本征缺陷对β-Ga2O3光催化性质影响的第一性原理研究

运用第一性原理杂化泛函研究了本征缺陷(O空位和Ga空位)对于β-Ga₂O₃的几何结构和电子性质的影响.计算结构表明:杂化泛函B3LPY能很好的描述β-Ga₂O₃的几何结构和电子结构,能与实验符合.含O缺陷的形成能在富氧和贫氧下分别为4.04和0.92 eV,优于含Ga缺陷的体系.空位缺陷的出现对于理想Ga₂O₃的晶格参数影响不显著,只是在O空位体系中,空位附近Ga-O键长有0.1?变化.含空位缺陷的体系的禁带中都有缺陷能级的出现,含Ga和O空位缺陷的Ga₂O₃的光跃迁能分别为1.93 eV(β自旋)和2.92 eV,有很明显的光吸收的拓展,从理论上解释了Ga₂O₃作为光催化材料的潜在应用.     

高氧空位简并锐钛矿TiO2半导体电子寿命的第一性原理研究

为了研究锐钛矿TiO₂晶体中高氧空位浓度对电子寿命的影响,利用基于局域密度泛函理论框架下的广义梯度近似平面波超软赝势方法, 用第一性原理对含高氧空位浓度的锐钛矿TiO₂晶体进行了结构优化处理、能带分布和态密度分布计算, 表明在温度一定和高氧空位浓度的条件下, 锐钛矿TiO₂的电子寿命随氧空位浓度的增大而减小;电子浓度的大小对电子寿命无影响.同时,锐钛矿TiO₂晶体中高氧空位浓度时,发现有莫特相变的现象. 关键词： 高氧空位 2半导体')" href="#">锐钛矿TiO₂半导体 电子寿命 第一性原理     

β型烧绿石结构氧化物超导体$lt;i$gt;A$lt;/i$gt;Os$lt;sub$gt;2$lt;/sub$gt;O$lt;sub$gt;6$lt;/sub$gt;($lt;i$gt;A$lt;/i$gt;=K,Rb,Cs)电子能带结构的第一性原理计算

用全势线性缀加平面波方法计算β型烧绿石结构氧化物超导体AOs₂O₆ （A=K,Rb,Cs）的电子能带结构及态密度.计算发现电子自旋轨道耦合和在位库仑势U的作用增大了费米面处态密度值.通过计算还得到这三种化合物电子关联常数λ_c分别为1.55,1.12和0.73.由实验测量与能带计算得到的电子比热容系数的比值得到电子质量提高参数.通过分析这三种化合物电子质量提高参数,推算出它们的电声子耦合常数λ_ep分别为1.56,0.78和1.08.由此提出KOs₂O₆为强电子关联和强电声子耦合系统,而RbOs₂O₆和CsOs₂O₆的电子关联性与电声子耦合为中等. 关键词： β型烧绿石超导体 能带结构 电子关联 电声子耦合     

Ti掺杂W$lt;sub$gt;18$lt;/sub$gt;O$lt;sub$gt;49$lt;/sub$gt;纳米线的电子结构与NO$lt;sub$gt;2$lt;/sub$gt;敏感性能的第一性原理研究

采用基于密度泛函理论框架下的第一性原理平面波超软赝势方法,通过理论建模,研究了Ti掺杂的非化学计量比W₁₈O₄₉纳米线的几何与能带结构以及电子态密度,并通过进一步计算NO₂/Ti-W₁₈O₄₉纳米线吸附体系的吸附能、电荷差分密度与电荷布居,分析了Ti掺杂W₁₈O₄₉纳米线的气体吸附与敏感性能. 计算发现,Ti掺杂改变了W₁₈O₄₉纳米线的表面电子结构,引入的额外的杂质态密度和费米能级附近能带结构的显著变化,使掺杂纳米线带隙与费米能级位置改变,纳米线导电性能增强. 吸附在W₁₈O₄₉纳米线表面的NO₂作为电子受体从纳米线导带夺取电子,导致纳米线电导降低,产生气体敏感响应. 与纯相W₁₈O₄₉纳米线相比,NO₂/Ti-W₁₈O₄₉纳米线吸附体系内部存在更多的电子转移,从理论上定量地反映了Ti掺杂对改善W₁₈O₄₉纳米线气敏灵敏度的有效性. 对Ti掺杂纳米线不同气体吸附体系电子布居的进一步计算表明,Ti掺杂纳米线对NO₂气体具有良好的灵敏度和选择性. 关键词： 密度泛函计算 Ti掺杂 18O₄₉纳米线')" href="#">W₁₈O₄₉纳米线 气敏     

