氢、氧原子刻蚀CVD金刚石涂层石墨相的机理研究

采用第一性原理分子模拟计算方法对氢、氧原子刻蚀石墨相的过程进行分子动力学仿真，分析了2种原子在石墨相上的吸附过程及刻蚀反应的反应热和反应能垒。结果表明:氧原子在石墨相表面的吸附能强于氢原子吸附能，同时氧原子的化学反应活性大于氢原子的，更容易在石墨结构表面发生电子转移反应；氢原子促使石墨相表面的C—C键断裂需要两步反应，而氧原子则只需要一步反应，氢原子刻蚀石墨相的反应能垒比氧原子的高，所需能量更多。同时，通入含氧气源可以有效降低CVD金刚石涂层的沉积温度，提高金刚石涂层的质量。      

Thermodynamic assessment of the cesium–oxygen system by coupling density functional theory and CALPHAD approaches

The thermodynamic properties of cesium oxides were calculated by combining ab initio calculations at 0 K and a quasi-harmonic statistical thermodynamic model to determine the temperature dependency of the thermodynamic properties. In a second approach, the CALPHAD method was used to derive a model describing the Gibbs energy for all the cesium oxide compounds and the liquid phase of the cesium–oxygen system. For this approach, available experimental data in the literature was reviewed and it was concluded that only experimental thermodynamic data for Cs₂O are reliable. All these data together with the thermodynamic data calculated by combining ab initio and the statistical model were used to assess the Gibbs energy of all the phases of the cesium–oxygen system. A consistent thermodynamic model was obtained. The variation of the relative stability of the different oxides is discussed using structural and bond data for the oxides investigated by ab initio calculations. This work suggests that the melting point for Cs₂O₂ reported in the literature (863 K) is probably overestimated and should be re-measured.     

SiO_2基质中包埋纳米晶Si光电性质的模拟计算

采用第一性原理方法,研究了SiO2基质中包埋纳米晶Si的电子结构及光学性质。结果表明:位于约1.7eV的吸收峰是–0.59eV能级上的电子向由价键畸变产生的1.2eV能级跃迁的结果。纳米Si粒中含不饱和键的Si原子的p轨道对可见光区光的吸收有主要的贡献。同时由于这些缺陷引入的能级使价带、导带在Fermi面发生交叠而表现出导电性。     

高熵合金电解水电极的研究进展

开发合适的催化材料,制备出高性能、大规模、低成本的催化电极,可减少电解水过程的能量消耗、提升制氢效率。高熵合金由于具有高催化活性,在催化电极应用方面受到广泛关注。综述了应用于电解水过程中析氢反应和析氧反应的高熵合金催化电极的研究进展。首先简述了电解水制氢的工业背景和电化学原理;分析了高熵合金催化活性的来源,即杂化能带结构带来的更为合理的表面吸附能和更多的表面活性位点,以及其特有的高熵效应与“鸡尾酒”效应对整体催化活性的影响;接着讨论了高熵合金的成分设计理念,即通过非贵金属元素的替代来降低成本,同时通过改变合金化元素含量提高高熵合金的内禀活性、增加表面活性位点数量;介绍了第一性原理计算在高熵合金催化机理研究、催化表面吸附能调控、合金成分高通量筛选中的应用;总结了高熵合金平板、多孔、负载纳米颗粒催化电极制备的工艺特点,以及其中的问题与挑战;最后对未来高熵合金电催化电极的发展前景和研究方向进行了展望。     

金属间化合物Mg_2Pb的电子结构和弹性性质

运用第一性原理方法计算了金属间化合物Mg_2Pb的电子结构以及弹性性质,并用Voigt-Reuss-Hill方法计算得到Mg_2Pb的弹性模量和切变模量.结果表明:Mg和Pb对态密度的贡献主要是Mg的2p轨道和Pb的5d轨道,其次为Mg的3s轨道和Pb的6p轨道,Pb的6s轨道贡献最小;在Mg原子周围有大量的电荷存在,呈典型的金属键特征,Mg、Pb之间存在共用的电荷,有较强的离域性,以共价键形式存在,但交界电荷的畸变不大,故共价键所占比例较少,金属键所占比例较大,Mg_2Pb化合物呈半金属性;Mg_2Pb的弹性模量和切变模量分别为68.6和27.9 GPa,Pugh经验判据和泊松比均表明Mg_2Pb具有脆性.     

