最短轨道凝聚模型的相变

应用重整化群计算最短轨道模型的生长几率分布{P_α,i}及其构型权重C_α(2×2原胞和3×3原胞),从而得出多分形热力学的配分函数Z(q,L),自由能F(q,L),能量E(q,L),比热c(q,L)和广义维数D_q,结果表明该模型在q=q_c≈0处发生相变,即当q < q_c时,生长几率分布{P_α,i}不具有多分形性质。     

AlAs相变及热动力学性质的第一性原理研究

利用基于密度泛函理论的全势能线性糕模轨函法研究了闪锌矿（B3）,NiAs（B8）和岩盐（B1）结构的AlAs的相变、结构性质以及热动力学性质.对B3-B8和B3-B1结构的能量体积曲线做公切线,得到了B3→B8相变压力为5.44 GPa,并预测到B3→B1相变压力为6.46 GPa.同时计算了高压下B8相的结构性质,结果显示当V/V₀≈0.7—1.05时,c/a基本保持恒定（仅有约 0.2%的波动）;当V/V₀≈0.4—0.7,c/a随着V/V₀的减小而近似线性地增大.通过状态方程拟合,得到了AlAs的相对体积V/V₀与压强P的函数关系,B8相的状态方程与实验结果符合很好.最后利用准谐德拜模型得到了AlAs的体弹模量B随压力P的变化关系以及不同压强下热容C_V与温度T的关系. 关键词： 相变 热力学性质 第一性原理     

La1-xSrxFeO3-δ（0≤x≤2/3）的低频内耗研究

对A位掺杂的La_1-xSr_xFeO_3-δ氧化物体系进行了低频内耗测量.研究发现此体系的内耗和模量-温度谱随Sr掺杂量（x）的不同而变化.当Sr含量x=0时,LaFeO_3-δ体系的内耗和模量在测量温度范围内（-150—380℃）没有明显变化;而当x=0.2,0.25,1/3以及0.5时,掺杂样品均观察到一个与正交—三角相变对应的相变型内耗峰P₁,且其峰温随x增加向低温移动.在x=0.25,1/3,0.5,0.6以及2/3的样品中还观察到一个弛豫型特征的内耗峰P₂,此峰伴随着模量的变化,可归于畴壁的运动.进一步分析表明畴壁是受氧空位钉轧的.在x=0.5,0.6以及2/3样品的模量-温度谱上呈现出的模量急剧变化是与三角—立方铁弹性相变有关的. 关键词： 内耗 畴壁 钉扎 铁弹性相变     

α稳定噪声驱动的非对称双稳随机共振现象

以微弱周期信号激励的非对称双稳系统为模型, 以信噪比增益为指标, 首先针对加性和乘性α 稳定噪声共同作用的随机共振现象展开了研究, 然后针对单独加性α 稳定噪声激励的随机共振现象进行了研究, 探究了α 稳定噪声特征指数α 和对称参数β 分别取不同值时, 系统结构参数a, b, 刻画双稳系统非对称性的偏度r以及α 稳定噪声强度放大系数Q或D对非对称双稳系统共振输出的作用规律. 研究结果表明, 无论在加性和乘性α 稳定噪声共同作用下还是在单独加性α 稳定噪声作用下, 通过调节a和b或者r均可诱导随机共振, 实现微弱信号的检测, 且有多个参数区间与之对应, 这些区间不随α 或β 的变化而变化; 在研究噪声诱导的随机共振现象时发现, 调节噪声强度放大系数也可使系统产生随机共振现象, 且达到共振状态时D的区间也不随α 或β 的变化而变化. 这些结论为α 稳定噪声环境下参数诱导随机共振中系统参数以及噪声诱导随机共振中噪声强度的合理选取提供了依据.     

纳米AT13陶瓷喷涂层结合强度的分形维数表征

应用分形维数对微弧等离子喷涂纳米AT13涂层的界面进行研究,结果表明：随喷涂电流的增加,纳米AT13涂层的界面分维不断增大,其结合强度也不断提高;随着氩气压力的增加,纳米AT13涂层的界面分维和结合强度都先增大后减小;界面分维D可用于表征涂层结合强度σ,σ随D的增大而增大,且ln(σ)与D之间呈近似线性关系：ln(σ)=17.6D-26.2. 关键词： 纳米涂层 分形数维 界面 结合强度     

CeO2热力学性质的第一原理研究

使用第一性原理方法结合准谐德拜模型研究压力0~30 GPa,温度0~2 000 K,二氧化铈立方结构的热力学性质,包括常压下平衡体积V、体弹模量B₀、热容c_p和熵S随温度的变化以及不同压强下热容c_p、熵S、德拜温度Θ,体膨胀系数α与温度的关系.常压下计算的热容c_p和熵S随温度的变化与实验数据符合很好.     

