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1.
马新国  江建军  梁培 《物理学报》2008,57(5):3120-3125
采用平面波超软赝势方法计算了锐钛矿型TiO2(101)面存在本征空位和间隙点缺陷的几何结构以及缺陷形成能.首先分析了点缺陷对表面结构的影响,发现不同类型缺陷导致缺陷周围原子有不同的位移趋势:O空位的产生导致空位周围的Ti原子向空位外移动,Ti1和Ti2空位的产生均使O1自发地与周围的O原子团聚,Oi原子易被周围的氧原子吸附而成键,而Tii2缺陷几乎 关键词: 第一性原理 2')" href="#">TiO2 点缺陷 表面结构  相似文献   

2.
The crystal structure, electronic structure, optical properties and photocatalytic activity of the native defects in anatase TiO2 were investigated based on the density-functional theory (DFT). The results show that oxygen vacancies (VO) have the lowest formation energy, and thus are easiest to form in the bulk structure. The conduction and valence band moves to the high or low energy region, and the energy gap becomes narrower for the native point defect models. In particular, oxygen interstitials (Oi) have a direct band gap, and new gap states appear in the band gap, which can be responsible for the high photocatalytic efficiency in anatase TiO2. The phenomenon of “impurity compensation” takes place for the oxygen and titanium interstitials. Ti vacancy (VTi) can promote the utilization of solar light by analyzing the absorption spectra. All the calculated results show that Oi and VTi are beneficial in improving the photocatalytic activity of TiO2 in the UV–visible light range.  相似文献   

3.
Formation energies of native defects and Pr impurities in orthorhombic CaTiO3 are explored using the first-principles calculations. The Ca vacancy (VCa), Ti vacancy (VTi) and Ca antisite (CaTi) are found to be energetically preferable. The Ti antisite (TiCa) and O vacancy (VO) are not energetically favorable in the wide range of Fermi level. In Pr-doped CaTiO3, Pr substituting for Ca (PrCa) is likely to form under condition A in which CaTiO3 is in equilibrium with CaO and O2. Under condition B (TiO2, CaTiO3 and O2 are in equilibrium), PrTi defect is energetically preferable depending on the Fermi levels. Several native defects and the two sites of Pr impurities in CaTiO3 are coincided with several different defects in Pr-doped CaTiO3 reported in the literature. Based on the present calculations, we can elucidate that the Ca deficiency design of the traditional formula Ca1−xVCa(x/2)PrxTiO3 is not the best for efficient red photoluminescence, which is realized via the experimental measurements.  相似文献   

4.
刘柏年  马颖  周益春 《物理学报》2010,59(5):3377-3383
采用基于密度泛函理论的第一性原理方法,研究了BaTiO3在四方相下的各种缺陷性质.计算结果表明,在富氧环境下,钛的中性氧空位、分肖特基缺陷2V3-Ti+3V2+O形成能分别为最低;而当体系处在还原环境下时,氧空位逐渐成为主要缺陷,其形成能最低.由于四方相下存在较强的Ti—O键共价杂化,四方相下全肖特基缺陷V2-Ba关键词: 缺陷 第一性原理 3')" href="#">BaTiO3  相似文献   

5.
Interaction of a zinc interstitial (Zni) with an oxygen vacancy (VO) was investigated to understand an origin of natively n-type characteristics of ZnO using density functional theory with the hybrid functional. The VO–Zni complex is formed with a formation of 3.82 eV and is a shallow donor with +1 charge state near the conduction band minimum. Its formation energy, however, is not low enough to be stable thermodynamically. Energy barrier for Zni migration in the VO–Zni complex is studied to consider its existence from kinetic aspect, and a high value of 1.3 eV is obtained with the kick-out process. Therefore, the bound Zni to VO can exist and supply electrons for native n-type ZnO kinetically.  相似文献   

6.
杨昌平  李旻奕  宋学平  肖海波  徐玲芳 《物理学报》2012,61(19):197702-197702
本文研究了在真空、空气和氧气中烧结制备的三种 CaCu3Ti4O12陶瓷材料的介电特性. 交流阻抗测量结果表明在10—300 K温度范围, 三种样品的介电温谱中均出现三个平台, 其电阻实部和电容虚部在相应温度出现损耗峰, 真空条件烧结的样品具有较高的介电平台和较明显的电阻实部与电容虚部峰值, 表明氧含量和氧空位对CaCu3Ti4O12的介电性质具有重要影响, 介电温谱出现的三个平台分别源于晶粒、晶界及氧空位陷阱.温谱分析表明晶粒的激活能与烧结气氛有较大关系,氧空位引起的电子短程跳跃及跳跃产生的极化子是晶粒电导和电容的主要起源.氧空位陷阱的激活能基本与烧结气氛无关,约为0.46 eV. 氧空位对载流子的陷阱作用是CaCu3Ti4O12 低频高介电常数的重要起源.  相似文献   

