本文選題：TiO_2 + O空位　； 參考：《蘇州大學(xué)》2015年博士論文

【摘要】：二氧化鈦(TiO_2),相比其他過渡金屬氧化物,具有化學(xué)性能穩(wěn)定、安全無毒和使用壽命長等優(yōu)點,因此得到學(xué)術(shù)界和工業(yè)界廣泛的關(guān)注�？紤]到TiO_2在阻變器件和光催化中的應(yīng)用,O空位、間隙離子或替代離子等缺陷勢必影響著TiO_2的物理和化學(xué)性能。為了進(jìn)一步量化此類影響,本工作借助以密度泛函理論為基礎(chǔ)的第一性原理,構(gòu)造四類缺陷結(jié)構(gòu)模型,對缺陷TiO_2的導(dǎo)電通道形成機(jī)制與光催化中光吸收系數(shù)性能修飾進(jìn)行了系統(tǒng)的理論計算研究。本文的主要研究工作和已取得的研究成果包括:1.分析電場對于含孤立O空位、含(110)面和[110]方向O空位以及含Ti列同側(cè)和異側(cè)O空位的缺陷TiO_2結(jié)構(gòu)模型的影響。發(fā)現(xiàn)含O空位的缺陷TiO_2結(jié)構(gòu)中臨近O空位的Ti-O鍵共價性在電場作用下增強(qiáng),而且電場引起含(110)面O空位的缺陷TiO_2結(jié)構(gòu)和含Ti列同側(cè)O空位的缺陷TiO_2結(jié)構(gòu)存在較多的Ti-O鍵斷裂,同時得出缺陷TiO_2結(jié)構(gòu)本身的靜態(tài)介電常數(shù)和CV曲線分布情況由O空位分布決定。2.闡明O空位組合形成導(dǎo)電通道的微觀物理機(jī)制。分析含O空位或O空位對缺陷在有限晶格空間中的不同組合結(jié)構(gòu)模型、含單列或雙列O空位鏈的結(jié)構(gòu)模型以及含單列遞增和雙列遞增O空位對的結(jié)構(gòu)模型以及在其中摻雜金屬離子的結(jié)構(gòu)模型,得到他們的結(jié)構(gòu)與導(dǎo)電通道形成的關(guān)系。我們在含雙列O空位鏈的結(jié)構(gòu)模型中觀察到導(dǎo)電通道的形成,將這種現(xiàn)象歸結(jié)為雙列O空位鏈間出現(xiàn)具有金屬性的Ti-Ti鍵,同時得到O空位對雙列遞增的TiO_2/TiO_2-x結(jié)構(gòu)模型的可靠性強(qiáng)于含O空位對倒置雙列遞增TiO_2-x/TiO_2結(jié)構(gòu)模型,而且在這兩種結(jié)構(gòu)的界面處,將Zr替代Ti離子能夠有效地提高導(dǎo)電通道的可靠性,此方法為導(dǎo)電通道性能改善提供了一個新的理論基礎(chǔ)。3.探究含O間隙離子和O空位的缺陷TiO_2結(jié)構(gòu)的導(dǎo)電通道形成機(jī)制。首先構(gòu)造含5個O間隙離子的結(jié)構(gòu)模型,將其中一個O離子替代為一個O空位,比較這兩種結(jié)構(gòu)導(dǎo)電通道的物理導(dǎo)電機(jī)制。然后分析含5個O間隙離子的結(jié)構(gòu)模型的導(dǎo)電通道特征與電場的關(guān)系。我們在含5個O間隙離子的缺陷TiO_2結(jié)構(gòu)模型中觀察到集聚O離子對伴隨著O-O鍵形成導(dǎo)電通道,將其導(dǎo)電機(jī)制歸屬于歐姆導(dǎo)電,而將其中一個O空位替代O離子后,發(fā)現(xiàn)空間電荷限制電流起主要作用。同時還發(fā)現(xiàn)2.6 MV/cm的電場弛豫后的結(jié)構(gòu)在0.5 V電壓下具有低電阻,相比之下,1.3 MV/cm電場弛豫后的結(jié)構(gòu)在0.36 V時有較高電阻。這些現(xiàn)象有力地拓展了基于化學(xué)價變化的阻變機(jī)制。4.揭示金屬間隙離子摻雜以及摻雜方位對TiO_2輸運系數(shù)和光吸收系數(shù)的影響。首先得出摻雜Zr、Ti間隙離子在Ti列促進(jìn)Ti4+離子的還原,他們的結(jié)構(gòu)對應(yīng)較高的輸運系數(shù)。然后在晶格空間中摻雜Ti間隙離子,發(fā)現(xiàn)此缺陷TiO_2結(jié)構(gòu)在[100]、[010]、[110]、[-110]和[001]極性方向上存在較強(qiáng)可見光吸收率,而在Ti列摻雜Cu間隙離子的缺陷TiO_2結(jié)構(gòu),它的可見光吸收率只有在[001]極性方向上得到增強(qiáng)。所以晶格Ti3+離子和Cu間隙離子能夠在[001]方向上形成有效的光路從而促進(jìn)缺陷TiO_2對可見光的吸收。這些特征對于利用金屬間隙離子摻雜改善TiO_2可見光吸收率的方法提供了晶向定位摻雜的理論依據(jù)。5.闡明Cu或CuO與TiO_2組合結(jié)構(gòu)與可見光吸收率的關(guān)系。首先分析含Ti列同側(cè)或異側(cè)Cu替代離子的結(jié)構(gòu)模型,發(fā)現(xiàn)Cu替代離子在Ti列異側(cè)的摻雜有效地提高了TiO_2結(jié)構(gòu)對可見光的吸收率,而且此結(jié)構(gòu)經(jīng)過高電場弛豫后具有較高的可見光吸收率。然后提出CuO/TiO_2表面結(jié)構(gòu)模型,得出CuO/TiO_2表面結(jié)構(gòu)經(jīng)過[010]方向電場弛豫后在界面處觀察到較多Cu-O鍵,從而提高[001]方向的可見光吸收率;也就驗證了電場使CuO/TiO_2表面結(jié)構(gòu)中CuO還原為Cu2O,從而降低CuO/TiO_2表面結(jié)構(gòu)可見光吸收率;此為解釋CuO/TiO_2表面結(jié)構(gòu)的較強(qiáng)可見光吸收率的現(xiàn)象提供了有力的理論依據(jù)。最后提出TiO_2/Cu/TiO_2復(fù)合層結(jié)構(gòu)模型,發(fā)現(xiàn)在TiO_2/Cu/TiO_2復(fù)合層中Cu層經(jīng)過結(jié)構(gòu)弛豫后重構(gòu),提高了結(jié)構(gòu)對可見光的吸收率。這些特征為TiO_2層中嵌入金屬層薄膜提高可見光吸收率的方法提供了可靠的理論依據(jù)。研究結(jié)論認(rèn)為,呼應(yīng)針對TiO_2導(dǎo)電機(jī)制等熱點難題的深刻理解,遵循主流研究范式,特別構(gòu)造了可能的有主要影響的缺陷作為自變量集合,通過計算得到主要表征參數(shù)的可解釋的結(jié)果體系,此舉將為深入開展新器件實驗提供有力的佐證。
[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.
【學(xué)位授予單位】：蘇州大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TQ134.11;O643.36

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