关于Zn1-xBexO电子结构和光学性质的研究

采用基于密度泛函理论和平面波赝势技术的CASTEP程序对Zn_1-xBe_xO合金电子结构和光学性质进行了计算.当0≤x≤1,其带隙从0.963 eV变化到7.293 eV.分析了晶格畸变和能带间排斥效应对带隙的影响.当Be含量x=0.125,0.25,0.375,0.5,0.625,0.75时,a/b轴压应变控制着带隙变化;当x=0.875,1时,c轴压应变控制着带隙变化.能带间的p-d排斥影响价带顶变动,Γ_1v与Γ_1c之间排斥影响导带底变动.这些能带间的排斥效应被用来分析Zn_1-xBe_xO带隙变动.另外,也分析了Zn_1-xBe_xO介电函数虚部ε₂. 关键词： 带结构 光学性质 应变 排斥     

Fe的结构与物性及其压力效应的第一性原理计算

采用基于密度泛函理论的平面波赝势方法，计算了Fe的几种不同晶体结构的总能量曲线，对HCP结构下晶体结构参数c/a随压强的变化关系做计算分析. 能量计算精度取为0.01 eV/atom. 计算得出： 1) 零温下Fe从bcc到hcp结构的相变压强约为15 GPa，与实验结果相一致； 2) 压强的升高会导致Fe的磁矩减小，最终破坏Fe的磁性； 3) 压强升高引起hcp晶体结构参数c/a缓慢增大，而在地核压强(135—360 GPa)范围内，c/a取常量约1.59能够满足计算精度的要求. 关键词： 第一性原理计算 压力效应 Fe的结构与物性     

Si在TiAl3中取代行为的第一性原理研究

采用基于密度泛函理论的第一性原理方法,研究了Si原子在TiAl₃中的格点取代行为.通过对不同原子被置换后的c/a值、形成能以及电子态密度的计算和比较,发现Si原子倾向于取代TiAl₃中的Al原子,其取代行为主要由系统的电子结构决定,计算结果与实验相符.为了进一步研究Si原子的取代行为,对Si原子占据的格点以松散或紧凑分布下体系的总能、形成能以及电子态密度进行了计算,结果表明Si原子倾向于取代TiAl₃中松散分布的Al（2）原子.对c/a值的计算表明,随Al（2）格点Si原子浓度的增加,c/a值逐渐增大;而当Si取代Al（1）格点时,c/a值随Si原子浓度的增加而减小.研究表明,Si在TiAl₃中的极限固溶度介于12.5at%—18.75at%之间. 关键词： 密度泛函理论 第一性原理 电子结构 3')" href="#">TiAl₃     

微弧等离子喷涂碳纳米管/纳米Al2O3-TiO2复合涂层的吸波性能研究

将碳纳米管与纳米Al₂O₃-TiO₂陶瓷粉末超声共混制备了碳纳米管/纳米Al₂O₃-TiO₂复合粉末,测试了复合粉末在2—18GHz波段的电磁参数.研究表明：随着碳纳米管质量分数的增加,碳纳米管/纳米Al₂O₃-TiO₂复合粉末的复介电常数和损耗角不断增大.当碳纳米管质量分数和厚度增加时,复合粉末对电磁波的反射率峰值先增加后减小,而谐振频率不断向低频移动.采用微弧等离子喷涂制备了7wt%碳纳米管/纳米Al₂O₃-TiO₂复合吸波涂层,当厚度为1.5mm时,涂层最小反射率为-24.0dB,当厚度为2.0mm时,涂层小于-10dB的频带宽为3.60GHz,当温度为500℃高温时,1.0mm厚的涂层最小高温反射率为-12.2dB,小于-10dB频带宽为2.0GHz.复合涂层的实际厚度D与理论厚度d呈线关系：d=0.898D+0.515. 关键词： 等离子喷涂 碳纳米管 2O₃-TiO₂')" href="#">纳米Al₂O₃-TiO₂ 吸波性能     

Formation and decay kinetics of nickel nitrides resulting from nitrogen ion implantation. The nickel–nitrogen phase diagram

Structural transformations in nickel films exposed to N⁺ ions were investigated through the use of electron diffraction, electron microscopy, Rutherford backscattering (RBS) of He⁺ ions, thermal desorption spectroscopy (TDS).

With an increasing exposure dose, there occurred a smooth transition of the FCC structure of Ni to the HCP phase -Ni₃N with the lattice parameters a=0.266 nm and c=0.430 nm. The completion of the transition was observed once the implanted nitrogen concentration corresponding to the stoichiometric ratio of Ni₃N was attained, this giving evidence for the chemical nature of the structural change observed.

