C掺杂锐钛矿TiO2的第一性原理研究

基于第一性原理的平面波超软赝势方法,本文研究了C分别代替Ti和O原子位置掺杂的锐钛矿TiO2的晶体结构,电子结构以及光学性质.结果表明,C在掺杂体系中的存在状态与掺杂位置密切相关;掺杂后引起晶格参数,键长等变化,导致晶体中结构单元偶极矩增大,从而可以改善光催化性能.C掺入后由于C 2p态与O 2p和Ti3d态发生杂化,...     

Ni掺杂锐钛矿型TiO2的第一性原理研究

采用基于密度泛函理论(DFT)的平面波超软赝势(PWPP)方法,对Ni掺杂前后锐钛矿型TiO_2的超晶胞体系进行了几何结构优化,从理论上给出了掺杂体系的晶格参数。模拟计算了Ni掺杂对锐钛矿型TiO_2的电子结构和光学性质的影响,得到了掺杂前后的能带结构、电子态密度分布、光吸收系数,分析了掺杂前后电子结构和光学性质的变化。结果表明:Ni掺杂锐钛矿型TiO_2后,在价带和导带之间出现了主要由O-2p和Ni-3d共同作用而产生的杂质能级,导致禁带宽度变窄;可见光区吸收系数增大,拓宽了光相应范围。这些计算结果很好地解释了Ni掺杂锐钛矿型TiO_2在可见光下具有良好的光催化性能的内在原因。由实验结果知:Ni掺杂锐钛矿TiO_2相应可见光的范围变宽。由此说明,计算结果与实验结果一致。     

Mn掺杂锐钛矿型TiO_2电子结构的第一性原理研究

[目的]研究Mn掺杂对锐钛矿TiO_2晶体可见光区催化活性的影响。[方法]采用基于密度泛函理论(DFT)框架下的第一性原理平面波赝势(PWPP)方法,研究掺杂对锐钛矿TiO_2晶体的晶体结构、能带结构、态密度的改变。同时我们也进行了Mn掺杂TiO_2的实验研究,从实验方面对掺杂后TiO_2光吸收性能变化进行研究。[结果]Mn掺杂TiO_2后,晶体的对称性和点群没有改变。通过对比纯TiO_2,Mn掺杂TiO_2的能带和态密度可以得出:Mn掺杂TiO_2后导带发生较大下移,且导带底部主要是Mn-3d的贡献,使禁带宽度变小,从而可见光吸收增强。实验结果也表明Mn掺杂后可见光吸收增强,和理论的红移结果一致。[结论]通过我们的计算和实验,说明Mn掺杂可以改善和提高TiO_2在可见光区的活性,这种材料具有很好的应用前景,值得做进一步的实验研究。     

Nb、Al共掺杂MoSi2弹性性质的第一性原理计算

Mo S2i是一种半金属化合物,有比较好的热传导性和导电性,一直作为一种耐高温合金被广泛使用。本文针对Nb和Al共掺杂Mo S2i后Mo S2i的弹性常数、导电性能、热传导性以及Mo S2i电子结构会发生的不同变化的情况,对Nb和Al共掺杂Mo S2i弹性性质的第一性原理计算做了具体相关探究。     

Ce-N共掺杂锐钛矿型二氧化钛的理论研究

[目的]研究Ce-N共掺杂对锐钛矿TiO2晶体可见光区催化活性的影响.[方法]采用基于密度泛函理论(DFT)框架下的第一性原理平面波赝势(PWPP)方法,研究掺杂对锐钛矿TiO2晶体的晶体结构、能带、态密度的改变,推断Ce-N共掺杂对锐钛矿TiO2晶体可见光区催化活性的影响.[结果]Ce-N共掺杂TiO2后,晶体的对称...     

