Hf掺杂锐钛矿TiO2电子结构的第一性原理研究

采用基于密度泛函理论的平面波超软赝势方法对Hf掺杂锐钛矿型TiO2的电子结构进行了第一性原理研究。对通过对能带和电子态密度的分析,发现在Hf掺杂后,导带底和价带顶同时降低,但是由于价带顶下降的比导带底多,从而使得锐钛矿型TiO2的禁带宽度变窄。     

Electronic and optical properties of the doped TiO2 system

By the total energy pseudo-potential approach of plane wave, we study the electronic and optical properties of the anatase TiO2 systems with Sc-doped, oxygen vacancies included, and Sc and oxygen vacancies co-existing, respectively. The obtained results show that the contribution by the doped Sc lies mainly in the valence band, and the light absorption in the visible region is obvious. A Mott phase transformation takes place in the presence of oxygen vacancies, and the light absorption in the visible region is also obvious. In particular, the absorption in the visible region of the co-doped system is enhanced coherently due to the influences both from doped Sc and oxygen vacancies.     

锐钛矿型TiO_2薄膜的低温制备及其光催化性能研究

采用改进的sol-gel法及浸渍–提拉工艺在低温条件下制备了纳米TiO2薄膜。利用X射线衍射仪(XRD)、傅里叶变换红外光谱仪(FTIR)、扫描电镜(SEM)及紫外–可见光光谱仪(UV-Vis)对所制TiO2薄膜的物相结构、表面形貌以及光吸收特性进行了表征,并利用紫外光照降解亚甲基蓝溶液的方法考察了TiO2薄膜的光催化活性。结果表明:低温制备的纳米TiO2薄膜为锐钛矿结构,表面均匀致密,且对紫外光表现出较强的吸收特性。在紫外光照射48 h后,该TiO2薄膜对亚甲基蓝溶液的降解率为67.4%。     

锐钛矿相TiO2电子结构和光学性质的第一性原理计算

采用第一性原理平面波超软赝势方法计算了锐钛矿相TiO2的电子结构和光学性质,并从理论上分析了它们之间的关系.利用精确计算的能带结构和态密度分析了电子带间跃迁占主导地位的锐钛矿相TiO2的介电函数、复折射率、反射率和吸收系数,理论计算得到的结果与实验测量结果基本一致.结果表明锐钛矿相TiO2在E//c和E上c两个极化方向上具有明显的光学各向异性,为锐钛矿相TiO2的应用提供了理论依据.     

锐钛矿相TiO2电子结构和光学性质的第一性原理计算

采用第一性原理平面波超软赝势方法计算了锐钛矿相TiO2的电子结构和光学性质,并从理论上分析了它们之间的关系.利用精确计算的能带结构和态密度分析了电子带间跃迁占主导地位的锐钛矿相TiO2的介电函数、复折射率、反射率和吸收系数,理论计算得到的结果与实验测量结果基本一致.结果表明锐钛矿相TiO2在E//c和E上c两个极化方向上具有明显的光学各向异性,为锐钛矿相TiO2的应用提供了理论依据.     

锐钛型掺铁TiO_2可见光催化降解苯胺的研究

为了研究掺铁TiO2对苯胺的光催化降解效果,以硫酸钛为原料采用水热法制备了锐钛型掺铁TiO2粉末,确定了它在可见光照射下对苯胺溶液的催化降解工艺条件。结果表明,在如下最佳条件下:苯胺初始质量浓度(0)为50 mg/L,溶液pH=7,掺铁0.2%(摩尔分数)的锐钛型TiO2的质量浓度为1.0 g/L,室温(17℃)下可见光照射反应1 h,苯胺的降解率达到71.46%。     

First principle study of Nb defects in anatase (101) TiO2 surface

In this work, effects of Niobium (Nb) defects on TiO₂ surface using density functional theory (DFT) are investigated. Based on formation energy of the defects, their occurrences in two different extreme conditions, O-rich and O-poor conditions, are evaluated. Effects of Nb defects on surface and its electronic structure are studied and it is demonstrated that Nb doping widens valence band in deep energy level leaving the band gap without any change and it also lowers oxygen vacancy defect concentration due to the stronger bonding of Nb_sub defect with oxygen atoms specially bridging oxygen (most probable defect site for Oxygen vacancy). Higher density of Nb substitutional defects (Nb_sub) are examined and it is shown that higher density doping of TiO₂ surface leads to uniform distribution of defects over the anatase structure as a result of interaction of Nb defects when they are close and this fact prevents segregation of Nb atoms in Nb-doped TiO₂.     

