Zn缺陷对纤锌矿结构ZnO电子性质的影响研究

采用密度泛函理论计算的方法研究了Zn空位缺陷下ZnO的电子结构性质.结果表明,所有ZnO材料均为直接带隙型材料,含有Zn空位缺陷的ZnO禁带宽度由0.78 eV分别增加至1.62 eV和1.58 eV.所有ZnO的总态密度曲线具有相似的形状,含有Zn空位缺陷的ZnO的总态密度曲线极值点数量减少,局域化能量点数量减少.含有Zn空位缺陷的ZnO费米能上的态密度降低.随着Zn空位缺陷浓度的增加,ZnO费米能上的p态电子数量逐渐增加,这主要由来自于Op态电子的贡献.     

Na:O共掺杂AlN晶体的第一性原理研究

基于密度泛函理论的第一性原理全势线性缀加平面波法,分别研究了Al N在Na单掺杂和Na:O共掺杂情况下的晶格结构、电子态密度及能带结构。计算结果表明:Na单掺杂Al N和Na:O共掺杂Al N均为直接带隙半导体材料,且表现出p型掺杂特性;相比于本征Al N晶体,两者的晶格结构均膨胀,而Na:O共掺杂相对Na单掺杂Al N晶格膨胀较小;Na单掺杂Al N的价带顶态密度具有较强的局域化特性,不利于掺杂浓度的提高;与Na单掺杂Al N相反,Na:O共掺杂Al N的价带顶态密度局域化特性明显减弱,受主能级变浅,有利于Al N的p型掺杂。     

一种新的氨基硫脲类阴离子受体的合成及其性质研究

合成了一种新的阴离子受体化合物PySN,通过1H NMR对其进行了表征。受体分子结合不同阴离子的紫外-可见光谱和荧光发射光谱变化表明:在非质子性溶剂中,PySN可选择性识别和传感氟离子、醋酸根及磷酸二氢根离子。     

阴离子型聚电解质盐溶液性质的研究进展

阴离子型聚电解质在极性溶剂中会发生电离,导致大分子链上带有大量的净负电荷。它在盐溶液中会与一些反离子,特剐是多价金属阳离子等发生作用,从而使大分子形态发生改变,光学性质,电化学性质随之发生变化,作用强烈时,可发生沉淀。     

基于氢键的阴离子比色探针的合成和性质研究

以5-溴水杨醛和4-苯基-3-氨基硫脲合成了一种新型希夫碱类阴离子比色探针,研究了该探针对常见阴离子的比色响应特性。结果表明,在DMSO体系中加入氟离子、乙酸根离子和磷酸二氢根离子后,探针的最大吸波长从352 nm红移到398 nm,肉眼可观察到溶液的颜色从淡黄色变成了黄色,而其它的阴离子如氯离子、溴离子和碘离子的加入基本不引起溶液紫外-可见吸收波长的任何变化。因此,这种探针可以用来识别氟离子、乙酸根离子和磷酸二氢根离子。     

钨湿法冶金中带有长链交联剂的阴离子交换剂的吸附性能研究

The macroporous anion exchangers with long-chained cross-linking agents were investigated for the tungsten recovery from salt solutions. The physical-chemical characteristics of these sorbents were studied by means of sorption-desorption experiment aswell as electron and IR-spectroscopy. The anion exchangers on the basis of macroporous copolymers of methylacrylate and divinyl-ester of diethyleneglycol or tetravinyl-ester of pentaerythritol possess the exchange capacity to tungsten 2--5 times greater than the porous anion exchangers on the basis of styrene and divinylbenzene, therefore they can be used for selective tungsten recovery from comulex salt solutions.     

