSexS1-x的晶格常数随着Se组分的增加呈线性增大趋势,态密度向低能级方向移动,禁带宽度减小,光吸收边发生一定程度的蓝移。当Se含量为0.5时,CdSexS1-x的光折射、反射和能量损失最大。除了Se和S的比例为1∶1时CdSexS1-x所属晶系为三斜晶系,其他比例下均为立方晶系。理论计算结果与实验符合。     

Cd_xZn_(1-x)O合金热力学性质的第一性原理研究

ZnO的能带工程是当前ZnO研究的热点之一通过等价阳离子如Cd,Be,Mg等部分取代Zn形成CdZnO,BeZnO,MgZnO等合金来调控ZnO带隙的研究己广泛开展.其中,Cd的掺杂可以减小ZnO的禁带宽度,使CdZnO合金在紫外一可见光波段光电器件中具有潜在的应用价值.本文利用第一性原理计算结合集团展开法,通过研究纤锌矿(WZ)和岩盐矿(RS)型Cd_xZn_(1-x)O合金不同Cd掺杂含量下各种构型的形成能,发现了纤锌矿结构的两种亚稳相Cd_(1/3)Zn_(2/3)O,Cd_(2/3)Zn_(1/3)O;对其晶格常数·键长·键角和电子结构的分析表明,随着Cd掺杂量的增大,晶格常数a,c均逐渐增大,而c/a值逐渐减小,O—Zn(Cd)—O键角及合金禁带宽度均逐渐减小.通过对Cd_xZn_(1-x)O合金的有效集团交互系数的分析得出,两个原子组成的集团中其有效集团交互系数最大,表明两原子集团对用集团展开法计算的形成能贡献最大.通过比较第一性原理计算的形成能和集团展开法拟合计算得到的形成能,发现两者相差很小,表明采用集团展开法拟合计算Cd_xZn_(1-x)O合金的形成能准确、可靠,通过对大量Cd_xZn_(1-x)O合金的形成能分析发现,大部分Cd_xZn_(1-x)O的形成能比同组分的ZnO与CdO混合相的能量高,表明ZnO和CdO互溶时会形成固溶度间隙,低温下难以实现全组分固溶.在此基础上,我们计算了WZ-和RS-Cd_xZn_(1-x)O随机合金的形成能并得到了相图.对于纤锌矿结构,其临界温度为1000 K;对于岩盐矿结构,其临界温度为2250 K.更高的临界温度表明Cd_xZn_(1-x)O难以形成岩盐矿结构的合金.进一步计算获得WZ-和RS-Cd_xZn_(1-x)O的两相相图,发现Cd较易固溶于WZ-ZnO中,而Zn较难固溶于RS-CdO中.     

金属间化合物RMn_2Ge_2(R=La,Pr,Nd,Sm,Gd,Tb和Y)中的自发磁相变及相变时的磁弹性异常

在 10— 80 0K的温度范围内用X射线衍射方法测量了RMn2 Ge2 (R =La ,Pr,Nd ,Sm ,Gd ,Tb和Y)的晶格常数与温度的变化关系 .在各种类型的自发磁相变观察到晶格常数的磁弹性异常现象 .实验得出 ,自发磁相变时的磁弹性异常主要由Mn次晶格引起 ,并且Mn Mn交换相互作用能不仅与晶格常数a有关 ,而且与晶格常数c有关 .用Kittle的交换反转模型讨论了低温时的铁磁—反铁磁一阶相变 .     

ZrH_2结构与热力学性质

基于密度泛函理论,采用全势线性缀加平面波加局域轨道方法和广义梯度近似研究了ZrH2的结构与弹性性质。结果表明:在基态条件下,ZrH2的晶格常数计算值与实验值及其它理论值相当吻合。在考虑声子作用的前提下,采用准谐德拜模型成功获得了不同条件下(0~50 GPa,0~1 300 K)ZrH2的热容、热膨胀系数和德拜温度等热力学性质。结果表明:定压热容预测值随温度升高而增大,并逐渐接近佩蒂特-杜隆极限;随压强增加,德拜温度呈增加趋势;随温度增加,德拜温度呈减小趋势;在压强一定的条件下,热膨胀系数随温度的升高而增大,且在高温高压条件下,热膨胀系数的增加趋势变缓。     

Ti_3(Ge_(1-x)Si_x)C_2固溶体力学和热力学性能的第一性原理研究

采用基于密度泛函理论(DFT)的第一性原理平面波超软赝势方法,系统研究了Ti_3(Ge_(1-x)Si_x)C_2(x=0, 0.5, 1)固溶体的晶体结构、弹性性质以及热力学性能.研究结果表明,Ti_3(Ge_(1-x)Si_x)C_2体系均具有力学和热力学稳定结构,并且为脆性材料;Ti_3(Ge_(1-x)Si_x)C_2固溶体的力学性能随Si含量的增加而提高;Ti_3(Ge_(1-x)Si_x)C_2固溶体在室温下具有稳定的晶格结构和较高的晶格热导率,有望用于一些需要良好散热性能电子元器件的封装材料.     