Ignition-proof mechanism of magnesium alloy added with rare earth La from first-principle study

The surface segregation of La and its effect on the oxygen adsorption on a Mg(0001)surface for a coverageΘ=0.25 monolayer were performed by using first-principles calculations.The calculated results showed that La atoms preferred occupying surface sites to the bulk sites,which suggested the La surface segregation.When oxygen atoms adsorbed on a pure or La alloyed Mg(0001)surface,certain amount of heat would release,and La alloying made the heat released less,which might increase the ignition point of Mg alloy.Both Mg and La had strong atomic affinity with oxygen,so the oxidation film of Mg-La alloys consisted of MgO,La2O3.The denser La2O3 turned oxide film into fine and close structure,and prevented oxygen from passing through the oxidation film.The La-O covalent bonding could explain why La2O3 was compact,and resulted in good ignition-proof of Mg-La alloys.     

Crystal structures and elastic properties of Ti(Cu,Pt)2 and Ti(Cu,Pt)3 phases

This paper focused on the crystal structures of two new ternary phases, Ti(Cu,Pt)₂ and Ti(Cu,Pt)₃, which were studied by X-ray powder diffraction data using Rietveld method. Electron probe microanalysis was used for sample composition examination. Elastic properties of these phases were further measured by nano-indentation, and meanwhile calculated with first-principle (FP) calculations. It is found that the crystal structure of Ti(Cu,Pt)₂ is of orthorhombic cell space group Amm2 (No. 38) with structural prototype of VAu₂. The resolved structure of Ti(Cu,Pt)₃ is of tetragonal AlPt₃ type, belonging to the space group P4/mmm (No. 123). The nano-indentation measurement and FP calculations show that the elastic modulus of Ti(Cu,Pt)₂ increases firstly then decreases with Pt content, whereas that of Ti(Cu,Pt)₃ almost linearly increases with Pt content.     

反应合成法制备Ag/SnO2复合材料中的反应路线

采用反应合成法制备Ag/SnO2复合材料,并从电子-原子层次详细阐述反应中合金中间化合物向富集区转变、寻找过渡态最后生成稳定相的过程。结果表明：Sn的活化性能高于Ag,氧源的参与对反应过程起主导作用,且初始反应混合物中分解游离态的O是氧化反应能持续、彻底进行的另一个重要途径,最后预测出完整的反应路径     

Al掺杂MgO保护层对二次电子发射系数的影响

采用基于密度泛函理论的第一性原理赝势法，研究了Al掺杂对于MgO保护层电子结构的影响。采用Hagstrum’s 理论计算了在不同放电气体环境下，不同Al掺杂比例的Mg1-xAlxO的能带结构和态密度分布，分别获得了基于俄歇中和和俄歇退激理论的二次电子发射系数。结果表明，Al掺杂MgO能有效提高二次电子发射系数，且在氦气环境下二次电子发射系数的提高尤为显著。当Al掺杂比例为0.375时，在氦气环境下基于俄歇中和和俄歇退激理论的二次电子发射系数最大，分别为0.419 1和0.431 6(纯MgO为0.354 3、0.406 0)。     

First-principle investigation on electronic structures and elastic properties of Al-doped MoSi2

The electronic structures and elastic properties of Al-doped MoSi₂ were calculated using the plane wave pseudo-potential method based on the density functional theory, in which the generalized-gradient approximation (GGA) was used to describe the exchange-correlation potential. Starting from the elastic constants, bulk modulus, shear modulus, elastic modulus and Poisson ratio of Al-doped MoSi₂ were obtained by using the Hill method. The results indicate that conductivity of Al-doped MoSi₂ is improved to some extent in comparison with that of pure MoSi₂ due to the orbit hybridization of Mo 4d, Al 3p and Si 3p electrons. In addition, calculations show that the elastic modulus and the brittleness of Al-doped MoSi₂ are smaller than those of pure MoSi₂, which implies that it is feasible to toughen MoSi₂ by doping Al. The agreement of the conclusion with experiment shows that the present theory is reasonable.