Y~(3+)掺杂对Mn-Zn铁氧体结构和性能的影响及正己烷磁流体的制备

用改进的化学共沉淀法首次合成了稀土钇离子掺杂的Mn0.8Zn0.2YxFe2-xO4(其中x=0、0.02、0.04、0.06、0.08、0.1)铁氧体纳米颗粒,利用X射线粉末衍射(XRD)和振动样品磁强计(VSM)研究了温度和Y3+掺杂量对磁性纳米颗粒结构和磁性能的影响。通过加入十二烷基硫酸钠(SDS)控制纳米颗粒的大小,并用油酸作为表面改性剂,制备了稳定的Mn0.8Zn0.2Y0.02Fe1.98O4正己烷磁流体,使用红外光谱(FTIR)、热重(TGA)和透射电镜(TEM)研究了p H值对油酸包裹的影响。研究发现:通过对化学共沉淀法进行改进,在沸腾的情况下制备出了目前饱和磁化强度最高的Mn0.8Zn0.2Fe2O4纳米磁性颗粒(Ms=63.8 A?m2?kg?1),适当掺杂Y3+不会破坏铁氧体的尖晶石结构并且随着掺杂量的增加,饱和磁化强度Ms先增加后减小,当x=0.02时Ms最大;在p H=5的乙醇-水体系中进行改性,油酸的包裹量最大,制备出的Mn0.8Zn0.2Y0.02Fe1.98O4正己烷磁流体长期放置不会分层。     

基于第一性原理的锐钛矿相EuxTi1-xO2-xNx电子结构及吸收光谱研究

基于第一性原理,采用密度泛函理论平面波超软赝势方法,建立了Eu单掺杂及Eu-N共掺杂的锐钛矿TiO2模型,对各模型的能带分布,态密度及吸收光谱进行计算.结果表明Eu-N共掺杂的锐钛矿TiO2在稳定性、光催化性能、吸收光谱红移等方面均优于Eu单掺杂的锐钛矿TiO2.     

钼酸镉晶体电子结构和光学性质的第一性原理研究

本文利用了基于密度泛函理论的第一性原理和平面波赝势方法计算了CdMoO4晶体的电子结构和光学性质.分别采用了广义梯度近似(GGA)和局域密度近似(LDA)对晶胞参数进行优化,得到了最稳定状态下的晶胞参数.在优化结构的基础上得到了两种近似下的能带结构,电子态密度和介电函数.能带结构表明CdMoO4的价带顶和导带底均在Γ点,直接带隙分别为2.342 eV (GGA),2.241 eV (LDA).电子态密度计算结果说明Mo4d和O2p轨道之间强烈杂化形成Mo-O共价键,且其键性强于Cd-O键.计算得到的介电函数实部与虚部和Abraham等用WIEN97软件计算的结果吻合得较好.     

LiFePO4系列电池材料的电子结构与性能研究

用离散变分密度泛函(DFTDVM)方法计算了I-iMPO1(M=Mn,Fe、Co、Ni)和FePO1,讨论了组成、电子结构、化学键等与性能之间的关系。从LiMnPO,到LiNiPO1离子键和共价键强度都降低,再加上态密度的比较都表明,从LiMnPO1到LiNiPO1电导率逐渐升高。LiFePO1,的离子键和共价键强度都些FePO1低,以及态密度的变化都表明,LiFePO1,的电导率比FePO1高。O2P分态密度主要贡献总态密度靠近费米能级的价带,M3d主要贡献总态密度靠近费米能级的导带,其它各个分态密度的主峰则离费米能级较远。     

2,4-二羟基苯甲酸在3种树脂上的吸附特性

通过静态和动态吸附实验, 研究了717(凝胶型,强碱)、D201(大孔型,强碱)和D301R(大孔型,弱碱)3种阴离子交换树脂对水溶液中2,4-二羟基苯甲酸的吸附特性. 结果表明,717和D201在pH 4~11时、D301R在pH 3~9时吸附能力最好. 在pH=5及温度293~313 K、初始浓度0.6488~6.488 mmol/L条件下,D301R, 717和D201对2,4-二羟基苯甲酸的等温吸附规律均符合Freundlich模型,最大平衡吸附量分别为2.98, 2.66和2.54 mmol/g(吸附未达饱和),均为物理性自发吸附的放热过程. 动力学实验数据用准一级模型方程拟合比准二级更接近实验值. 5%(w) NaCl+2%(w) NaOH脱附液100 mL均可有效洗脱3种树脂上吸附的2,4-二羟基苯甲酸,脱附率达99%. 相同条件下,D301R树脂对2,4-二羟基苯甲酸的吸附性能优于D201和717树脂.     

