缺陷二氧化钛阻变及催化机制的第一性原理研究

发布时间：2018-06-09 20:46

本文选题：TiO_2 + O空位　；参考：《苏州大学》2015年博士论文

【摘要】：二氧化钛(TiO_2),相比其他过渡金属氧化物,具有化学性能稳定、安全无毒和使用寿命长等优点,因此得到学术界和工业界广泛的关注。考虑到TiO_2在阻变器件和光催化中的应用,O空位、间隙离子或替代离子等缺陷势必影响着TiO_2的物理和化学性能。为了进一步量化此类影响,本工作借助以密度泛函理论为基础的第一性原理,构造四类缺陷结构模型,对缺陷TiO_2的导电通道形成机制与光催化中光吸收系数性能修饰进行了系统的理论计算研究。本文的主要研究工作和已取得的研究成果包括:1.分析电场对于含孤立O空位、含(110)面和[110]方向O空位以及含Ti列同侧和异侧O空位的缺陷TiO_2结构模型的影响。发现含O空位的缺陷TiO_2结构中临近O空位的Ti-O键共价性在电场作用下增强,而且电场引起含(110)面O空位的缺陷TiO_2结构和含Ti列同侧O空位的缺陷TiO_2结构存在较多的Ti-O键断裂,同时得出缺陷TiO_2结构本身的静态介电常数和CV曲线分布情况由O空位分布决定。2.阐明O空位组合形成导电通道的微观物理机制。分析含O空位或O空位对缺陷在有限晶格空间中的不同组合结构模型、含单列或双列O空位链的结构模型以及含单列递增和双列递增O空位对的结构模型以及在其中掺杂金属离子的结构模型,得到他们的结构与导电通道形成的关系。我们在含双列O空位链的结构模型中观察到导电通道的形成,将这种现象归结为双列O空位链间出现具有金属性的Ti-Ti键,同时得到O空位对双列递增的TiO_2/TiO_2-x结构模型的可靠性强于含O空位对倒置双列递增TiO_2-x/TiO_2结构模型,而且在这两种结构的界面处,将Zr替代Ti离子能够有效地提高导电通道的可靠性,此方法为导电通道性能改善提供了一个新的理论基础。3.探究含O间隙离子和O空位的缺陷TiO_2结构的导电通道形成机制。首先构造含5个O间隙离子的结构模型,将其中一个O离子替代为一个O空位,比较这两种结构导电通道的物理导电机制。然后分析含5个O间隙离子的结构模型的导电通道特征与电场的关系。我们在含5个O间隙离子的缺陷TiO_2结构模型中观察到集聚O离子对伴随着O-O键形成导电通道,将其导电机制归属于欧姆导电,而将其中一个O空位替代O离子后,发现空间电荷限制电流起主要作用。同时还发现2.6 MV/cm的电场弛豫后的结构在0.5 V电压下具有低电阻,相比之下,1.3 MV/cm电场弛豫后的结构在0.36 V时有较高电阻。这些现象有力地拓展了基于化学价变化的阻变机制。4.揭示金属间隙离子掺杂以及掺杂方位对TiO_2输运系数和光吸收系数的影响。首先得出掺杂Zr、Ti间隙离子在Ti列促进Ti4+离子的还原,他们的结构对应较高的输运系数。然后在晶格空间中掺杂Ti间隙离子,发现此缺陷TiO_2结构在[100]、[010]、[110]、[-110]和[001]极性方向上存在较强可见光吸收率,而在Ti列掺杂Cu间隙离子的缺陷TiO_2结构,它的可见光吸收率只有在[001]极性方向上得到增强。所以晶格Ti3+离子和Cu间隙离子能够在[001]方向上形成有效的光路从而促进缺陷TiO_2对可见光的吸收。这些特征对于利用金属间隙离子掺杂改善TiO_2可见光吸收率的方法提供了晶向定位掺杂的理论依据。5.阐明Cu或CuO与TiO_2组合结构与可见光吸收率的关系。首先分析含Ti列同侧或异侧Cu替代离子的结构模型,发现Cu替代离子在Ti列异侧的掺杂有效地提高了TiO_2结构对可见光的吸收率,而且此结构经过高电场弛豫后具有较高的可见光吸收率。然后提出CuO/TiO_2表面结构模型,得出CuO/TiO_2表面结构经过[010]方向电场弛豫后在界面处观察到较多Cu-O键,从而提高[001]方向的可见光吸收率;也就验证了电场使CuO/TiO_2表面结构中CuO还原为Cu2O,从而降低CuO/TiO_2表面结构可见光吸收率;此为解释CuO/TiO_2表面结构的较强可见光吸收率的现象提供了有力的理论依据。最后提出TiO_2/Cu/TiO_2复合层结构模型,发现在TiO_2/Cu/TiO_2复合层中Cu层经过结构弛豫后重构,提高了结构对可见光的吸收率。这些特征为TiO_2层中嵌入金属层薄膜提高可见光吸收率的方法提供了可靠的理论依据。研究结论认为,呼应针对TiO_2导电机制等热点难题的深刻理解,遵循主流研究范式,特别构造了可能的有主要影响的缺陷作为自变量集合,通过计算得到主要表征参数的可解释的结果体系,此举将为深入开展新器件实验提供有力的佐证。
[Abstract]:Titanium dioxide (TiO_2), compared with other transition metal oxides, has the advantages of stable chemical properties, safety, innocuity and long service life. Therefore, it is widely concerned in the academic and industrial circles. Considering the application of TiO_2 in the resistive devices and photocatalysis, the defects of O vacancy, gap or replacement ions are bound to affect the physical and physical properties of TiO_2. In order to further quantify this effect, the four type of defect structure model was constructed with the help of the first principle based on density functional theory. The theoretical calculation of the formation mechanism of the conductive channel of the defective TiO_2 and the performance modification of the optical absorption coefficient in the photocatalysis was studied. The main research work and the results have been taken in this paper. The results obtained include: 1. analysis of the effect of the electric field on an isolated O vacancy, the (110) surface and the [110] direction O vacancies and the TiO_2 structural model containing the ISO and ISO O vacancies of the Ti column. It is found that the Ti-O bond covalence of the Ti-O bond near O vacancy in the TiO_2 structure containing O vacancies is enhanced by the electric field, and the electric field causes (110) plane O space. The defect TiO_2 structure and the defective TiO_2 structure containing the same side O vacancy in the Ti column have many Ti-O bonds broken. At the same time, the static dielectric constant and the distribution of the CV curve of the defective TiO_2 structure are determined by the O vacancy distribution, which determines the.2. mechanism of the O vacancy combination to form the conductive channel. The structural models of different composite structures in limited lattice space, structural models containing single or double column O vacancy chains and structural models with single column increasing and double row incremented O vacancy pairs and the structure model of doped metal ions in it, the relationship between their structure and the formation of conducting channels is obtained. We are in the structure model containing a double column O vacancy chain. The formation of the conductive channel is observed, which is attributed to the emergence of a metal Ti-Ti bond between the diallel O vacancy chains, and the reliability of the O vacancy to the double column TiO_2/TiO_2-x structural model is stronger than the O vacancy to the inverted diallel TiO_2-x/TiO_2 structure model, and the