7.
By means of thermogravimetric measurements, it has been possible to obtain information on the nature of the intrinsic and extrinsic defects of TiO2, NbO2 and solid solutions NbyTi1?yOx Pure TiO2 is an oxygen-deficient oxide The main defects are oxygen vacancies, doubly ionized V..o or singly ionized V.o, and interstitial titanium Ti3i NbO2 is a metal-deficient oxide The main defects are neutral niobium vacancies. The solid solutions NbyTi1?yOx may be divided into two groups If y > 0 04, the behavior is analogous to that of NbO2; with the same defects, but the width of the homogeneity range decreases with the titanium content and Nb0 04Ti0 96O2 is a stoichiometnc oxide If y < 004, the oxides are both metal deficient and oxygen deficient according to the oxygen partial pressure. We have particularly studied the solution Ti0 995Nb0 005O2 In the oxygen-deficient domain, the main defects are assumed to be neutral or singly ionized oxygen vacancies In the metal-deficient domain, the main defects are metal vacancies V4Ti From these results we have deduced the nature of intrinsic defects in TiO2 to be Schottky defects: 2V..O + V4T1.  相似文献   

8.
p型K:ZnO导电机理的第一性原理研究   总被引:1,自引:0,他引:1       下载免费PDF全文
基于密度泛函理论,利用局域密度近似的第一性原理平面波赝势方法,对掺K以及含有氢填隙(Hi)、氧空位(VO)、锌填隙(Zni)和锌空位(VZn)的K:ZnO电子结构分别进行了研究.结果表明,1) 单独掺K可引入浅受主,但系统总能增高;2) K与H共掺可降低系统总能,提升稳定性;3) VO在K+H:ZnO中的形成比Zni困难得多,二者都是 关键词: 氧化锌 p型 第一性原理 电子结构  相似文献   

9.
S.H. Cheung 《Surface science》2007,601(7):1754-1762
We describe the growth and properties of well-defined epitaxial TiO2−xNx rutile for the first time. A mixed beam of atomic N and O radicals was prepared in an electron cyclotron resonance plasma source and Ti was supplied from a high-temperature effusion cell or an electron beam evaporator, depending on the required flux. A very high degree of structural quality is generally observed for films grown under optimized anion-rich conditions. N substitutes for O in the lattice, but only at the ∼1 at.% level, and is present as N3−. Epitaxial growth of TiO2 and TiO2−xNx rutile prepared under anion-rich conditions is accompanied by Ti indiffusion, leading to interstitial Ti (Tii), which is a shallow donor in rutile. Our data strongly suggest that Tii donor electrons compensate holes associated with substitutional N2− (i.e., Ti(III) + N2− → Ti(IV) + N3−), leading to highly resistive or weakly n-type, but not p-type material. Ti 2p core-level line shape analysis reveals hybridization of N and Ti, as expected for substitutional N. Ti-N hybridized states fall in the gap just above the VBM, and extend the optical absorption well into the visible.  相似文献   

10.
The effects of fast neutron irradiation on oxygen atoms in Czochralski silicon (CZ-Si) are investigated systemically by using Fourier transform infrared (FTIR) spectrometer and positron annihilation technique (PAT). Through isochronal annealing, it is found that the trend of variation in interstitial oxygen concentration ([Oi]) in fast neutrons irradiated CZ-Si fluctuates largely with temperature increasing, especially between 500 and 700℃. After the CZ-Si is annealed at 600℃, the V4 appearing as three-dimensional vacancy clusters causes the formation of the molecule-like oxygen clusters, and more importantly these dimers with small binding energies (0.1--1.0eV) can diffuse into the Si lattices more easily than single oxygen atoms, thereby leading to the strong oxygen agglomerations. When the CZ-Si is annealed at temperature increasing up to 700℃, three-dimensional vacancy clusters disappear and the oxygen agglomerations decompose into single oxygen atoms (O) at interstitial sites. Results from FTIR spectrometer and PAT provide an insight into the nature of the [Oi] at temperatures between 500 and 700℃. It turns out that the large fluctuation of [Oi] after short-time annealing from 500 to 700℃ results from the transformation of fast neutron irradiation defects.  相似文献   