锐钛矿TiO2(101)面电子性质和光学性质的第一性原理研究

The TiO₂（101） surface was studied using the plane-wave ultrasoft pseudopotential method based on the density functional theory,with emphasis on the structure,surface energy,band structure,density of states, and charge population.The anatase TiO₂（101） crystal surface structure,whose outermost and second layers were terminated by twofold coordinated oxygen atoms and fivefold coordinated titanium atoms,was found to be much more stable.The surface energy of the 18-layer atoms model was 0.580 J/m2.The surface electronic structure was similar to that of the bulk and no surface state.Compared with the bulk structure,the band gap increased 0.36 eV, the Ti5c-02c bond lengths reduced 0.171（?） after relaxation,and the charges of the surface were transferred to the body.Analysis of the optical properties of the TiO₂（101） surface showed that it did not absorb in the low-energy region.An absorption edge in the ultraviolet region corresponding to the energy of 3.06 eV was found.     

N、Yb共掺杂二氧化钛的第一性原理计算

本文采用基于密度泛函理论的平面波超软赝势方法研究了N、Yb共掺杂TiO2的晶体结构、电子结构和光学性质,计算结果表明：掺杂后TiO2的晶格常数、原子间的键长和原子电荷都发生了变化,导致掺杂后的八面体偶极矩增加,从而有利于光生电子-空穴对的分离,提高了TiO2的光催化性能。电子在O的Pπ轨道和Yb的4f之间的跃迁使N、Yb共掺杂后的TiO2在可见光区有较好的光吸收特性。     

Anatase (101) Reconstructed Surface with Novel Functionalities: Desired Bandgap for Visible Light Absorption and High Chemical Reactivity

Unreconstructed surfaces of anatase TiO₂ are known to have two main limitations for their application as photocatalysts, namely, low efficiency for sun‐light absorption due to the wide bandgap, and low chemical reactivity. Strategies to overcoming the two limitations and to enhancing TiO₂'s photocatalytic efficiency have been highly sought. To this end, a global search of anatase reconstructed surfaces is performed based on the evolutionary method. It is found that the newly predicted anatase (101) reconstructed surface possesses a desired bandgap whose value is within the energy domain of visible light as well as notably high chemical reactivity compared to the unreconstructed anatase (101) surface. In particular, it is predicted that under Ti‐richness condition, the anatase (101) reconstructed surface is energetically very stable. The anatase (101) reconstructed surface exhibits similar topmost surface structure as the unreconstructed anatase (101) surface but different subsurface structure. Not only the fivefold coordinated Ti atoms (Ti_5c) in the topmost surface layer but also the sixfold coordinated Ti atoms in the subsurface layer contribute to the desirable gap states. The high chemical reactivity of anatase (101) reconstructed surface can be attributed to the extra electrons drawn by the surface Ti_5c atoms and subsurface Ti_6c atoms.     

KrF脉冲激光退火制备锐钛矿TiO2薄膜

在常温下,用射频磁控溅射在石英衬底上沉积厚度约为200 nm 的TiO2薄膜,然后使用波长为248 nm 的KrF脉冲激光器,在不同功率密度下对薄膜样品进行辐照退火处理,并采用X射线衍射（XRD)、拉曼(Raman)、X射线电子能谱（XPS）、原子力显微镜(AFM)、扫描电子显微镜(SEM)、高分辨率扫描隧道显微镜（HRTEM）以及选择区域电子衍射（SAED）、紫外可见分光光度计等方法分析不同激光功率密度退火对TiO2薄膜的结构、表面形貌和透射率等性能的影响。结果表明当激光功率密度为0.5 J/cm2时,可获得高质量的锐钛矿TiO2薄膜,当继续增大光功率密度时,TiO2薄膜变为(1 1 0)取向的金红石相,其薄膜表面粗糙度也相应增大。     

超声喷雾热解法制备 TiO2 薄膜

成功地利用超声喷雾热解法在玻璃衬底上制备了TiO2薄膜。Ti（SO4）2作为钛源,甲醇作为溶剂。利用超声波的雾化作用将反应物形成细小的雾滴,并喷射到预热的玻璃衬底上分解而形成稳定的TiO2薄膜。为获得致密均匀的薄膜,优化了反应物浓度、温度、沉积时间等参数。利用X射线衍射与原子力显微镜表征了薄膜的晶体结构与表面形貌。X射线结果表明薄膜为多晶锐钛矿结构TiO2薄膜,并在（101）方向呈现出择优趋势。     

