Theortical Research Of Electronic Structures And Optical Absorption Properties For ?-AgVO₃

Semiconductor photocatalysts have drawn much attention in the application of wastewater treatment and air purification because of serious surroundings and environmental chemistry pollution.The monoclinic ?-AgVO₃,which has narrow band gap?2.11 eV?and can respond to visible light,has been considered as a promising semiconductor photocatalyst.Systematic study on the mechanism of photocatalytic activity for ?-AgVO₃ is still lacking.In this thesis,perfect?-AgVO₃,?-AgVO₃ with vacancy defects and Cu or Fe doped ?-AgVO₃ have been investigated based on first-principle calculations.The geometric structures,electronic properties and optical absorption properties of the systems have been systematically analyzed.The main results obtained are summarized as below:1.The structure of perfect ?-AgVO₃ was calculated using the GGA method and GGA + U method,respectively.By comparing the lattice parameters and the band gap values,it can be concluded when U values are 6 eV and 2.7 eV for Ag-4d orbital electrons and V-3d orbital electrons respectively,the reasonable lattice parameters and band gap value were abtained.By calculating the band structure and density of states for the perfect ?-AgVO₃,it is known that thevalence band is mainly formed by Ag-4d orbit and O-2p orbit,and the conduction band is mainly composed of V-3d orbit.2.By comparing the formation energies of different Ag and O vacancies,we found that the dominating vacancy defect in ?-AgVO₃ is Ag3 and O1 vacancy,and the Ag vacancies form more easily than O vacancies.With Ag3 or O1 vacancy,the band gap of ?-AgVO₃ decreases slightly.With Ag3 vacancy,?-AgVO₃ presents p-type semiconductor properties,while with O1 vacancy it exhibits n-type semiconductor features.Ag3 vacancy and O1 vacancy have little effect on the light absorption of in the visible range.3.Cu doped ?-AgVO₃ and Fe doped ?-AgVO₃ have been studied.Cu doping and Fe doping both lead to the impurity states in the band gap of?-AgVO₃.The impurity states of Cu doped ?-AgVO₃ are in the middle of the band gap and the impurity states of Fe doped ?-Ag VO₃ are close to the bottom of the conduction band.The existence of the impurity states can enhance the visible light and infrared absorption ability.