稀土元素(Nd/Sm/Gd/Dy)掺杂SnO2的第一性原理计算

基于密度泛函理论的第一性原理,计算分析了Nd、Sm、Gd和Dy四种稀土元素掺杂SnO2的电子结构和光学性质.计算结果表明:掺杂稀土元素Nd、Sm、Gd、Dy后,Sn7 XO16体系的晶胞体积及晶格常数都有不同程度的增大,禁带宽度减小,在费米能级附近出现了杂质能级.光学性质方面,掺杂稀土元素Nd、Sm、Gd、Dy后,体系的吸收边都向低能方向移动,发生了红移,拓宽了光谱响应范围,与未掺杂之前相比,掺杂稀土元素Nd后的静态介电常数减小,其余三种体系增大.     

Sn1-xNxO2材料光电性质的研究

基于密度泛函理论的第一性原理,采用广义梯度近似(GGA)下的线性缀加平 面波(FP-LAPW)方法,应用WIEN2K软件计算了超晶胞结构Sn1-xNxO2材料的总态密度、能带结构和光学折射率及介电函数虚部.计算结果表明掺杂后费米能级向低能方向移动,随着掺杂量的增加,Sn1-xNxO2材料的价带和导带的分裂程度增强,禁带宽度逐渐减小,并且在1.35～ 2.50 eV的能量范围上形成了杂质带,其主要来源是N的2p态上的电子.分析Sn1-xNxO2材料的能带结构可知掺杂前后均是直接跃迁半导体,掺杂后其介电函数谱和折射率也与带隙相对应地发生红移,介电谱的跃迁峰与电子从价带到导带的跃迁有关,从理论上指出光学性质与电子结构之间的内在关系.     

C-X(X=Y,Zr)共掺杂SnO2电子结构的第一性原理研究

基于第一性原理方法研究了C单掺杂SnO2和C-X(X=Y,Zr)共掺杂SnO2的能带结构、态密度以及分电荷分布.结果表明:C掺杂、C-Y、C-Zr共掺杂SnO2的带隙值分别为1.109 eV、1.86 eV、1.214 eV,较超胞结构的带隙值降低,有利于电子的跃迁;C-Y共掺杂SnO2的导带底部有3条杂质能级分离出来,C-Zr共掺杂SnO2的能带价带顶部能级中有3条能级分离出来,其中1条能级贯穿费米能级;C-Y,C-Zr共掺杂SnO2的态密度中在低能区会产生1个态密度峰值,部分态密度的峰值由Y、Zr的d轨道贡献;C-Y、C-Zr共掺杂SnO2会打破SnO2电子平衡状态,致使电荷的重新分布.     

γ-Bi2Sn2O7的水热合成及其可见光区光电响应研究

本文采用水热法制备了γ-Bi2Sn2O7并研究了其在可见光区的光电响应.Bi2Sn2O7的晶体结构和光电响应特性分别用X射线衍射和表面光电压谱进行表征.研究结果表明,合成的Bi2Sn2O7呈现γ相立方结构,通过吸收光谱估算光学带隙为2.67eV,比α-Bi2O3(2.85eV)的光学带隙小.Bi2Sn2O7的光电响应相对于α-Bi2O3在可见光区展现出一定的优势,同时对外加电压有很强的响应.     

Cu替位与空位及Cu、S共掺SnO2的光磁性质研究

运用第一性原理,基于密度泛函理论,计算了Cu分别以替位和空位两种方式掺杂SnO2的电子结构和光电特性,并对两种掺杂方式做了一定的比较研究;磁性方面,主要研究了Cu、S共掺SnO2后的磁学性能.计算表明,两种方式掺杂,都使SnO2具有半金属特性,Cu原子将与周围的O原子发生强烈的交换作用,Cu原子对态密度的贡献主要在费米能级附近.相比之下,空位掺杂后的晶胞体积略大于替位掺杂后的SnO2,对光的能量损耗也比替位掺杂的低.对于Cu、S共掺的体系,计算表明:每个Cu原子的掺入将产生0.46μB的磁矩,而一个S原子将引入0.36μB的磁矩,Cu原子周围的O原子也对磁矩有一定的贡献.经过分析,发现体系的磁性来源主要是Cu-3d和S-3p,以及Cu-3 d与O-2 p间的强烈耦合作用.     

