热原子层沉积钛掺杂氧化镓薄膜的光学性能

在250℃的低温下，以三甲基镓、四(二甲氨基)钛为前躯体源，O₃为反应气体，采用热原子层沉积制备了Ti掺杂Ga₂O₃(TGO)薄膜。Ga₂O₃和TiO₂的生长速率分别为0.037 nm/cycle和0.08 nm/cycle,TGO薄膜厚度低于理论计算值。X射线光电子能谱仪测试结果表明膜中Ti浓度随Ga₂O₃/TiO₂循环比减少而增加，O 1s、Ga 2p和Ti 2p的峰位置向较低的结合能移动，这是因为Ti原子取代了Ga原子的某些位点引起了结合能降低，表明Ti元素成功掺杂到Ga₂O₃薄膜中。TiO₂和Ga₂O₃的芯能级光谱分析表明薄膜中存有Ti⁴⁺和Ga³⁺离子。TGO薄膜的O 1s芯能级光谱中Ga-O键随着Ti-O键含量增加而下降，表明T...     

Fe2O3上AsH3催化氧化反应机理的理论研究

本文采用密度泛函理论方法研究了Fe₂O₃上AsH₃的催化氧化反应机理.该反应以Fe₂O₃中的两个Fe原子为不同的活性中心进行研究,每个活性中心均设计了3个步骤. AsH₃分子依次与3个O₂分子在催化剂上相互作用分别形成中间体H₃AsO₂、H₃AsO₄及最终产物H₃AsO₆.研究发现,当氧化反应发生在1号铁原子(Fe1)附近,其速度控制步骤活化自由能垒为49.99 kcal/mol;当氧化反应发生在2号铁原子(Fe2)附近,其活化自由能垒为21.20 kcal/mol,与直接氧化(50.14 kcal/mol)相比大大降低.可见AsH₃在Fe₂O₃上的催化氧化反应更易发生在Fe2附近.     

Fe:Mg:LiNbO3晶体电子结构和吸收光谱的第一性原理研究

基于密度泛函理论的第一性原理, 研究了LiNbO₃晶体以及不同Mg浓度的Fe:Mg:LiNbO₃晶体的电子结构和吸收光谱. 研究结果显示: 掺铁铌酸锂晶体的杂质能级由Fe 的3d轨道和O的2p轨道贡献, 禁带宽度为2.845 eV; 对于Mg, Fe共掺样品, Mg的浓度小于或等于阈值时, 禁带宽度分别为2.901 和2.805 eV; 掺铁铌酸锂晶体的吸收谱在2.3和2.6 eV处分别存在一个吸收峰, 其强度因Mg的浓度不同而发生变化. 研究结果还表明, 不同浓度的Mg对晶体内Fe²⁺和Fe³⁺的浓度以及占位产生了不同的影响. 还提出了光电子的形成不应单独考虑铁的轨道电子态, 而应同时考虑与铁成键的氧的轨道电子态的观点.     

Cr4+在八面体格位中的光谱特性研究

采用提拉法生长了Cr单掺和Cr，Mg共掺Al₂O₃晶体，后者具有900—1600nm的宽带吸收.研究了该吸收带在不同气氛、不同温度退火下的变化规律.通过建立合理的晶格缺陷模型，成功地解释了所有的实验结果，并确定Cr，Mg共掺Al₂O₃晶体红外波段宽吸收带属于八面体格位中的Cr⁴⁺离子. 关键词： 4+离子')" href="#">Cr⁴⁺离子 八面体格位 晶格缺陷     

Y2O3: Eu,Dy的制备与红色长余辉发光性能研究

采用高温固相法合成发光样品Y₂O₃：Eu³⁺_0.01和Y₂O₃：Eu³⁺_0.01,Dy³⁺_0.01.X射线衍射分析(XRD)表明样品保持Y₂O₃晶格结构,掺入的Eu³⁺和Dy³⁺对Y_{2关键词： 长余辉 2}O₃')" href="#">Y₂O₃ 稀土掺杂 陷阱     

Er/Yb共掺体系的光致荧光行为及相关物理过程研究

采用固相反应方法，制备了Er₂O₃浓度固定为0.5mol%，Yb₂O₃浓度范围为0.0mol%—5.5mol%的Er/Yb共掺激光玻璃.通过吸收光谱、光致荧光光谱和上转换荧光光谱，研究了Yb₂O₃浓度对Er³⁺荧光特性的影响，并探讨了相关的物理机制.研究结果表明：Yb³⁺共掺对Er³⁺的⁴ 关键词： Er/Yb共掺 光致荧光 能量传递 合作上转换     