Theoretical Studies of the Electronic Properties of Ceramic Materials

The first-principles orthogonalized linear combination of atomic orbitals (OLCAO) method for electronic structure studies has been applied to a variety of complex inorganic crystals. The theory and the practice of the OLCAO method in the local density approximation are discussed in detail. Recent progress in the study of electronic and optical properties of a large list of ceramic systems are summarized. Eight selected topics on different ceramic crystals focusing on specific points of interest are presented as examples. The materials discussed are AIN, Cu₂O, β-Si₃N₄, Y₂O₃, LiB₃O₅, ferroelectric crystals, Fe-B compounds, and the YBa₂Cu₃O₇ superconductor. The results include the band structure, density of states, charge density distribution, spin density distribution, effective charges, total energy and totalenergy-derived results, optical absorption, positron annihilation spectra, and more. Extension of the band theoretical approach to the study of other areas of fundamental ceramic science is also discussed.     

Electronic Properties and Molecular Simulations of Polyoxometalates

Taking classical polyoxometalates such as Lindqvist, Keggin, Dawson, and Preyssler anions as the starting point, a walk is taken through the electronic and structural properties of polyoxoanions in solution. We will discuss nucleation mechanisms, redox properties, and isomerism of polyoxometalates. The effects of confinement on water molecules and cation distributions inside nanocapsules are other topics discussed in the present review.     

Effect of Ni Substitution on the Structural,Magnetic, and Electronic Structure Properties of Gd0.4Tb0.6(Co1−xNix)2 Compounds

The comprehensive research of magnetic and electronic structure properties of the new class of Gd_0.4Tb_0.6(Co_1−xNi_x)₂ compounds, crystallizing in the cubic Laves phase (C15), is reported. The magnetic study was completed with electrical resistivity and electronic structure investigations. The analysis of Arrott plots supplemented by a study of temperature dependency of Landau coefficients revealed that all compounds undergo a magnetic phase transition of the second type. Based on magnetic isotherms, magnetic entropy change (ΔS_M) was determined for many values of the magnetic field change (μ₀H), which varied from 0.1 to 7 T. For each compound, the ΔS_M had a maximum around the Curie temperature. Both values of the |ΔS_M^max| and relative cooling power RCP parameters increased with increasing nickel content. It is shown that structural disorder upon Co/Ni substitution influences some magnetic parameters. The magnetic moment values of Co atoms determined from different methods are quantitatively consistent. From the M(T) dependency, the exchange integrals J_RR, J_RT, and J_TT between rare-earths (R) and transition metal (T) moments were evaluated within the mean-field theory (MFT) approach. The experimental study of the electronic structure performed with the use of the X-ray photoelectron spectroscopy (XPS) was completed by calculations using the full-potential linearized augmented plane waves (FP-LAPW) method based on the density functional theory (DFT). The calculations explained experimentally observed changes in the XPS valence band spectra upon the Ni/Co substitution.     

类石墨结构氮化碳的合成及其应用

氮化碳是一种根据理论计算设计并人工合成的无机化合物。本文介绍了以单氰胺,二聚氰胺,三聚氰胺等碳氮化合物为原料,通过缩聚反应制备类石墨结构氮化碳(g-C3N4)的研究现状。类石墨结构氮化碳具有特殊的半导体光学特性,作为可见光响应的催化剂被应用于光催化反应中,本文阐述了其在光解水制氢方面的应用。     

失配层钴酸盐与掺镧系列的电子结构与热电性能

用离散变分密度泛函方法(DFT-DVM)计算了失配层钴酸盐Ca3Co4O9及其掺La系列，讨论了电子结构、化学键等与热电性能之间的关系。计算结果表明，Ca3Co4O9的态密度费米能级附近的价带和导带主要由Ca3Co4O9层中的O2p和Co3d原子轨道贡献，Ca3Co4O9的热电性能主要由Ca3CoO3层决定，而与CoO2层无直接联系，这与一般的二元氧化物无热电性能，而三元氧化物可能有较好的热电性能的结论一致。随着掺La量的增加，费米能级处价带和导带之间的能隙首先减小，随之达到最小值，进而又增大。由于能隙直接影响材料的热电性能，因此，存在一个最佳掺杂量以达到热电性能的最佳改善，这与实验结论一致。     

