过渡金属氮化物中单原子固溶和力学性能的第一性原理研究

基于密度泛函理论(DFT)的第一性原理,计算Si原子在Ti族和V族氮化物中以及B、C和Ge原子在TiN晶体中固溶的稳定结构,讨论置换型和间隙型固溶的低能量稳定结构与晶体间距的关系,研究金属氮化物和固溶原子固溶结构的力学性能.结果表明:Si原子在TiN、ZrN、HfN和TaN晶体中固溶以及Ge原子在TiN晶体中固溶情况为,单原子不进入对应过渡金属氮化物晶体中形成间隙固溶或置换固溶,随着晶体间距离变化单原子可以在晶体之间形成间隙固溶或置换固溶;Si原子在NbN以及B原子在TiN晶体中可以实现间隙固溶,而不能形成置换固溶;Si原子在VN和C原子在TiN晶体中固溶结构形式均为置换固溶.单原子固溶形成低能量置换型固溶体和间隙型固溶体的弹性常数、体模量和剪切模量均低于原过渡金属氮化物的对应值.     

Co、Ni和Ga合金化对DO_(19)-Ti_3Al弹性性能影响的第一性原理研究

采用第一性原理的方法研究了Co、Ni和Ga元素对DO_(19)-Ti_3Al晶体的弹性性能的影响,结果表明:Co和Ni原子倾向于置换Ti原子而Ga原子则更倾向于置换Al原子;Co和Ni元素固溶可以减弱晶体内部电子杂化效应从而增大Ti_3Al晶体的本征塑性,其中Co元素的对晶体的本征塑性的增大效果显著;Ga元素固溶后Ti_3Al晶体的强度和硬度将得到提高.     

磁控溅射(Ti,N)/Al纳米复合薄膜的微结构和力学性能

采用Al和TiN靶通过磁控共溅射方法, 制备了一系列Ti:N≈1的不同(Ti, N) 含量的铝基纳米复合薄膜, 利用X射线能量分散谱仪、X射线衍射仪、透射电子显微镜和纳米力学探针表征了薄膜的成分、 微结构和力学性能, 研究了(Ti, N)含量对复合薄膜微结构和力学性能的影响. 结果表明: Ti, N原子的共同加入使复合薄膜形成了同时具有置换固溶和间隙固溶特征的"双超过饱和固溶体", 薄膜的晶粒随着溶质含量的增加逐步纳米化, 并进一步形成非晶结构, 晶界区域形成溶质原子的富集区. 相应地, 复合薄膜的硬度在含1.8 at.%(Ti, N) 时就可迅速提高到3.9 GPa; 随着TiN含量的增加, 薄膜的硬度进一步提高到含17.1 at.%(Ti, N)时的8.8 GPa. 以上结果显示出Ti和N"双超过饱和固溶"对Al薄膜极其显著的强化效果.     

B元素添加对FePBCCu合金非晶形成能力、磁性能和力学性能的影响

铁基非晶合金因其低矫顽力、高磁导率和低铁耗等被广泛应用于变压器、电抗器等电力电子领域,然而,较低的饱和磁感值限制了其进一步应用.铁含量增大可有效提高合金的饱和磁感,但相应非磁性元素含量的降低又将引起合金非晶形成能力的下降,导致后续纳米晶带材的软磁性能及弯折韧性的恶化.针对上述问题,文章基于金属-类金属间的杂化作用,通过原子百分比为7%的B替代P,利用单辊甩带法制备了厚度约为25μm的FePBCCu非晶薄带,并研究了B添加对薄带非晶形成能力、磁性能和力学性能的影响.热动力学行为揭示出小原子B添加能够降低合金结构的异质性,有效提高非晶基体的热稳定性;熔化与凝固曲线表明B元素能够促使合金系接近共晶成分且具有较大的过冷度.因此合金的非晶形成能力显著提高,其临界厚度从基体的约21μm提高到约30μm. B添加促使合金系磁性原子有效磁矩的增大,导致非晶薄带的饱和磁感值增大.纳米压痕实验结果表明, B添加合金的约化模量值较大且在一个较小范围内波动,这与合金的结构均匀性密切相关.     

Zr,Nb,V在a-Fe(C)中的占位、电子结构及键合作用的第一性原理研究

采用第一性原理的方法计算了Zr, Nb, V固溶于a-Fe(C)后形成晶胞的体积变化率、晶胞总能、结合能、态密度、电荷布居数及力学性能,并由此研究了Zr, Nb, V与a-Fe(C)的微观作用机理.结果表明, V优先置换a-Fe(C)晶胞中顶角位置的Fe原子,而Zr, Nb优先置换a-Fe(C)晶胞中体心位置的Fe原子. Zr, Nb降低了铁素体的稳定性, Zr比Nb更难固溶于a-Fe(C). V固溶后增加了晶胞结合能,对晶胞主要起到提高韧性的作用. Zr, Nb, V固溶于铁素体后, Zr, Nb仅与Fe原子形成金属键,而V与铁素体晶胞中的Fe原子形成了金属键和Fe—V离子键,其离子键的作用均强于Zr, Nb原子与铁素体晶胞中的键合作用,是晶胞结合能增加的主要因素. Zr, Nb主要是通过弥散强化的方式改善钢铁材料的力学性能, V固溶能在一定程度上提高铁素体的韧性,是提高力学性能的主要原因.     