高氧空位浓度对金红石TiO2导电性能影响的第一性原理研究

采用基于密度泛函理论的平面波超软赝势方法研究了 纯的和不同高氧空位浓度金红石型TiO_2-x (x=0, 0.083, 0.125, 0.167, 0.25)超胞的能带结构分布、态密度分布.同时, 采用局域密度近似+U方法调准了带隙.结果表明, 高氧空位浓度越高, 金红石型TiO₂的最小带隙越变窄、电子有效质量越减小, 自由电子浓度越高, 电子迁移率越低、电导率越低.计算结果与实验结果的变化趋势相符合. 关键词： 高氧空位 2')" href="#">金红石型TiO₂ 电导率 第一性原理     

Si掺杂β-Ga2O3的第一性原理计算与实验研究

采用基于密度泛函理论(DFT)的第一性原理平面波超软赝势(USPP)法, 在广义梯度近似(GGA)下计算了本征β-Ga₂O₃和Si掺杂β-Ga₂O₃的能带结构、电子态密度、差分电荷密度和光学特性. 在蓝宝石衬底(0001)晶面上用脉冲激光沉积(PLD)法制备了本征β-Ga₂O₃和Si掺杂β-Ga₂O₃薄膜, 测量了其吸收光谱和反射光 关键词： 第一性原理 超软赝势 密度泛函理论 2O₃')" href="#">Si掺杂β-Ga₂O₃     

双层钙钛矿氧化物Sr2CrBO6 (B = Os,Re,W)电子结构和光学性质的第一性原理研究

Sr₂CrBO₆(B=Os, Re, W)被证实是具有最高磁转变温度的双钙钛矿氧化物.论文采用基于密度泛函理论的第一性原理方法,计算了Sr₂CrBO₆的电子结构和光学性质,并通过计算结果分析了二者之间的内在关系.总体来看,B位元素的改变对材料的电子结构和光学性质都产生了较大的影响.由能带结构的计算,Sr₂CrOsO₆为半导体,Sr₂CrReO₆和Sr₂CrWO₆为半金属.晶体介电函数虚部ε₂(ω)曲线在所考察的能量范围内存在明显的介电特征峰,论文结合态密度和能带结构讨论了这些介电峰所对应的电子跃迁过程. Sr₂CrOsO₆和Sr₂CrReO₆在可见光区域均有较强的吸收,其中,Sr₂CrReO₆在394 nm处的峰值吸收...     

Co掺杂β-Ga2O3的电学性质和电荷转变能级的第一性原理计算

采用基于密度泛函理论的第一性原理计算方法,研究了Co掺杂β-Ga₂O₃体系的电学性质和转变能级.研究发现,Co原子代替Ga原子后会导致电子结构发生显著变化.利用杂化泛函(HSE06)计算了体系的能带结构,发现随着Co掺杂浓度增加,β-Ga₂O₃禁带宽度逐渐减小,增加化合物对光的吸收,增强它们的光学性能和载流子输运能力.在β-Ga₂O₃体系的四面体格位掺入Co原子,将引入了4.00μ_B的磁矩,磁矩主要来源于Co原子.通过对电子局域函数的分析,可知,Ga, Co和O原子之间是共价键和离子键共同结合.在富镓的条件下,1×3×2超胞模型下,Co掺杂会形成浅受主杂质能级.     

