IrO_2(110)表面弛豫行为与电子结构的第一性原理研究

采用基于密度泛函理论的第一性原理方法对IrO_2(110)表面几何和电子结构进行了计算。结果表明,弛豫后,表层的五配位Ir原子和二配位的氧原子(桥氧)相对于理想表面向体相方向移动,而六配位的Ir原子和三配位的O原子向真空方向弛豫。表面原子弛豫不仅导致表层结构的变化,而且使表层的电子结构发生变化。从表面态密度分布可知,对表面电子结构造成主要影响的是最外三层原子。同时,由构型的(010)平面的电荷密度分布可知相邻层间存在着强烈的Ir-O共价键作用;由于电荷在真空层的消耗和在第一、二原子层间的积累,导致最外原子层间距的减小,相应的Ir-O化学键得到增强。计算得到该IrO_2(110)面的表面能大小为1.434 J·m~(-2)。     

Al(001)、Al(110)、Al(111)面表面能的密度泛函理论计算

用密度泛函理论方法，采用超晶胞模型，计算了Al(001)、Al(110)、Al(111)面的表面能.计算表明，Al(001)面的表面能为0.87 eV，Al(110)面为1.07 eV，Al(111)面为0.76 eV.分析了表面能差异与表面电荷平均面密度的关系，表面原子层和次表面原子层的电荷面密度在s,p轨道上重新分布.表面原子层电荷密度越大，表面能越低.计算结果与已有的实验和计算值比较吻合.      

TiN(111)/DLC界面粘附功和电子结构的第一性原理研究

利用基于密度泛函理论的第一性原理,采用平面波赝势方法,研究了Ti N(111)/DLC界面的粘附功和电子结构,阐明了Ti N过渡层改善金属基体和DLC薄膜结合性能的内在机理。根据Ti N(111)面不同的表面终端(Ti终端和N终端)和界面原子配位类型(顶位、中心位和孔穴位),构建和计算了6种可能的Ti N(111)/DLC界面理论构型。结果表明:当Ti N(111)以Ti原子为终端时,中心位堆垛界面(Ti-center)的粘附功最大;当Ti N以N原子为终端时,顶位堆垛界面(N-top)为最稳定的界面模型,弛豫后的粘附功为8.281J/m2。差分电荷密度、分态密度、Mulliken布居数的计算结果均表明:Ti-center界面Ti原子和C原子形成的Ti-C键包含共价性和离子性;N-top界面处C原子和N原子形成C-N共价键。相比之下,N-top模型更有可能在Ti N/DLC界面中出现。     

铝晶体自由表面的稳定性计算

采用第一原理赝势平面波方法,计算铝晶体学自由表面(100)、(110)和(111)的能量、几何与电子结构.根据表面能计算预测铝自由表而结构的稳定性.结果表明:铝自由表面结构稳定性由强到弱的顺序为(111)、(100)、(110);表面原予驰豫不仅引起表面几何结构的变化,而且使表面层的电子结构与键合特性发生改变;(100)、(110)和(111)表层驰豫分别为3.337%、-6.147%和-2.364%:表面电荷密度不同引起表面能差异,表面原子层和次表面原子层的电荷面密度在S和P轨道上重新分布;表面原子层电荷密度越大,表面能越低.     

锂辉石表面环烷酸吸附行为的量子化学

采用量子化学计算、红外光谱分析研究了环烷酸在锂辉石表面的吸附行为。通过计算表面能选取锂辉石(110)面为最佳解理面,并构建了无虚频的稳定环烷酸分子模型,运用分子动力学模拟得到环烷酸与锂辉石(110)面的最佳吸附构型。对最优吸附构型进行了量子化学计算,研究了其结构、电荷分布、差分电荷密度以及态密度等。结果表明:锂辉石(110)面吸附环烷酸分子后表面原子都向锂辉石内部弛豫,环烷酸吸附后的构型发生明显的变化,其羰基氧原子负电性得到增强,非羰基原子的负电性得到削弱,环烷酸与锂辉石的作用是通过羰基氧原子实现的。环烷酸与锂辉石吸附后,锂辉石(110)面的电子云重新分配,氧原子的电荷云密度增强并向周围区域发散开来,环烷酸整体态密度峰左移且费米能级附近的态密度峰由价带变为导带,体系趋向于稳定存在。红外光谱分析进一步表明:环烷酸在锂辉石表面吸附是物理吸附作用。     

