钪与氧空位共掺杂锐钛矿相TiO2的形成能与电子结构的第一性原理研究

采用基于密度泛函理论的第一性原理研究了钪(Sc)、氧空位(O_V)单/共掺杂锐钛矿相TiO₂,对晶体结构、形成能以及电子结构进行了对比分析.研究结果表明,Sc-TiO₂在富氧环境下缺陷形成能为负值,富钛环境下缺陷形成能为正值,表明Sc-TiO₂只能在富氧环境下制备;O_V-TiO₂、Sc-O_V-TiO₂在富氧或富钛环境下缺陷形成能均为负值,但富氧环境下形成能更低;O_V-TiO₂的0/1-缺陷电荷转变能级为深能级,而Sc-TiO₂的0/1-缺陷电荷转变能级则属于相对较浅能级;与纯锐钛矿相TiO₂相比,Sc-TiO₂的禁带宽度略有减小,但O_V-TiO₂、Sc-O_V-TiO₂禁带宽度变宽.     

含空位二维六角氮化硼电子和磁性质的密度泛函研究

基于密度泛函理论的第一性原理计算, 研究了含B原子空位(V_B), N原子空位(V_N), 以及含B–N键空位 (V_B+N)缺陷的二维氮化硼(h-BN)的电子和磁性质. 在微观结构上, V_B体系表现为在空位附近的N原子重构成等腰三角形, V_N体系靠近空穴的B 原子形成等边三角形, V_B+N体系靠近空穴处的B和N原子在h-BN平面上重构为梯形. 三种空位缺陷都使h-BN的带隙类型从直接带隙转变为间接带隙. V_B体系的总磁矩为1.0 μ_B, 磁矩全部由N原子贡献. 其中空穴周围的三个N原子磁矩方向不完全一致, 存在着铁磁性和反铁磁性两种耦合方式. 对于V_N 体系, 整个晶胞内的总磁矩也为1.0 μ_B, 磁矩在空穴周围区域呈现一定的分布. 关键词： 二维h-BN 空位 电子结构 磁性     

Al掺杂对HfO2俘获层可靠性影响第一性原理研究

采用基于MS(Materials Studio)软件和密度泛函理论的第一性原理方法, 研究了HfO₂ 俘获层的电荷俘获式存储器(Charge Trapping Memory, CTM)中电荷的保持特性以及耐擦写性. 在对单斜晶HfO₂中四配位氧空位(V_O4) 缺陷和V_O4 与Al替位Hf掺杂的共存缺陷体(Al+V_O4)两种超晶胞模型进行优化之后, 分别计算了其相互作用能、形成能、Bader电荷、态密度以及缺陷俘获能. 相互作用能和形成能的计算结果表明共存缺陷体中当两种缺陷之间的距离为2.216 Å时, 结构最稳定、缺陷最容易形成; 俘获能计算结果表明, 共存缺陷体为双性俘获, 且与V_O4缺陷相比, 俘获能显著增大; Bader电荷分析表明共存缺陷体更有利于电荷保持; 态密度的结果说明共存缺陷体对空穴的局域能影响较强; 计算两种模型擦写电子前后的能量变化表明共存缺陷体的耐擦写性明显得到了改善. 因此在HfO₂俘获层中可以通过加入Al杂质来改善存储器的保持特性和耐擦写性. 本文的研究可为改善CTM数据保持特性和耐擦写性提供一定的理论指导.     

本征缺陷对β-Ga2O3光催化性质影响的第一性原理研究

运用第一性原理杂化泛函研究了本征缺陷(O空位和Ga空位)对于β-Ga₂O₃的几何结构和电子性质的影响.计算结构表明:杂化泛函B3LPY能很好的描述β-Ga₂O₃的几何结构和电子结构,能与实验符合.含O缺陷的形成能在富氧和贫氧下分别为4.04和0.92 eV,优于含Ga缺陷的体系.空位缺陷的出现对于理想Ga₂O₃的晶格参数影响不显著,只是在O空位体系中,空位附近Ga-O键长有0.1?变化.含空位缺陷的体系的禁带中都有缺陷能级的出现,含Ga和O空位缺陷的Ga₂O₃的光跃迁能分别为1.93 eV(β自旋)和2.92 eV,有很明显的光吸收的拓展,从理论上解释了Ga₂O₃作为光催化材料的潜在应用.     

