无序二元合金（NixCu1－x）不同解理面上O吸附对Cu偏析的影响

应用计算机编程构造出了存在和不存在表面偏析的无序二元合金Ni_xCu_1-x (x=0.4)(１００)表面及(１１０)表面的原子集团模型，然后按覆盖度θ=0.5，构造 出了O吸附后的原子集团模型，应用Recursion方法计算了O在Ni_xCu_{1-x(存在偏析和不存在偏析时)无序二元合金(１００)和(１１０)表面吸附的电子结构.由此 得出：1)O吸附使合金表面态密度峰降低，带宽加宽，并且表面Ni原子的d电子与吸附质O原 子的s，p电子的共价作用比Cu更强烈；2)O吸附在NixCu1-x(x=0.4) (１１０)表面比(１００)表面更稳定；3)O的吸附抑制了Cu在表面富集，且这种作用主要表 现在表面一层. 关键词： 化学吸附 表面偏析 Recursion方法 态密度}     

无序二元合金（NixCu1-x）表面CO吸附及对表面偏析的影响

根据计算机编程构造出了存在和不存在表面偏析的无序二元合金Ni_xCu_1-x（x=0.4）的原子集团模型，然后按覆盖度θ=0.5，构造出了CO表面吸附的模型 ，应用Recursion方法计算了CO在（Ni_xCu_1-x）（存在偏析和不存在偏析时）合金表面不同位置（顶位和芯位）吸附的电子结构 .由此得出：1)CO在顶位吸附时较稳定；2)CO吸附使合金表面态密度峰降低，带宽加宽，使d轨道的局域性变弱；3)CO的吸附抑制了Cu 关键词： 化学吸附 表面偏析 Recursion方法 态密度     

Co,Zn元素对YBa2Cu3O7-δ的不同的掺杂效应

对单相掺杂样品YBa₂Cu_3-xCo_xO_y (x=0.00,0.025,0.05,0.075,0.10,0.125,0.15,0.20,0.25,O.275,0.30,0.325,0.35,0.375,0.40)和YBa₂Cu_3-xZn_xO_y(x=O.025,0.05,0.075,0.10,0.15,0.20,0.30)作了室温下的 关键词：     

Y1-xCaxBa2Cu3-xMxO7-δ (M=Fe,Ni)体系的超导电性

本文报道,通过对Y_1-xCa_xBa₂Cu_3-xMxO_7-δ(M=Fe,Ni)体系样品的晶体结构、氧含量、正常态电阻率与温度的关系,以及超导转变温度等测量,并与YBa₂Cu_3-xMxO_7-δ(M=Fe,Ni)体系进行比较,发现Y_1-xCa_xBa₂Cu_3-xFe_xO_7-δ体系的T_c显著地高于相应x值的YBa₂Cu_3-xFe_xO_7-δ体系,而Y_1-xCa_xBa₂Cu_3-xNi_xO_7-δ体系则相反,T_c低于仅Ni替代的体系,表明Ca和Fe同时替代时两者引起的载流子浓度(n_H)变化相互补偿,抑制了仅Fe替代时引起的n_H和T_c急剧下降;而作Ca和Ni同时替代时主要的不是两者引起载流子浓度变化的相互补偿,Ca和Ni替代效应之间的关联较弱。作者认为,对Y_1-xCa_xBa₂Cu_3-xFe_xO_7-δ体系属于CuO₂平面外的元素替代,这时载流子浓度是决定Tc的主要因素;而对Y_1-xCa_xBa₂Cu_3-xNi_xO_7-δ体系,由于Ni²⁺离子主要占据Cu(Ⅱ)位,它导致磁拆对效应,Ni²⁺离子的拆对效应是引起T_c下降的直接原因。 关键词：     

杂质对吸附系统O/RhxPt1-x衬底合金(110)表面偏析的影响

构造了考虑吸附与偏析相互作用情况下无序二元合金Rh_xPt_1-x(110)吸附氧表面的原子集团模型,其中O的覆盖度为0.5;构造了考虑杂质Ni,Cu,W对合金可能产生影响的吸附表面原子集团模型,杂质的掺入采用替位式.应用recursion方法计算了合金表面的环境敏感镶嵌能和电子结构.环境敏感镶嵌能计算表明杂质Ni,Ｃu和Ｗ均使O吸附Rh_xPt_1-x(110)合金表面 关键词： 化学吸附 表面偏析 recursion方法 态密度     

AgxCu50-xZr50非晶态合金及其晶化

采用高频熔炼后的真空单辊急冷技术制备了Ag_xCu_50-xZr₅₀金属玻璃,发现在x<12的范围内都可得到完全的非晶态。测量了x=2,4,6和10的Ag_xCu_50-xZr₅₀金属玻璃的玻璃转变温度和晶化温度,并采用Kissinger方法测定了晶化激活能E_a。发现在金属玻璃Ag_xCu_50-xZr_{50关键词：}     