11.
采用脉冲激光沉积方法在单晶Si(100)衬底上制备出c轴取向的Zn1-xMgxO单晶薄膜,通过荧光光谱仪研究了薄膜的光致发光特性.实验结果表明,Mg含量增加,Zn1-xMgxO单晶薄膜的紫外发光峰蓝移,发光峰强度减弱,缺陷发光强度增强.同时发现,由于Mg的掺杂,引入了一些束缚能较大的局域束缚态.对于氧气氛下制备的样品,实验发现紫外峰和绿光带发光峰同时增强,但是R值减小,紫外峰红移.对绿光发光机理研究发现,绿光发光带主要与锌空位、氧间隙(Oi)或锌位氧(OZn)等缺陷有关,它是由多个缺陷发光峰组成,各缺陷发光峰强度相对变化导致了绿光发光带的整体移动. 关键词: 1-xMgxO薄膜')" href="#">Zn1-xMgxO薄膜 光致发光 脉冲激光沉积  相似文献   

12.
The adsorption, photoreduction and chemical activity of oxygen molecules on the (1 0 0) anatase surface have been investigated here together with the effects that surface oxygen vacancies (VO) can have on these O2-related processes. We use an original approach by treating molecules on the TiO2 surface like surface defects in the same framework successfully used for defects in semiconductors. The achieved results: (i) give the first theoretical evidence of an acceptor behaviour of an adsorbed O2 molecule, which is at the origin of its photoreduction; (ii) show that the VO donor character is strongly affected by the interaction with O2; and (iii) suggest that the release of radicals as well as the formation of O2-related radicals may be favoured by photogenerated electrons in presence of surface VO’s.  相似文献   

13.
管东波  毛健 《物理学报》2012,61(1):17102-017102
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  相似文献   

14.
Mg2SnO4 exhibits green photoluminescence and persistent luminescence, which originate from oxygen vacancies. When Ti4+ ions were doped, an interesting Mg2SnO4:Ti4+ phosphor with bluish white photoluminescence under ultraviolet irradiation and with green persistent luminescence was first obtained. Our investigation reveals that two emission centres exist in Mg2SnO4:Ti4+. The centres responsible for the green emission are considered to be the F centres (oxygen vacancies) and the blue centres are the TiO6 complex. Trap clusters in the band gap with different depths, such as [SnMg—Oi], [SnMg—VO·], [SnMg—VO×] and MgSn, correspond to the components at 85 ℃, 146 ℃ and 213 ℃ of the thermoluminescence curve.  相似文献   

15.
The effect of low pressure radio frequency (rf) plasma treatment on TiO2 surface states has been studied using X-ray photoelectron spectroscopy. Three different oxidation states of oxygen in untreated TiO2 powder were observed, which suggests the existence of adsorbed water and carbon on the surface. The ratio of oxygen to titanium (O/Ti) was decreased for the low ion dose plasma treated samples due to desorption of water from the surface. In the case of Ti 2p about 20% of surface states were converted to Ti3+ 2p3/2 state after plasma treatment with a very good stability, whereas untreated TiO2 remained mostly as Ti4+ state. A rapid decrease in the ratio of carbon to titanium (C/Ti) at TiO2 surface was also observed after plasma treatment and more than 90% of carbon atoms were removed from the surface. Therefore, the plasma treatment of TiO2 has advantages to surface carbon cleaning, increasing O and Ti3+ surface states, hence improving the activity of TiO2 for different environmental, energy and biological applications.  相似文献   

16.
非掺杂ZnO薄膜中紫外与绿色发光中心   总被引:29,自引:2,他引:27       下载免费PDF全文
林碧霞  傅竹西  贾云波  廖桂红 《物理学报》2001,50(11):2208-2211
用直流反应溅射方法在硅衬底上淀积了ZnO薄膜,测量它们的光致发光(PL)光谱,观察到两个发光峰,峰值能量分别为3.18(紫外峰,UV)和2.38eV(绿峰).样品用不同温度分别在氧气、氮气和空气中热处理后,测量了PL光谱中绿峰和紫外峰强度随热处理温度和气氛的变化,同时比较了用FP-LMT方法计算的ZnO中几种本征缺陷的能级位置.根据实验和能级计算的结果,推测出ZnO薄膜中的紫外峰与ZnO带边激子跃迁有关,而绿色发光主要来源于导带底到氧错位缺陷(OZn)能级的跃迁,而不是通常认为的氧空 关键词: ZnO薄膜 热处理 光致发光光谱 缺陷能级  相似文献   

