Au2Gen-/0 (n=1∽8)团簇结构演化和电子性质的光电子能谱和理论计算研究

本文利用尺寸选择的负离子光电子能谱和理论计算探索Au₂Ge_n^-/0 (n=1∽8)团簇的结构演化和电子性质. 通过比较理论模拟谱与实验谱,并使用CCSD(T)理论方法计算异构体的相对能量,从而确定金锗混合团簇的全局最小结构. 本文发现Au₂Ge_n^-/0 (n=1∽8)团簇的两个Au原子具有较高的配位数和较弱的亲金相互作用. 负离子团簇和中性团簇的最稳定结构分别处于自旋双重态和自旋单重态. 除了Au₂Ge₄^-/0和Au₂Ge₅^-/0,负离子团簇和中性团簇的全局最小结构具有相似的结构特点. Au₂Ge₁^-/0团簇是一个C_2v对称的V形结构,而Au₂Ge₂^-/0团簇是一个C_2v对称的双桥连结构. Au₂Ge₁^-负离子团簇是两个Au原子盖帽的Ge₄四面体结构,而Au₂Ge₄中性团簇是两个Au原子盖帽的Ge₄菱形结构. Au₂Ge_5∽8^-/0团簇主要采用三棱柱、四棱柱、及五棱柱结构. Au₂Ge₆是一个C_2v对称的四棱柱结构,并表现出σ和π双键性质.     

TiGen-(n=7~12)团簇的光电子能谱及密度泛函理论研究

利用光电子能谱及密度泛函理论计算对TiGe_n^-(n=7~12)团簇的几何结构及电子特性等进行了系统研究. 对于TiGe_n^-负离子及中性TiGe_n,在n=8时出现了钛原子半内嵌的船型结构;在n=9~11时,新增的锗原子加盖到这种船型结构上,逐步形成钛原子完全内嵌的结构. TiGe₁₂^- 团簇具有一种钛原子内嵌的变形六棱柱结构. 自然布居分析结果显示,对于n=8~12的TiGe_n^-/0 团簇,随着内嵌结构的形成,有电子从锗原子转移到钛原子,说明其电荷转移方式与结构演变密切相关.     

Al_nC_4~(-/0)(n=2～4)团簇的结构和成键性质:光电子能谱和理论计算（英文）

本文采用尺寸选择的负离子光电子能谱与高精度理论计算,对Al_nC_4~(-/0)(n=2～4)团簇的结构和成键性质进行了研究.Al_2C_4~-团簇负离子的最稳定结构是一个C_(2v)对称的平面结构,其中两个C_2单元与两个铝原子分别相连.Al_2C_4~-团簇负离子的次稳定结构是一个线型结构,两个铝原子位于C_4线型结构两端,能量仅比最稳定结构高0.05 eV.中性Al_2C_4团簇是一个线型结构.Al_3C_4~-团簇负离子是一个平面结构,其中三个铝原子分别与两个C_2单元相连.而中性Al_3C_4团簇则是一个V字型结构.Al_4C_4~-团簇负离子和中性Al_4C_4团簇均为C_(2h)对称的平面结构,四个铝原子分别位于两个C_2单元的末端.Al_nC_4~(-/0)(n=2～4)团簇负离子的自适应自然密度配分的分析结果表明这些团簇中铝原子与C_2单元之间的化学键具有σ和π键特征.     

4s和4p半核态引入价态(导致杂化指数降低)可以减弱Mon (n=2∽18)团簇的二聚体现象的第一性原理研究

钼团簇因具有独特的结构、电子和物理化学性质,被期待在未来的纳米科技中扮演重要角色,但是它们的基态结构至今还存在争议. 本研究采用粒子群优化(CALYPSO)方法对Mo_n (n=2∽18)团簇的晶体结构进行全局域能量最小化搜索,并结合第一性原理方法进一步优化. 计算表明：当4s和4p半核态不作为价态时,Mo_n (n=2∽18)团簇有明显的二聚体趋势,原子数为偶数的团簇往往是“幻数”团簇,具有较高的稳定性;但是,将4s和4p电子作为价电子后,平均杂化指数H_sp、H_sd和H_pd显著降低,二聚体趋势急剧减弱. 本文报道了Mo_n(n=11,14,15)团簇的新基态结构,证明了半核态对于Mo_n团簇是十分重要的.     