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     

锰酸锂掺杂Fe和Co的性质的第一性原理计算

文章基于密度泛函理论的第一性原理计算,研究了LiMn₂O₄电池材料在掺杂Fe和Co离子时的电子结构和电化学性能.发现Fe\Co取代Mn³⁺在热力学上是会更加稳定,提升电化学性能.掺杂Fe后,LiMn₂O₄电池材料晶格参数减小(约0.3%);掺杂Co后,LiMn₂O₄电池材料晶格参数减小(约0.5%).这两种掺杂方式让与之相邻的Mn³⁺被氧化成Mn⁴⁺,从而降低了Jahn-Teller畸变情况产生可能性.对于掺Fe尖晶石型锰酸锂(Li₈Mn₁₅FeO₃₂),Mn环境中的Li离子会更容易被提取,第一次放电电压从原来的3.7 V增加至4.623 V;对于掺Co尖晶石型锰酸锂(Li₈Mn₁₅CoO₃₂),第一次放电电压从原来的3.7 V增加至4.101 V.研究为锂电池...     

Magnli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Magneli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,Ti₈O₁₅Fermi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.     

掺铋BaF2晶体的制备及其近红外发光研究

通过温度梯度法制备了Bi₂O₃:BaF₂以及BiF₃:BaF₂晶体.在Bi₂O₃:BaF₂晶体中观察到了发光峰位于961 nm,半高宽202 nm的超宽带红外发光.在BiF₃:BaF₂晶体中检测到Bi²⁺和Bi³⁺可见区的发光,但是没有观察到红外发光.通过γ射线辐照实现了BiF₃:BaF₂晶体的近红外发光, 发光峰位于1135 nm,半高宽192 nm.讨论了Bi₂O₃和BiF₃掺杂BaF₂晶体的红外发光的机理. 关键词： 近红外发光 铋 氟化钡晶体 γ辐照     

Thermal behavior,microstructure, phase transformation,and crystal growth kinetics of nano-scale Fe3+-doped TiO2 xerogel powders

Titania based ceramics are promising materials for environmental sensors, high efficiency photocatalyst. Ion doping is an effective method to improve the properties by modifying their microstructure and phase composition. In this study, TiO₂ particles doped with Fe³⁺ were prepared by sol-gel method using Ferric nitrate and tetrabutyl titanate as precursors. Fe³⁺ was incorporated in the TiO₂ matrix during thermal treatment in different temperatures. Thermal analysis, TEM and X-ray diffraction were used to characterize the TiO₂ powder. Microstructure, phase content, and cell parameters were calculated according to Rietveld refinement software GSAS. The interaction mechanism of Fe³⁺ in crystal lattice of titanium dioxide and the crystal growth kinetics of Fe³⁺-doped TiO₂ are discussed.     

CEMS study on diluted magneto titanium oxide films prepared by pulsed laser deposition

6% ⁵⁷Fe doped titanium oxide films, prepared by pulsed laser deposition (PLD) on sapphire substrate at 650°C under various vacuum conditions, were characterized mainly by conversion electron Mössbauer spectrometry (CEMS). Two magnetic sextets with hyperfine fields 33 and 29 T, and one doublet were observed in the CEMS spectra of TiO₂ films prepared under PO₂ = 10^?6 and 10^?8 torr, which showed ferromagnetism at room temperature, whereas only the doublet of paramagnetic Fe³⁺ species was observed for the film prepared under PO₂ = 10^?1 torr.     

Various types of photoactive behavior of the Y<Subscript>3</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> ferrimagnetic insulator

The photomagnetic behavior of single-crystal yttrium iron garnet Y₃Fe₅O₁₂ doped with iridium, substituting the cation of iron in the octahedron, is investigated upon illumination at room temperature. It is shown that the photomagnetic properties of Y₃Fe_4.97Ir_0.03O₁₂ samples are to a large degree related to the impurity distortion of the sublattice of iron atoms in octahedral coordination, rather than solely to the possible presence of Fe⁴⁺ cations, which are inactive at room temperature and may even be lacking in single crystals doped with iridium. It is concluded that the photoinduced change in the magnetic parameters of this material is determined by the location of impurity cations and increased surface imperfection of the material. The reasons for the different photoactive behavior of this promising material for spintronics, that is, a singlecrystal yttrium iron garnet, are summarized.     

Photomagnetic effects and disaccommodation in Co-doped YIG

Y₃Fe₅O₁₂ (YIG) doped with ≦ 0.01 Co per molecule in combination with small dopes of V or (and) Mn show a decrease of the permeability in the dark (disaccommodation, DA) as well as when irradiated (photomagnetic effect, PE) with white light. All materials investigated exhibit DA and PE at 77 K, whereas in some cases effects occur at room temperature. The origin is attributed to domain wall pinning by magnetically anisotropic Co²⁺ ions that exchange electrons with Co³⁺ or other (V⁵⁺, Mn³⁺) ions. In view of the wide separation between the cobalt ions (?30 Å) the charge transport via iron ions is supposed to play an essential part.For a sample with higher cobalt dope the shape of the hysteresis loop at 77 K changes in the dark and the change can be hastened by irradiation. This phenomenon is attributed to the growth of a uniaxial anisotropy in the bulk of the material by Co²⁺, Co³⁺ ordering.From the electric resistivity of certain V and Si doped YIG materials it is concluded that V⁵⁺ ions oxidize Fe²⁺ ions according to V⁵⁺+Fe²⁺ → V⁴⁺+Fe³⁺.     