退火时间对TiO2薄膜光学性能的影响

研究退火时间对薄膜相结构、形貌及光学性能的影响。采用射频磁控溅射法在单晶硅片和石英玻璃片上负载TiO2薄膜,通过X-射线衍射(XRD)、原子力显微镜(AFM)和紫外可见光谱(UV-Vis)对其进行表征。结果表明,在相同的退火温度下,与退火0.5 h相比,退火1 h的薄膜中锐钛矿相TiO2减少,金红石相TiO2增多,对可见光透射率有所减小,1 000℃以上退火时,透射率减小更明显。与退火1 h相比,退火0.5 h薄膜晶粒较小,明显呈纳米团簇状,薄膜表面粗糙度增大。     

First principles study of the Be-C co-doped MgB_2 system

We study the Be-C doped MgB_2 system by the first principles method based on density functional theory. The compensation effect between electron type doping and hole type doping is shown in the total density of states on the Fermi level, the real part of optical conductivity, and the number of effective carriers. The compensation mechanisms are discussed. The critical temperatures for different systems are calculated.     

First principles study of the Be-C co-doped MgB_2 system

We study the Be-C doped MgB2 system by the first principles method based on density functional theory. The compensation effect between electron type doping and hole type doping is shown in the total density of states on the Fermi level, the real part of optical conductivity, and the number of effective carriers. The compensation mechanisms are discussed. The critical temperatures for different systems are calculated.     

Se和Cd掺杂GaN电子结构与光学性质的第一性原理研究

基于密度泛函理论的第一性原理,使用GGA+U方法分别计算Se和Cd单掺与共掺杂GaN体系的晶格常数、电子结构及光学性质.结果表明:与本征GaN相比,掺杂后体系的晶格常数发生了改变,禁带宽度减小,吸收光谱均发生红移,表明掺杂使体系的光谱响应范围得到更大拓展.其中,Cd单掺GaN体系的禁带宽度最小,并在费米能级附近有杂质能...     

空位缺陷金红石型TiO2电子结构和光学性质的理论研究

基于密度泛函理论(DFT)的第一性原理模守恒赝势 方法,对纯金红石型TiO₂和Ti、O两种空位缺 陷相的几何结构、能带结构、态密度(DOS)以及光学性质进行了 系统地对比研究。结果发现,含有空 位缺陷的TiO₂键长增大,原子布局值减小并出现微弱的磁性;空位缺陷导致导带变窄,导 带和价带 都向低能级方向移动,由空位原子贡献的载流子增强了体系的电导率,费米能级上移进入导 带;与 纯金红石型TiO₂的直接带隙宽度(3.0eV)相比较,Ti空位缺陷相转 变为P型半导体且直接带隙为1.816 eV,而O空位缺陷相转变为n型半导体且间接带隙为1.961eV。同时, 两种空位缺陷结构的介电峰显 著红移,折射率有明显变化,对可见光区的吸收系数均比纯TiO₂高。与O空位结构相比,Ti 空位结构的 介电常数、折射率、消光因子和对可见光的吸收强度更大,更能增强电子在低能端的光学跃 迁,具有更佳的可见光催化性能。     

氮掺杂对4H—SiC电子结构的影响

采用广义梯度近似的密度泛函理论方法计算了4H—SiC的本征态的电子结构以及4H—SiC材料N掺杂后的电子结构,计算结果表明：与本征态相比,N掺杂后的4H—SiC的导带与价带均向低能端移动,导带移动幅度大于价带,使得掺杂后的禁带宽度小于本征态的禁带宽度：导带底进入N的2s态和2p态,但它们所占比重小,掺杂浓度变化对导带底...     

强激光下4H-SiC晶体电子特性的第一性原理研究

为了研究4H-SiC晶体在强激光辐照下电子特性及其变化,采用基于密度泛函微扰理论的第一性原理赝势的方法,对纤锌矿4H-SiC晶体在强激光照射下的电子特性的变化进行了理论分析和实验验证。结果表明,电子温度T_e在0eV~2.75eV范围内时,4H-SiC仍然是间接带隙的半导体晶体;当电子温度T_e升高达到并超过3.0eV以上时,4H-SiC变为直接带隙的半导体晶体;电子温度T_e在0eV~2.0eV变化时,带隙值随电子温度升高而增大;电子温度T_e在2.0eV~3.5eV变化时,带隙值随电子温度T_e的升高而迅速地减小;当电子温度T_e高于3.5eV以后,带隙已经消失而呈现出金属特性。该研究对制作4H-SiC晶体特殊功能电子元件是有帮助的。