金红石型TiO2(110)表面与Ag相互作用的第一性原理研究

采用第一性原理计算Ag与金红石型TiO2(110)晶面的相互作用。通过计算金红石型TiO2(110)面上2种键桥对Ag原子的吸附能，发现键桥Ti形式与Ag原子结合的吸附能低于键桥O形式的吸附能；通过进一步的电荷布居、单位键长以及电子结构的计算，发现键桥Ti形式的Ti-Ag之间的结合能大于键桥O形式的Ti-Ag之间的结合能，这说明Ag原子更容易与金红石型TiO2(110)面上的键桥Ti上的Ti原子发生反应生成相应的化合物。     

SO_2和H_2O在Cu(100)表面共吸附行为的密度泛函计算(英文)

利用基于密度泛函GGA-r PBE方法的平板模型研究SO2和H2O在面心立方金属Cu(100)表面的共吸附行为。SO2和H2O在Cu(100)表面单分子吸附的计算结果表明,在覆盖度为0.25分子层和0.5分子层的情况,二者均不能以化学键的形式吸附在Cu(100)表面上。针对SO2和H2O在Cu(100)表面的共吸附行为,计算弛豫后的吸附结构、吸附能和电子性质(包括差分电荷密度、价电荷密度、Bader电荷分析和分态密度分析)。结果表明,覆盖度为0.25分子层时,H2O和SO2以化学吸附的形式各自吸附在表面不同Cu原子上;覆盖度为0.5分子层时,H2O分子解离成OH和H,OH吸附在表面Cu原子上,而H与SO2键合后共同远离表面。     

TiC(100)/α-Fe(100)界面稳定性及电子特性的第一性原理研究

采用第一性原理方法,研究了 TiC(100)/Fe(100)界面稳定性和电子特性.建立了 4种不同原子堆垛方式的界面模型,采用界面粘附功、界面能和断裂功评价界面稳定性;采用差分电荷密度、Mulliken布居和态密度分析了电子特性.结果表明:Fe原子位于C原子上方的堆垛模型界面粘附功最大,界面能最小,界面结构最稳定.其界...     

黄铁矿(100)表面性质的密度泛函理论计算及其对浮选的影响

采用密度泛函理论(DFT)平面波赝势方法计算理想黄铁矿(100)表面的结构弛豫、原子的Mulliken布居以及电子结构,并解释黄铁矿体相中电荷分布异常的原因.从浮选角度分析表面结构和性质对黄铁矿浮选行为的影响.结果表明:黄铁矿(100)表面弛豫较小,表面Fe-s相互作用相对于体相增强;表面5配位的铁原子具有较高的活性;表而层铁硫原子的能隙降低;表面层的导电性强于体相的,表面的电化学活性增强.     

金刚石表面镀钛及界面微结构的研究

本文研究了应用真空微蒸发镀方法实现了金刚石表面镀钛.X-射线衍射分析表明:镀钛层物相为TiC和Ti,反应形成的界面结构层次为:金刚石-TiC-Ti.TiC层一般厚度在几百到上千埃,镀Ti层总厚度大约150 nm-200 nm.根据金刚石、TiC和Ti的晶体结构特点,应用结构对应原则,创建了金刚石/TiC/Ti共格界面模型.金刚石和TiC之间的共格界面为:(111)金刚石∥(111)TiC,C原子的周期性对应关系为:6 ×0.252 nm≈5×0.304 nm,C原子错配率为0.526%;金刚石和TiC界面间的C原子形成垂直的键、偏斜的键和桥式三中心键.六方结构α-Ti的和面心立方的TiC之间的共格界面为:(1000)α-Ti∥(111)TiC,形成垂直键,Ti原子错配率为0.66%.     

First-principles study of bulk and (001) surface of TiC

The structural and electronic properties of bulk and (001) plane of TiC were investigated by the first-principles total-energy pseudopotential method based on density functional theory. The calculated bulk properties indicate that bonding nature in TiC is a combination of ionicity, covalency and metallicity, in which the Ti-C covalent bonding is the predominate one. The calculated results of structural relaxation and surface energy for TiC(001) slab indicate that slab with 7 layers shows bulk-like characteristic interiors, and the changes of slab occur on the outmost three layers, which shows that the relaxation only influences the top three layers. Meanwhile, the strong Ti-C covalent bonding can be found in the distribution of charge density on the (110) and (001) planes. Ti-C covalent bonding is enhanced by the charge depletion and accumulation in the vacuum and the interlayer region between top two atomic layers.     