固溶体Fe_(2-x)Yb_xMo_3O_(12)的相变、吸水性及热膨胀性能

采用固相烧结法,以Yb2O3、MoO3、Fe3O4为原料制备了Fe2-x Ybx Mo3O12(x=0,0.2,0.4,0.6,0.8,1,1.2,1.4,1.6,1.8,2)系列固溶体,并通过X射线衍射图样、Raman光谱、热分析以及膨胀系数测试对其结构、相变、吸水性及热膨胀性能进行了研究。结果表明Fe2-x Ybx Mo3O12当x≤0.4时是单斜相,当x≥0.6时是正交相,随着x值的增加Fe2-x Ybx Mo3O12材料的相变温度逐渐降低。Fe2-x Ybx Mo3O12含有的水分子可以分为两类,一类吸附在晶体表面对晶格振动没有影响,第二类进入晶体内部对晶格振动产生较大影响,导致负膨胀性质的消失,只有完全失去水分子后才表现负热膨胀性能。     

用热分解法气相外延生长GaAs_(1—x)P_x生长实验

采用有机金属化合物热分解方法进行GaAs_(1-x)Px气相生长的实验,比过去歧化反应法(不均等化反应法)在重复性和批量生产上都更有前途。用三甲基镓、Ca(CH_3)_3、三氢化砷AsH_3和三氢化磷PH_3的混合气体做原料,通过高频感应加热,使GaAs_(1-x)Px混晶(x=0～1.0)在GaAs(100)衬底上外延生长,发现在600～900℃的生长温度之间存在着对应混晶比x的最佳生长温度。调节三甲基镓的供给速度,就能控制这种混晶的生长速度。混晶比x可根据气相中的气体组成随意进行控制。确定了生长层晶格常数和x的关系,大致上遵循Vegard定律。发现生长速度随着x的增加急剧减小,并研究了生长层的结晶性能和电学性质。从这些热分解法的基本结果可以得出用三甲基镓外延生长GaAs_1—xPx将有可能付诸实用。     

金属间化合物RMn2Ge2(R=La,Pr,Nd,Sm,Gd,Tb和Y)中的自发磁相变 及相变时的磁弹性异常

在10—800K的温度范围内用X射线衍射方法测量了RMn₂Ge₂(R=La,Pr ,Nd,Sm,Gd,Tb和Y)的晶格常数与温度的变化关系.在各种类型的自发磁相变观察到晶格常数 的磁弹性异常现象.实验得出,自发磁相变时的磁弹性异常主要由Mn次晶格引起,并且Mn-Mn 交换相互作用能不仅与晶格常数a有关,而且与晶格常数c有关.用Kittle的交换反转模型讨 论了低温时的铁磁—反铁磁一阶相变. 关键词： 稀土金属间化合物 磁相变 磁弹性     

Al_xIn_(1-x)As电子结构和光学性质的第一性原理研究

基于密度泛函理论,对各组分Al_xIn_(1-x)As(x为0～1)的晶体结构,电子结构和光学性质进行了第一性原理计算.结果显示,随Al组分x增加,Al_xIn_(1-x)As晶体各键长将缩短,键角发生变化,晶胞体积也将减小,晶格常数的变化符合Vegard定律.另外,随着Al组分x的增加,Al_xIn_(1-x)As的禁带宽度变宽,且能带有从直接带隙结构转变为间接带隙结构的趋势.具有较高In组分的Al_xIn_(1-x)As晶体在可见光区域中的光吸收能力更强,光谱响应范围更大.     