p型K:ZnO导电机理的第一性原理研究

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(H_i)、氧空位(V_O)、锌填隙(Zn_i)和锌空位(V_Zn)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) V_O在K+H:ZnO中的形成比Zn_i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     

氧空位对Eu2+, Dy3+掺杂的Ca5MgSi3O12发光及余辉性能的影响

利用高温固相法合成了稀土离子Eu²⁺, Dy³⁺掺杂的Ca₅MgSi₃O₁₂长余辉发光材料. 利用光谱学证明了在材料内部存在与氧空位有关的缺陷发光. 通过对比不同条件下合成样品的发光及余辉性能, 发现氧空位对材料的发光及余辉均起到促进作用. 同时发现氧空位发光可以向发光中心传递能量. 利用热释光曲线系统的分析了氧空位对余辉性能的影响. Ca₅MgSi₃O₁₂:Eu²⁺,Dy³⁺是一种潜在的长余辉发光材料. 关键词： 长余辉 氧空位 能量传递 热释光     

Zn吸附到含有氧空位(VO)以及羟基(-OH)的锐钛矿相TiO2(101)表面电子结构的第一性原理计算

基于密度泛函理论的第一性原理平面波超软赝势方法, 计算了Zn吸附到TiO₂(101)清洁表面、含有氧空位(V_O)的缺陷表面以及既含有氧空位(V_O)又含有羟基(-OH)表面的能量、Mulliken重叠布居数以及电子结构, 并找到了Zn在每种表面的最稳定结构(分别为模型(c), 模型(aI)以及模型(aII)). 通过对三种表面稳定结构的分析、对比发现: 首先, Zn原子吸附到清洁TiO₂(101)表面上, 主要与表面氧相互作用, 形成Zn–O共价键; 其次, 当Zn原子吸附到缺陷表面时, 吸附能减小到-1.75 eV, 说明Zn更容易吸附到氧空位上(模型(aI)); 最后, 纵观表面模型的能带结构以及态密度图发现, -OH的引入并没有引进新的杂质能级, Zn吸附此表面, 即Zn-TiO₂-V_O-OH, 使得禁带宽度缩短到最小(1.85 eV), 从而有望提高TiO₂的光催化活性. 关键词： 密度泛函理论 氧空位 羟基 Zn原子     

电荷俘获存储器数据保持特性第一性原理研究

本文研究HfO₂掺入Al替位Hf杂质和氧空位共同掺杂对电荷俘获型存储器存储特性的影响. HfO₂作为高介电常数材料由于具有缩小器件尺寸、提高器件性能等优势, 被广泛用于CTM的俘获层. 采用MS和VASP研究了HfO₂俘获层中掺入Al对氧空位形成能的影响. 同时计算了两种缺陷在不同距离下的相互作用能. 计算结果表明在HfO₂中掺入Al使得氧空位的形成能降低, 并且三配位氧空位的形成能比四配位氧空位的形成能降低的更多. 通过研究Al和三配位氧空位两种缺陷间不同距离的三种情况, 计算结果表明当缺陷间距为2.107 Å时, 体系的电荷俘获能最大; 量子态数最多; 布居数最小、Al–O键最长. 通过研究三种体系写入空穴后键长的变化, 得出当缺陷间距为2.107 Å时, 写入空穴后体系的Al–O键长变化最小. 以上研究结果表明, 掺入Al后可以有效提高电荷俘获型存储器的数据保持能力. 因而本文的研究为改善电荷俘获型存储器数据保持特性提供一定的理论指导.     

高氧空位简并锐钛矿TiO2半导体电子寿命的第一性原理研究

为了研究锐钛矿TiO₂晶体中高氧空位浓度对电子寿命的影响,利用基于局域密度泛函理论框架下的广义梯度近似平面波超软赝势方法, 用第一性原理对含高氧空位浓度的锐钛矿TiO₂晶体进行了结构优化处理、能带分布和态密度分布计算, 表明在温度一定和高氧空位浓度的条件下, 锐钛矿TiO₂的电子寿命随氧空位浓度的增大而减小;电子浓度的大小对电子寿命无影响.同时,锐钛矿TiO₂晶体中高氧空位浓度时,发现有莫特相变的现象. 关键词： 高氧空位 2半导体')" href="#">锐钛矿TiO₂半导体 电子寿命 第一性原理     

