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Cu-doped TiO_2 powder structure and magnetic properties

Author: WangWenJie
Tutor: WuPing
School: Tianjin University
Course: Materials Physics and Chemistry
Keywords: Sol - gel method Nanopowders Ferromagnetism F-center model
CLC: TB383.3
Type: Master's thesis
Year: 2010
Downloads: 40
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Abstract


In recent years, especially those with room temperature ferromagnetism in dilute magnetic semiconductor material, due to their spintronics devices has potential applications , causing widespread concern . Wide band gap TiO 2 -based diluted magnetic semiconductors whether ferromagnetism become one of the most talked about research topics . In this thesis, the sol - gel method prepared anatase and rutile Cu-doped TiO 2 nanopowders , systematic study of their structure and magnetic properties. Dried in air at 450oC and 800 oC gel sintered 2h, respectively, to obtain anatase and rutile TiO 2 powder. The structural analysis shows that the Cu -doped TiO 2 powder system , Cu -doped anatase to rutile conducive phase transition ; sintering temperature is higher the more likely precipitated CuO. By XPS analysis showed that the Ti powder samples with positive tetravalent ions are present , replace the Ti ions of Cu ions are present in positive monovalent . Anatase band structure analysis of samples found in the undoped samples , because the presence of oxygen vacancies in the conduction band forming a shallow donor impurity level ; in Cu-doped samples , not only by the formation of oxygen vacancies a shallow donor impurity levels , but also because Cu 3d orbital and the O 2p orbital hybridization in the valence band formed impurity band . Anatase and rutile phase similar to the magnetic properties of the sample , all with room temperature ferromagnetism , and with the increasing concentration of Cu ions doping saturation magnetization first increased and then decreased . However, compared with anatase , the actual doping concentration of Cu ions and small surface area , resulting in the rutile phase is weak saturation magnetization . By the anatase phase samples treated under different conditions to discuss the problem of ferromagnetism . First anatase phase samples annealed under different atmospheres , found in the atmosphere of oxygen annealing treatment , enhanced ferromagnetism , and in an atmosphere of oxygen annealing treatment is ferromagnetic weakened. The anatase phase samples at different pressures pressed into blocks and found that with the pressure to enhance or increase the doping concentration , along with enhanced ferromagnetism . With the F-center model can explain both phenomena . So we think that Cu-doped TiO 2 ferromagnetic powder system sources can be used F-center model to explain .

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