First Principles Investigation of Electronic Property and High Pressure Phase Stability of SmN

An investigation of electronic property and high pressure phase stability of SmN has been conducted using first principles calculations based on density functional theory. The electronic properties of SmN show a striking feature of a half metal, the majority-spin electrons are metallic and the minority-spin electrons are semiconducting. It was found that SmN undergoes a pressure-induced phase transition from NaCl-type (B1) to CsCl-type structure (B2) at 117 GPa. The elastic constants of SmN satisfy Born conditions at ambient pressure, indicating that B1 phase of SmN is mechanically stable at 0 GPa. The result of phonon spectra shows that B1 structure is dynamically stable at ambient pressure, which agrees with the conclusion derived from the elastic constants.     

Nb元素影响TiAl金属间化合物键合特征的第一原理计算

采用第一原理方法, 研究了Nb元素对TiAl金属间化合物电子结构及其对Ti, Al和O原子键合作用的影响. 研究结果表明, Nb元素对富Ti和富Al的TiAl金属间化合物体系电子结构及键合作用的影响不同. 对于富Ti的TiAl金属间化合物体系, Nb原子取代Ti晶格位置后, 减小了Ti费米能级处的电子密度, 削弱了Ti原子与O原子间的相互作用; 同时增强了Al原子中s电子和O原子中p电子的相互作用. 而Nb原子对富Al的TiAl金属间化合物体系中Ti/Al与O的相互作用影响较小. 同时, 向TiAl金属间化合物中掺杂Nb元素, 增大了TiO2的生成能垒, 减小了Al2O3的生成能垒, 有利于促进抗氧化膜Al2O3的生成. 因此, 添加合金化元素Nb有利于提高TiAl金属间化合物的抗氧化性能, 这与实验报道相一致.     

分子基磁体Cr[N(CN)2]2电子结构和半金属性的第一性原理研究

The electronic structure and half-metallicity of molecule-based ferromagnet Cr[N(CN)₂]₂ have been investigated using first-principles with generalized gradient approximation. The total energy, spin-polarized electronic band structure, density of states (DOSs) and spin mag-netic moments were all calculated. The calculations reveal that the compound Cr[N(CN)₂]₂ is a really half-metallic ferromagnet with a integral magnetic moment of 2.0000 μB per molecule in the optimized lattice constant. Based on the spin distribution and the DOS, it is found that the total magnetic moment is mainly from the Cr²⁺ with relative small contribution from C and N atoms. The sensitivity of the half-metallicity to small change in lattice constant is also discussed.     

Low-compressibility and hard material carbon nitride imide C2N2(NH): First principles calculations

First principles calculations are performed to investigate the structural, mechanical, and electronic properties of C₂N₂(NH). Our calculated lattice parameters are in good agreement with the experimental data and previous theoretical values. Orthorhombic C₂N₂(NH) phase is found to be mechanically stable at an ambient pressure. Based on the calculated bulk modulus and shear modulus of polycrystalline aggregate, C₂N₂(NH) can be regarded as a potential candidate of ultra-incompressible and hard material. Furthermore, the elastic anisotropy and Debye temperatures are also discussed by investigating the elastic constants and moduli. Density of states and electronic localization function analysis show that the strong C-N covalent bond in CN₄ tetrahedron is the main driving force for the high bulk and shear moduli as well as small Poisson's ratio of C₂N₂(NH).     

基于第一性原理研究铱(111)和(100)表面的原子吸附（英文）

本文利用第一性原理密度泛函理论研究了九种不同的吸附原子在铱(Ir)的(111)和(100)表面上的吸附性质.探讨了Ir表面的功能化,因此吸附能、稳定的结构、态密度和磁矩,这将为进一步研究其在催化和其他表面应用中的可能展现的功能提供重要信息.研究表明,三/四重空位点是Ir(111)/(100)表面最有利的吸附位点.通过对大范围的覆盖率(从0.04到1个单层)的研究,表明吸附原子的吸附能具有很强的覆盖率依赖性.吸附能随着覆盖率的增加而增加,这意味着吸附物之间存在排斥相互作用.吸附原子和衬底电子态之间的强杂化会影响吸附性质,同时吸附原子的磁矩被抑制.通过Bader电荷分析,揭示了吸附原子和衬底之间的大量电荷转移.与(111)表面的结合相比,(100)表面吸附原子的结合更强.     

