单斜BiScO3和BiCrO3的电子结构和光学性质的第一性原理比较研究

采用基于密度泛函理论的第一性原理赝势平面波方法,对单斜BiScO3和BiCrO3的电子结构和光学性质进行了比较研究。结果表明：BiScO3为无磁绝缘体,带隙为直接带隙,BiCrO3为间接带隙磁性半导体;BiScO3和BiCrO3都不吸收能量小于1.02 eV的光子,BiScO3吸收可见光的能力强于BiCrO3。     

BaHfO3纳米薄膜电子结构、光学和弹性性质的第一性原理研究

采用基于密度泛函理论的第一性原理方法,在局域密度近似（LDA）下研究了厚度为0.626～2.711nm (100)面BaHfO3薄膜的电子结构、光学和弹性性质．电子结构和光学性质计算结果表明：以BaO为表面层原子的BaHfO3纳米薄膜均为直接带隙半导体材料,带隙随薄膜厚度减小而逐渐减小,表现出明显的量子尺寸效应,此时薄膜的光学吸收边发生红移,吸收带出现窄化现象．以HfO2作为表面层原子的BaHfO3薄膜则属于间接带隙半导体材料,且带隙随薄膜厚度减小而微弱增加．弹性性质计算结果表明：体弹模量、剪切模量和杨氏模量等表征材料硬度的力学参数均随BaHfO3纳米薄膜厚度减小而显著减小,呈现尺寸效应．电荷密度分布分析揭示了薄膜厚度改变了BaHfO3纳米薄膜的价健特性,这是材料硬度改变的内在原因．该研究结果为BaHfO3纳米薄膜材料的设计与应用提供了理论依据．     

高压下BaHfO3电子结构与光学性质的第一性原理研究

从第一性原理出发,在局域密度近似下,采用基于密度泛函理论的平面波超软赝势计算方法系统地研究了高压对BaHfO₃电子结构与光学性质的影响.能带结构分析表明;无压强和施加正压强作用时,BaHfO₃为直接带隙绝缘体,而施加负压强时,BaHfO₃则转变为间接带隙半导体;BaHfO₃的带隙随压强增加而减小,且具有明显的非线性关系.对光学性质的分析发现:施加正压强后,光学吸收带边产生蓝移;负压强作用时介电函数虚部尖峰减少,光学吸收带边产生红移;施加压强后BaHfO₃的静态介电常数和静态折射率均增大.上述研究表明施加高压有效调制了BaHfO₃的电子结构和光学性质,计算结果为BaHfO₃光电材料的设计与应用提供了理论依据.     

高压下BaHfO3电子结构与光学性质的第一性原理研究

从第一性原理出发,在局域密度近似下,采用基于密度泛函理论的平面波超软赝势计算方法系统地研究了高压对BaHfO3电子结构与光学性质的影响．能带结构分析表明：无压强和施加正压强作用时,BaHfO3为直接带隙绝缘体,而施加负压强时,BaHfO3则转变为间接带隙半导体;BaHfO3的带隙随压强增加而减小,且具有明显的非线性关系．对光学性质的分析发现：施加正压强后,光学吸收带边产生蓝移;负压强作用时介电函数虚部尖峰减少,光学吸收带边产生红移;施加压强后BaHfO3的静态介电常数和静态折射率均增大．上述研究表明施加高压有效调制了BaHfO3的电子结构和光学性质,计算结果为BaHfO3光电材料的设计与应用提供了理论依据．     

La掺杂3C-SiC电子结构和光学性质的第一性原理研究

采用基于密度泛函理论的第一性原理计算方法,对未掺杂及稀土材料La掺杂3C-SiC的电子结构和光学性质进行理论计算.计算结果表明,La掺杂引起3C-SiC晶格体积增大,掺杂体系能量更小,掺杂体系的结构更稳定;未掺杂3C-SiC是直接带隙半导体,其禁带宽度为1.406 eV,La掺杂后带隙宽度下降为1.161 eV,La掺杂3C-SiC引入了3条杂质能级,能量较高的1条杂质能级与费米能级发生交叠,另外2条杂质能级都在费米能级以下价带顶之上,La掺杂引起3C-SiC吸收谱往低能区移动,未掺杂3C-SiC的静态介电常数为2.66,La掺杂引起静态介电常数增加为406.01,La掺杂3C-SiC是负介电半导体材料.     

BaZrO3和CaZrO3能带和光学性质的第一性原理研究

采用基于密度泛函理论基础上的CASTEP软件包,计算了BaZrO3和CaZrO3的能带以及光学性质.计算得到BaZrO3直接带隙和间接带隙分别为3.49 eV和3.23eV,CaZrO3直接带隙和间接带隙分别为3.73 eV和3.38 eV.对这两种材料的介电函数、吸收系数、反射系数、折射系数、湮灭系数和能量损失系数等光学系数进行了计算,并基于电子能带对光学性质进行了解释.得出,光学特性的异同是由于其内部微观结构上的异同所引起的.     

