半休氏勒合金LiMgAs结构和热力学性质的第一性原理计算

本文利用基于密度泛函理论的第一原理方法研究了Half-Heusler合金LiMgAs的结构性质以及热力学性质.所计算的晶格常数、弹性模量以及弹性模量对压强的导数均与实验及其他理论值相吻合.本文还计算了α、β和γ三种相的LiMgAs声子频率,发现没有虚频的α-LiMgAs热力学结构稳定,其他两相均有虚频,不稳定.本文通过准谐德拜模型,研究并获得了不同温度0～1500 K和不同压强0～70 GPa下的热膨胀系数、热容、熵、德拜温度和Grüneisen参数.我们发现,热膨胀系数、热容、熵和Grüneisen参数随温度的增加而增加,随压强的增加而减小;而温度和压强对德拜温度和弹性模量的影响和对上面其他物理量的影响恰好相反.另外,当温度高于1000 K时,热容值变化很小,遵循Dulong-Petit定律.     

Ge50Sn50有序合金压力下电子性质的计算机模拟

使用第一性原理和赝势方法研究了Ge50Sn50有序合金直到9GPa压力下的能带结构和带隙的压力依赖性。发现该合金的直接带隙随着压力的增大几乎是线性增加，在4．7GPa时达到最大值0．72eV：在该压力下发生直接带隙至间接带隙的转变，其导带在4．7GPa～8GPa时与Ge类似，在高于6．8GPa压力时与Si类似。同时还研究了自旋轨道耦合作用对合金能带结构的影响。     

Precipitation of ordered α2 phase in a near-α titanium alloy with duplex microstructure

The precipitation of ordered α2 phase in a near-α Ti-6.3A1-4.8Sn-2.0Zr-1.0Mo-0.34Si-0.9Nd (mass fraction) alloy with duplexmicrostructure, during aging at various temperatures, was investigated. It is concluded that the precipitation and growth of the α2 phasecan be controlled by suitable selection of the aging temperature. Aging at higher temperatures can result in the uniform precipitation andgrowth of α2 ordered phase in αp whereas the α2 ordered phase precipitated only at the lamella boundaries and dislocations in βt. Aging ata moderate temperature can promote the tendency of uniform precipitation of α2 phase in both αp and βt-Aging at a relatively low tem-perature is suitable for the uniform precipitation and growth of fine α2 particles throughout both the αp and βt matrix.     

First-principles exploration of the stabilization mechanism of long-period stacking ordered structures in high performance Al alloys

Long-period stacking ordered(LPSO) structures, like 9 R, 12 R, 15 R and 18 R phases etc., play a key role in improving the mechanical properties of Al alloys. In the present study the Gaussian-Like distribution(GLD)model was utilized to investigate the effects of solute atoms(Cu, Fe, Ga, Ge, Li, Mg, Sc, Si, Sn, Sr, Ti, Y, Zn) on these phase stabilizations in Al alloys by first-principles calculations. The interaction energies between solute atoms and these phases were strictly calculated. The results suggested that the solute segregations showed different characteristics in these phase structures, and solute atoms(Ga, Ge, Si, Sn, Sr, Y) tended to segregate to the stacking fault(SF) planes of them, and Sr atom was the easiest to promote the stabilization of 15 R phase compared to other structures. High solute concentrations promoted the stabilizations of these phases, while high temperature inhibited their stabilizations. In the light of the degrees of reducing the intrinsic stacking fault energies(ISFEs), the solute atoms can be ranked by:(a) For 9 R and 12 R phases, Sr Y Sn Sc;(b) For15 R and 18 R phases, Sr Y Sc Sn. Thus, it may be concluded that Sr and Y atoms are hopeful to become the underlying candidates for exploring and exploiting high-performance Al alloys with LPSO structures.     

Au-Ag合金纳米管填充碳纳米管特性的第一性原理研究

基于密度泛函理论框架下的第一性原理计算,研究了Au-Ag合金纳米管同轴填充不同线径锯齿型(n, 0)碳纳米管所形成复合系统的稳定性、电子特性和力学性能.结果表明,内、外管间距约为4.20?的Au_xAg_(4-x)@(15, 0)复合系统为具有较大填充率的最稳定结构.能带结构分析表明,相对于自由Au-Ag合金纳米管复合系统的量子电导有所增加,电子态密度分析表明复合系统中的传导电子主要来源于内部Au原子和Ag原子的s电子以及外部C原子的p电子.相对于自由金属纳米管而言,碳纳米管的包裹使得金属纳米管的轴向拉伸临界应变和理想强度大大增加,有效地提高了其力学性能.     

First-principles calculations to study the optical/electronic properties of 2D VS2 with Z doping (Z = N,P, As,F, Cl and Br)

Monolayer VS₂ is expected to be an encouraging candidate for optoelectronic devices owing to its excellent optical/electrical performance. In this paper, first-principles calculations were conducted to figure out the optical/electrical performance of 2D VS₂ doped with Z doping (Z ?= ?N, P, As, F, Cl and Br). The results show that there was a downward trend in formation energies when the doping element ranged from left to right and from bottom to top in the periodictable of elements. VS₂ became more conductive with N, P and As doping, and transited from the semiconducting to metallic state with F, Cl and Br doping. For the optical properties, N, P, As and Br doping reduced the reflectivity of pristine VS₂ in the near-infrared region (0.6 eV–1.6 ?eV). Moreover, P, F, Cl and Br-doping reduced the migration energy barrier of Li atoms in VS₂, which may help to design the rechargeable Li ion batteries with high rate capability.     

ZnO中若干p型杂质与氢相互作用行为的理论研究

本文综述了我们对ZnO中几种重要的p型受主杂质与H原子相互作用行为的理论研究结果.我们的研究表明,ZnO中H原子可以通过不同的路径迁移到受主杂质（N,Li和Ag）附近,形成稳定的NO-H,LiZn-H和AgZn-H复合体.我们进一步发现在这些复合体形成的过成中,H原子所需克服的能量势垒几乎不超过0.5eV,但NO-H,LiZn-H和AgZn-H复合体的离解所需要的激活能却分别为1.25-1.48eV,1.10-1.35eV,1.10-1.30eV.这表明ZnO中H原子和p型受主杂质形成的复合体在室温下能稳定存在.此外,我们也介绍了这些复合体的电子结构和振动性质.     

硬质合金高压喷嘴毛坯压制模具耐磨性的研究

研究了硬质合金（YG14）和45钢渗硼层、硼铬共渗层的耐磨性。在此基础上，进行了模具寿命对比试验，确定了合理的模具选材和表面强化工艺。