Zr is replaced by the Zr instead of Ti at the interface of the two structures. This method can effectively improve the reliability of the conductive channel. This method provides a new theoretical basis for the performance improvement of the conductive channel,.3. to explore the formation mechanism of the conductive channel with the defect TiO_2 structure containing the O gap ion and the O vacancy. First, the structure model containing 5 O gap ions is constructed, and one of the O ions is replaced by a O vacancy, and the ratio of one of the O ions is replaced by a O space. The physical conduction mechanism of the two structure conductive channels is compared with the electric field characteristics of the structure model containing 5 O gap ions. In the defect TiO_2 structure model containing 5 O gap ions, we observe that the concentrated O ions form the conductive channel with the O-O bond, and the conduction motor is attributed to the ohmic conduction. After replacing the O ion with one of the O vacancies, it is found that the space charge limiting current plays a major role. It is also found that the structure after the relaxation of the 2.6 MV/cm electric field has a low resistance at the voltage of 0.5 V. In contrast, the structure after the relaxation of the 1.3 MV/cm electric field has a higher resistance at 0.36 V. These phenomena strongly extend the change based on the chemical valence change. The mechanism.4. reveals the influence of the doping of metal gap ions and the influence of doping position on the transport coefficient and absorption coefficient of TiO_2. First, it is concluded that doping Zr, Ti gap ions promote the reduction of Ti4+ ions in the Ti column, their structure corresponds to the higher transport coefficient. Then the Ti gap ions are mixed in the lattice space, and the TiO_2 structure of this defect is found to be in [1. In the polar direction of 00], [010], [110], [-110] and [001], there is a strong visible light absorption rate, while the Ti column doped with the defective TiO_2 structure of Cu gap ions, its visible absorption rate is enhanced only in the direction of [001] polarity. So the lattice Ti3+ ion and Cu gap ions can form an effective light path in the [001]] direction to promote the defect. 2 absorption of visible light. These features provide a theoretical basis for crystal orientation doping by using interstitial ion doping to improve the visible absorption of TiO_2. The relationship between the structure of Cu or CuO and TiO_2 composite structure and the absorption rate of visible light is clarified by.5.. First, the structural model of the Cu substitutional ions containing the same side or the opposite side of the Ti column is analyzed, and the substitution of Cu to replace the Cu is found. The doping of ions at the different side of the Ti column effectively improves the absorption rate of the visible light in the TiO_2 structure, and the structure has a higher visible light absorption rate after the relaxation of the high electric field. Then the CuO/TiO_2 surface structure model is put forward. It is concluded that the surface structure of the CuO/TiO_2 has been observed more Cu-O bonds at the interface after the relaxation of the electric field in the direction of [010]. The visible light absorption rate in the high [001] direction shows that the electric field can reduce the CuO to Cu2O in the surface structure of the CuO/TiO_2, thus reducing the visible absorption rate of the CuO/TiO_2 surface structure. This provides a powerful theoretical basis for the explanation of the strong visible absorption rate of the CuO/TiO_2 surface structure. Finally, the structure mode of the TiO_2/Cu/TiO_2 composite layer is put forward. It is found that the structural relaxation of the Cu layer in the TiO_2/Cu/TiO_2 composite layer improves the absorption rate of the visible light. These features provide a reliable theoretical basis for the method of embedding the metallic layer film in the TiO_2 layer to improve the visible light absorption. The solution, following the mainstream research paradigm, specially constructed the possible major influence defects as the set of independent variables, and obtained the interpretable result system of the main characterization parameters by calculation, which will provide a powerful support for the development of new device experiments.
【学位授予单位】：苏州大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ134.11;O643.36

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