Elastic, electronic and thermal properties of YSZ from first principles

First principles calculations were performed to investigate the elastic, electronic and thermal properties of 14% cubic yttria-stabilized zirconia (YSZ) using the pseudo potential plane-wave method within the gradient generalized approximation (GGA) for the exchange and correlation potential. Computed lattice constant parameters are in good agreement with the available experimental results. The three independent elastic constants were computed by means of the stress-strain method, indicating that 14% cubic YSZ is a mechanically stable structure. From the knowledge of the elastic constants, a set of related properties, namely bulk, shear modulus, Young’s modulus, sound velocity, Debye temperature, thermal capacity and minimum thermal conductivity are numerically estimated in the frame work of the Voigt-Reuss-Hill approximation for YSZ polycrystalline. The calculated bulk modulus, shear modulus, Young’s modulus, sound velocity, Debye temperature, thermal capacity and minimum thermal conductivity are in reasonable agreement with the available experimental and theory data. Density of states, charge density and Mulliken population analysis show that the 14% cubic YSZ is covalent and possess ionic character.     

计算金属间化合物热力学性质的新方法

用一简单的相关函数式对金属间化合物的热力学性质进行拟合，提出了一种计算金属间化合物热力学性质的新方法，并用此方法计算了二元金属间化合物的常温热容和熵。计算结果表明，该方法简单，且能满足一定的计算精度，有一定的实用价值。     

Predicting H2S Oxidative Dehydrogenation over Graphene Oxides from First Principles

Spin-polarized periodic density functional theory was performed to characterize H₂S adsorption and dissociation on graphene oxides (GO) surface. The comprehensive reaction network of H₂S oxidation with epoxy and hydroxyl groups of GO was discussed. It is shown that the reduction reaction is mainly governed by epoxide ring opening and hydroxyl hydrogenation which is initiated by H transfer from H₂S or its derivatives. Furthermore, the presence of another OH group at the opposite side relative to the adsorbed H₂S activates the oxygen group to facilitate epoxide ring opening and hydroxyl hydrogenation. For H₂S interaction with -O and -OH groups adsorption on each side of graphene, the pathway is a favorable reaction path by the introduction of intermediate states, the predicted energy barriers are 3.2 and 10.4 kcal/mol, respectively, the second H transfer is the rate-determining step in the whole reaction process. In addition, our calculations suggest that both epoxy and hydroxyl groups can enhance the binding of S to the C-C bonds and the effect of hydroxyl group is more local than that of the epoxy.     

Pt基金属间化合物及其在质子交换膜燃料电池阴极氧还原反应中的应用

质子交换膜燃料电池是一种能够将燃料的化学能直接高效地和环境友好地转化为电能的绿色能源技术。质子交换膜燃料电池具有能量转化效率高、启动快速、零排放或者低排放等优点,被认为是后石油时代最为重要的能源替代技术之一。然而目前使用的电催化剂存在铂用量高和稳定性不足等问题。开发高性能低Pt催化剂对于降低质子交换膜燃料电池成本、促进质子交换膜燃料电池的大规模商业化应用具有十分重要的意义。Pt基金属间化合物是一类具有严格元素化学计量比和规整原子排列结构的合金化合物,其氧还原反应催化活性明显优于相应的Pt基无序合金及纯Pt催化剂,被认为是最具应用前景的低Pt催化剂之一。本文着重从催化机理、制备技术、组成调控、颗粒度调控、形貌调控和晶体结构等几个方面介绍了Pt基金属间化合物催化剂近来的研究进展,以及这类催化剂在质子交换膜燃料电池阴极氧还原反应中的应用研究情况,指出了这类催化剂目前尚存在的不足及挑战,并展望了未来的研究发展思路及方向。     

在LiCl-KCl共晶熔体中电化学制备钬镍金属间化合物(英文)

采用循环伏安、方波伏安和开路计时电位等方法研究了Ho(Ⅲ)离子在LiCl-KCl共晶熔体中的电化学行为及Ho-Ni合金化机理。在惰性W电极上,Ho(Ⅲ)离子在-2.06 V(vs Ag/Ag Cl)发生电化学还原,该还原过程为3个电子转移的一步反应。与惰性W电极上的循环伏安相比,Ho(Ⅲ)离子在活性Ni电极的循环伏安曲线上还出现了3对氧化还原峰,是Ho与Ni形成了金属间化合物,导致了Ho(Ⅲ)离子在活性Ni电极发生了欠电位沉积。在不同的电位进行恒电位电解制备的3个不同的Ho-Ni合金,采用X-射线衍射(XRD)和扫描电子显微镜-能谱仪(SEM-EDS)等测试手段进行表征,结果表明:制备的3种合金分别是Ho2Ni17,Ho Ni5和Ho Ni23种合金化合物。     

Structural,electronic and elastic properties of the Laves phases WFe2, MoFe2, WCr2 and MoCr2 from first-principles

