Study of Photo-catalytic Properties and d~0 Ferromagnetism of Oxide Semiconductor

Author:Liu Yan Zuo

Supervisor:wu ping

Database:Doctor

Degree Year:2017

Download:21

Pages:122

Size:9361K

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The work includes two parts:the first part is to control the electronic structure of TiO2 nanosheet by donor-acceptor codoping and soild-solution methods and bulk SrTiO3 by donor-acceptor codoping to realize the catalytic activity under visible light.The second part is to explore the origin of the d0 ferromagnetism in common oxide semiconductors(ZnO,TiO2 and SrTiO3).The appropriate band edge positions and stable chemical structure yeild TiO2 and SrTiO3 outstanding in photo-catalytic field.However,due to the wide band gap(more than 3.0 eV),they only respond to the ultraviolet light,which severely limits their photo-catalytic efficiency.Therefore,to improve the catalytic efficiency,the primary task is to realize the visible light absorption.In this paper,using first-principle density-functional theory,we perform a series of research work.In order to keep the reduction capacity of TiO2 and SrTiO3,we use B,C,N asp-type doping to replace O atom while TM = Nb,Ta,Mo,W as n-type doping to substitude Ti or Sr atom.The p orbital energy of B,C,N is higher than that of O,while the d orbital energy of TM is comparable with that of Ti.The calculated results show that their synergistic effect is able to lift the valence band maximum or introduce impurity states within the band gap,realizing the overall water splitting under visible light.The discovery of d0 ferromagnetism challenges the traditional understanding of magnetism,which sparked a hot debate for d0 ferromagnetism.Different defects are responsible for the d0 ferromagnetism in the oxide semiconductors.Obviously,the origin of the unexpected d0 ferromagnetism is controversial.In this paper,the d0 ferromagnetism origin of the non-magnetic low-valent and high-valent metal doped oxide semiconductors,such as Li,Mg and Al doped SrTiO3,was studied using the first-principles with some experimental work,such as K doped ZnO films and Al doped ZnO nanoparticles prepared by RF-magnetron sputtering and sol-gel method,respectively.It is found that d0 ferromagnetism in the low-valent metal doped oxides and high-valent metal Al doped ZnO induced by the hole introduced by low-valent metal doping and the charge transter between the adsorbed Al atoms and the surface atoms(Zn and O atoms),respectively.