掺杂BaHfO3电子结构与力学性能的第一性原理研究

在广义梯度近似(GGA)下,采用基于密度泛函理论的第一性原理方法研究了掺杂对BaHfO3的电子结构与力学性能的影响.电子结构计算表明:优化的BaHfO3晶格常数与实验值吻合较好,BaHfO3为一种间接带隙的绝缘体材料.掺杂Sr和Ti后该材料仍为间接带隙材料,Ba0.5Sr0.5HfO3的带隙增大,绝缘体特征增强,而BaHf0.5Ti0.5O3的带隙显著减小,呈现出半导体材料的特征.由态密度分析可知,掺杂后带隙的变化主要是由于导带底的移动造成的.力学性能分析表明:与BaHfO3相比,Ba0.5 Sr0.5 HfO3的剪切模量和杨氏模量均明显减小,材料硬度减弱;BaHf0.5Ti0.5O3的剪切模量及杨氏模量均明显增大,材料硬度增强.电子密度分布分析揭示了掺杂改变体系价电子浓度的分布情况,使BaHfO3的价健特性发生了变化,这是材料硬度改变的内在原因.可见,掺杂能够有效地调控体系的硬度,该研究结果为掺杂BaHfO3力电材料的设计与应用提供了理论依据.     

Ru2Si3在应力作用下的第一性原理研究

采用基于第一性原理的密度泛函理论(Density functional theory)赝势平面波方法,对应力下Ru2Si3的电子结构和光学性质进行了理论计算和比较.计算结果表明:随着正应力的逐渐增大,导带向高能方向移动,带隙Eg明显展宽;随着负应力的逐渐增大,带隙缓慢减小并且始终为直接带隙.光学性质曲线随着负应力的不断...     

α-Mg3Sb2的电子结构和力学性能

运用第一性原理研究了Mg-Sb合金中典型沉淀相α-Mg3Sb2的几何、电子结构和力学性能.结构优化得到的晶格常数和形成能与实验值符合很好.电子结构分析表明,具有半导体性质的α-Mg3Sb2带隙为0.303 eV,是间接带隙半导体.通过计算得到了α-Mg3Sb2的弹性常数,进而得到模量、泊松比等力学参数,对力学参数进行分析发现,α-Mg3Sb2有很好的延展性而塑性相对较差.通过对α-Mg3Sb2施加应变前后态密度的变化分析,发现对于六角结构的α-Mg3Sb2,与剪切模量相关的C11+C12,C33/2和与体模量相关的C11+C12+2C13+C33/2对体积变化不保守,而(C11-C12)/4和C44对体积变化保守.     

Sc2O3电子结构和光学性质的第一性原理研究

本文基于第一性原理平面波赝势(PWP)和广义梯度近似(GGA)方法,研究了Sc2O3的电子结构、态密度和光学性质. 计算结果表明：Sc2O3是一种直接带隙半导体,其能带宽度为3.79eV,价带顶部主要由O的2p和Sc的3p3d杂化而成,导带主要由Sc的3d和O的2p构成. 同时,文中也分析了Sc2O3的介电函数、折射率、光电导率和吸收谱等光学性质. 计算得到静态介电常数 ,折射率n0=1.25,在紫外区有较大的吸收系数.     

The gas phase infrared band contours of s-triazine and s-triazine-d3: The fundamentals of C3N3H3 and C3N3D3 and some overtone and combination bands of C3N3H3

The systematic application of band contour techniques to account for most of the observed features of the ir spectra of s-triazine and s-triazine-d₃ have been made as well as a critique as to the limitations of such methods. The experimental and computer methods used to study the gas phase infrared band contours of s-triazine and s-triazine-d₃ are out-lined. Contours of the five E′ fundamentals of s-triazine have been recorded under moderate resolution and analyzed to give the Coriolis constants $\text{ζ}{}_{\mathrm{i}}{}^{\mathrm{z}}$, i = 6–10. The effects of l-resonance are very apparent for ν₈ and ν₉, in the form of holes in the Q branches of these bands. Under the highest resolution available, ν₆ and ν₁₀ also show l-resonance effects. Values of the l-doubling constants $\text{q}{}_{\mathrm{i}}{}^{\mathrm{(+)}}$ were obtained for these four fundamentals. One of the parallel A₂″ fundamentals of C₃H₃N₃ (ν₁₂) has also been studied. It lies close to ν₁₀(E′) and an A × E type of second-order Coriolis resonance may be the cause of the intensity enhancement observed in the inner wings of the ν₁₂ and ν₁₀ bands. Hot bands of the type (ν_i + nν₁₄ ? nν₁₄) have been observed in the contours of ν₈, ν₁₀, and ν₁₂. This is felt to be responsible for the large difference between our observed zeta sum (?1.30) and the theoretical sum (?1.00).The gas phase infrared band contours of the five E′ and 2A₂″ fundamentals of C₃N₃D₃ have also been recorded under moderate resolution. From P-R separations and by computer simulation of the contours, values of the Coriolis constants $\text{ζ}{}_{\mathrm{i}}{}^{\mathrm{z}}$ have been obtained for the E′ modes. The effects of l-resonance have been observed for ν₈(E′) and ν₁₀(E′) and values of the l-doubling constants $\text{q}{}_{\mathrm{i}}{}^{\mathrm{(+)}}$ have been estimated. An extensive series of hot bands of the type (ν₁₂ + nν₁₄ ? nν₁₄) has been observed in the contour of the ν₁₂ (A₂″) fundamental. The mass effect on the Coriolis constants has been discussed.Infrared band contours of the overtone 2ν₇ and seven degenerate E′ combination bands of C₃N₃H₃ have been recorded under moderate resolution. Analysis of these contours using the P-R separation method and computer simulation of the contours has given values of $\text{ζ}{}_{\mathrm{<mtext>eff</mtext>}}{}^{\mathrm{z}}$ for these bands. Fermi resonance between 2ν₇ and ν₆ has been analyzed. The importance of considering both the observed contour as well as the observed frequency when assigning higher tone bands is illustrated.     