氧空位对Eu2+, Dy3+掺杂的Ca5MgSi3O12发光及余辉性能的影响

利用高温固相法合成了稀土离子Eu²⁺, Dy³⁺掺杂的Ca₅MgSi₃O₁₂长余辉发光材料. 利用光谱学证明了在材料内部存在与氧空位有关的缺陷发光. 通过对比不同条件下合成样品的发光及余辉性能, 发现氧空位对材料的发光及余辉均起到促进作用. 同时发现氧空位发光可以向发光中心传递能量. 利用热释光曲线系统的分析了氧空位对余辉性能的影响. Ca₅MgSi₃O₁₂:Eu²⁺,Dy³⁺是一种潜在的长余辉发光材料. 关键词： 长余辉 氧空位 能量传递 热释光     

Magnéli相亚氧化钛Ti8O15的电子结构和光学性能的第一性原理研究

采用基于密度泛函理论的平面波超软赝势法研究了Magnéli相亚氧化钛Ti₈O₁₅的电子结构和光学性能. 计算出的能带结构显示Ti₈O₁₅相比锐钛型TiO₂禁带宽度大幅度降低. 态密度分析表明, 其原因在于Ti₈O₁₅的O原子的2p轨道以及Ti原子的3p, 3d轨道相对于TiO₂的相应轨道向左产生了偏移, 同时由于O原子的缺失使得Ti原子的3d, 3p轨道多余电子在Fermi能级附近聚集形成新的电子能级. 态密度分析结果还显示, 相对于TiO₂, Ti₈O₁₅ Fermi能级附近电子格局发生了如下变化: O原子的2p轨道电子贡献减少, Ti原子的3d轨道的电子对Fermi能级贡献增大. 光吸收计算图谱表明, TiO₂仅在紫外光区有较高的光吸收能力, 而Ti₈O₁₅由于禁带宽度变窄引起光吸收范围红移到可见光区, 从而在紫外光区和可见光区都有较高的光吸收能力, 计算结果与实验得到的紫外-可见漫反射吸收光谱结果一致. 关键词： 第一性原理 8O₁₅')" href="#">Magnéli相亚氧化钛Ti₈O₁₅ 电子结构 光学性能     

Mössbauer study of amorphous Fe2RE (RE=Ce,Er) alloys

Among amorphous Fe₂RE (RE=Er, Ce, Gd, La, Pr, Sm, Dy, Ho) alloys, Fe₂Ce exhibits a tendency toward short range order, while the other Fe₂RE compounds show clustering. However, we have almost no information about environments around Fe atoms. Using Mössbauer spectroscopy we have determined the quadrupole splitting distributionsP(QS) of two representative amorphous Fe₂RE (RE=Ce, Er) alloys, leading to local environments of Fe atoms. The analysis of the mixed magnetic dipole and quadrupole interactions in Fe₂Er shows two kinds of electrical field gradients (EFT) with the positive and negative signs in the sample, indicating a random packing of Fe atoms. Furthermore, the analyzed quadrupole splitting distributionP(QS) of Fe₂Er also supports random packing in this amorphous alloy. On the other hand, the amorphous Fe₂Ce alloy shows two kinds of distributions of quadrupole splitting; the major component indicating random packing and the minor component Ce-rich Ce-Fe clusters.     

Thermoluminescent properties of Eu and RE co-doped phosphors CaGa2S4:Eu, RE (RE=Ln, excluding Pm, Eu and Lu)