Ca$lt;sub$gt;0.64$lt;/sub$gt;WO$lt;sub$gt;4$lt;/sub$gt;:Eu$lt;sub$gt;0.24$lt;/sub$gt;陶瓷的高温相变机理及其对发光性能的影响

纯的CaWO₄具有优异的耐压、耐热稳定性,化学组成为Ca_0.64WO₄:Eu_0.24的陶瓷也具有CaWO₄结构,但Ca²⁺晶格位置含有12 mol%的肖特基缺陷. 这种缺陷浓度高的CaWO₄ 相是否具有良好的高温稳定性还有待研究. 本文探讨了过度烧结对Ca_0.64WO₄:Eu_0.24陶瓷相结构的影响,揭示了在高温下产生相变的可能原因,并研究了该相变对材料发光性能的影响. 研究表明,当烧结温度超过1100 ℃时,被肖特基缺陷束缚的部分氧离子会解离,造成Ca_0.64WO₄:Eu_0.24陶瓷体相中氧元素含量严重不足,诱发CaWO₄相发生相变,析出单斜晶系的Eu₂WO₆;研究还发现,CaWO₄相的晶面间距在高温相变后会增大;这可能是导致Ca_0.64WO₄:Eu_0.24陶瓷发光强度显著降低的一个重要原因. 关键词： 相变 钨酸钙 铕 发光     

锐钛矿型TiO2(101)面本征点缺陷的理论研究

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,O_i原子易被周围的氧原子吸附而成键,而Ti_i2缺陷几乎 关键词： 第一性原理 2')" href="#">TiO₂ 点缺陷 表面结构     

金红石相和锐钛矿相TiO2本征缺陷的第一性原理计算

采用第一性原理的计算方法, 分别研究了金红石相和锐钛矿相TiO₂各种缺陷态形成的类型, 以及几何结构、生长气氛和Fermi能级位置对缺陷形成能的影响, 从理论上预测产生点缺陷的实验条件. 重点是讨论带电点缺陷的形成能, 并对结果进行适当修正. 研究发现, 本征缺陷的类型和浓度对 TiO₂的性能有一定的影响: 在富O条件下, TiO₂容易形成V_Ti(Ti空位)缺陷; 在富Ti条件下, TiO₂的Ti_i⁴⁺和V_O(O空位)缺陷将大量出现, 形成Schottky缺陷.     

Electronic structures and optical properties of rutile TiO2 with different point defects from DFT + U calculations

The electronic states and formation energies of four types of lattice point defects in rutile TiO₂ are studied using the first-principles calculations. The existence of oxygen vacancy leads to a deep donor defect level in the forbidden band, while the Ti interstitial forms two local states. It is predicted that oxygen vacancy prefers to combine with Ti-interstitial to form V_O–Ti_i dimer by a partial 3d electron transfer from the Ti_i to its neighboring V_O. The charge distribution between a Ti interstitial and its neighboring Ti ions partially shields the Coulomb interactions. Lastly, optical properties of these defective lattices are discussed.     

Native defects and Pr impurities in orthorhombic CaTiO3 by first-principles calculations

Formation energies of native defects and Pr impurities in orthorhombic CaTiO₃ are explored using the first-principles calculations. The Ca vacancy (V_Ca), Ti vacancy (V_Ti) and Ca antisite (Ca_Ti) are found to be energetically preferable. The Ti antisite (Ti_Ca) and O vacancy (V_O) are not energetically favorable in the wide range of Fermi level. In Pr-doped CaTiO₃, Pr substituting for Ca (Pr_Ca) 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), Pr_Ti 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 Ca_1−xV_Ca(x/2)Pr_xTiO₃ is not the best for efficient red photoluminescence, which is realized via the experimental measurements.     

Schottky defects in cubic lattice of SrTiO3

Structural and electronic properties produced by formation of Schottky defects in cubic structure of SrTiO₃ crystal are investigated by means of a quantum-chemical simulation based on the Hartree-Fock methodology. The occurrence of Sr partial Schottky defect (V_Sr+V_O) and two types of Ti partial Schottky defects (V_Ti+2V_O) is modeled using a supercell containing 135 atoms. Vacancy-induced changes in the positions of their neighboring atoms are analyzed in light of the computed electron density redistribution in the defective region of supercell. The observed local one-electron energy levels in the gap between the upper valence band and the conduction band can be attributed to the presence of anion and cation vacancies.     