Fe,Mn共掺SnO2超晶格电子结构和光学性质研究

基于密度泛函理论的第一性原理,采用了广义梯度近似(GGA)处理交换相关势,用Wien2k软件计算了SnO2超晶格掺杂单层Mn、双层Mn及Fe、Mn共掺情况下的态密度、能带结构、光学性质.结果表明SnO2超晶格单掺Mn时,材料表现为半金属性,这是由于Mn-3d与O-2p的耦合作用,而双层Mn掺杂时仅有O-2p提供.随Mn掺杂层数的增加,其光学性质在低能级处的峰值增大,光学吸收边发生红移,材料透光性能增强.当Fe、Mn共掺时,态密度向低能方向移动,能带结构在Fermi能级附近出现自旋极化,材料表现为半金属性,这是由于Fe与Mn强烈耦合所致.材料的吸收谱、反射谱、能量损失图谱变化趋势一致,但共掺杂比单掺时各谱更向低能方向移动.     

稀土元素Sm与C共掺SnO2的电子结构和光学性质的第一性原理研究

利用第一性原理密度泛函理论,计算了Sm-C共掺SnO2体系的能带结构、能态密度、光学性质.计算结果表明:Sm-C近邻共掺体系的晶胞的结构比较稳定.在电子结构方面,共掺体系的禁带宽度值最小,表明电子从价带激发到导带所需的能量最小.在光学性质方面,掺杂体系都发生了红移,其中Sm-C共掺体系的红移程度最大,增强了对可见光的响应范围;在可见光区,掺杂体系的反射系数、静态介电常数、静态折射率的值都大于纯SnO2,且Sm-C共掺杂体系的值最大.     

Fe掺杂BN催化CO/SO2还原N2O的反应机理研究

通过第一性原理计算,研究在CO或SO2存在下,廉价金属Fe掺杂六方氮化硼(Fe-BN)对N2O还原反应的催化性能.从吸附构型与电子性质分析,发现N2O在Fe-BN的表面自发解离,这是衬底和N2O之间大量电荷转移所致,对N2O的吸附能也远大于CO或SO2,将有利于反应的进行.计算CO、SO2和N2O与O*的反应能垒分别为0.52 eV、1.06 eV和2.61 eV,N2O的反应能垒最高,表明此反应不会发生.Fe-BN对反应产物CO2的吸附较弱,通过反应过程释放的能量便可完成解吸,而反应产物SO3则不能,可见CO作为还原剂更有利.由此得出,Fe-BN是还原N2O的高活性催化剂.本研究为低成本、高活性的基于廉价金属掺杂六方氮化硼催化剂的开发开辟了新的途径.     

Ce、N共掺杂锐钛矿相TiO2光学性能的第一性原理研究

采用密度泛函理论研究了Ce、N共掺杂锐钛矿相TiO2的电子结构、态密度和光学特性.计算结果表明,不同位置Ce、N共掺杂对TiO2的杂质形成能、带隙和光学性质是有影响的.共掺杂带隙比单掺杂TiO2的更窄,导致电子从杂质能级激发到导带的概率增大,这会提高共掺杂TiO2的光量子效率.Ce、N共掺杂后TiO2吸收带边红移至可见光区的更远处,光学吸收系数比单掺杂时更强,这主要是由Ce、N共掺杂的协同效应引起的.带边位置的计算结果表明掺杂TiO2的强氧化还原能力得到保持.因此,Ce、N共掺后TiO2在可见光区具有良好的光催化性能.     

N和As掺杂二维GeC光电性质的第一性原理研究

本文基于密度泛函理论第一性原理,系统研究了单层GeC,N掺杂、As掺杂及N-As共掺杂GeC体系的稳定性、电子结构及光学性质等。结果表明,单层GeC是一种禁带宽度为2.10 eV的直接带隙半导体。与单层GeC相比,掺杂后体系的禁带宽度和功函数均减小,表明体系的电子跃迁所需的能量相对较少。并且,掺杂后体系的光吸收系数均有所提高,同时吸收带边也发生了红移,有效拓宽了体系对光的响应范围,提高了体系对光子的吸收能力。此外,As掺杂GeC体系不仅在费米能级附近出现了杂质能级,而且在低能区的吸收系数、静介电函数及消光系数等光学性质最优。本研究可为GeC光电相关实验制备提供理论基础。     