A theoretical analysis of the phase stability, electronic and mechanical properties, and Debye temperatures of the C14-type Laves phases (WFe₂, MoFe₂, WCr₂ and MoCr₂) has been presented from density functional theory. The phase stability follows the order: WFe₂>MoFe₂>WCr₂>MoCr₂. An exchange of electrons takes place between Fe and W/Mo atoms, and there is also electron transfer between Cr and W/Mo. The W–W and Mo–Mo bonds are of the valence character, while the Fe–W/Mo and Cr–W/Mo bonds are of ionic character. The bonding force of A–A is greater than that of A–B in C-14 AB₂ type Laves phases (WFe₂, MoFe₂, WCr₂ and MoCr₂). The ductility of MoCr₂ is higher than others. The hardness of WFe₂ (14.1 GPa) is the highest, and the hardness of MoCr₂ is the lowest. The incompressibility for these laves phases along c-axis is larger than that along a-axis. The Debye temperature (θ_D) of MoFe₂ is 619 K, which is the highest in those phases. These laves phases also have high melting points, which follows the order: WFe₂>MoFe₂>WCr₂>MoCr₂.     

The disproportionation reaction phase transition,mechanical, and lattice dynamical properties of the lanthanum dihydrides under high pressure: A first principles study

The pressure-induced disproportionation reaction phase transition, mechanical, and dynamical properties of LaH₂ with fluorite structure under high pressure are investigated by performing first-principles calculations using the projector augmented wave (PAW) method. The phase transition of 2LaH₂ → LaH + LaH₃ obtained from the usual condition of equal enthalpies occurs at the pressure of 10.38 GPa for Perdew–Wang (PW91) functional and 6.05 GPa for Ceperly–Adler (CA) functional, respectively. The result shows that the PW91 functional calculations agree excellently with the experimental finding of 11 GPa of synchrotron radiation (SR) X-ray diffraction (XRD) of Machida et al. and 10 GPa of their PBE functional theoretical result. Three independent single-crystal elastic constants, polycrystalline bulk modulus, shear modulus, Young's modulus, elastic anisotropy, Poisson's ratio, the brittle/ductile characteristics and elastic wave velocities over different directions dependences on pressure are also successfully obtained. Especially, the phonon dispersion curves and corresponding phonon density of states of LaH₂ under high pressure are determined systematically using a linear-response approach to density functional perturbation theory (DFPT). Our results demonstrate that LaH₂ in fluorite phase can be stable energetically up to 10.38 GPa, stabilized mechanically up to 17.98 GPa, and stabilized dynamically up to 29 GPa, so it may remain a metastable phase above 10.38 GPa up to 29 GPa, these calculated results accord with the recent X-Ray diffraction experimental finding and theoretical predictions of Machida et al.     

在LiCl-KCl共晶熔体中电化学制备钬镍金属间化合物

采用循环伏安、方波伏安和开路计时电位等研究了Ho(Ⅲ)离子在LiCl-KCl共晶熔体中的电化学行为及Ho-Ni合金化机理。在惰性W电极上,Ho(Ⅲ)离子在-2.06 V(vs Ag/AgCl)发生电化学还原,该还原过程为3个电子转移的一步反应。与惰性W电极上的循环伏安相比,Ho(Ⅲ)离子在活性Ni电极的循环伏安曲线上还出现了3对氧化还原峰,是Ho与Ni形成了金属间化合物,导致了Ho(Ⅲ)离子在活性Ni电极发生了欠电位沉积。在不同的电位进行恒电位电解制备的3个不同的Ho-Ni合金,采用X-射线衍射(XRD)和扫描电子显微镜-能谱仪(SEM-EDS)等测试手段进行表征,结果表明:制备的3种合金分别是Ho₂Ni₁₇,HoNi₅ 和 HoNi₂ 3种合金化合物。     

Properties of Bulk In-Pt Intermetallic Compounds in Methanol Steam Reforming

Heterogeneous catalysts are often complex materials containing different compounds. While this can lead to highly beneficial interfaces, it is difficult to identify the role of single components. In methanol steam reforming (MSR), the interplay between intermetallic compounds, supporting oxides and redox reactions leads to highly active and CO₂-selective materials. Herein, the intrinsic catalytic properties of unsupported In₃Pt₂, In₂Pt, and In₇Pt₃ as model systems for Pt/In₂O₃-based catalytic materials in MSR are addressed. In₂Pt was identified as the essential compound responsible for the reported excellent CO₂-selectivity of 99.5 % at 300 °C in supported systems, showing a CO₂-selectivity above 99 % even at 400 °C. Additionally, the partial oxidation of In₇Pt₃ revealed that too much In₂O₃ is detrimental for the catalytic properties. The study highlights the crucial role of intermetallic In−Pt compounds in Pt/In₂O₃ materials with excellent CO₂-selectivity.     