Equilibrium point defects in TiAl studied by PAC

Site fractions of dilute¹¹¹In/¹¹¹Cd probe atoms in different lattice locations in quenched, equi-atomic TiAl are measured using perturbed angular correlations of gamma rays (PAC). The vacancy-free substitutional site fraction, observed via its nuclear quadrupole interaction, is observed to decrease with increasing quenching temperature, reflecting an increase in the thermal defect concentration. Assuming that the thermal defect is the Schottky defect, the law of mass action, and a binding energy of 0.2 eV between vacancies and the In probe, the experimental temperature dependence is analysed to yield a formation enthalpy of 4.7(4) eV and entropy of 25(4)k _B for the Schottky defect. The vacancy concentration on one sublattice is given in terms of these parameters by the expression [v]=exp(S _F/2k _B) exp(–E _F/2k _B T), and is found, for example, to have the value 1.4% at 1350°C, a large value.     

First-principles calculation of point-defective structures of B2-NiSc intermetallics

A pseudo-potential plane-wave method based on first principles was used to calculate the physical parameters of B2-NiSc intermetallics and the geometrical, energetic, and electronic structures of point defects. The possible types of point defects in B2-NiSc intermetallics were analyzed and predicted by comparing the formation enthalpy and formation energy for different kinds of point defect structures. The results show that Ni vacancy defects and Ni anti-position defects are the main point defects in the B2-NiSc intermetallics, and that these point defects emerge as double vacancy defects or double anti-position defects. When the double Ni atoms at Sc sites are in the first nearest neighborhood, the point defect structures are found to be the most stable. An analysis of the electronic structure of NiSc point defects shows that the Ni anti-position defect is more stable than the Sc vacancy defect in the Ni-rich alloy, and the Ni vacancy defect is more stable than the Sc anti-position defect in the Sc-rich alloy. These results are consistent with the energy calculation. Through analysis of C₁₁–C₁₂, G/B and Poisson's ratio, it was found that the Ni_Sc point defect has little effect on crystal plasticity, and that the V_Ni point defect improves crystal plasticity.     

The first-principle calculation of structures and defect energies in tetragonal PbTiO3

The first-principle calculation had been adopted to investigate various neutral vacancies and vacancy pairs under seven thermodynamic conditions in bulk PbTiO₃. The electronic structures, atomic relaxations, and formation energies of vacancies were obtained. Depending on the thermodynamic condition, the main and stable defects are different. It was found that V_O is the main defect under the reducing condition, whereas V_Pb becomes dominating under the oxidizing condition. The Pb-O vacancy pair forms more easily than the isolated vacancies under certain thermodynamic condition. Due to the introducing of vacancies, the acceptorlike levels and donorlike levels appear in the cases of the cation and anion vacancies, respectively.     

Effects of native defects on the electronic structure and photocatalytic activity in anatase TiO2 by first principles calculations

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 (V_O) 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 (O_i) 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 (V_Ti) can promote the utilization of solar light by analyzing the absorption spectra. All the calculated results show that O_i and V_Ti are beneficial in improving the photocatalytic activity of TiO₂ in the UV–visible light range.     

N2微空心阴极放电特性及其阴极溅射的PIC/MC模拟

采用两维PIC/MCC模型模拟了氮气微空心阴极放电以及轰击离子 (N₂⁺,N⁺) 的钛阴极溅射. 主要计算了氮气微空心阴极放电离子 (N₂⁺,N⁺) 及溅射原子Ti的行为分布, 并研究了溅射Ti 原子的热化过程. 结果表明: 在模拟条件下, 空心阴极效应是负辉区叠加的电子震荡; 在对应条件下, 微空心较传统空心放电两种离子 (N₂⁺,N⁺) 密度均大两个量级, 两种离子的平均能量的分布及大小几乎相同; 在放电空间N⁺的密度约为N₂⁺的1/6, 最大能量约大2倍; 在不同参数 (P, T, V)下, 轰击阴极内表面的氮离子(N₂⁺,N⁺)的密度近似均匀, 其平均能量几乎相等; 从阴极溅射出的Ti原子的初始平均能量约6.8 eV, 离开阴极约0.15 mm处几乎完全被热化. 模拟结果为N₂微空心阴极放电等离子体特性的认识提供了参考依据. 关键词： 微空心阴极放电 PIC/MC模拟 2等离子体')" href="#">N₂等离子体