Effects of atomic relaxation and the electronic structure of niobium (100) and (110) surfaces

A comparative analysis of the atomic relaxation and electronic structure of niobium (100) and (110) surfaces has been carried out using the VASP-PAW method. The relaxation-induced changes in interlayer spacings of surface layers demonstrate an oscillating behavior but they substantially differ for the two analyzed surfaces; namely for the (110) surface with the closest atomic packing two outermost surface layers are contracted by 4.3% and the relaxation becomes noticeable for three outer layers, while for the more “open” (100) surface these quantities equal 13.1 and six layers, respectively. An analysis of the layer-by-layer distribution of the densities of states, spatial distribution of the charge density, and densities of states at the Fermi level indicates that the most considerable changes near Fermi level take place for (100) surface.     

Ag表面性质的第一原理计算

采用第一原理赝势平面波方法,计算了Fcc-Ag晶体及其Ag(111)、Ag(110)与Ag(100)自由表面的能量、几何与电子结构.根据表面能的计算,预测了Ag表面的结构稳定性,结果表明密排Ag(111)面结构稳定性最好,低指数奇异面Ag(100)面次之,Ag(110)面的结构稳定性最差.通过对不同表面几何与电子结构的比较,初步分析了其结构稳定性差异的产生原因.表面原子驰豫不仅引起表面几何结构的变化,而且使表面层的电子结构与键合特性发生改变.驰豫后表面层原子的部分价电子跑到了表面层以上的真空区,使表面层原子的电子态密度峰形发生变化,还新形成了表面态,这是表面能产生的主要原因,而Ag(110)表面相对于Ag(111)与Ag(110)表面具有高表面活性的主要原因则源于其表面层原子显著的结构驰豫.     

Elektrochemische Charakterisierung von TiC- und Ti(C,N)-Schichten auf WC/Co-Hartmetallen

Electrochemical characterization of TiC and Ti(C,N) layers on WC/Co hard metals TiC and Ti(C,N)layers deposited on WC/Co hard-metal substrates by Chemical Vapour Deposition (CVD) can be characterized using a combination of electrochemically controlled dissolution and voltammetric signals with respect to stoichiometry (C/N ratio) and depth profile. A regular layer-by-layer dissolution with proportionality between charge and depth as well as with a good etching quality (edges, lateral homogenity) could be realized in sulphuric acid. The influence of the C/N ratio in Ti(C,N) on the electrochemical signal has been investigated with defined powders using the Carbon-Paste-Electrode. These results were used for calibration of the signals at CVD layers.     

Performance Degradation of TiN-and TiC-deposited AISI316 bipolar plates for proton exchange membrane fuel cells

TiN and TiC were deposited on AISI316 bipolar plates for proton exchange membrane fuel cells (PEMFCs) and their effects on the corrosion resistance and overall cell performance were investigated. TiN with a Ti interlayer and TiC with a Ti interlayer were deposited on AISI316 bipolar plates by hollow cathode discharge (HCD) ion plating. The electrochemical behavior of the metallic bipolar plates was examined using a potentiodynamic method, an electrochemical impedance spectroscopy (EIS), and a single cell test. These results revealed that the TiN and TiC coatings considerably improved the corrosion resistance of AISI316. However, the TiN-deposited AISI316 bipolar plates showed a better cell performance than the TiC-deposited AISI316 bipolar plates. The differences in the cell performance stemmed from the differences in the ohmic resistance and charge transfer resistance.     

钛过渡层与硬质合金基体表面结合状况对金刚石薄膜附着力的影响

以WC-6％Co为基体,采用磁控溅射法,在原始试样、酸腐蚀试样以及酸蚀后进行氢等离子体脱碳处理的试样上制备Ti过渡层,然后碳化过渡层为TiC。在热丝化学气相沉积装置中,制备金刚石薄膜。研究三种不同试样上的金刚石薄膜与基体的附着力。结果表明,在原始试样上的金刚石薄膜在冷却过程中自动脱落;在经等离子体处理后的试样上,金刚石薄膜与基体间附着力高于在经酸蚀处理的试样上的金刚石薄膜与基体附着力。造成这种现象的主要原因可能是等离子体脱碳还原处理降低WC晶粒表面能,增强Ti与WC间的结合强度,导致TiC过渡层与WC基体结合强度增加,从而增加金刚石薄膜附着力。     