离子晶体中固溶胶粒的形成和生长以及施主原子浓度(Ⅰ)

本文利用自由能的概念并作了固溶粒子(包括胚芽和胶粒)都是同样大小的假定,讨论了在离子晶体中由于杂质原子浓度的增加,该固体由半导体过渡到固溶胶体的物理条件;推导出杂质原子临界浓度公式;讨论了胚芽的临界值和施主原子临界浓度与激活条件的关系。并指出当温度改变时,出现临界温度,超过此温度时,固溶胶体将转化为半导体。最后分析了自由能曲面的特点和出现固溶胶粒的充分条件。下一篇文章将讨论固溶胶粒有一定分布的情况,和胶粒的生长以及施主原子浓度等问题;并且还指出只要对这些讨论作简单的修正就可以应用于原子晶体和合金系统。     

Al元素含量对高熵合金Al_xFeTiCrZnCu力学性能的影响

采用第一性原理密度泛函理论,结合平面波赝势和广义梯度近似(GGA),用虚拟晶体近似(VCA)的方法建立高熵合金的固溶结构模型,计算了高熵合金Al_xFeTiCrZnCu的结构性能、弹性性能和生成热.计算结果表明,Al_xFeTiCrZnCu高熵合金的密度随着Al元素含量的增加而减小,晶格常数在Al元素摩尔含量为1时最小. Al元素含量的增加能提高高熵合金Al_xFeTiCrZnCu的力学稳定性.基态总能量和生成热都随着Al元素含量的增加而增加,但是合金系的稳定性和热力学稳定性有所下降.     

Al元素含量对高熵合金Al_xFeTiCrZnCu力学性能的影响

采用第一性原理密度泛函理论，结合平面波赝势和广义梯度近似(GGA)，用虚拟晶体近似(VCA)的方法建立高熵合金的固溶结构模型，计算了高熵合金Al_xFeTiCrZnCu的结构性能、弹性性能和生成热.计算结果表明，Al_xFeTiCrZnCu高熵合金的密度随着Al元素含量的增加而减小，晶格常数在Al元素摩尔含量为1时最小.Al元素含量的增加能提高高熵合金Al_xFeTiCrZnCu的力学稳定性.基态总能量和生成热都随着Al元素含量的增加而增加，但是合金系的稳定性和热力学稳定性有所下降.     

Ta-10W合金压缩力学性能实验研究

利用MTS材料试验机和分离式Hopkinson压杆(SHPB)实验装置对非退火状态Ta-10W合金进行了准静态和动态压缩实验,给出了材料的静态压缩屈服强度和应变率在700~3 100 s-1范围内的动态压缩应力-应变曲线,并获得了不同应变率下材料的动态屈服强度。通过对实验结果的分析可以发现,非退火状态Ta-10W合金具有较好的韧性,在所进行的实验中试件表面均未出现可见裂纹;试件材料具有较高的静、动态屈服强度,静态屈服强度达到930 MPa,动态屈服强度在1 GPa以上,在所进行的700~3 100 s-1应变率范围内,材料的动态屈服强度随应变率的增加略有提高。     

合金元素韧化或脆化FeAl金属间化合物的微观机制

通过测量二元FeAl以及含B，Zr或Si的FeAl合金的正电子寿命谱参数，计算合金基体和缺陷处的价电子密度.结果表明，当Al原子和Fe原子结合形成FeAl合金时，Al原子提供价电子与Fe原子的3d电子形成局域的共价键.FeAl合金基体的价电子密度很低，FeAl合金中金属键和共价键共存.FeAl合金晶界缺陷的开空间大于Fe空位或Al空位的开空间，FeAl合金晶界处的金属键合力很弱.在FeAl合金中加入少量的B，一部分B原子以间隙方式固溶到FeAl基体中，增加基体的价电子密度；另一部分B原子偏聚到FeAl合金的晶界上，也增加了晶界处的价电子密度.在FeAl合金中加入Zr，增加了合金中的金属键成分，使基体中的价电子密度增加，增强了基体中金属键合力.Zr原子的加入还降低了FeAl合金的有序度，使合金晶界容易弛豫，晶界缺陷的开空间变小.Zr原子在晶界附近出现，还增加了晶界处的价电子密度.在FeAl中加入B或Zr有利于提高合金的韧性.在FeAl合金中加入Si，晶界处的Si原子与邻近的原子形成强的共价键，使得在晶界处参与形成金属键的价电子密度降低.在FeAl中加入Si使合金更脆. 关键词：     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.