The Mechanism Of Resistive Switching And Catalysis On Defective Titania:First-Principle Analysis

As a transition-metal oxide with a relatively simple crystal structure, rutile TiO₂ has been giving a large amount of attention in fundamentally and technologically motivated research. Defects in transition-metal oxides control a wide range of their physical and chemical properties, such as resistive swiching or catalysis. Here, focusing on these two aspects, we employ the First-Principle software（CASTEP, Dmol3, CPMD and Virtual Nanolab）, to investigate the defective TiO₂ with the oxygen vacancies, O interstitials, Ti interstitials, Cu substitutions and the mutilayer bwteen the Cu layer, or Cu O layer and the TiO₂ layer. The main works are listed in the following:1. The impact of the electric field on the defective TiO₂ with one oxygen vacancy, the oxygen vacancies in（110） facet and [110] direction, or in same side and different sides around the Ti column. We find the covalent properties of the Ti-O bond adjacient the oxygen vacancy enhanced in defective TiO₂ with one oxygen vacancy as the electric field; the more broken bonds are formed in defective TiO₂ with the oxygen vacancies in（110） facet or in same side around the Ti column; the static dielectric constants and the CV curves are determined by the oxygen vacancy rather than by the electric field.2. The impact of the oxygen vacancies on the formation of the conduction path. Based on the structure models in defective TiO₂ with the oxygen vacancies, the pairs of the oxygen vacancies, the ordering oxygen vacancies in one side or two sides around the Ti column, or the ordering oxygen divacancies in two sides around the Ti column, we focus on the impact of the fine structure on the formation of the conduction path. It’s found that as the occurrence of the metallic Ti-Ti bonds in the structure with the ordering oxygen divacancies in two sides around the Ti column, the conduction path are observed; the structure of TiO₂/TiO₂-x produces the better reliability than the structure of TiO₂-x/TiO₂,which implies that the former strueture could endure higher electric field than the latter; the Zr substitutions for the Ti-ions in the interface of TiO₂/TiO₂-x or TiO₂-x/TiO₂ improve the reliability of the conduction path.3. The mechanism of the conduction path in the defective TiO₂ with O interstitials and oxygen vacancy. In the defective TiO₂ with five O interstitials, the conduction path in the ohmic conductivity is produced in the serious O-O bonds. After one oxygen ion substituted for the oxygen vacancy, the conductivity of the space charge limited current play the key role in the conduction path. The relaxed structure in 2.6 MV/cm exhibits the lower resistane at 0.5 V. In contrast, the structure relaxed under 1.3 MV/cm produces the higher resistance at 0.36 V.4. The impact of the metal interstitials and their locations in defective TiO₂ on the transmission coefficient or the visible light absorption. We find that the Zr or Ti interstitials doping in the Ti column improve the reduction of Ti4+-ions to generate the higher transmission coefficient. The Ti interstitials doping in the lattice space also enhances the visible light absorption in [100], [010], [110], [-110] and [001] directions. In contrast, the Cu interstitials doping in the Ti column only improve the visible light absorption in [001] direction. The Ti3+-ions and the Cu interstitials could build the effective light path to promote the visible light absorption.5. The impact of the mutilayer between the Cu layer, Cu O layer and the TiO₂ layer on the visible light absorption. We find that the Cu substitutions doping in the different sides around the Ti column promote the visible light absorption; the structure of defective TiO₂ relaxed under the higher electric field produces the higher visible light absorption. These characteristics help to extend the theoretical guidances of the doping principle in defective TiO₂. Moreover, the more Cu-O bonds in the Cu O/TiO₂ surface relaxed under the electric field in [010] direction are found than that relaxed in [001] direction. So, it improves the visible light absorption. These characteristics verify the occurrence of Cu2 O in Cu O/TiO₂ surface would induce the inefficient absorption over the visible light. Furermore, the reconstruction of the Cu layer in TiO₂/Cu/TiO₂ mutilayer also improve the visible light absorption. The reconstruction of Cu layer mainly originates from the switch of lattice constants in xy dimensions. It provides the theoretical evidence for the films with metal inserted on the improved visible light absorption.It’s believed that the conclusions focus on the mechnisam of resistive swiching or catalysis through main stream paradigm and by our selected defects as focused self-parameters, so provide the powerful proofs for designing and optimizing novel devices.