Corrosion-Free EMF Measurements of Zinc-Based Intermetallic Compounds at Ambient Temperature

Material development requires in many cases information about the necessary stability of the materials against oxidation, which is encoded in the chemical activity of the constituting elements. Determination of the chemical activity is tedious, especially for metallic materials at or close to ambient temperature. To determine the chemical activity of Zn at ambient temperature, electromotive force (EMF) measurements on the intermetallic compounds ZnPd, ZnPt and Cu₅Zn₈ within their respective homogeneity range were conducted. The single-phase nature of the samples was confirmed by powder X-ray diffraction, light microscopy as well as SEM/EDX analysis. To exclude oxidation, and therefore faulty determination of the electrochemical potentials, a method was developed to conduct the electrochemical measurements under non-corrosive conditions in inert atmosphere. Corrosion by the electrolyte was avoided using anhydrous dimethylformamide as aprotic solvent. From the EMF the respective intrinsic activities of zinc in the corresponding intermetallic compounds was determined. Measurements on Cu₅Zn₈ and comparison to available data in literature verified the developed method allowing to retrieve thermodynamic data of ZnPd and ZnPt for the first time at ambient temperature. The herein developed and easy-to-use methodology is applicable to a wide range of metallic material by choosing appropriate compositions of the electrolyte and has the potential to boost material development.     

第一性原理研究LuAlO3中掺杂Ce3+的4f-5d跃迁性质

We have investigated properties of the compound LuAlO₃:Ce³⁺ associated with the Ce³⁺ 4f-5d transition by using the periodic density functional theory. A hybrid functional has been used for the 4f states and a constrained approach has been employed for the excited 5d state. It is found that the average distance between Ce³⁺ and the eight nearest-neighbor O atoms decrease by 0.05 ?on going from 4f to 5d state. The calculated Stokes shift is in good agreement with experiment. Based on the optimized structure around Ce³⁺, the energy level scheme of the 5d states has been evaluated using the angular overlap model, in reasonable agreement with experiment.     

Phase Formation and Kinetics of Electrochemical Intercalation of Lithium into Intermetallic Compounds MgCd and MgCd3

Electrochemical intercalation of lithium into intermetallic compounds (IMC) MgCd and MgCd₃ out of propylene carbonate solutions of LiBF₄ is studied. According to chronopotentiometry data, during the intercalation, lithium forms compounds with cadmium: Li₃Cd on MgCd or LiCd and Li₃Cd on MgCd₃. Reactions of solid-phase substitution, which occur on the electrodes, are accompanied by the destruction of initial IMC and generation of magnesium atoms. Chronoamperometry of MgCd–(Li) and MgCd₃–(Li) shows the lithium intercalation to be limited by nonstationary diffusion of lithium in the solid phase. The lithium diffusion in MgCd is slower and that in MgCd₃is faster than in Cd. The calculated potential dependences of the diffusion coefficient for lithium in MgCd and MgCd₃ are linear in semilogarithmic coordinates.     

单质Si晶格稳定性的第一原理研究

采用SGTE纯单质数据库中Gibbs能的表达式, 结合JANAF热力学数据, 采用最小二乘法对SGTE纯单质数据库中元素Si的Gibbs能表达式进行了重新评估, 得到了比SGTE数据库更精确的结果; 同时, 将SGTE数据库中CALPHAD方法得到的晶格稳定参数外推至0 K, 与第一原理总能赝势平面波和投影缀加波方法的结果进行了对比, 发现第一原理总能赝势平面波方法得到的晶格稳定参数结果为 ＞ ＞ ＞0, 与CALPHAD方法外推结果一致. 同时, 研究发现: 第一原理总能平面波赝势方法计算的diamond-Si的晶格常数和原子体积比实验值大, fcc-, hcp-和bcc-Si的结果比第一原理投影缀加波方法的小, 总能绝对值出现了类似的结果; 四种结构中所有的价态电子密度分布到0至－15 eV区间, 部分s态电子转化为p态电子, 其中diamond-Si的转化数目最多, 结构最稳定, 这与电子态密度的计算结果一致.     

The First Principles Investigations of the Thermoelectric Properties of GaN with p- and n-Type Doping

We investigate the thermoelectric properties of GaN with p-and n-type doping by the first principles calculation and the semi-classical Boltzmann theory. We find that the power factors (S2σof p-type GaN (-3500 W/mK2) is about twice that of the n-type (-1750 W/mK2), which indicates the thermoelectric properties of p-type GaN would be better. Thermal conductivity of GaN crystal decreases rapidly as the temperature increases, but it is still too large for thermoelectric applications. The figure of merit (ZT) estimated at 1500 K is 0.134 for p-type GaN crystal and 0.062 for the n-type.     

非平衡凝固法制备金属间化合物SbSn的表面结构

锡-锑系统的研究由于其重要的的理论意义和应用价值而受到重视，但是各个相图之间并不是完全一致的。大部分对于金属间化合物SbSn的研究集中在平衡态，对于金属间化合物SbSn的结构研究尚存在着一些不同的看法，对于锡锑的相图和金属间化合物SbSn的晶体结构还需要进一步的研究。