理论研究ZnO掺杂Al;Ga;In电子结构与光学属性(英文)

计算了Ga、Al、In掺杂对ZnO体系电子结构和光学性质的影响.所有计算都是基于密度泛函理论(DFT)框架下的第一原理平面波超软赝势方法.计算结果表明:Ga、AI、In掺杂在ZnO中占据了Zn位置,为n型浅施主掺杂,导带底引入了大量由掺杂原子贡献的导电载流子,明显提高了体系的电导率.同时,光学带隙展宽,且向低能方向漂移,可作为优良的透明导电薄膜材料.同时,计算结果为我们制备基于ZnO透明导电材料的设计与大规模应用提供了理论依据,也为监测和控制ZnO透明导电材料的生长过程提供了可能性.     

非金属元素C、N、F掺杂锐钛矿型TiO2的缺陷形成能和电子性质

非金属杂质掺杂TiO2半导体改善对可见光区域的光催化性质是近年来的一个研究热点,但相关杂质缺陷的形成能研究却不多。通过基于密度泛函理论的平面波超软赝势方法,研究了非金属元素C、N、F掺杂锐钛矿型TiO2之后的缺陷形成能与电子性质。结果表明,3种元素掺杂进入TiO2后缺陷形成能的大小排序为C>N>F,说明F元素最容易掺杂进入TiO2晶格。但是掺入F元素后对TiO2禁带宽度的改变不大,在提高TiO2对可见光的响应方面F元素的效果不如N、C两种元素。因此,对于掺杂来改善TiO2对可见光的响应方面,N元素比C、F的效果更好。     

First-principles calculations on structural,magnetic and electronic properties of oxygen doped BiF3

First-principles calculations based on density function theory within the generalized gradient approximation (GGA) have been carried out to investigate the effects of O doping on the structural, magnetic and electronic properties of BiF₃. Based on the calculated cohesive energies, O impurities prefer substituting F atom at tetrahedral sites (0.25, 0.25, 0.25). And the geometry of BiF₃ changes little due to similar radius of O and F atoms. By analyzing density of states (DOS) of Bi₄OF₁₁ (II)_, it has been found that Bi₄OF₁₁ (II) presents magnetic character and half-metallic state, implying its potential applications in Li-ion batteries. Finally, the character of bond in Bi₄OF₁₁ (II) was discussed by analysis of charge density and bader charge. The result shows that O doping weakens ionic bond in BiF₃.     

高压对Gd掺杂ZnO的电子结构和磁性影响研究

压力可以作用于物质的晶体结构内部,影响并改变物质整体性质.为进一步探究高压对Gd掺杂ZnO试样的电子结构及磁性影响,运用金刚石对顶砧压机和Materials Studio4.4软件包中的CASTEP运算程序,完成高压实验制备工作;利用基于密度泛函理论的第一性原理计算高压作用下Gd掺杂ZnO试样内部分子的变化情况,并对G...     

Elucidating the electronic and magnetic properties of epitaxial graphene grown on SiC with a defective buffer layer

Journal of Materials Science - The epitaxial graphene layer (EG) grown on silicon carbide (SiC) is severely affected by the presence of the underlying graphene buffer layer (BL). However, little...     

Investigation on structural, electronic, and magnetic properties of Mn-doped Ga12N12 clusters

The structural, electronic, and magnetic properties of Ga₁₂N₁₂ cluster doped with monodoped and bidoped Mn atoms have been investigated based on the density functional theory. Substitutional, exohedral, and endohedral configurations are considered. The substitutional doping is found to be most favorable for monodoped clusters, while the bidoped clusters prefer the exohedral isomers. For all the isomer, the magnetic moment is mainly derived from 3d orbitals of Mn atom. The exohedral and endohedral bidoped Ga₁₂N₁₂ clusters all favor antiferromagnetic state.     

Mn、Co掺杂SiC薄膜结构与光致发光性能研究

采用射频磁控溅射技术和复合靶材方法制备了掺Mn,掺Co和Co、Mn共掺的SiC薄膜,经高温退火后进行了光致发光(PL)谱的测量,还用X射线衍射(XRD),傅立叶变换红外光谱(FTIR),扫描电镜(SEM)等表征手段分析了薄膜的相结构和表面形貌,并与光致发光的结果进行了对比研究.结果表明,掺Mn、Co使SiC晶格发生畸变,X射线衍射峰强度下降,Si-C吸收谱变宽,Si-C键振动减弱,Si-O基团的振动增强.样品在室温条件下均呈现出强的紫光发射特性,发光峰均位于414nm(3.0eV),认为414nm处的光致发光峰对应于光激发产生的电子从导带底到Si空位浅受主能级之间的辐射跃迁,其强度取决于Si空位的浓度.     