Perovskite-like system (Sr,La)(Fe,Ga)O3−δ: structure and ionic transport under oxidizing conditions

The maximum solid solubility of gallium in the perovskite-type La_1−xSr_xFe_1−yGa_yO_3−δ (x=0.40–0.80; y=0–0.60) was found to vary in the approximate range y=0.25–0.45, decreasing when x increases. Crystal lattice of the perovskite phases, formed in atmospheric air, was studied by X-ray diffraction (XRD) and neutron diffraction and identified as cubic. Doping with Ga results in increasing unit cell volume, while the thermal expansion and total conductivity of (La,Sr)(Fe,Ga)O_3−δ in air decrease with gallium additions. The average thermal expansion coefficients (TECs) are in the range (11.7–16.0)×10⁻⁶ K⁻¹ at 300–800 K and (19.3–26.7)×10⁻⁶ K⁻¹ at 800–1100 K. At oxygen partial pressures close to atmospheric air, the oxygen permeation fluxes through La_1−xSr_xFe_1−yGa_yO_3−δ (x=0.7–0.8; y=0.2–0.4) membranes are determined by the bulk ambipolar conductivity; the limiting effect of the oxygen surface exchange was found negligible. Decreasing strontium and gallium concentrations leads to a greater role of the exchange processes. As for many other perovskite systems, the oxygen ionic conductivity of La_1−xSr_xFe_1−yGa_yO_3−δ increases with strontium content up to x=0.70 and decreases on further doping, probably due to association of oxygen vacancies. Incorporation of moderate amounts of gallium into the B sublattice results in increasing structural disorder, higher ionic conductivity at temperatures below 1170 K, and lower activation energy for the ionic transport.     

Molecular dynamics simulation of P-V-T relationship of ZnO with rock-salt structure using pair-wise interactions

Molecular dynamics (MD) method is used to investigate the behavior of the pressure-volume-temperature (P-V-T) relationship, lattice constant and thermal expansivity for ZnO with rock-salt structure at high pressures and temperatures. The interionic potential is taken to be the sum of pair-wise additive Coulomb, van der Waals attraction, and repulsive interactions. The isothermal and isobaric properties are discussed from the corresponding P-V-T relationship, and it is shown that the MD simulation is successful in reproducing the measured volumes of ZnO over a wide range of temperature and pressure. Meanwhile, the equations of state parameters including lattice constant, linear thermal expansion coefficient, and isothermal bulk modulus are calculated and compared with the available experimental data and the latest theoretical results. At an extended pressure and temperature range, P-V-T relationship, lattice constant, and linear thermal expansion coefficient have been predicted. The structural and thermodynamic properties of ZnO with rock-salt structure are summarized in the pressure 0-100 GPa ranges and the temperature up to 3100 K.     

Magnetic and Magneto-optical properties of Heusler alloys of the type Ni3-xMnxSn

The crystallographic, magnetic and magneto-optical properties of Heusler compounds of the type Ni_3-xMn_xSn were investigated. The thermal expansion behaviour of a limited number of these compounds was also studied. The cubic L2₁ structure was found to exist in the range 0.6 x 2.2. With increasing x the saturation moment first increases, then decreases again. The main peak in the Kerr rotation spectra measured in the energy range 0.5-4.5 eV shows a similar trend. The Curie temperature and the lattice constant increase with x, both quantities showing a discontinuity near x = 1. All these features are discussed in terms of relative site occupancies of the Mn atoms at the tetrahedral and octahedral sites in the L2₁ structure.     

Ln1−xSrxCoO3(Ln = Sm, Dy) for the electrode of solid oxide fuel cells

The perovskite-type oxides were synthesized in the series of Ln_1−xSr_xCoO₃(Ln = Sm, Dy). The formation of solid solutions in Dy_{1 − x}Sr_xCoO₃ was limited, compared with that in Sm_{1 − x}Sr_xCoO₃. The electrical conductivities of the sintered samples were measured as a function of x in the temperature range 30 to 1000 °C. The highest conductivity of around 500 S/cm at 1000 °C was found in Sm_0.7Sr_0.3CoO₃. The reactivity of all the samples with YSZ was examined at 800–1000 °C for 96 h. The Sr-doped perovskite oxides were more reactive with YSZ and produced SrZrO₃ at 900 °C after 96 h. However, no reaction product between SmCoO₃ and YSZ was observed at 1000 °C for 96 h. The cathodic polarization of the oxide electrodes, sputtered on yttria stabilized zirconia (YSZ), was studied at 800–1000 °C in air. SmCoO₃ shows no degradation of the electrode performance at higher temperatures. The thermal expansion measurements on the sintered samples were carried out from room temperature to 1000 °C. Large thermal expansion coefficients were found in these samples.     