金属氧化物掺杂对TiO2气敏特性的影响

掺杂金属氧化物可显著提高TiO2的气敏这一特性，正逐渐成为研究的热点。本文综述了掺杂金属氧化物对TiO2气敏特性的主要影响及机理；总结了目前研究中所掺杂的十多种金属氧化物，并就各种掺杂物对TiO2气敏特性的作用进行了具体分析。     

TiO2掺杂α—Fe2O3薄膜的制备与气敏性能

以钛酸丁酯和二茂铁为源物质,用氧气做氧化剂,采用等离子体化学气相沉积的方法,合成了具有良好气敏性能的TiO_2掺杂α-Fe_2O_3薄膜。采用SEM,XRD、DTG、IR、XPS和XRF等方法对薄膜的结构和成份进行了分析和观察。气敏测试的结果表明,TiO_2掺杂有助干提高α-Fe_2O_3薄膜的气敏选择性和气体灵敏度,并降低其工作温度。     

溶胶-凝胶法制备纳米TiO2的凝胶机理研究

以硝酸为催化剂,钛酸丁酯为前驱物,用溶胶-凝胶法制备TiO2凝胶,研究了不同的掺水量、硝酸含量、反应温度、搅拌速度等反应条件下的凝胶过程,采用X射线衍射和透射电镜对纳米粒子的性能进行分析,找出制备纯度较高的锐钛矿型的纳米TiO2粉体的最佳工艺条件。     

N掺杂TiO_2的催化活性与电子结构关系探究

以钛酸四丁酯和三乙醇胺为主要原料,采用钛溶胶水热合成方法,制备氮掺杂锐钛矿型纳米TiO2.利用XRD、DRS对其进行表征,以甲基橙为目标物,研究产物的光降解活性.实验结果表明,N掺杂造成了 TiO2的晶格缺陷,禁带宽度减小,光响应范围红移,光催化活性增强.从第一性原理出发,结合密度泛函理论计算,探讨N掺杂.TiO2的电子结构,发现其能带结构中出现了杂质能级,这可以很好地解释N掺杂TiO2光响应波长范围红移和光降解效果优于P25的实验观测结果.     

PM6法研究粒径对纳米TiO_2的热力学性质的影响

本文从热力学角度,研究粒径对锐钛矿型纳米二氧化钛的影响,为更好地应用该物质提供理论支持。通过构建不同粒径的锐钛矿型纳米二氧化钛的模型,用PM6量子化学方法来计算其热力学性质。结果表明:纳米二氧化钛的粒径对其热力学性质有显著的影响,随着纳米二氧化钛球簇的粒径降低,纳米二氧化钛的表面能和比表面能增加,摩尔生成吉布斯自由能和摩尔生成焓均增大,而其摩尔熵减小。     

Density functional theory study of adsorption geometries and electronic structures of azo-dye-based molecules on anatase TiO2 surface for dye-sensitized solar cell applications

Structural and electronic properties of eight isolated azo dyes (ArNNAr′, where Ar and Ar′ denote the aryl groups containing benzene and naphthalene skeletons, respectively) were investigated by density functional theory (DFT) based on the B3LYP/6-31G(d,p) and TD-B3LYP/6-311G(d,p) methods The effect of methanol solvent on the structural and electronic properties of the azo dyes was elucidated by employing a polarizable continuum model (PCM). Then, the azo dyes adsorbed onto the anatase TiO₂ (101) slab surface through a carboxyl group. The geometries and electronic structures of the adsorption complexes were determined using periodic DFT based on the PWC/DNP method. The calculated adsorption energies indicate that the adsorbed dyes preferentially take configuration of the bidentate bridging rather than chelating or monodentate ester-type geometries. Furthermore, the azo compounds having two carboxyl groups are coordinated to the TiO₂ surface more preferentially through the carboxyl group connecting to the benzene skeleton than through that connecting to the naphthalene skeleton. The dihedral angles (Φ_B-N) between the benzene- and naphthalene-skeleton moieties are smaller than 10° for the adsorbed azo compounds containing one carboxyl group. In contrast, Φ_B-N > 30° are obtained for the adsorbed azo compounds containing two carboxyl groups. The almost planar conformations of the former appear to strengthen both π-electrons conjugation and electronic coupling between low-lying unoccupied molecular orbitals of the azo dyes and the conduction band of TiO₂. On the other hand, such coupling is very weak for the latter, leading to a shift of the Fermi level of TiO₂ in the lower-energy direction. The obtained results are useful to the design and synthesize novel azo-dye-based molecules that give rise to higher photovoltaic performances of the dye-sensitized solar cells.     

