快离子导体AgxTiS2中Ag+离子－空位的二维基态结构与能量性质研究

根据Ag⁺离子-空位的二维有序结构建立了三维晶胞模型.采用局域密度近似下的平面波赝势方法,对有序Ag_xTiS₂(x=0,1/4,1/3,1/2,2/3,3/4,1)系列进行了几何结构优化和总能量计算,并与Li_xTiS₂系列进行了对比研究.有序Ag_xTiS₂系统的晶格参量增量Δa_{关键词： x}TiS₂')" href="#">Ag_xTiS₂ 有序—无序相变 离子扩散 第一性原理计算     

阶梯化对快离子导体LixTiS2的结构与能量性质的影响

根据密度波理论建立了stage-2有序LixTiS2(x=1/8,1/6,1/4,1/3,3/8,1/2)系统的晶胞模型.采用平面波赝势方法,对stage-2有序系统和stage-1有序LixTiS2(x=0,1/4,1/3,1/2,2/3,3/4,1)系统进行了几何结构优化和总能量计算,并进行了对比研究.发现stage-2晶胞的参量c(d)与stage-1晶胞的参量2c0(d)有相似的变化规律.但在stage-2有序系统中,有插层离子的夹层间距c1(d)相对于stage-1有序系统的夹层间距c0(d)额外膨胀,而与之对应的无插层离子的夹层间距c2(d)被压缩.这种额外膨胀和压缩有一定的互补关系.阶梯化对TiS2夹层中的原子结构也有显著影响.stage-2有序Li1/2TiS2系统的形成能明显高于stage-1有序Li1/2TiS2系统,表明后者更稳定.这与已报道的实验结果一致.stage-2有序Li1/4TiS2系统的形成能低于stage-1有序Li1/4TiS2系统,预言了一种新的有序结构.     

阶梯化对快离子导体LixTiS2的结构与能量性质的影响

根据密度波理论建立了stage-2有序Li_xTiS₂(x=1/8,1/6,1/4,1/3,3/8,1/2)系统的晶胞模型.采用平面波赝势方法,对stage-2有序系统和stage-1有序Li_xTiS₂(x=0,1/4,1/3,1/2,2/3,3/4,1)系统进行了几何结构优化和总能量计算,并进行了对比研究.发现stage-2晶胞的参量c(d关键词： xTiS₂')" href="#">Li_xTiS₂ 阶梯结构 有序—无序相变 第一性原理计算     

第一性原理研究厚度和空位缺陷对Si/SiO2界面电子结构与光学性质的影响

采用基于密度泛函理论的平面波超软赝势方法,在局域密度近似（LDA）下研究了Si纳米层厚度和O空位缺陷对Si/SiO2界面电子结构及光学性质的影响．电子结构计算结果表明：在0.815~2.580nm的Si层厚度范围内,Si/SiO2界面结构的能隙随着厚度减小而逐渐增大,表现出明显的量子尺寸效应,这与实验以及其他理论计算结果一致;三种不同的O空位缺陷的存在均使得Si/SiO2界面能隙中出现了缺陷态,费米能级向高能量方向移动,且带隙有微弱增加．光学性质计算结果表明：随着Si纳米层厚度的减小,Si/SiO2界面吸收系数产生了蓝移;O空位缺陷引入后,界面光学性质的变化主要集中在低能区,即低能区的吸收系数和光电导率显著增加．可见,改变厚度和引入缺陷能够有效地调控Si/SiO2界面体系的电子和光学性质,上述研究结果为Si/SiO2界面材料的设计与应用提供了一定的理论依据．     

第一性原理研究厚度和空位缺陷对Si/SiO2界面电子结构与光学性质的影响

采用基于密度泛函理论的平面波超软赝势方法,在局域密度近似（ LDA）下研究了Si纳米层厚度和O空位缺陷对Si／SiO2界面电子结构及光学性质的影响．电子结构计算结果表明：在0.815～2.580nm的Si层厚度范围内, Si／SiO2界面结构的能隙随着厚度减小而逐渐增大,表现出明显的量子尺寸效应,这与实验以及其他理论计算结果一致;三种不同的O空位缺陷的存在均使得Si／SiO2界面能隙中出现了缺陷态,费米能级向高能量方向移动,且带隙有微弱增加．光学性质计算结果表明：随着Si纳米层厚度的减小, Si／SiO2界面吸收系数产生了蓝移; O空位缺陷引入后,界面光学性质的变化主要集中在低能区,即低能区的吸收系数和光电导率显著增加．可见,改变厚度和引入缺陷能够有效地调控Si／SiO2界面体系的电子和光学性质,上述研究结果为Si／SiO2界面材料的设计与应用提供了一定的理论依据．     