A review of measurement of thermophysical properties of silicon melt

Measurements of thermophysical properties of Si melt and supplementary study of X-ray scattering/diffraction by the authors' group were reviewed. The values obtained differed variously from those of literature. Density was 2–3% larger, surface tension 20–30% smaller, viscosity up to 40% larger, electrical conductivity 8% smaller, spectral emissivity more or less in good agreement with literature values, and thermal diffusivity a few percent larger. An anomalous density jump was found near the melting point. Surface tension and viscosity also showed anomaly. A strange time-dependent change of density was observed over 3 h after melting. X-ray analyses suggested a slight change in local atom ordering, but showed no sign of cluster formation. An addition of 0.1 at% gallium caused the density jump to disappear, while that of boron caused no change. An EXAFS study of the former melt indicated a strong interaction between Ga and Si atoms as if molecules of GaSi₃ existed. The implications of the measured properties are a possibility of soft-turbulence in an Si melt in a relatively large crucible, a more complicated manner of intake of oxygen depleted molten Si from the free surface region to underneath the growing crystal, and a relaxation of the melt after melting arising from trapped gas species.     

Effect of alumina on enthalpy of mixing of mixed alkali silicate glasses

The enthalpy of mixing of mixed alkali (Na₂O and K₂O) silicate glasses containing various concentrations of alumina was determined using an ion-exchange equilibrium method. For glasses with a constant alkali concentration, the enthalpy of mixing was found to become less negative with alumina addition. Consistent with our previous results on the enthalpy of mixing of alumina-free mixed alkali silicate glasses, the magnitude of enthalpy of mixing exhibited a good correlation with the molar volume mismatch of the corresponding two single alkali glasses as well as with the extent of conductivity mixed alkali effect, e.g. excess activation energy of conductivity, ΔE. The reduction of the magnitude of the enthalpy of mixing with alumina addition can be attributed to the reduction of non-bridging oxygen and ionic field strength. Combining the present results with results obtained earlier, the magnitude of the enthalpy of mixing for all mixed alkali (Na₂O and K₂O) silicate glasses with and without alumina was expressed by a simple function of a modified Tobolsky parameter, which takes into account the alkali concentration and the difference in cation-to-effective anion distances. The enthalpy of mixing data of the mixed alkali glasses was then compared with reported experimental data on the conductivity of mixed alkali aluminosilicate glasses. What appears to be conflicting experimental data can be understood in terms of the magnitude of the enthalpy of mixing and we can conclude that the mixed alkali effect is closely correlated with the negative enthalpy of mixing.     

Mesomorphism Dependence on the Position of Substitution of a Pair of Esters

A novel homologous series of ethylene derivatives of thermotropic liquid crystals has been synthesized. The methoxy to octyloxy derivatives are nematogenic, the decyloxy to tetradecyloxy derivatives are smectogenic, in addition to nematogenic, and the hexadecyloxy homologue is smectogenic only. All the members of the series are enantiotropically mesogenic. Thermotropic behavior was determined by an optical polarizing microscope equipped with a heating stage and Differential Scanning Calorimetry (DSC) study. Analytical and spectral data confirm the molecular structures of homologues (infrared, nuclear magnetic resonance, mass spectra, X-ray, and DSC data). Textures of the nematic phase are threaded or Schlieren and that of smectic phase are focal conic fan-shaped of smectic A or C. Transition curves of the phase diagram behave in a normal manner except one or two deviations from the normal trend. The mesophase range (Sm+N) varies from 3°C to 44°C. The average thermal stability for smectic is 93°C and that for nematic 117.4°C. The LC behavior of the novel series is compared with a structurally similar known series.     

原位氮化法制备TiN纳米粉体

用溶胶凝胶法合成的纳米TiO2粉体作为原料,将该粉体在氨气中进行原位氮化制备了TiN纳米粉体.用XRD,TEM,化学分析等手段对合成的TiN纳米粉体的物相组成、形貌、成分进行了分析.实验分析表明:在1000℃和1100℃下分别氮化5h,可以制备粒径大约为40nm和80nm的TiN粉体,其TiN的含量分别为95.40;和98.37;;而在1000℃条件下氮化时间减少到2h时,TiN的含量仅为58.36;.氮化温度和氮化时间是合成纳米TiN的重要因素,提高合成温度和延长氮化时间均可形成纯度较高的TiN纳米粉体,但延长氮化时间更有利于获得粒径小的氮化钛粉体.     