17.
By means of thermogravimetrie and electrical measurements, it has been possible to give accurate informations on the nature of the defects produced by reduction of TiO2 between 800 and 1100°C. For small partial pressures of oxygen Po2. interstitial titanium Ti4i prevails at temperature higher than 900°C. When PO2 increases, oxygen vacancies are produced at first in the doubly ionized form V″o and a progressive transition to singly ionized vacancies V″o can be assumed. The formation enthalpies associated with these defects as calculated from our experimental results are 10.1 eV for Ti4i, 4.6 eV for V″o and 3.6–4.0 eV for V′o. The electronic drift mobility μ is independent both of nature and concentration of the defects. The shape of its temperature dependence leads to conclude that the conduction in spite of the low μ value (0.06 cm2 V?1 s?1 at 1100°C) is of the classical type for wide band semiconductors and not a hopping process.  相似文献   

18.
赵庆勋  马继奎  耿波  魏大勇  关丽  刘保亭 《物理学报》2010,59(11):8042-8047
采用基于密度泛函理论的第一性原理研究了在氮氢混合气氛中退火后Bi4Ti3O12铁电性的退化机理. 分别计算了无氢、含氢模型中Ti沿c轴位移时体系总能量的变化,电子云密度分布,以及电子结构的总能态密度的变化. 结果表明含氢Bi4Ti3O12铁电相Ti-O,Bi-O间的电子云重叠布居分布较无氢情况下变化明显,氢氧之间较强的轨道杂化使它们趋于形成共价键;晶格中氢氧键的 关键词: 氮氢混合气氛退火 铁电性 4Ti3O12')" href="#">Bi4Ti3O12 第一性原理  相似文献   

19.
ZnO thin films were epitaxially grown on sapphire (0 0 0 1) substrates by radio frequency magnetron sputtering. ZnO thin films were then annealed at different temperatures in air and in various atmospheres at 800 °C, respectively. The effect of the annealing temperature and annealing atmosphere on the structure and optical properties of ZnO thin films are investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL). A strong (0 0 2) diffraction peak of all ZnO thin films shows a polycrystalline hexagonal wurtzite structure and high preferential c-axis orientation. XRD and AFM results reveal that the better structural quality, relatively smaller tensile stress, smooth, uniform of ZnO thin films were obtained when annealed at 800 °C in N2. Room temperature PL spectrum can be divided into the UV emission and the Visible broad band emission. The UV emission can be attributed to the near band edge emission (NBE) and the Visible broad band emission can be ascribed to the deep level emissions (DLE). By analyzing our experimental results, we recommend that the deep-level emission correspond to oxygen vacancy (VO) and interstitial oxygen (Oi). The biggest ratio of the PL intensity of UV emission to that of visible emission (INBE/IDLE) is observed from ZnO thin films annealed at 800 °C in N2. Therefore, we suggest that annealing temperature of 800 °C and annealing atmosphere of N2 are the most suitable annealing conditions for obtaining high quality ZnO thin films with good luminescence performance.  相似文献   

20.
Experimental observations indicate that removing bridging oxygen atoms from the TiO2 rutile (1 1 0) surface produces a localised state approximately 0.7 eV below the conduction band. The corresponding excess electron density is thought to localise on the pair of Ti atoms neighbouring the vacancy; formally giving two Ti3+ sites. We consider the electronic structure and geometry of the oxygen deficient TiO2 rutile (1 1 0) surface using both gradient-corrected density functional theory (GGA DFT) and DFT corrected for on-site Coulomb interactions (GGA + U) to allow a direct comparison of the two methods. We show that GGA fails to predict the experimentally observed electronic structure, in agreement with previous uncorrected DFT calculations on this system. Introducing the +U term encourages localisation of the excess electronic charge, with the qualitative distribution depending on the value of U. For low values of U (?4.0 eV) the charge localises in the sub-surface layers occupied in the GGA solution at arbitrary Ti sites, whereas higher values of U (?4.2 eV) predict strong localisation with the excess electronic charge mainly on the two Ti atoms neighbouring the vacancy. The precise charge distribution for these larger U values is found to differ from that predicted by previous hybrid-DFT calculations.  相似文献   

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