First-principles study of hydrogen diffusion mechanism in Cr_2O_3

The system energy of H atom occupying different positions in Cr2O3 crystal lattice is calculated by adopting the first-principles calculation method based on density functional theory in this paper. The results indicate that the most stable position of H atom in Cr2O3 crystal lattice locates at the bilateral positions of the center of the unoccupied O octahedral interstice. The reason resulting in this situation is analyzed by comparing the change of Cr2O3 lattice distortion and density of states in Cr2O3_H...     

First-principles study of the Cu-Pd phase diagram

The equilibrium phase diagram of a Cu-Pd alloy has been computed using cluster expansion and Monte Carlo simulation methods combined with density functional theory. The computed phase boundaries show basic features that are consistent with the experimentally reported phase diagram. Without vibrational free energy contributions, the order-disorder transition temperature is underestimated by 100 K and the critical point is inconsistent with experimental result. The addition of vibrational free energy contributions yields a more qualitatively correct Cu-Pd phase diagram in the Cu rich region.     

First-principles study on segregation of ternary additions for MoSi2/Mo5Si3 interface

We investigate segregation behavior of additional elements M (=Ni, Co, Ta) at the C11_b/D8_m interface for MoSi₂–Mo₅Si₃ alloys, based on first-principles calculation. We first find energetically stable interface structure with interface energy of 0.08 eV/Ų (1.3 J/m²). Based on the stable interface, segregation energy for additional elements is calculated for individual atomic layer, which is applied to Monte Carlo statistical simulation under grand-canonical ensemble to quantitatively predict interface segregation profile. We find that our simulation successfully captures the characteristics in measured segregation tendency of (i) similarity in strong segregation at interface both for Ni and Co compared with bulk composition while Ta does not exhibit interface segregation and (ii) stronger segregation for Ni than for Co. The present results indicate that measured segregated interface for MoSi₂–Mo₅Si₃ alloys can be thermodynamically stable.     

First-principles study of ground-state properties and phase stability of vanadium nitrides

Using a series of density functional electronic structure total energy calculations, we have systematically studied the ground-state properties and phase stability of vanadium nitrides. Comparison of enthalpy of formation shows that V ₂N is equally stable (polymorphic) in , and Fe₂C phases within a few meV. Formation enthalpy of the various phases considered for perfect stoichiometric V N_1.0 shows that it has enhanced stability in hexagonal WC and NiAs structures in relation to NaCl-type δ-phase. The TiAs phase of VN has nearly same energy as NaCl structure. Comparison of energetics of -type , for x=0 and 0.3333 and of , for x=0, 0.0625, 0.125 and 0.25 shows that vacancies on the nitrogen sublattice lowers the formation enthalpy in relation to respective stoichiometric phases which is in agreement with experiments, as bulk vanadium nitrides are known to be generally non-stoichiometric. The calculated dilute heat of solution for the interstitial nitrogen is found to be in good agreement with experimental values and shows that nitrogen prefers to occupy the octahedral sites in bcc vanadium. The α^′-FeN and martensite structures, considered for the metastable phases of vanadium nitrides, have higher formation enthalpy in relation to equilibrium phases. Analysis of electronic density of states of V ₂N shows that the low energy , and Fe₂C phases are characterized by broad V 3d-N 2p and V 3d bonding bands. Density of states of VN shows that in the low energy WC and NiAs phases some of the antibonding states are made empty, leading to a minimum near the Fermi level. For and , density of states shows that vacancies on the nitrogen sublattice introduce additional filled states in the 3d band below Fermi level enabling enhanced bonding. Comparison between bulk moduli and atomic volumes for the various phases of vanadium nitrides shows that higher bulk moduli are dominated by increased V–N bonds combined with low atomic volumes.