Doping effects on the stacking fault energies of the γ’ phase in Ni-based superalloys

The doping effects on the stacking fault energies(SFEs),including the superlattice intrinsic stacking fault and superlattice extrinsic stacking fault,were studied by first principles calculation of the/phase in the Ni-based superalloys.The formation energy results show that the main alloying elements in Ni-based superalloys,such as Re,Cr,Mo,Ta,and W,prefer to occupy the Al-site in Ni3 AI,Co shows a weak tendency to occupy the Ni-site,and Ru shows a weak tendency to occupy the Al-site.The SFE results show that Co and Ru could decrease the SFEs when added to fault planes,while other main elements increase SFEs.The double-packed superlattice intrinsic stacking fault energies are lower than superlattice extrinsic stacking fault energies when elements(except Co) occupy an Al-site.Furthermore,the SFEs show a symmetrical distribution with the location of the elements in the ternary model.A detailed electronic structure analysis of the Ru effects shows that SFEs correlated with not only the symmetry reduction of the charge accumulation but also the changes in structural energy.     

贵金属掺杂锐钛矿TiO2光催化性能的第一性原理研究

本研究采用基于密度泛函理论的第一性原理方法,对纯锐钛矿TiO2及贵金属（Ru、Pd、Pt、Ag和Au）掺杂锐钛矿TiO2的晶格结构、能带结构、电子态密度及光学性质进行了计算。结果表明：贵金属掺杂后TiO2的晶格体积都出现了不同程度的增大;Pd和Pt掺杂后TiO2体系的禁带宽度减小,Ru、Ag和Au掺杂后体系表现出了一定的金属属性,五种贵金属掺杂TiO2后吸收光谱都有红移的趋势。掺杂形成能计算表明,除Ru金属外,富氧条件下掺杂更容易实现。     

3d过渡金属在NiAl中的占位及对键合性质的影响

通过赝势平面波方法系统地研究了3d过渡金属元素在B2-NiAl中的占位以及对键合性质的影响.通过形成能得出Sc,Ti,V 和Zn元素优先取代NiAl中的Al位,而Cr,Mn,Fe,Co和Cu优先取代Ni位.通过分析晶格常数变化量、电荷聚居数、交叠聚居数以及价电荷密度分布, 讨论了晶格畸变和键合性质的变化.结果表明: 取代Al的Sc,Ti,V和Zn元素掺杂使NiAl中晶格发生畸变,这对NiAl键合性质的变化起着重要作用,这些掺杂元素与第一近邻Ni原子产生强烈的排斥作用,形成反键,同时它们之间发生较大的电荷转 关键词： NiAl金属间化合物 3d过渡金属 第一性原理 键合性质     

Density functional theory calculation of platinum surface segregation energy in Pt3Ni (111) surface doped with a third transition metal

We have used density functional theory method to calculate the Pt surface segregation energy in the Pt₃Ni (111) surface doped with a third transition metal M and thus investigated the influence of component M on the extent of Pt segregation to the outermost layer of these Pt₃Ni/M (111) surface. As a third component in the Pt₃Ni/M (111) surface, V, Fe, Co, Mo, Tc, Ru, W, Re, Os, and Ir were predicted to lead to even more negative Pt surface segregation energies than that in the based Pt₃Ni (111) surface; Ti, Cr, Mn, Cu, Zr, Nb, Rh, Hf, and Ta would still retain the preference of Pt segregation to the surface but with less extent than the replaced Ni, while Pd, Ag, and Au would completely suppress the Pt segregation to the Pt₃Ni/M (111) surfaces. Furthermore, we examined the relation between the Pt surface segregation energy in the Pt₃Ni/M (111) surfaces and the material properties (lattice parameter, heat of solution, and Pt surface segregation energy) of binary alloys Pt₃M. It was found that the surface energy effect, strain effect, and heat of solution effect induced by the doped element M would collectively affect the Pt surface segregation energy in the Pt₃Ni/M (111) surfaces.     

过渡金属原子掺杂的锯齿型磷烯纳米带的磁电子学特性

利用基于密度泛函理论的第一性原理方法,研究了掺杂铁、钴和镍原子的锯齿型磷烯纳米带(ZPNR)的磁电子学特性.研究表明,掺杂和未掺杂ZPNR的结构都是稳定的.当处于非磁态时,未掺杂和掺杂钴原子的ZPNR为半导体,而掺杂铁或者镍原子的ZPNR为金属.自旋极化计算表明,未掺杂和掺杂钴原子的ZPNR无磁性,而掺杂铁或者镍原子的...     