ConCm±(n=1-5; m=1,2)团簇的密度泛函理论研究

本文采用基于自旋极化的密度泛函理论系统研究了Co_nC_m^± (n=1-5; m=1,2)团簇的几何结构和电子结构特性. 将Co_nC^± (n=2-5)团簇中的一个Co替换为C原子, 个体的基态几何结构发生明显变化; 在Co_nC₂^± (n=1-5)团簇的生长序列中, 发现从n=3开始团簇中的两个C原子有彼此分离分布的趋势, 我们分析, 这是Co金属能够维持单壁碳纳米管(SCNTs)保持开口生长, 成为非常有效的一种催化剂的重要原因. 同时, 将Co_nC^± (n=2-5)团簇中添加一个Co原子后系统的总磁矩出现大幅下降的趋势, 但仍保持奇偶交替的规律. 通过比较中性及带电的Co_nC以及Co_nC₂ (n=1-5)团簇的碎裂能, 本工作发现: 由实验获取的SCNTs应均为带正电的体系, 这一结论与已有的实验模型拟合得很好.     

[Co(CO2)n]+团簇的红外解离光谱实验和理论研究

本文利用红外光解离光谱研究了一价钴阳离子与二氧化碳之间的相互作用. 通过密度泛函理论计算得到[Co(CO₂)_n]⁺团簇的几何结构,并且模拟了它们的振动光谱与实验数值进行比较. 研究结果表明,在[Co(CO₂)_n]⁺(n=2∽6)团簇中,钴阳离子通过电四极矩静电作用以端点结合的方式与二氧化碳中的氧原子结合在一起. 团簇的红外光谱都集中在二氧化碳反对称伸缩的波数附近,并且随着团簇尺寸的变化出现蓝移,最后把[Co(CO₂)_n]⁺的红外光解离光谱与稀有气体贴附的[Co(CO₂)_n]⁺-Ar的红外光解离光谱进行了比较.     

小尺寸VmOn+团簇的激光光解和密度泛函计算

通过激光溅射法产生了V₂O_n⁺ (n=1, 2), V₃O_n⁺ (n=1, 2, 3)和V₄O₃⁺等缺氧的钒氧团簇,并采用532和266 nm波长的激光对它们进行了光解研究. 利用密度泛函理论计算与激光光解实验相结合确定了这些团簇的几何结构和可能的光解通道. 激光光解实验表明V相似文献   

AuCn-/0 (n=3-8)的负离子光电能谱和密度泛函理论研究：电子结合能和几何结构的奇偶效应

本文测量了AuC_n^- (n=3-8)的光电子能谱,并且对AuC_n^-/0 (n=3-8)的结构和性质进行了理论研究. 研究发现,AuC_n^-的光电子能谱表现出明显的奇偶交替变化,AuC₃^-、AuC₅^-、AuC₇^-的光电子能谱峰明显宽于AuC₄^-、AuC₆^-、AuC₈^-的光电子能谱峰,AuC₃^-、AuC₅^-、AuC₇^-的电子垂直脱附能低于AuC₄^-、AuC₆^-、AuC₈^-的电子垂直脱附能. AuC_n^- (n=3-8)的最稳定结构是链状结构. 在中性团簇AuC_n(n=3-8)中,除了AuC$₃和AuC₅的结构轻微弯曲外,其他团簇均是直线型结构. 理论计算的∠AuCC角度,Au-C键长和Au原子的电荷分布均呈现奇偶变化,与实验观测一致.     

用于团簇负离子的共线光电子速度成像仪

描述了包含共线的光电子速度成像仪,以及与双阀激光溅射团簇源联用的时间飞行质谱装置．为了避免预混气体,两个脉冲阀和一个反应通道被用来产生反应负离子．共线的光电子成像仪采用了改进的速度成像透镜系统,它的能量分辨率优于3%．此外还报道了Si₄^-团簇在532和355 nm,以及Si₃C^- 团簇在532 nm的光电子速度成像．从实验图像中可以获得光电子能谱和各向异性参数．从Si₄^-团簇能谱上获得了中性的Si₄团簇的基态和第一激发态的振动频率分别为330和312 cm^-1．初步的实验结果证明这套光电子成像装置对研究团簇负离子的电子结构以及光脱附动力学非常有效.     