Mg_2B_n(n=4～9)团簇结构与性质的DFT研究

用密度泛函理论(DFT)的B3LYP方法在6-31G*的基组水平上对Mg2Bn(n=4～9)团簇的各种可能的几何构型进行优化,得到了Mg2Bn(n=4～9)团簇的最稳定结构,并对其几何结构、振动光谱、电离能、能隙、电荷布局、成键特性等性质进行了计算.结果表明:Mg2Bn(n=4～9)团簇中大部分B原子为负电性且总是处在团簇的中心,Mg原子总是处在端位上并显正电性;随着n的增大,团簇最稳定结构逐渐由平面结构向立体结构转变;n=4、8时的结构相对较稳定.     

The absorption spectrum and excitons in an Ag2CdI4 ionic conductor

The electron absorption spectrum of thin stochiometric Ag₂CdI₄ films produced by thermal vacuum deposition on a quartz substrate in is investigated. The spectrum shape is sensitive to the method of preparation (the substrate temperature and deposition rate). Under optimal preparation conditions, the films are free of AgI and CdI₂ impurities and the fundamental absorption edge is at 3.28 eV. The long-wavelength exciton A band at 3.31 eV (90 K) is associated with the excitation of excitons in the AgI sublattice of the compound. An investigation of the temperature dependence of the spectral position and half-width of the A band in the range 90–430 K revealed that the exciton-phonon interaction makes the major contribution to the broadening of the band at T ≤360 K. At higher temperatures, the contribution associated with the generation of Frenkel defects with activation energy U _F=0.200±0.025 eV appears.     

From ultraslow to fast lithium diffusion in the 2D ion conductor Li0.7TiS2 probed directly by stimulated-echo NMR and nuclear magnetic relaxation

7Li stimulated-echo NMR and classical relaxation NMR techniques are jointly used for the first time for a comprehensive investigation of Li diffusion in layer-structured Li0.7TiS2. One single 2D Li diffusion process was probed over a dynamic range of almost 10 orders of magnitude. So far, this is the largest dynamic range being measured by 7Li NMR spectroscopy directly, i.e., without the help of a specific theoretical model. The jump rates obey a strict Arrhenius law, determined by an activation energy of 0.41(1) eV and a preexponential factor of 6.3(1)x10(12) s-1, and range between 1x10(-1) s-1 and 7.8x10(8) s-1 (148-510 K). Ultraslow Li jumps in the kHz to sub-Hz range were measured directly by recording 7Li spin-alignment correlation functions. The temperature and, in particular, the frequency dependence of the relaxation rates fully agree with results expected for 2D diffusion.     

Superconducting and normal state properties of Ag1−xSn1 + xSe2−y

The occurrence of superconductivity in a new ternary non-transition element compound with the cubic NaCl structure is reported. The composition of this compound is Ag_1?xSn_{1 + x}Se_2?y, with a maximum homogeneity range given by ?0.02 ?x?0.24 and 0 ? y ?0.1. The superconducting transition temperature (T_c) ranges from a minimum of 4.5 K for x = ?0.02, y = 0 to a maximum of 6.9 K for x = 0.24,y = 0. These T_c's are higher than previously observed in nontransition element NaCl structure compounds. Electrical resistivity data show a positive temperature coefficient, and room temperature magnetic susceptibility measurements reveal a rapidly increasing density of states at the Fermi level with increasing x. Two ionic models for calculating the carrier concentration of Ag_1?xSn_{1 + x}Se_2?y are discussed, and a third model based on the band picture is proposed. The composition dependence of the magnetic susceptibility was used to test the validity of each of the models.     

插层化合物LixTiS2中Li离子-空位二维有序结构稳定性的第一性原理研究

根据局域密度近似下的密度泛函理论,用第一性原理方法对TiS2,LiTiS2和LixTiS2(x=1/4,1/3,1/2,2/3,3/4)有序系统进行了几何优化和总能量计算.将计算结果与已有的实验和理论结果进行了对比,得到的归一化结构参量增量△a0和△c0随离子浓度单调地增加,与实验结果符合较好.LixTis2(x=1/4,1/3,1/2,2/3,3/4)有序结构的形成能均小于零,表明这些结构的稳定性.具有√3a0×a0有序结构的Li1/2TiS2系统的形成能最低、结构最稳定.研究结果表明,对上述系统使用局域密度近似下的密度泛函理论是合理的.