Magnetic properties of Gd2(Fe1−x−yCoyTix)17

Serial single-phase Gd₂(Fe_1−x−yCo_yTi_x)₁₇ compounds have been synthesized. These compounds have a crystal structure belonging to rhombohedral lattice with space group. The lattice parameters of compounds decrease with cobalt content and increase with titanium content, respectively. The saturation magnetization decreases with increasing cobalt and titanium contents. The anisotropy fields increase to maximum then decrease with cobalt concentration. The magnetocrystalline anisotropy constants increase with cobalt content from negative to positive maximum and then decrease with Co concentration. The saturation moment of the compounds decreases linearly with cobalt concentration and decreases nonlinearly with titanium concentration.     

Oxygen permeability of La2Cu(Co)O4+δ solid solutions

Formation of the La₂Cu_1−xCo_xO_4+δ solid solutions with orthorhombic K₂NiF₄-type structure was found to be in the range of 0≤x≤0.30 at temperatures above 1270 K. Incorporating cobalt into the copper sublattice of lanthanum cuprate leads to increasing oxygen hyperstoichiometry and decreasing electrical conductivity. Thermal expansion coefficients of the La₂Cu_1−xCo_xO_4+δ (x=0.02–0.30) ceramics at 470–1100 K were calculated from the dilatometric data to vary in the range (12.2–13.2)×10⁻⁶ K⁻¹. Studying the dependence of oxygen permeation fluxes through La₂Cu(Co)O_4+δ on the membrane thickness demonstrated that the oxygen transport at the thickness values below 1 mm is limited by both surface exchange rate and bulk ionic conductivity. Oxygen permeability of the La₂Cu_1−xCo_xO_4+δ solid solutions was ascertained to increase with cobalt concentration at x=0.02–0.10 and to decrease with further dopant additions, indicating a participation of interstitial oxygen in the ionic transport.     

Crystal structure, electrical and magnetic properties of La1 − xSrxCoO3 − y

The crystal structure and properties of La_{1 − x}Sr_xCoO_{3 − y} with strontium contents ranging from x = 0.1 to x = 0.7 have been studied. The lattice parameters were measured as a function of temperature (4.2–400 K) and the crystal structure was found to change from rhombohedral (at low temperatures and values of x) to cubic. While LaCoO₃ is paramagnetic the oxides in the composition range 0.2 < x < 0.6 are soft ferromagnets. The strontium additions are compensated by the formation of Co⁴⁺ (cobalt ions with one positive effective charge, Co_Co^.) and oxygen vacancies (V_o^..). From the results it is concluded that the relative importance of oxygen vacancies increases with increasing temperature and decreasing oxygen activity. As a result the concentration of electronic charge carriers — and the resultant electrical conductivity — decrease with increasing temperature. The defect structure is discussed and it is concluded that defect associations — probably between oxygen vacancies and strontium ions — and formation of microdomains of perovskite-related phases are important aspects of the overall structure of these perovskite phases.     

Elasticity of a magnetic lattice near the magnetic critical point

The isothermal elastic constants and the coefficient of anomalous thermal expansion of a magnetic lattice are discussed. The spin system is described by the Ising model with an exchange coupling depending on lattice spacing. A behavior of the elastic constants and the coefficient of thermal expansion is found which is in qualitative agreement with experiments. The isothermal compressibility remains positive nearT _c and no thermo-mechanical instability occurs (which would lead to a first-order phase transitions), in contrast to earlier theories.     

Influence of magnetization on lattice constants of 3d transition metal alloys

A simple relation is found in 3d transitional metal alloys between the lattice constant and the magnetization, which can be described with an equation: a(x) = a₀^A· (1 − x) + a₀^B. x + C μ(x). It is proposed that studies of lattice constants at high temperatures may serve as an experimental method to detect the existence of localized moments above T_c. The anomalous thermal expansion of the Invar alloy is explained as a result of the collapse of localized moments above T_c.     

Thermal expansivity and bulk modulus of ZnO with NaCl-type cubic structure at high pressures and temperatures

The thermal expansivity and bulk modulus of ZnO with NaCl-type cubic structure were estimated by using the constant temperature and pressure molecular dynamics technique with effective pair potentials which consist of the Coulomb, dispersion, and repulsion interaction at high pressures and temperatures. It is shown that the calculated thermodynamic parameters including linear thermal expansion coefficient, isothermal bulk modulus and its pressure derivative are in good agreement with the available experimental data and the latest theoretical results. At an extended pressure and temperature ranges, linear thermal expansion coefficient and isothermal bulk modus have also been predicted. The thermodynamic properties of ZnO with NaCl-type cubic structure are summarized in the pressure 0–150 GPa ranges and the temperature up to 3000 K.