立方晶系晶体本征铁弹相变序参量的选取

在本征铁弹相变的软模理论的基础上,依据弹性本构关系和居里原理,给出了立方晶系晶体所有可能的自发应变的种类,研究了立方晶系晶体本征铁弹相变序参量的选取问题.以Th群和Oh群为例,阐明了不同类的序参量导致晶体对称性变化相同的的原因,提出了该情况下序参量选取的“就少不就多”的原则.得到了发生本征铁弹相变时所有可能的序参量及晶体的对称性的变化.     

On the influence of structural features of DNA on the possibility of metabolic transfer of electrons

Abstract

A fragment of a DNA molecule is considered as one of the channels of metabolic electron transfer. The heterogeneity of the complementary chains is effectively taken into account. This made it possible to find the speed of the electron injected into the DNA conduction band and the current density that it creates. Estimates of electron mobility in nucleic acid chains are made. They were an order of magnitude smaller than that of typical semiconductors. For the specific conductivity of nucleic acid chains, estimates provide a conductivity of one to two orders of magnitude lower than in graphite.     

Features of transformations in REE-containing systems of nitrate precursors in preparatory processes of formation of multifunctional oxide materials

Abstract

The complex study provides a reliable idea of ??the trends in the joint behavior of structural components in the water-salt systems of nitrate precursors of REE, alkaline, alkaline earth metals in the preparatory stages of the processes of forming multicomponent oxide polyfunctional materials on their basis with thermal activation. Stages of such transformations are revealed; The regularities of complex and phase formation in systems and factors influencing them are determined; A number of physicochemical properties of the intermediate phases formed - coordination lanthanides nitrates: their composition, types of compounds, atomic-crystalline structure, regularities of transformations during heat treatment were studied.     

Growth and characterization of semicarbazone of cyclohexanone

A new organic single crystal of semicarbazone of cyclohexanone (SCCH) has been synthesized and grown as a bulk single crystal by low temperature solution growth technique for the first time in the literature. The grown crystal has been confirmed by X‐ray diffraction and proton nuclear magnetic resonance spectral analyses and also characterized by FT‐ir and FT‐Raman studies. Thermal properties of the grown crystals were studied by thermogravimetric and differential thermal analyses. Optical transmittance was studied by ultraviolet‐visible spectrum and the second harmonic generation property was tested by using Q switched Nd: YAG laser as a source. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of density of states on optical properties of GaSe thin film

A systematic investigation on the effect of substrate temperature on the structure, optical absorption and density of states of vacuum evaporated gallium monoselenide (GaSe) thin films is reported. The X‐ray diffraction analysis shows an occurrence of amorphous to polycrystalline transformation in the films deposited at higher‐temperature substrates (573K). The compositional analysis is made with Auger Electron Spectroscopy (AES). The thickness of the film (175nm) is measured by a multiple beam interferometery. Optical characteristics of the GaSe sample have been analyzed using spectrophotometer in the photon energy range of 1.0 ‐ 4 eV. The absorption mechanism has been recognized and the allowed indirect as well as forbidden direct transitions have been found. As‐deposited films show two indirect and allowed transitions due to spin‐orbit splitting of the valence band, as reported here for the first time. Low field conduction have enabled us to determine the density of states in amorphous and poly‐GaSe films. The amorphous and polycrystalline GaSe thin films have localized states density values of N (E_F) = 1.686 × 10¹⁷ cm^‐3 eV^‐1 and 1.257 × 10¹⁵ cm^‐3 eV^‐1 respectively. The experimental results are interpreted in terms of variations in the density of localized states due to progressive decrease of the unsaturated bonds during deposition. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

电子显微分析在表征纳米晶体化学组分中的应用

纳米材料的化学组分及含量影响其光、电、声、热、磁等物理性能,电子显微分析是表征纳米晶体化学组分的重要方法之一.本文综述了X-射线能谱(EDS)、X-射线波谱(WDS)、电子能量损失谱(EELS)和选区电子衍射(SAED)等现代电子显微分析技术在表征纳米晶体化学组分、形貌、尺寸和结构等方面的应用及其研究进展,并比较了这些分析方法存在的差异,提出了其应用中存在的不足及今后的研发方向.