Stability,electronic and magnetic properties of the Octagraphene-like boron nitride Nanosheets: In silico studies

The characterization of the structural, electronic, and magnetic properties of octagraphene-like boron-nitride: BN (B₃₂N₃₂H₂₄, B₃₇N₂₇H₂₄, and B₂₇N₃₇H₂₄), nanosheets were performed by means of density functional theory all-electron calculations at the HSEh1PBE/GGA level. Orbital 6–311G(d,p) basis sets were used. Non-stoichiometric B₃₇N₂₇H₂₄ and B₂₇N₃₇H₂₄ compositions: rich in boron or nitrogen atoms, forming homonuclear B or N bonds, respectively, were chosen. The obtained results reveal that these BN nanosheets reach structural stability in the anionic form, where semiconductor behaviors are promoted. Indeed, the HOMO-LUMO gap values are: 5.09, 1.48 and 2.53 eV, for stoichiometric and non-stoichiometric models, respectively. Whereas the magnetic moments are coming from the boron atoms in all cases (1.0 bohrs magneton). The rich in boron and nitrogen nanosheets presents high-polarity; either in the gas phase or embedded in aqueous mediums like water. Also appears low chemical reactivity, signifying potential applicability as nanovehicles of pharmaceutical species. The nanosheets rich in boron atoms are promising candidates for the design of nanosensors, because they possess low-work functions, mainly arising from the homonuclear boron bond formation.     

Al掺杂NdFeO_3体系的晶体结构精修与磁特性研究

利用固相反应法制备了Al掺杂的NdFe1-xAlxO3系列化合物。通过X射线粉末衍射和结构精修分析发现,随着Al掺杂量的增加,样品晶胞参数变小,晶胞内Fe—O键长、Fe—O—Fe键角也发生了很大程度的改变,并且在a、b、c方向上存在不同的变化规律。Al掺杂导致样品结构上的改变对其磁学性质具有重要影响。磁测量结果表明,随着Al掺杂量的增加,由dzyaloshinsky-moriya(D-M)相互作用导致的宏观磁性逐渐减弱;由Nd离子磁晶格与Fe离子磁晶格耦合作用导致的体系自旋重取向相变温度向低温方向移动,样品的饱和磁化强度随着Al掺入浓度的增加呈减小趋势。表明Fe位非磁性元素Al的掺入,使得样品内部由D-M相互作用所引起的倾角反铁磁结构受到了明显的调制。     

Phase transitions and hard magnetic properties for rapidly solidified MnAl alloys doped with C,B, and rare earth elements

MnAl alloys are attractive candidates to potentially replace rare earth hard magnets because of their superior mechanical strength, reasonable magnetic properties, and low cost. In this study, the phase transitions and magnetic properties of melt spun Mn₅₅Al₄₅ based alloys doped with C, B, and rare earth (RE) elements were investigated. As-spun Mn–Al, Mn–Al–C, and Mn–Al–C–RE ribbons possessed a hexagonal ε crystal structure. Phase transformations between the ε and the L1₀ (τ) phase are of interest. The ε → τ transformation occurred at ~500 °C and the reversed τ → ε transformation was observed at ~800 °C. Moderate carbon addition promoted the formation of the desired hard magnetic L1₀ τ-phase and improved the hard magnetic properties. The Curie temperature T _C of the τ phase is very sensitive to the C concentration. Dy or Pr doping in MnAlC alloy had no significant effect on T _C. Pr addition can slightly improve the magnetic properties of MnAlC alloy, especially J_S. Doping B could not enhance the magnetic properties of MnAl alloy since B is not able to stabilize either the ε phase or the L1₀ hard magnetic τ phase.     

Novel magnetic half-metallic materials based on ionic insulators doped with nonmagnetic impurities: MgO + B,C, N Systems

It is established that magnesium oxide (a nonmagnetic ionic insulator) exhibits a transition to the state of a magnetic half-metal upon the introduction of nonmagnetic impurities (boron, carbon, or nitrogen) into the crystal lattice. The possibility of obtaining novel magnetic materials for spintronics by doping ionic insulators with nonmagnetic impurities is discussed.     

Creep properties of (Si–Al–O–N)SiC whisker composites

(Si–Al–O–N) (sialon)–SiC whisker (SiC_w) composites containing up to 10 mass% SiC_w were prepared by hot isostatic pressing. The strengths and the fracture toughness of composites remained relatively unchanged with the amount of SiC_w. The addition of SiC_w enabled us to improve the creep properties of sialon ceramics. The total creep strain and steady-state creep rate at 1473 K under a stress of 400–500 MPa decreased with increasing the amount of SiC_w. The experimental creep exponent values of monolithic sialon and sialon–SiC_w composites were nearly 1. It is supposed that the creep of both monolithic sialon and sialon–SiC_w composites are dominated by the viscous flow of the interglanular glassy phase.     