机械合金化Fe100-xCux体系的X射线吸收精细结构研究

利用X射线吸收精细结构(XAFS)方法研究机械合金化制备的Fe_100-xCu_x(x=0,10,20,40,60,70,80,100,x为原子百分比)合金中Fe和Cu原子的局域环境结构.对于Fe_100-xCu_x(x≥40)二元混合物,球磨160h后,Fe原子的近邻配位结构从bcc转变为fcc,但Cu原子的近邻结构保持其fcc不变.与之相反,在Fe₈₀Cu₂₀和Fe₉₀Cu₁₀(x≤20)合金中,Fe原子的近邻配位保持其bcc结构而Cu原子的近邻配位结构从fcc转变为bcc结构.XAFS结果还表明,fcc结构的Fe_100-xCu_x样品中Fe的无序因子σ(0.0099nm)比bcc结构的Fe_100-xCu_x中的σ(0.0081nm)大得多;并且在机械合金化Fe_100-xCu_x(x≥40)样品中Fe原子的σ(0.0099nm)比其Cu原子的σ(0.0089nm)大.这表明机械合金化Fe_100-xCu_x样品中Fe和Cu原子可以有相同的局域结构环境但不是均匀的过饱和固溶体,而是由Fe富集区和Cu富集区组成的合金.我们提出互扩散和诱导相变机理来解释在球磨过程中Fe_100-xCu_x合金产生从bcc到fcc和从fcc到bcc变化的结构相变 关键词： XAFS 100-xCu_x合金')" href="#">Fe_100-xCu_x合金 机械合金化     

铁基非晶合金磁致伸缩的温度效应

本文研究了Fe_80-xCu_xSi₅B₁₅,(Fe_1-xCo_x)₈₂Cu_0.4Si_4.4B_13.2两系列非晶合金的磁致伸缩系数λ₄随温度T的变化关系,温度范围分别为室温至非晶态居里点和室温至晶在居里点。分析了Fe基非晶合金随温度变化所产生的结构变化,并讨论了其磁致伸缩的单离子微观机制。 关键词：     

YBa2Cu3O7-x高温导电性的研究

本文将以YBa₂Cu₃O_7-x的高温实验为基础,分析和讨论了氧对YBa₂Cu₃O_7-x高温导电性的影响以及一维Cu—0链的导电作用。还报道了一种新现象,即在高温下,一旦氮气被换成氧气,YBa₂Cu₃O_7-x就迅速地发生从半导体到金属的结构相变。 关键词：     

FexMn1-x合金在GaAs(001)表面外延的结构和磁性

报道了对于0≤x≤1的Fe_xMn_1-x合金在GaAs(001)表面上分子束外延的结构与磁性的实验结果,当x>0.8时,Fe_xMn_1-x合金以单晶体心立方结构生长;当x<0.35时,则以单晶面心立方结构生长;对于0.35xMn_1-x生长的结构比较复杂,而正是在这一区域中,该合金发生了从铁磁相到反铁磁相的转变. 关键词：     

Structural,magnetic and optical properties of diluted magnetic semiconductor (DMS) phase of Ni modified CuO nanoparticles

Control on the size of copper oxide (CuO) in the nano range is a highly motivating approach to study its multifunctional nature. The present investigation reports a sol-gel derived Ni doped CuO nanoparticles (Cu_1-xNi_xO). Rietveld refinement of the XRD spectra confirms the formation of single monoclinic phase of Cu_1-xNi_xO nanoparticles having crystallite size within the range of 19–21 nm. Raman spectra show the presence of characteristics Raman active modes and vibrational bands in the Cu_1-xNi_xO samples that corroborate the monoclinic phase of the samples as revealed by refinement of XRD data. The estimated band gap of pure CuO is found to be ∼1.43 eV, which decreases with the increase of dopant concentration into CuO matrix. This result is in line with estimated crystallite size. Magnetization curves confirm the weak ferromagnetic nature of Cu_1-xNi_xO nanoparticles which reveal the DMS phase. This weak magnetic nature may be induced in the samples due to the exchange interaction between the localized magnetic d-spins of Ni ions and carriers (holes or electrons) from the valence band of pristine CuO lattice. Replacement of Cu⁺² by Ni⁺² ions into the host CuO lattice induces the magnetization. The quantified value of squareness ratio (S < 0.5) confirms the inter-grain magnetic interactions in the Cu_1-xNi_xO nanoparticles which is also the reason of weak induced magnetization.     

