过渡族金属碳化物在WC-Co硬质合金中的界面偏析与固溶行为

过渡族金属碳化物是最常见的硬质合金微观组织结构与性能调控添加剂,添加剂在硬质合金中赋存状态的研究是WC晶粒生长抑制机理研究的基础,也是硬质合金材料与工艺设计的基础。从基于第一性原理计算的理论研究、基于高分辨透射电镜和原子探针层析法的实验观察分析等2个方面,综述了过渡族金属碳化物在WC/β(钴基固溶体粘结相)相界偏析行为的研究现状。基于过渡族金属碳化物在硬质合金中晶界与相界的偏析行为、在硬质相与粘结相中的固溶行为,讨论了硬质合金中WC晶粒生长机理与晶粒生长抑制机理以及过渡族金属碳化物对硬质合金性能的影响机理,提出了硬质合金材料与工艺设计的建议。     

Stability and vibrational properties of the hydrogen atom for p-type AlN doped with group-Ⅱ:a first-principles study

The stability and local vibrational mode (LVM) of hydrogen related p-type AlN have been studied by first-principles calculations based on density functional theory. The stable and metastable microscopic geometries ofgroup-Ⅱ (Be, Mg, Ca, Sr, Ba)-H complexes have been investigated. The calculated results indicate that BCⅡ is the most stable configuration for isolated interstitial H+ and Be-H complexes, while it is ABN,⊥ for Mg-H, Ca-H, Sr-H and BaH complexes. Moreover, the vibrational frequencies and the values ofk and |α| for the H atom with LVM are calculated. Here, the values of k and |α| are used to describe the parameters of the harmonic and anharmonic contributions, re-spectively. The calculated results indicate that the larger the size of the doped ion is, the shorter the N-H bond length is, and the larger the potential energy, the vibrational frequencies, the values of k and |α| are. This implies that the size of the doped ion has an important influence on the vibrational properties of H.     

Ca原子修饰的g-C3N4增强储氢能力的机理研究

利用第一性原理计算,发现Ca原子修饰的g-C₃N₄（Ca-C₃N₄）具有高的储氢能力。H与Ca-C₃N₄之间增强的吸附能主要归功于H-1s和Ca-1s轨道之间较强的化学吸附以及H-1s和Ca-3d轨道之间的杂化。在外加电场下,Ca与g-C₃N₄之间的极化具有良好的可调特性,这对于H的吸附和释放具有重要的作用。该理论计算结果能够为提高金属原子修饰的g-C₃N₄的储氢能力开辟一条可行之路。     

In-As共掺杂GaSb的第一性原理研究

采用基于密度泛函理论的第一性原理平面波超软赝势法,计算未掺杂,In、As单掺及In-As共掺GaSb的晶格参数、能带结构、态密度和吸收光谱。结果表明:掺杂后GaSb晶格发生畸变,As单掺GaSb的晶格常数增大,带隙减小,导致吸收光谱蓝移;而In单掺和In-As共掺GaSb晶格常数变大,且禁带宽度均减小,致使吸收光谱红移,这也是实验上造成掺杂GaSb热光伏电池吸收光谱扩展的原因。     

Mg单原子替位掺杂β-Ga2O3的电子结构和光学性质计算研究

宽禁带半导体β-Ga2O3因其出色的物理化学性能而备受关注,通过掺杂改善β-Ga2O3性能一直是研究的热点.采用基于密度泛函理论的第一性原理方法,利用广义梯度近似加U对Mg单原子掺杂β-Ga2O3体系的晶体结构、电子结构和光学性质等进行了研究和分析.总能量和结合能的对比显示:单原子替位掺杂β-Ga2O3时,Mg优先替代八面体位的Ga原子形成Mg-Gao体系.电子结构显示,Mg-Gao体系变为间接半导体,带隙变窄为4.672eV;其自旋极化率为100％,呈现半金属特性.作为光学材料,Mg-Gao体系可在紫外、深紫外区域工作,并且折射率、反射率和吸收率有所降低,透射率明显提高.     