Effect of hydrogenation vs. re-heating on intrinsic magnetization of Co doped In2O3

Influence of Co doping for In in In₂O₃ matrix has been investigated to study the effect on magnetic vs. electronic properties. Rietveld refinement of X-ray diffraction patterns confirmed formation of single phase cubic bixbyite structure without any parasitic phase. Photoelectron spectroscopy and refinement results further revealed that dopant Co²⁺ ions are well incorporated at the In³⁺ sites in In₂O₃ lattice and also ruled out formation of cluster in the doped samples. Magnetization measurements infer that pure In₂O₃ is diamagnetic and turns to weak ferromagnetic upon Co doping. Hydrogenation further induces a huge ferromagnetism at 300 K that vanishes upon re-heating. Experimental findings confirm the induced ferromagnetism to be intrinsic, and the magnetic moments to be associated with the point defects (oxygen vacancies V_o) or bound magnetic polarons around the dopant ions.     

合金化元素Ru和Re在Ni3Al中的相互作用及其对力学性质的影响

采用基于密度泛函理论和广义梯度近似的第一原理方法,探究了Ru元素和Re元素在Ni₃Al中的相互作用及其对力学性质的影响.计算表明：在绝大多数化学计量比范围内,Ru原子优先占据Ni₃Al中的Ni位,Re原子优先占据Ni₃Al中的Al位,Ru和Re易于聚集分布,占据近邻的Ni-Al原子对.通过差分电荷密度图和态密度图分析得到Ru和Re掺杂会与近邻Ni原子产生轨道相互作用,Ru和Re之间也会产生轨道相互作用.通过计算弹性模量,应用经验判据得到Ru的加入使得Ni₃Al材料抗压缩能力和韧性明显增强,但硬度有所降低.而Ru、Re的同时加入使其抗压缩能力、韧性和硬度都有所增强.     

镁离子电池正极材料VS_4掺杂改性的第一性原理研究

阳离子掺杂能够有效提高材料的电化学性能,而对掺杂材料结构和电化学性质的研究能从理论上解释产生这种变化的原因.本文采用基于密度泛函理论的第一性原理方法,研究了过渡族金属掺杂的镁离子电池正极材料TM_(0.125)V_(0.875)S_4(TM=Mo、Fe、Co、Ni)的几何和电子结构变化,计算结果显示:通过采用范德华力修正的GGA+vdw-DF方法,获得了和实验结果相一致的晶格常数.阳离子掺杂后,a轴和b轴晶格常数减小,而c轴晶格常数增大.电子态密度分析表明离子掺杂能够有效降低带隙,提高材料的电子电导率.通过对镁离子扩散进行微动弹性带(NEB)计算,发现Fe掺杂能够有效降低扩散能垒,提高材料的离子迁移率.     

Effects of alloying elements on the electronic structure and ductility of NiAl compounds investigated by X-ray absorption fine structure

The Ni L_3,2-edge spectra of the pure Ni, pure NiAl and alloying-element-doped NiAl compounds were obtained by synchrotron radiation X-ray absorption fine structure (XAFS). Due to orbital hybridization effect, directional covalent-type bonds formed and decreased the ductility during forming NiAl. Combining the XAFS spectra analysis and electronegativity comparison, the effects of alloying elements on the electronic structure and then the ductility of the NiAl compounds were obtained. The results showed that Cr, Co, Mo, Ru and W doping could be beneficial to the ductility by both weakening the directional bonds along the <111> direction and enhancing the d–d interactions of the transition metals–Ni atom pair, namely by the transition from covalent bonds to metallic bonds which was beneficial for dislocation to migrate. The results agreed well with the available experimental data and other theoretical results, proving that the model linking the electronic structure and ductility is reliable and can be used as guidance for alloy design.     

过渡金属元素X(X=Mn,Fe,Co,Ni)掺杂对ZnO基阻变存储器性能的影响

实验表明掺杂是一种改善阻变存储器性能的有效手段,但其物理机理鲜有研究.本文采用第一性原理方法系统研究了过渡金属元素X(X=Mn,Fe,Co,Ni)掺杂对ZnO基阻变存储器中氧空位迁移势垒和形成能的影响.计算结果表明Ni掺杂可同时有效降低+1和+2价氧空位在掺杂原子附近的迁移势垒,X掺杂均减小了氧空位的形成能,特别是掺杂Ni时氧空位的形成能减小最为显著(比未掺杂时减少了64%).基于该结果制备了未掺杂和Ni掺杂ZnO阻变存储器,研究表明通过掺杂控制体系中氧空位的迁移势垒和形成能,可以有效改善器件的初始化过程、操作电压、保持性等阻变性能.研究结果有助于理解探究影响阻变的微观机制,并可为掺杂提高阻变存储器性能提供一定的理论指导.     