Magnetocaloric effects in Ni-Mn-X based Heusler alloys with X=Ga, Sb, In

The Mn-based Heusler alloys encompass a rich collection of useful materials from highly spin-polarized systems to shape memory alloys to magnetocaloric materials. In this work we have summarized our studies of magnetostructural transitions from paramagnetic austenite to ferromagnetic martesite phases at TMC in Ni₂MnGa-based alloys (Ni₂Mn_0.75Cu_0.25-xCo_xGa, Ni₂Mn_0.70Cu_0.30Ga_0.95Ge_0.05, Ni₂Mn_1-xCu_xGa, Ni_2+xMn_1-xGa, and Ni₂Mn_0.75-xCu_xGa), and martensitic transitions from the ferromagnetic austenite to the martesite state in off-stoichiometric Ni-Mn-(In/Sb) Heusler alloys. The phase transition temperatures and respective magnetic entropy changes (ΔS) depend on composition in these systems and have been determined from magnetization measurements in the temperature interval 5-400 K, and in magnetic fields up to 5 T. It is shown that, depending on the composition and doping scheme the “giant” ΔS=40-60 J/(kgK) (for a field change of 5 T) can be observed in the temperature range (300-360 K) for the Ga-based alloys. The interplay between or coupling of the various transitions in Ni₂Mn(Mn,X) systems with X=Sb and In leads to exchange bias effects, giant magnetoresistance, and both inverse and “normal” magnetocaloric effects.     

On the selective catalytic behaviour of the Cu-NI alloy surface

The selective catalytic behaviour of the Cu_xNi_1?x alloy surface is studied. The concentration dependence of the catalytic activity with respect to chemical reactions involving cracking and non-cracking of C-C bonds is calculated for a simple model for C-C bonds. Surface segregation and local environment effects on chemisorption both calculated from a microscopic electronic theory using tight-binding approximation are taken into account.     

Calculation of chemisorption and absorption induced surface segregation

Using a pair bond type model for the interatomic interactions, we determine surface segregation on clean, H, O and CO covered surfaces of various alloys. Furthermore, we study surface segregation caused by bulk hydrogen absorption. Numerical results are presented for Pd_x Zr_1?x H_y We find, that strong surface segregation may result from chemisorption of O and CO and from absorption of H in the bulk of an alloy.     

A density functional theory study on the adsorption of CO and O2 on Cu-terminated Cu2O （111） surface

The adsorptions of CO and 02 molecules individually on the stoichiometric Cu-terminatcd Cu20 （111） surface are investigated by first-principles calculations on the basis of the density functional theory. The calculated results indicate that the CO molecule preferably coordinates to the Cu2 site through its C atom with an adsorption energy of-1.69 eV, whereas the 02 molecule is most stably adsorbed in a tilt type with one O atom coordinating to the Cu2 site and the other O atom coordinating to the Cul site, and has an adsorption energy of -1.97 eV. From the analysis of density of states, it is observed that Cu 3d transfers electrons to 2π orbital of the CO molecule and the highest occupied 5σ orbital of the CO molecule transfers electrons to the substrate. The sharp band of Cu 4s is delocalized when compared to that before the CO molecule adsorption, and overlaps substantially with bands of the adsorbed CO molecule. There is a broadening of the 2π orbital of the 02 molecule because of its overlapping with the Cu 3d orbital, indicating that strong 3d-2π interactions are involved in the chemisorption of the 02 molecule on the surface.     

Theoretical studies of CO/Ni(100): Geometry,vibrational frequencies and ionization potentials for the on-top site

The chemisorption of CO on the (100) surface of Ni has been studied using an Ni₁₄ cluster and generalized valence bond (GVB) methods. CO is found to bond perpendicular to the Ni surface with optimized NiC and CO bond distances of 1.94 and 1.15 Å, respectively. The calculated NiCO bond strength is 29.7 kcal (experimental values 30–32 kcal). Vibrational frequencies are calculated to be 401 cm^?1 for NiC stretch, 327 cm^?1 for NiCO bend, and 2129 cm^?1 for CO stretch. This decrease of the CO frequency by 71 cm^?1 from the free molecule value is consistent with experiment based on self-consistent calculations of the positive ion states. We propose a new explanation for the loss of one PES peak upon chemisorption.     

Structure and magnetoresistive properties of three-layer thin films of spin-valve type

Three-layer thin films of spin-valve type Co/Сu/Ni_xFe_100-x at x = 20–80 at.% were prepared by electron-beam sputter deposition. The investigated phase state and magnetoresistive properties were done for as-deposited and annealed to 400, 550, and 700 K films. The measurements of field dependences of magnetoresistance were held at different temperatures. It was demonstrated that phase state, crystal structure, and magnetoresistive properties of Co/Сu/Ni_xFe_100-x systems strongly dependent on both Ni_xFe_100-x composition Ni_xFe_100-x and heat treatment conditions.