The thermo-luminescence (TL) of rare earth ions RE³⁺ (RE=Ln, excluding Pm, Eu and Lu) co-doped phosphors CaGa₂S₄:Eu²⁺, RE³⁺ was studied between room temperature and 300 °C, and 3D thermo-luminescence of the phosphors were measured from room temperature to 400 °C. The basic material CaGa₂S₄:Eu²⁺, showed at least two bands in the TL glow curve. Changing the auxiliary activator RE³⁺ (rare earth ion), intensities and the positions of the TL glow curve peaks were affected significantly. For the phosphors with long afterglow, auxiliary activator such as Ce³⁺, Pr³⁺, Gd³⁺, Tb³⁺, Ho³⁺, or Y³⁺ created some new defects in these compounds at lower trap levels and enhanced their TL intensities. The Nd³⁺ or Er³⁺ auxiliary activator only enhanced TL intensities to a low extent, so these two phosphors have short persistent luminescence at room temperature. TL intensities of La³⁺, Sm³⁺, Tm³⁺ or Yb³⁺ co-doped phosphors were suppressed greatly and no afterglow was shown. The relationship between auxiliary activators and corresponding thermo-luminescence curves of phosphors CaGa₂S₄:Eu²⁺, RE³⁺ are discussed in detail. According to our results, suitable activation energy and enough high corresponding trap density are necessary for the phosphor with long afterglow.     

Transport properties and mangetoresistance of (RE,Sr)2NiO4 (RE=Pr,Nd, Sm and Eu)

We report on the crystal growth and the measurements of resistivity, magnetoresistance and photoemission spectroscopy of (RE,Sr)₂NiO₄ in the heavily Sr-doped region. Although the in-plane resistivity of the heavily Sr-doped crystals was rather small at room temperature, it increased for several orders of magnitude with decreasing temperature. A large negative magnetoresistance was observed for NdSrNiO₄ at low temperature, while only small magnetoresistance was observed for the single crystals of RE=Pr, Sm and Eu. Photoemission spectroscopy measurements revealed a significant influence of the RE 4f states to the electronic structure at relatively low binding energies in PrSrNiO₄ and NdSrNiO₄.     

Growth and spectroscopic properties of RE, Mn:YAP (RE=Yb and Ce) photorefractive crystals

RE, Mn:YAP (RE=Yb and Ce) crystals with dimension of Φ 25×60 mm were successfully grown by the Czochralski method. The spectroscopic properties of RE, Mn:YAP (RE=Yb and Ce) crystals before and after γ-irradiation were investigated at room temperature. The results show that the content of Mn⁴⁺ ions was increased with the Yb³⁺ ions co-doping, but decreased by Ce³⁺ ions co-doping. Thermoluminescence (TL) spectra of the crystals indicate three steps of recombination, and the probable recombination processes were discussed.     

Photoluminescence studies of NaCaPO4:RE (RE=Dy, Mn or Gd)

The purpose of the present study is to develop an understanding of photoluminescence properties of Dy³⁺, Mn²⁺ or Gd³⁺doped NaCaPO₄ phosphors, which have served as efficient phosphors in many industrial applications. The phase formation was confirmed by the X-ray powder diffraction (XRD) measurement. Photoluminescence (PL) excitation spectrum measurement of NaCaPO₄:Dy³⁺ shows this phosphor can be efficiently excited by near-ultraviolet (UV) light from 300 to 400 nm and presents dominant luminescence band centered at 480 nm (blue) and 573 nm (yellow). The PL excitation of NaCaPO₄:Mn²⁺ and Gd³⁺ under UV wavelength shows the emissions at 520 and 313 nm, respectively. A scanning electron microscope (SEM) shows an average crystallite size in sub-micrometer range. The obtained results show that the phosphors have the potential for application in the lamp industry and medical applications.     

CaAl3BO7：RE(RE=Ce,Gd,Tb)中稀土离子的光谱特性

采用固相反应法合成了CaAl₃BO₇RE(RE=Ce,Gd,Tb),研究了Ce³⁺,Gd³⁺和Tb³⁺的光谱特性。发现铈离子周围存在较强的晶场,使基态的4f能级劈裂较大,从而导致铈离子的特征发射峰重叠较大;Ce³⁺的5d能级明显低于Gd³⁺的⁶I、⁶P能级;Ce³⁺和Tb³⁺之间存在有效的能量传递。     

Crystal chemistry and physical properties of the ternary compounds RE5B4C5 (RE=Ce,Pr, Nd)