During annealing, structure variations were traced, enabling one to observe the following four nickel nitrides: (1) -Ni₃N with a disordered arrangement of nitrogen atoms (HCP-phase with a=0.266 nm and c=0.430 nm), (2) β-Ni₃N with an ordered arrangement of nitrogen atoms (two hexagonal lattices: one with a=0.266 nm, c=0.430 nm, and the other with a=0.466 nm and c=0.43 nm), (3) Ni₄N having a primitive cubic lattice structure with a=0.377 nm, (4) Ni₈N having the FCC structure with a=0.725 nm.

The results of an investigation have led to building up a phase diagram for the Ni–N system.     

色关联噪声对林木Logistic生长模型的影响

在林木生长Logistic模型中, 引入加性和乘性关联色噪声, 运用统一色噪声近似、刘维方程以及诺维科夫原理, 推导了近似福克-普朗克方程, 分析了相关参数对稳态概率分布函数的影响. 结果表明: 改变乘性色噪声强度D和加性色噪声强度Q均能导致稳态概率分布曲线峰值高度的改变以及峰位置的移动, 对概率密度分布呈现出漂移作用. 但是在D和Q增大的过程中, 稳态概率分布曲线峰位置的移动方向是不同的: D增大时, 峰的位置向左移动; Q增大时, 峰的位置向右移动. 另外, 当λ >0时, 随着|λ|的增大, 稳态概率分布函数峰的位置向右移动, 且峰值的高度变大; 而λ<0时, 随着|λ|的增大, 稳态概率分布函数峰值的高度也变大, 而峰的位置却向左移动. 关键词： 林木生长 Logistic模型 色噪声 稳态概率分布     

Transport in solid oxide porous electrodes: Effect of gas diffusion

We extend our previous treatment of a mixed ionic electronic conductor membrane, consisting of a porous cathode and anode separated by a thin non-porous layer, to the case where mass transport of molecules in the porous electrodes can be the rate-limiting step. The linearized transport equations for the ion-hole pairs in the solid and of the gas molecules in the pores are characterized by the length scales L_P = √L_d(1 − φ)/Sτ_s and L_g = 2L_p√[τ_sφ/τ(1 − φ)][D_gc_g/D_IEc_i] respectively, where L_d = D_IE/K is the length scale that determines the transition from diffusion limited to surface exchange limited transport in the non-porous electrodes, K is the surface exchange coefficient, D_IE and D_g are the diffusion coefficients of the ion-hole pairs and of the molecules, c_i and c_g are the concentrations of the ions and molecules, S is the pore surface area per unit volume, φ the porosity and τ_s and τ the tortuosities of the solid and pore phases respectively. When L_g L_p, which is the case treated previously, the rate-limiting step in the transport is ionic diffusion and surface exchange. Enhancements in oxygen ion current of two orders in magnitude, over non-porous electrodes, are in principle achievable with porous perovskite MIEC having surface area s = 10⁶ cm⁻¹. When L_g L_p the rate-limiting step is mass transport in the pores and the enhancement in ion current is substantially reduced.     

Crumpling transition of self-avoiding tethered membranes caused by screening

A system of D-dimensional self-avoiding tethered membranes embedded in a d-dimensional space is considered for the seni-dilute case. The effect of the screening is taken into account, and the crumpled phase diagram in the (d, D) plane is obtained. For D = 2, membranes are in the swollen crumpled phase. The possobility of a crumpling transition caused by the screening is discussed. The density dependences for some quantities such as the screening length and radius of gyration are obtained from a scaling argument.     

Specific heat and anisotropic superconducting and normal-state magnetization of HoNi2B2C

The magnetization of single-crystal HoNi₂B₂C has been measured as a function of applied field (H) and temperature in order to probe the interplay between superconductivity and magnetism in this complex layered system. The normal-state magnetic susceptibility of HoNi₂B₂C is highly anisotropic with a Curie-Weiss-like temperature dependence for H applied perpendicular to the c-axis and with a much weaker temperature dependence for H applied parallel to the c-axis, indicating that the Ho⁺³ magnetic moments lie predominately in the tetragonal a−b plane below 20 K. High-field magnetization (2000 Oe), low-field magnetization (20 Oe) and zero-field specific heat all give an antiferromagnetic ordering temperature of T_N=5.0 K. Remarkably, in 20 Oe applied field both superconductivity (T_c=8.0 K) and antiferromagnetism (T_N=5.0 K) clearly make themselves manifest in the magnetization data. From these magnetization data a phase diagram in the H−T plane was constructed for both directions of applied field. This phase diagram shows a non-monotonic temperature dependence of H_c2 with a deep minimum at T_N=5 K. The high-field magnetization data for H applied perpendicular to the c-axis also reveal a cascade of three phase transitions for T < 5 K and H < 15 000 Oe, contributing to the rich H versus T phase diagram for HoNi₂B₂C at low temperatures.     