AgO分子C2∏-X2∏(0,0)带高分辨光谱再研究

本文利用激光诱导荧光技术对AgO分子C²∏-X²∏(0,0)带光谱在∽0.02 cm^-1分辨率水平开展了高分辨研究. 在超声射流条件下利用银针电极对O₂/Ar混合气高压放电制备AgO分子，利用自行研制的窄线宽单纵模光参量振荡器作为可调谐激光光源，实验记录了同位素分辨的¹⁰⁷Ag¹⁶O和¹⁰⁹Ag¹⁶O分子C²∏-X²∏(0,0)带的高分辨光谱. 通过对实验光谱的转动分析获得了两个同位素分子的精确光谱常数，其中¹⁰⁷Ag¹⁶O分子C²∏态常数为首次实验测定. 结合文献和理论计算，实验观测的C²∏态自旋-轨道耦合效应很可能来自于与四重解离态⁴Σ^-或⁴∏的态混合.     

Li4SiO4-Li3VO4赝二元系和Li4GeO4-Li4SiO4-Li3VO4赝三元系中新的锂离子导体

本文在室温到300℃的温度范围内研究了Li₄SiO₄-Li₃VO₄和Li₄GeO₄-Li₄SiO₄-Li₃VO₄体系中的离子导电性,发现γ_II相固溶体Li_3+xV_1-xSi_xO₄是好的锂离子导体。所研究的成分中Li_3.3V_0.7Si_0.3O₄的离子电导率最高,室温下为1×10^-5Ω^-1·cm^-1,在42—192℃的电导激活能为0.36eV,电子电导率可以忽略,因而这是迄今所发现的最好的锂离子导体之一。粗略确定了Li₄GeO₄-Li₄SiO₄-Li₃VO₄三元系中电导率高的范围,发现在Li_3.5V_0.5Ge_0.5O₄中Si部分取代Ge可以使电导率进一步提高,Li_3.5V_0.5Ge_0.4Si_0.1O₄的室温电导率可达1.3×10^-5Ω^-1·cm^-1,电导激活能为0.40eV。 关键词：     

Li3VO4-Li4SiO4-Li4GeO4赝三元系相图的研究

本文用差热分析法和高温、室温X射线衍射法对Li₃VO₄,Li₄SiO₄的相变过程,Li₃VO₄-Li₄SiO₄,Li₃O₄-Li-4GeO₄赝二元系相图以及Li₃VO₄-Li₄SiO₄-Li₄GeO₄赝三元系相图室温截面进行了研究。发现在Li₃VO₄-Li₄SiO₄,Li₃VO₄-Li₄GeO₄赝二元系中,由于Li₄SiO₄或Li₄GeO₄的加入而使Li₃VO₄的高温γ_II相稳定存在于室温,从而得到一种新的具有高电导率的锂离子导体。作者认为探寻使高温态稳定存在于室温的方法是探索新的离子导体研究中有效途径之一。 关键词：     

NH4H2PO4和ND4D2PO4晶体微结构的拉曼光谱研究

本文利用偏振拉曼光谱和第一性原理, 对磷酸二氢铵(NH₄H₂PO₄, ADP)和不同氘含量磷酸二氢铵DADP晶体的晶格振动模式进行了研究. 实验测得了不同几何配置、200–4000 cm^-1范围的偏振拉曼光谱, 分析在不同氘含量条件下921 cm^-1和3000 cm^-1附近拉曼峰的变化. 在ADP晶体中, 基于基本结构单元NH₄⁺ 和H₂PO₄^-基团的振动模, 用第一性原理进行了数值模拟, 进一步明确拉曼峰与晶体中原子振动的对应关系; 通过洛伦兹拟合不同氘含量DADP晶体的拉曼光谱中2000–2600 cm^-1处各峰的变化讨论了DADP 晶体的氘化过程, 结果表明氘化顺序是先NH₄⁺ 基团后H₂PO₄^-基团, 研究结果为今后此类材料的生长和性能优化奠定了基础.     

Photoelectron spectra of As4S3, P4S3, P4Se3 and As4O6

The He(I) UV photoelectron spectra of As₄S₃, P₄S₃, P₄Se₃ and As₄O₆ are reported in this paper. The spectra of As₄S₃ and the isostructural molecules P₄S₃ and P₄Se₃ comprise seven broad but clearly defined peaks, whilst the spectrum of As₄O₆ consists of six peaks and two shoulders. By comparing the spectra with one another and with the photoelectron spectra of other arsenic and phosphorus compounds, the character and symmetry species of the highest-energy occupied molecular orbitals of the molecules have been assigned.     