The ternary rare-earth metal boride carbides RE₅B₄C₅ (RE=Ce, Pr, Nd) were prepared by arc melting the mixtures of the pure elements and subsequent annealing at 1270 K. Their crystal structures were determined from single crystal X-ray diffraction data. They crystallize in the Ce₅B₄C₅ type of structure (space group Pna2₁, Z=8). Two new compounds were found, Pr₅B₄C₅: a=24.592(2) Å, b=8.4563(5) Å, c=8.4918(5) Å, R₁=0.043 (wR₂=0.076) for 2871 reflections with I_o?2σ(I_o)); for Nd₅B₄C₅: a=24.301(1) Å, b=8.3126(5) Å, c=8.3545(4) Å, R₁=0.035 (wR₂=0.069) for 3707 reflections with I_o?2σ(I_o)). Its structural arrangement consists of a three-dimensional framework of rare-earth atoms resulting from the stacking of slightly corrugated two-dimensional square nets, leading to voids filled with B₄C₄, B₃C₃, BC₂ finite chains and isolated carbon atoms. Ce₅B₄C₅ is an antiferromagnet at 5 K followed by a metamagnetic transition in elevated external fields. Pr₅B₄C₅ and Nd₅B₄C₅ are ferromagnets below T_C=12 and 15 K, respectively.     

Effect of RE as a co-dopant in long-lasting phosphorescence CdSiO3:Mn (RE=Y, La, Gd, Lu)

Effect of RE³⁺ as a co-dopant in long-lasting phosphorescence CdSiO₃:Mn²⁺ (RE=Y, La, Gd, Lu) has been investigated. A longer orange emitting phosphorescence phenomenon was observed in the co-doped CdSiO₃:Mn²⁺,RE³⁺ phosphors after exciting with ultraviolet (UV) light. The luminescence properties, including photoluminescence (PL) spectra and thermoluminescence (TL) spectra, as well as the afterglow decay curves, were studied. The results revealed that one of the origins of the improvement is due to nonequivalent substitution to produce more e-traps, and energy transfer from Gd³⁺ to Mn²⁺ to boost the performance of CdSiO₃:Mn²⁺,Gd³⁺. Role of RE³⁺ co-doped into CdSiO₃:Mn²⁺ matrix and the possible long-lasting phosphorescence process are discussed in this paper.     

Glass formation and microstructure evolution in Al–Ni–RE (RE = La,Ce, Pr,Nd and misch metal) ternary systems

Glass formation has been systematically studied in melt-spun Al-rich Al–Ni–RE (RE?=?La, Ce, Pr, Nd and Mm; Mm?=?misch metal) alloys by navigating the compositions following the observation of microstructure evolution in the resulting ribbons. The optimum glass-forming regions are similarly located around Al₈₅Ni₁₀RE₅ and found in the centre of the composites with primary phase α-Al, Al₁₁RE₃ and Al₃Ni. The similarities in the critical cross-section below which a component is fully amorphous and the optimum compositions in these Al–Ni–RE systems are interpreted in terms of their competing crystalline phases and thermodynamic properties. Interestingly, it is indicated that Ni content is markedly higher than RE content in the best glass-forming alloys, which may be associated with strong interaction between Ni–Al atom pairs and the dense packing due to Ni-centred clusters.     

Properties of amorphous CoZr(RE) (RE=Gd,Sm, Dy) films with various uniaxial anisotropies,prepared by a new process

If a DC magnetic field is applied parallel to the plane of amorphous CoZr(RE) thin films during sputter depositing, a uniaxial anisotropy is formed the direction of which depends upon the choice of RE substituted and its concentration. When RE=Gd a perpendicular anisotropy K_p forms over a large concentration range, a spin reorientation process being at the origin of the process. A well-defined K_p is developed also in CoFeZrGd and CoZrGdSm films. CoZrGdDy films exhibit simultaneously a perpendicular and an in-plane uniaxial anisotropy. The related magnetization process and domain structures are quite peculiar.