LiAl分子基态、激发态势能曲线和振动能级

利用单双激发多参考组态相互作用方法获得了LiAl分子基态X¹∑⁺及七个激发态a³∏, A¹∏, b³∑⁺, c³∑⁺, B¹∏, C¹∑⁺, d³∏的势能曲线, 通过势能曲线得到各态的平衡核间距R_e, 进而求得绝热激发能和垂直激发能.计算结果表明:c³∑⁺ 电子态是一个不稳定的排斥态, A¹∏态是一个较弱的束缚态, 其余6个电子态均为束缚态; b³∑⁺与 c³∑⁺态之间存在预解离现象; 8个电子态分别解离到两个通道, 即Li(²S)+Al(²P⁰)与Li(²P⁰)+Al(²P⁰). 接着将势能曲线拟合到Murrel-Sorbie解析势能函数形式, 据此获得各态的光谱数据:基态X¹∑⁺的平衡键长为0.2863 nm, 谐振频率为316 cm^-1, 解离能D_e为1.03 eV, 激发态a³∏, A¹∏, b³∑⁺, c³∑⁺, B¹∏, C¹∑⁺, d³∏的垂直激发能依次为0.27, 0.83, 1.18, 1.14, 1.62, 1.81, 2.00 eV; 解离能依次为1.03, 0.82, 0.26, 排斥态, 1.54, 1.10, 0.93 eV, 相应谐振频率 ω_e为339, 237, 394, 排斥态, 429, 192, 178 cm^-1. 通过求解核运动的薛定谔方程找到了J=0时 LiAl分子7个束缚电子态的振动能级和转动惯量. 关键词： LiAl 光谱常数 势能曲线 振动能级     

Magnetic properties of TmFeO3 and TmGa0.13Fe0.87O3 orthoferrites

The magnetization σ_c has been observed to depend strongly on temperature and biasing field in the Γ₄-phase. Two families of σ_c (T) occur corresponding to the poly-domain (H < 200 Oe), and mono-domain (H > 200 Oe) states of the samples. This was proved by observation of domain structures in these samples. In addition to the maximum due to the second-order phase transition Γ₂-Γ₄, we have revealed a maximum in the susceptibility curves _Xc(T) at the high-temperature point of phase transition. The second maximum strongly depends on the biasing field value. Domain structure behaviour in that temperature range, and in various external fields, allowed us to suggest that there exists a relation between this maximum and the shifting processes of domain boundaries, which create a significant susceptibility along the c-axis.     

A path integral approach to electronic friction of a nanometer-sized tip scanning a metal surface

In this work, we study the dissipation mechanism and frictional force of a nanometer-sized tip scanning a metal surface via a path integral approach. The metal, with internal degrees of freedom (c, c^†) and a tip with an internal degree of freedom (d, d^†) couple with one another by means of an exchanged potential, V. Having integrated out all internal degrees of freedom, we obtain the in-out amplitude. Moreover, we calculate the imaginary part of the in-out amplitude and the frictional force. We find the imaginary part of the in-out amplitude to be positive, and correlated to the sliding velocity in most cases. The frictional force is proportional to the sliding velocity for the case where v < 0.01. However, for cases where v > 0.01, the frictional force demonstrates nonlinear dependence on sliding velocity.     

极端条件下锆的动力学稳定性研究

过渡金属Zr具有优良的物理、化学及力学性能, 具有广泛的应用价值. 主要通过新近发展的自洽晶格动力学方法, 充分考虑声子间的相互作用, 成功获得了β-Zr的高温高压声子色散曲线, 预测了β-Zr在相图中能够稳定存在的区域, 进一步比较α-Zr, ω-Zr和β-Zr的自由能, 获得了α-β 及ω-β 相变的相边界, 构建了Zr的参考相图. 同时, 也获得了β-Zr的高温状态方程及热膨胀系数, 能够为构建Zr的全区物态方程提供有益的参考.     

Pressure-induced phase transition in transition metal trifluorides

As a fundamental thermodynamic variable, pressure can alter the bonding patterns and drive phase transitions leading to the creation of new high-pressure phases with exotic properties that are inaccessible at ambient pressure. Using the swarm intelligence structural prediction method, the phase transition of TiF₃, from R—3c to the Pnma phase, was predicted at high pressure, accompanied by the destruction of TiF₆ octahedra and formation of TiF₈ square antiprismatic units. The Pnma phase of TiF₃, formed using the laser-heated diamond-anvil-cell technique was confirmed via high-pressure x-ray diffraction experiments. Furthermore, the in situ electrical measurements indicate that the newly found Pnma phase has a semiconducting character, which is also consistent with the electronic band structure calculations. Finally, it was shown that this pressure-induced phase transition is a general phenomenon in ScF₃, VF₃, CrF₃, and MnF₃, offering valuable insights into the high-pressure phases of transition metal trifluorides.