Fine structure and isotope shift of the 3s4d 3 D-3s3p 3 P, 3s5d 3 D-3s3p 3 P and 3p 2 3 P-3s3p 3 P Transitions of MgI

Summary We report the measurements of the³ D(3s4d)-³ P(3s3p)³ D(3s5d)-³ P(3s3p), and³ P(3p ²)-³ P(3s3p) transition frequency of MgI, the fine-structure separation and isotope shift between²⁴Mg and²⁶Mg. The measurements have been performed in a metastable atomic beam; a good agreement is found for data already existing in the literature. The accuracy of the measurements reported in this paper is mainly limited by the Doppler broadening of theI ₂ transitions used as a reference and by the precision in the knowledge of the related wavelengths.     

Dielectric investigations of solid solutions SrTiO3-KTaO3 and SrTiO3-KNbO3

The temperature dependences of the dielectric constant and dielectric hysteresis loops in ceramic samples of (1 ? x)SrTiO_3?x KNbO₃ and (1 ? x)SrTiO_3?x KTaO₃ (0 ≤ x ≤ 0.3) solid solutions prepared using different heat treatments have been investigated. Phase diagrams of the studied solid solutions have been constructed in the T-x coordinates. It has been shown that, after quenching of samples (spontaneous cooling at room temperature after long-term heating at the sintering temperature of the ceramic samples), the temperature of the induced phase transition increases because of the weakening of random electric fields associated with nonisovalent impurities due to their “frozen” nonequilibrium redistribution. For small concentrations x, strong dielectric relaxation is observed in the temperature range of 150–250 K. A model of relaxing centers, which is based on the local charge compensation of heterovalent impurities, has been proposed.     

Modulated magnetic structures of ErPb3, HoPb3, ErTl3 and HoTl3

Neutron diffraction experiments have been carried out on the magnetically ordered phases of ErPb₃, HoPb₃, ErTl₃ and HoTl₃. The magnetic moments were found to be sinusoidally modulated with a propagation vector of (0, 0.2, 0.5) for the Pb-compounds and (0.38, 0.38, 0.16) for the Tl-compounds.Work supported by the Bundesministerium für Forschung und Technologie     

Scintillation properties of Ce3+-doped YCl3 and YBr3

The dependence of the scintillation properties of Ce³⁺-doped YCl₃ and YBr₃ on activator concentration (0.5, 1 and 2 mol%) has been studied. The radioluminescence spectra of both materials contain asymmetric bands with maxima located at 3.13 eV (383 nm) for YCl₃:Ce³⁺ and 2.84 eV (422 nm) for YBr₃:Ce³⁺. The scintillation pulse decay curves for both materials are described by two components with decay constants of 37 and 640 ns for YCl₃:Ce³⁺ and 36 and 450 ns for YBr₃:Ce³⁺, the fractions of the faster component being 86 and 79 per cent, respectively. The dependences of the light yield of the studied materials on Ce³⁺ concentration pass through a maximum near 1 mol% of the activator, and the maximum light yields (relative to NaI:Tl) are 8700 photons per MeV for YCl₃:Ce³⁺ and 20,600 photons per MeV for YBr₃:Ce³⁺.     

Far Infrared Spectra of Ammonia-Boron Trifluoride: NH3BF3 and ND3BF3

Abstract

Spectra of polycrystalline samples of NH₃BF₃ and ND₃BF₃ at 300 K and 98 K have been recorded in the frequency range 20-400 cm^?1. Isotopic frequency ratios are used to interpret the observed features in terms of the known molecular and crystal structures.