Mechanism of dc conduction in polyaniline doped with sulfuric acid

A temperature variation of dc conductivity in the range 77–300 K has been carried out in order to explore the mechanism of charge transport in polyaniline (PAN) doped with sulfuric acid. The variable range hopping (VRH) exponent changes as the transition of the PAN lattice takes place in a narrow pH range thereby indicating that the charge transport is crucially composition dependent. A decrease in activation energy has been observed as the doping level is increased. Spin concentration of charge carriers determined by electron spin resonance spectroscopy has also been found to depend on the doping level of the specimen. Polarons and bipolarons formed during the doping process are the charge carriers in this system. The temperature dependence of dc conductivity and activation energy data are indicative of existence of both VRH and mixed conduction for various doping levels in these samples.     

过渡金属原子掺杂对单层MoS_2磁性的影响

本文利用基于密度泛函理论的第一性原理平面波赝势方法分别计算了本征及过渡金属掺杂单层MoS_2的晶格参数、电子结构和磁性性质.计算结果显示,过渡金属掺杂所引起的晶格畸变与杂质原子的共价半径有联系,但并不完全取决于共价半径的大小.分析电子结构可以看到,VIIB、VIII和IB族杂质中除Ag和Re外的掺杂体系都对外显示磁性,磁矩主要集中在掺杂的过渡金属原子上.掺杂体系的禁带区域都出现了数目不等的杂质能级,这些杂质能级主要由杂质的d、S的3p和Mo的4d轨道组成.     

Atomistic modeling of ternary additions to NiTi and quaternary additions to Ni–Ti–Pd,Ni–Ti–Pt and Ni–Ti–Hf shape memory alloys

The behavior of ternary and quaternary additions to NiTi shape memory alloys is investigated using a quantum approximate method for the energetics. Ternary additions X to NiTi and quaternary additions to Ni–Ti–Pd, Ni–Ti–Pt, and Ni–Ti–Hf alloys, for X=Au, Pt, Ir, Os, Re, W, Ta,Ag, Pd, Rh, Ru, Tc, Mo, Nb, Zr, Zn, Cu, Co, Fe, Mn, V, Sc, Si, Al and Mg are considered. Bulk properties such as lattice parameter, energy of formation, and bulk modulus of the B2 alloys are studied for variations due to the presence of one or two simultaneous additives.     

First principles studies on the electronic structures of LiMxFe1-xPO4 （M = Co, Ni and Rh）

The local crystal structures and electronic structures of LiMxFe1-xPO4 （M = Co, Ni, Rh） are studied through first-principles calculations. The lattice constants and unit cell volumes are smaller for the Co and Ni doped materials than for pure LiFePO4, while larger than for the Rh doped material. The local structures around M atoms in the doped materials are studied in details. The total density of states （DOS） and atomic projected DOS （PDOS） are all calculated and analysed in detail. The results give a reasonable prediction to the improvement of electronic conductivity through Fe-site doping in LiFePO4 material.     

Undersize solute element effects on defect structure development in copper under electron irradiation

We conducted systematic experiments of defect structure development in Cu base binary alloys under 1000 kV electron irradiation at temperatures higher than 300 K, using in situ observations with high voltage electron microscopy. This report describes the effects of undersize elements: Co (–3.78%), Ni (–8.45%) and Be (–26.45%). The volume size factors are given in parentheses. The amounts of the respective elements were 2, 0.3, 0.05 at.%, or less. In Cu–Ni and Cu–Co and in the reference Cu, temperature dependence of the number density of interstitial-type dislocation loops had a down peak (i.e. loops hardly formed) at approximately 373 K, attributed to unexpected impurity atoms. Above the down-peak temperature, the addition of Co or Ni increased the loop number density through continuous nucleation of loops, extended the loop formation to higher temperatures, and decreased the apparent activation energy of loop growth rate. The addition of Be for 0.3 at.% or more delayed loop formation after formation of stacking fault tetrahedra (SFTs) around 300 K. The apparent mobility of self-interstitial atoms is expected to be smaller than that of vacancies because of strong binding with Be. Loop formation at temperatures higher than 373 K was enhanced by Be for 0.3 or 2 at.%, although it was suppressed greatly for 0.05 at.% or less. All undersize atoms increased the stability of SFTs under irradiation. Mechanisms of those effects were discussed and were briefly compared with earlier results found for oversize elements in Cu.     

Linking surface stress to surface structure: measurement of atomic strain in a surface alloy using scanning tunneling microscopy

Annealed submonolayer CoAg/Ru(0001) films form an alloy with a structure that contains droplets of Ag surrounded by Co [G. E. Thayer, V. Ozolins, A. K. Schmid, N. C. Bartelt, M. Asta, J. J. Hoyt, S. Chiang, and R. Q. Hwang, Phys. Rev. Lett. 86, 660 (2001)]. To understand how surface stress contributes to the formation of this structure, we use scanning tunneling microscopy to extract atomic displacements at the boundaries between regions of Co and Ag. Comparing our measurements to Frenkel-Kontorova model calculations, we show how stress due to lattice mismatch contributes to the formation of the alloy droplet structure. In particular, we quantitatively evaluate how competing strain and chemical energy contributions determine surface structure.     