Effects of Li doping and point defect on the magnetism of ZnO

The magnetism sources and magnetic mechanism of Li doping and point defect, which coexist in the presence of hexagonal wurtzite ZnO, are controversial. To solve these problems, the effects of Li doping and point defect on the magnetism of ZnO were studied using geometry optimization and energy calculation based on the first-principle generalized gradient approximation + U (GGA + U) method of density functional theory. Results showed that the coexistence of Li doping and Zn vacancy can achieve ferromagnetic long-range order, and the Curie temperature of the doping system can achieve room temperature. In addition, results showed that magnetic moments are significantly different when the structures of the systems are also different with the same doping amount and doping method, which are advantageous for the enhancement of the magnetic properties of dilute magnetic semiconductors. The magnetism source of Zn₁₄LiO₁₆ is the hybrid coupling electron exchange effect between O-2p and Zn-3d orbits. With the coexistence of Li replacing Zn and Zn vacancy, the closest relative distance between doping and vacancy leads to the lowest formation energy and highest stability. In the condition of the highest stability of the ground state, all the doping systems of Li replacing Zn and O vacancy, doping system of interstitial Li and Zn vacancy, and doping system with the coexistence of Li replacing Zn, interstitial Li, and Zn vacancy are non-magnetic, which are considered worthless in the design and preparation of diluted magnetic semiconductors (DMSs).     

溶胶凝胶法制备的Mn,Li共掺ZnO粉晶性能研究

利用溶胶-凝胶法合成了名义组分Zn0.993-xMn0.007LixO(x=0,0.005,0.02)粉晶,分别采用SEM,EDX,XPS,XRD,UV-VIS和VSM对样品的形貌、成分、晶体结构、光学特性和磁性进行了研究。结果表明:Li的引入明显提高了Zn0.993Mn0.007O的室温磁化强度。当x=0.005时,Li以间隙原子的形式进入ZnO晶格,结晶性能下降,磁化强度的提高归因于ZnO晶格间隙电子掺杂和缺陷,使Mn2+-Mn2+间接铁磁性交换耦合增强;当x=0.02时,Li以替代原子形式进入ZnO晶格,相对于x=0.005其结晶性能提高,磁化强度的提高归因于ZnO中空穴载流子的增加,空穴载流子来自于Li+的受主作用。     

活化温度对无灰煤基活性炭结构及性能的影响

以无灰煤(HPC)为原料,KOH为活化剂,采用直接活化法制备无灰煤基活性炭(HAC),并在不同活化温度下探究HAC孔结构的衍化规律。结果表明:活化温度较低时,活化过程表现为无规则碳的烧失,同时微晶单元参与反应,片层明显减小,主要形成0.5 nm以下的微孔,以开孔作用为主。随活化温度的升高,KOH刻蚀微晶结构加剧,以扩孔作用为主,孔径大于0.5 nm的孔居多,同时发展超微孔和中孔。将HAC作为电极材料应用于水系双电层电容器(EDLC)时,其显示出优异的电化学性能,在电流密度为50 mA/g时的比电容达258.2 F/g,在电流密度为5000 mA/g时的比电容保持率在80%以上。研究还发现,EDLC的比电容随HAC电极中0.5 nm^1.5 nm微孔的增加而增大。     

Zn3V2O8的电子结构与光学性质的理论研究

采用平面波超软赝势密度泛函理论的方法研究了Zn3V2O8的能带结构、电子态密度和光学特性.能带结果显示Zn3V2O8呈间接带隙的绝缘体型能带,其禁带宽度为2.9 eV.详细的电子态密度结果显示其费米面上的态密度达到20 e/eV,费米能级附近的能级由Zn3p、V3p和O2p电子形成,Zn3d和O2s之间有强的杂化作用.介电性能结果显示在4.4 ～5.7 eV附近有强的吸收峰,在20.6 eV附近有一个次强吸收峰;吸收光谱显示在6.8 eV处有强吸收,在20.7 eV处有一个较弱的吸收峰.