紫外非线性光学晶体分子设计

紫外非线性光学晶体对全固态激光器的发展起着举足轻重的作用,对性能优秀的紫外非线性光学晶体的探索是光电功能材料领域的研究热点.如何在种类繁多的晶体材料中高效地搜索并获得结构优化的紫外非线性光学晶体,是当前该领域研究的关键问题.对非线性光学材料构效关系研究的发展历史进行了回顾,重点介绍了阴离子基团理论以及第一性原理方法在新型紫外非线性光学材料探索中的重要应用.材料计算模拟方法不仅能够较准确地预测紫外非线性光学晶体的关键光学参数,并可以定量和直观地分析其与晶体结构特征之间的内在关系.通过将理论模拟与结构搜索、化学合成、粉末倍频效应测试、单晶生长等实验手段紧密结合,建立了快速高效的非线性光学材料分子设计专家系统.具体的科研数据及成果显示,发展和完善这一基于分子工程学基础的专家系统,将能加快非线性光学晶体的研究步伐,提升其自主创新水平.     

甲醛在TiO2表面吸附的第一性原理研究

利用密度泛函理论研究了HCHO分子在TiO2金红石(110)面和锐钛矿(101)面上的吸附,结果表明甲醛在这些面上均能形成稳定的化学吸附与物理吸附。在物理吸附中,分子构型受吸附的影响均十分微弱。而在化学吸附中,甲醛分子明显变形,甲醛分子与表面的2配位O原子(O2C)一起形成双氧甲基(CH2O2)物种。化学吸附导致HCHO分子中的羰基延长14%~17%,表明吸附削弱了分子内原子之间的作用,从而有利于分解。此外,在这两种表面中,金红石(110)面对HCHO较强的吸附显示了其活性比锐钛矿(101)面高。     

First-principles study on transport properties of zigzag graphene nanoribbon with different spin-configurations

The current-voltage (I-V) characteristics and the transmission spectrums of zigzag graphene nanoribbon with different spin-configurations are investigated by using the first-principles calculations. It is shown that the current-voltage curves and the transmission spectrums strongly depend on the spin-configurations of the two sides of the ribbon. For the spin-parallel configuration structure, the curve is linear under lower bias voltage; For the spin-antiparallel configuration structure, there is a strong spin-polarization-dependent transmission which implies the ribbon can be used as a spin filter; while for other spin-configurations structures, the curve has the characteristic of semiconductor. It is found that there is a large magneto-resistance(MR) when the bias voltage is small. The impurity in the central scattering region significantly influences the spin-dependent current and the spin filter efficiency, which may lead the large MR to disappear.     

Ce-C共掺SnO2导电性能和力学性质的第一性原理研究

AgSnO2触头材料由于优异的性能成为代替AgCdO的电接触材料之一,但由于SnO2导电性能较差以及硬度大,会使材料变脆,容易形成裂纹,降低了AgSnO2触头的使用寿命。本文采用基于密度泛函理论的第一性原理方法,研究了稀土元素Ce和C单掺杂以及共掺杂SnO2的导电性能和力学性质的理论计算。通过超晶胞结构优化后的能量计算,得到了超晶胞的晶格常数、掺杂形成能、能带结构、态密度、弹性常数和德拜温度。结果表明：通过掺杂后的带隙值减小,增加了杂化轨道,能够提高SnO2的导电性能以及改善SnO2的脆韧性,从而改善AgSnO2触头的成型和使用寿命。相对于Ce、C单掺杂,Ce-C共掺杂时的电子有效质量减小,并且带隙宽度变窄,Ce-C共掺杂SnO2的导电性能更好,硬度的改善更大。     

First-principles calculations of phase equilibria and transformation dynamics of Fe-based alloys

Theoretical procedures of first-principles calculations of phase stability and phase equilibria are summarized. The present scheme is shown to be able to reproduce the transition temperatures with surprisingly high accuracy for Fe−Pd and Fe−Pt systems. The main emphasis of the present report is placed on the extension of the first-principles calculation to transition dynamics calculations. This is performed by combining the cluster variation method with the phase-field method via a coarse graining operation. The time evolution process of antiphase boundaries associated with L1₀ ordering for Fe−Pd system is demonstrated. This paper was presented at the International Symposium on User Aspects of Phase Diagrams, Materials Solutions Conference and Exposition, Columbus, Ohio, 18–20 October, 2004.