Cation ordering and crystal structures in AGa2X4 compounds (CoGa2S4, CdGa2S4, CdGa2Se4, HgGa2Se4, HgGa2Te4)

Single crystals of some AGa₂X₄ compounds (CoGa₂S₄, CdGa₂S₄, CdGa₂Se₄, HgGa₂Se₄, HgGa₂Te₄) were prepared by chemical vapour deposition and flux method.The X-ray structural investigations indicated blende or defect chalcopyrite structures.A simple relationship is suggested between the c/a ratio and the cationic sublattice ordering.     

Ion diffusion in the high-temperature phases Li2SO4, LiNaSO4, LiAgSO4 and Li4Zn(SO4)3

Diffusion in the four high-temperature sulphate phases Li₂SO₄, LiNaSO₄, LiAgSO₄ and Li₄Zn(SO₄)₃ was studied extensively some 20–30 years ago. We have now carried out a re-evaluation where we include information obtained from a number of studies of other properties. The data are adjusted slightly due to the use of another type of regression analysis. It is characteristic of the four phases that they are both plastic crystals and solid electrolytes (superionic conductors). The cause of the high conductivity is that the mobility of the cations is strongly enhanced by the rotational motion of the translationally static sulphate ions. This is observed not only for the abundant cations, but also for other cations present (mono- as well as polyvalent) and for monovalent anions. Furthermore, both bulk diffusion and transfer along high diffusivity paths are affected. In addition, one can distinguish between different contributions to the bulk diffusion. The ionic radius is a very important parameter, since it determines the solid solubility and the distribution of the ions between the sites that are available in the lattice. All this affects the relative importance of several competing diffusion mechanisms. This gives a qualitative explanation of an anomalous correlation which has been observed in FCC Li₂SO₄ for monovalent ions (cations as well as anions), namely that both the diffusion coefficients D, and the activation energies Q, decrease when the radius is increased. This holds for hard-core cations (Li, Na, K, Rb), polarizable cations (Ag, Tl) and anions (F, Cl, Br). On the other hand, the situation is normal for divalent cations for which an increase in D corresponds to a decrease in Q. This is the case for hard-core ions (Mg, Ca) as well as for polarizable ones (Zn, Cd, Pb). Migration of the large ions Cs⁺ and SO²⁻₄ appears to be specially sensitive to how the experiment is prepared. Diffusion in BCC LiNaSO₄ and LiAgSO₄ has been studied for the two main cations as well as for some dopant ions. A general conclusion is that studies of diffusion of several ions in the same structure can give information that cannot be obtained by other types of experiments.     

Electron energy-loss spectroscopy of LiMn2O4, LiMn1.6Ti0.4O4 and LiMn1.5Ni0.5O4

The dielectric properties of LiMn₂O₄, LiMn_1.6Ti_0.4O₄ and LiMn_1.5Ni_0.5O₄ powders, synthesized by sol-gel method, were determined by analyzing the low-loss region of the electron energy-loss spectroscopy (EELS) spectrum in a transmission electron microscope. From these data, the optical joint density of states (OJDS) was obtained by Kramers-Kronig analysis. Since maxima observed in the OJDS spectra are assigned to interband transitions above the Fermi level, these spectra can be interpreted on the basis of calculated density of states (DOS), carried out with the CASTEP code. Experimental and theoretical results are in good agreement.     

Magnetoresistance of Fe3O4/Au/Fe3O4 and Fe3O4/Au/Fe spin-valve structures

A detailed study of the in-plane magnetotransport properties of spin valves with one and two Fe₃O₄ electrodes is presented. Fe₃O₄/Au/Fe₃O₄ spin valves exhibit a clear anisotropic magnetoresistance in small magnetic fields but no giant magnetoresistance (GMR). The absence of GMR in these structures is due to simultaneous magnetization reversal in the two Fe₃O₄ layers. By contrast, a negative GMR effect is measured on Fe₃O₄/Au/Fe spin valves. The negative GMR is attributed to an electron spin scattering asymmetry at the Fe₃O₄/Au interface or an induced spin scattering asymmetry in the Au interfacial layers.     

Dielectric properties of CsH2PO4 and CsD2PO4

Orthorhombic CsH₂PO₄ undergoes a ferroelectric transition at T_c = ?119.5°C, whereas the ferroelectric transition temperature in isomorphous CsD₂PO₄ is T_c = ?5.55°C. The transitions are of first order in both cases. The rather large isotope effect demonstrates the importance of the OHO bonds in the transition mechanism.