What Oxidation State of Iron Determines the Amethyst Colour?

A colourless quartz crystal doped with ⁵⁷Fe³⁺ was obtained by hydrothermal synthesis in an NH₄F solution. The crystal was transformed into violet amethyst by gamma-irradiation. The change in colour was accompanied by changes in the Mössbauer spectrum that can be interpreted as the conversion of trivalent iron into the tetravalent state: Fe³⁺→Fe⁴⁺.

     

ODMR and EPR investigations of Fe centers in KTaO3

The analysis of EPR spectra obtained from iron doped KTaO₃ crystals in the as-grown state revealed three dominant iron centers: Fe³⁺-O_I, axial Fe-centers with spinS = 3/2 and rhombic Fe³⁺. By comparison with data from literature possible assignments for the center withS = 3/2 are discussed. For the rhombic species the temperature dependence of the main parameters of the Spin- Hamiltonian was measured. The result makes it most plausible that only one rhombic iron center exists in KTaO₃, in contrast with literature. The understanding of the EPR spectra allows us to assign transitions, observed at very low magnetic fields by optically detected magnetic resonance (ODMR), to this rhombic Fe center. On this basis, the magnetic circular dichroism (MCD) of this defect could be identified using the method of tagged-MCD. This spectrum is compared to the tagged-MCD of Fe³⁺-O₁ and of axial Fe⁴⁺ centers, which may be generated metastably by optical charge transfer. Considerably different structures in the MCD spectra of both Fe³⁺ centers indicate different local surroundings and electronic states.Dedicated to O. F. Schirmer on the occasion of his 60th birthday     

ESR of Fe3+ -Rhombic,Fe2+ -Vo and Fe1+ -Vo complexes in SrTiO3

Three new Fe-defect complexes have been identified by ESR in Fe doped crystals of SrTiO₃. These are an Fe³⁺ center with rhombic fine structure in the “as-grown” crystals, and the vacancy associated complexes Fe²⁺ -V_o and Fe¹⁺ -V_o in “reduced” crystals. Photo-excited charge transfer effects are observed for these centers.     

EPR spectra of Fe centers in layered TlGaSe2 single crystal

A single-crystal TlGaSe₂ doped by paramagnetic Fe ions has been studied at room temperature by electron paramagnetic resonance (EPR) technique. The fine structure of EPR spectra of paramagnetic Fe³⁺ ions was observed. The spectra were interpreted to correspond to the transitions among spin multiplet (S=5/2, L=0) of Fe³⁺ ion, which are splitted by the local ligand crystal field (CF) of orthorhombic symmetry. Four equivalent Fe³⁺ centers have been observed in the EPR spectra and the local symmetry of crystal field at the Fe³⁺ site and CF parameters were determined. Experimental results indicate that the Fe ions substitute Ga at the center of GaSe₄ tetrahedrons, and the rhombic distortion of the CF is caused by the Tl ions located in the trigonal cavities between the tetrahedral complexes.     

Structure and magnetic properties of FeCoN films

We obtained crystals of RuS₂ doped with ⁵⁷Fe from a Bi melt and determined the EPR hyperfine structure corresponding to ⁵⁷Fe³⁺ in low-spin configuration. In crystals that were doped with both Fe and Cr an increase of the Fe³⁺ resonance and a simultaneous decrease of the Cr³⁺ resonance occurred by IR irradiation and revealed the same wavelength dependence. Compared with as-grown crystals the iron-doped crystals turned out to have a rather high electrical resistivity of about 10⁴Omega cm at room temperature. For these iron-doped crystals two different activation energies of 0.04 eV and 0.35 eV of the free charge carriers (electrons) were determined from measurements of the electrical conductivity in the range of 94 K and 294 K. Received: 29 July 1996/Accepted: 13 November 1996     

Ferromagnetic ordering of iron impurities in the valence-fluctuating semiconductor SmB6

The electron paramagnetic resonance (EPR) of the valence-fluctuating semiconductor SmB₆ doped by 1 at % Fe is studied. The EPR measurements are performed on a SmB₆ single crystal in a temperature range of 1.6–300.0 K. A number of resonance lines whose g factors indicate the presence of iron ions in the Fe⁰, Fe⁺, Fe²⁺, and Fe³⁺ states have been detected. The iron ions are ferromagnetically ordered below a Curie temperature T = 100 K, and this ordering can be caused by the exchange interaction of impurity ions due to matrix polarization (a similar mechanism is observed in PdFe alloys). This exchange interaction is estimated to be significantly higher than that in PdFe; this fact can result from a very high density of states in the narrow f band, which is characteristic of a valence-fluctuating material.