几种氨基酸类缓蚀剂在铁表面吸附的 第一性原理研究

目的 氨基酸是一类重要的环境友好型金属有机缓蚀剂,研究缓蚀剂分子在金属表面的吸附行为,对深入理解缓蚀机理及设计新型缓蚀剂分子有重要的理论意义.方法 基于第一性原理框架下的原子轨道线性组合方法,采用Dmol3软件研究了甘氨酸、丙氨酸和亮氨酸三种分子在铁表面的吸附行为.首先对铁晶体表面的形貌学参数进行了计算,然后选取合适的晶面作为吸附表面.最后通过计算三种分子在铁表面的吸附能和分波态密度等参数分析缓蚀机制.结果 铁的三种常见晶面中,Fe(110)面为最佳吸附表面.三种氨基酸分子在Fe(110)表面呈竖直型吸附构型,甘氨酸、丙氨酸和亮氨酸的吸附能绝对值大小分别为2.233、2.254、2.472 eV,这与其实验缓蚀效率大小顺序相一致.结论 缓蚀剂分子吸附可导致金属基底的功函数减小.Hirshfeld电荷分析表明,吸附过程中存在从氨基酸分子到Fe(110)表面的电子转移现象.态密度分析表明,氨基酸分子中的活性原子与铁表面原子形成了共价键,键能的大小对缓蚀剂分子的缓蚀效率起决定性作用.     

Microstructural characteristics of PTA-overlayed NbC on pure Ti

This study uses the technique of PTA (plasma transferred arc) to overlay NbC reinforcing particles on the surface of commercially pure Ti in order to investigate the microstructural features of the overlayer and the interface between the overlayer and base metal by changing the overlaying current. The results indicate that the matrix phase of the overlayer was -Ti containing about 10 at.% Nb and 1 at.% C. NbC and precipitated TiC produced by dissolved NbC reacted with Ti dispersed in the matrix. The microstructure of the cross-section of the overlayer (from surface to base metal), which was composed of -Ti, can be separated into three layers: an upper overlayer with TiC, a middle overlayer with TiC and NbC, and a lower overlayer (interfacial layer and heat affected zone, HAZ). Due to solidification beginning at the interface and the effect of dilution, the TiC in the interfacial layer was finer. Owing to faster solidification under low-current conditions, the TiC particles were finer than under high-current conditions. Also, dendritic TiC under a low-current in the upper overlayer was also finer than under a high-current. Meanwhile, TiC precipitate that resulted from heterogeneous nucleation and Gibbs' free energy was also found around NbC. This NbC diffusion layer between TiC and NbC may have been βNb₂C phase.     

激光熔覆原位合成TiC/Ti复合材料试验研究

利用激光熔覆技术，在工业纯钛表面原位合成了TiC／Ti复合材料。结果表明：选择不同的激光熔覆工艺参数，可使碳粉和Ti粉通过原位合成反应在钛表面生成TiC／Ti复合材料熔覆层；激光功率和扫描速率是影响熔覆层质量的主要因素：激光功率越大，形成的增强相颗粒尺寸越大，相应合金元素氧化也越严重；扫描速率越大，Ti与C的作用时间变短，增强相颗粒尺寸越细小，且增强相所占的体积分数也相应减少。用XRD、DES和SEM证明了TiC颗粒的存在，同时发现颗粒分布具有一定的均匀性，原位生成的TiC颗粒主要以等轴状和块状两种形态存在。     

The connection between the electronic structure and the properties of binderless tungsten carbides

Using first principles density functional calculations, we here connect the physical properties of binderless tungsten carbides with the theoretical electronic structure as calculated from density functional theory calculations. We show that electronic structure calculations predict and explain various known phenomena in these systems, an example of how such theoretical studies can be a valuable tool in materials science. For example, changes in the energy of formation from 25% substitution with Mo or Ti is used to explain the differences in intermixing between binderless tungsten carbides using TiC or Mo₂C as γ binder phase. Substitutions with Ti atoms are also predicted to stabilize tungsten carbide in the NaCl-structure. A study of the charge density redistribution after substitution is also made.