高体积分数SiCP/Al复合材料的拉伸、压缩与弯曲特性

对高体积分数碳化硅颗粒增强铝基(SiC P/ Al)复合材料的拉伸、 压缩和三点弯曲特性进行了实验研究。结果表明 : 高体积分数 SiC P/ Al 复合材料与低体积分数 SiC P/ Al复合材料相比 , 没有明显的线性屈服阶段。进一步的加载2卸载实验表明 , 在外载荷作用下 , 材料宏观上呈现一种类似金属材料的塑性 , 卸载后留有较大的残余应变 , 再次加载时沿上次卸载路线上升 , 而且拉应力导致的残余应变大于压应力。三点弯曲时材料内部产生残余塑性变形的潜力最大 , 切线模量更稳定。宏观断口分析表明 , 金属基体的非均匀分布导致产生局部渐进的微屈服 ,是使材料性能宏观上类似塑性材料的主要原因。制备过程中的残余应力和基体内部的微缺陷是拉应力比压应力产生更大残余应变的主要原因。     

First-principles study on electronic properties of SiC nanoribbon

Under the generalized gradient approximation (GGA), the electronic properties are studied for SiC nanoribbon with zigzag edge (ZSiCNR) and armchair edge (ASiCNR) by using the first-principles projector-augmented wave (PAW) potential within the density function theory (DFT) framework. Distinct variation behaviors in band gap are exhibited with increasing ribbon width. The ZSiCNR is metallic except for the thinner ribbons (N _z = 2–4) with small direct band gaps, while the direct band gaps of ASiCNR exhibit sawtooth-like periodic oscillation features and quench to a constant value of 2.359 eV as width N _a increases. The PDOS onto individual atom shows that a sharp peak appeared at the Fermi level for broader ZSiCNR comes from the edge C and Si atoms with H terminations. The charge density contours analysis shows the valence charges are strongly accumulated around C atom, reflecting a significant electron transfer from Si atom to C atom and thus an ionic binding feature. In addition, the Si–H bond is also ionic bond while the C–H bond is covalent bond. The dangling bonds give rise to one (two) flat extra band at the Fermi level for ZSiCNR with either bare C or bare Si edge (for ZSiCNR with bare C and Si edges as well as for ASiCNR with either bare C edge or bare Si edge), except for ASiCNR with bare C and Si edges in which two nearly flat extra bands appear up and below the Fermi level.     

用铝丝掺杂溅射ZnO薄膜的光电性能研究

本文采用射频磁控反应溅射法于常温下在硅片和玻璃基片上制备ZnO和掺铝ZnO薄膜,将铝丝置于ZnO靶材上共同溅射来达到掺杂的效果,利用不同长度的铝丝以获得不同的掺杂量。通过X射线衍射法对薄膜进行结构分析,利用紫外-可见分光光度计获得薄膜的透过率光谱,霍尔效应仪测量薄膜的电学性能。发现所制备的样品在可见光区域透过率达到80%以上,达到了透明膜的要求;掺Al后的ZnO膜电阻率最低达到了4.25×10-4Ω·cm;结构表征发现样品的(002)晶面有明显衍射峰。基于包络线方法通过透射谱拟合计算了薄膜样品的折射率和厚度。     

On magnetic properties of Fe-Si-Mn alloy sheet

Fe-Si-Mn alloys composed of 3.5-7,5%, 0-3.5%Mn and 90-96.5%Fe were melted in argon and hot-rolled. Measurements of their magnetic properties and electrical resistivity indicate that the addition of manganese to higher silicon-iron alloys improves in permeability and coercive force of the alloys. Maximum permeability as high as 83000 is obtained when the alloy of 6.70%Si, 0.55%Mn and 92.75%Fe is quenched into oil from 400° after annealing at 1200° for 5 hr. The alloy exhibits the coercive force of 0.06 Oe for the maximum induction of 10 kG. The electrical resistivity of the alloy is 86 μΩ-cm, with the Vickers hardness of 355.     

B/N/Si掺杂的(9,0)型碳纳米管电子结构第一性原理研究

基于密度泛函理论(DFT)的DMol3软件包,研究了(9,0)型碳纳米管(CNT)顶端掺杂B/N/Si等元素对其几何结构及电子结构的影响.结果表明,掺杂原子对非掺杂区几何结构影响微弱;加电场后,各种掺杂CNT顶端局域态密度(LDOS)峰位向价带移动;B/N/Si掺杂不仅引起CNT费米能级(Ef)处LDOS增大,而且最低空轨道与最高占有轨道的差值(LUMO-HOMO)降低.由此可预期CNT顶端掺B/N/Si均有利于场致电子发射,且改善幅度依次增强.     

Mechanical properties Of Si3N4 cerarnics reinforced with SiC whiskers and SiC platelets

Silicon nitride ceramics reinforced with SiC whiskers and SiC platelets were fabricated by hot pressing and their mechanical properties were studied. They showed higher fracture energy than conventional composites, particularly when they were consolidated by gas-pressure hot pressing at high temperature. A high fracture toughness (10.7 MPa m^1/2) which was measured by the single-edge pre-cracked beam method was achieved. Furthermore, a unique method to observe the crack propagation behaviours directly in a scanning electron microscope with loading devices was developed. As a result, much bridging and pull-out of the whiskers and the elongated Si₃N₄ grains, and crack deflection along the platelets, were observed behind the crack tip. This means that these grains are effective in enhancing the fracture resistance during crack propagation.     

Investigation of structural,optical, magnetic,and electrical properties of PMMA doped with magnetite nanoparticles

Journal of Materials Science: Materials in Electronics - This research deals with structural, optical, electrical, and magnetic properties of nanocomposite composed of polymethyl methacrylate...