磁性和非磁性元素掺杂的自旋梯状化合物Sr_(14)(Cu_(0.97)M_(0.03))_(24)O_(41)(M=Zn,Ni,Co)的结构和电输运性质

利用固相反应法制备了Sr14Cu24O41及其系列B位掺杂Sr14(Cu0.97M0.03)24O41(M=Zn,Ni,Co)的样品.X射线衍射分析显示,所有样品均为纯相,晶格常数a与c没有明显的变化;Zn掺杂样品晶格常数b没有明显变化,而Ni,Co掺杂样品晶格常数b分别稍有增加.选区电子衍射研究揭示:磁性元素Ni,Co及非磁性元素Zn掺杂,可能主要替代了Sr14Cu24O41结构中自旋链上的Cu原子,从而影响了自旋链上的dimer排列,破坏电荷有序超结构.电输运测量显示:Zn2+,Ni2+,Co3+离子掺杂样品的电阻率降低,但仍体现半导体行为,所有的掺杂样品都存在一个渡越温度Tρ,当TTρ时,其导电机理是以单空穴热激发导电占主要地位,在TTρ时,配对的局域化空穴的一维变程跳跃导电占主要优势;在相同的掺杂量下,非磁性元素Zn掺杂对电阻率值的影响大于磁性元素Ni,Co掺杂的影响,而磁性元素Ni,Co掺杂对渡越温度Tρ的影响大于非磁性元素Zn掺杂的影响.     

Influence of (Mn or Co)-doping on structural,magnetic and electronic properties of nano Zn0.75Cd0.25S

Nano Zn_0.75Cd_0.25S doped with Mn or Co was prepared using the thermolysis method. The nano nature and particle morphology of the formed samples were investigated by the transmission electron microscope. The effect of doping with Co or Mn on the structural characteristics was investigated. Also, the phase percentage of cubic zinc-blende and hexagonal wurtzite phases, developed in the prepared samples, was characterized in detail using Rietveld analysis for synchrotron x-ray diffraction data. An extra phase (CoS) is formed in the sample doped with 20% Co, while the sample with 20% Mn- doping has no extra phase. The behavior of lattice parameters of zinc-blende and wurtzite phases upon doping and the occupancies of magnetic ions were also examined. Magnetic measurements revealed the transformation of Zn_0.75Cd_0.25S from diamagnetic nature to a weak ferromagnetic upon doping it by either 20% Co or 20% Mn. Density function theory calculation was used to understand the ferromagnetic behavior of the doped samples and also to investigate the effect of doping on the other optical parameters.     

3d过渡金属掺杂锐钛矿相TiO2的第一性原理研究

采用基于密度泛函理论的平面波超软赝势方法研究了纯锐钛矿相TiO₂及掺杂3d过渡金属TiO₂的几何、电子结构及光学性质. 计算结果表明掺杂能级的形成主要是掺杂过渡金属3d轨道的贡献，掺杂能级在禁带中的位置是决定TiO₂吸收带边能否出现红移的重要因素. Cr，Mn，Fe，Ni，Co，Cu掺杂使TiO₂的吸收带边产生红移，并在可见光区有一定的吸收系数； Sc，Zn掺杂使TiO₂的吸收带边产生蓝移，但在可见光区有较大的吸收系数；掺V不但使TiO₂的吸收带边产生红移，增强了在紫外光区的光吸收，而且在可见光区有非常大的吸收系数.     

Ni掺杂对ZnO磁光性能的影响

在掺杂浓度范围为2.78%—6.25%(物质的量分数)时,Ni掺杂ZnO体系吸收光谱分布的实验结果存在争议,目前仍然没有合理的理论解释.为了解决存在的争议,在电子自旋极化状态下,采用密度泛函理论框架下的第一性原理平面波超软赝势方法,构建不同Ni掺杂量的ZnO超胞模型,分别对模型进行几何结构优化和能量计算.结果表明,Ni掺杂量越大,形成能越高,掺杂越难,体系稳定性越低,掺杂体系带隙越窄,吸收光谱红移越显著.采用LDA(局域密度近似)+U方法调整带隙.结果表明,掺杂体系的铁磁性居里温度能够达到室温以上,磁矩来源于p-d态杂化电子交换作用.Ni掺杂量越高,掺杂体系的磁矩越小.另外还发现Ni原子在ZnO中间隙掺杂时,掺杂体系在紫外光和可见光区的吸收光谱发生蓝移现象.