First Principles Study On The Effect Of The Pressure And Vacancies On The High-pressure Properties Of Window-material (LiF And MgO)

Abstract By first-principles method, the electronic structure and optical properties of window-materials (LiF and MgO) perfect-crystal without and with charged-vacancy were calculated within100GPa, whose results were used to explore the experimental measurement data.This paper is divided into five chapters. Chapter1sets out the background of this paper, experimental and theoretical studies of the status, and the full test of the research ideas. Chapter2gives an introduction on the first-principle method and the software used in the calculations of this paper. Chapter3contents are:we performed first-principles calculations of refractive-index and density of LiF crystal without and with charged Li or F vacancy were calculated within102GPa. Chapter4contents are:we performed first-principles calculations of electronic structure and optical properties of MgO perfect-crystal up to100GPa. Chapter5contents are:we performed first-principles calculations of electronic structure and optical properties of MgO crystal with charged Mg and O vacancy point-defects up to100GPa.The main work and results of these parts are as follows:1. By first-principles method, the refractive-index and density of LiF crystal without and with charged Li or F vacancy were calculated within102GPa, whose results indicate that the calculated refractive-index of perfect LiF crystal increase more rapidly with increasing pressure than those determined by shock experiments and above～50-60GPa there is also similar behavior in density-pressure curve. It is found that Li+1vacancy-induced decrease in refractive-index and density are supposed to be a possible source causing these differences.2. For the similarities of the electronic structure and optical properties of MgO perfect-crystal up to100GPa. The calculations of MgO suggests that effects of shock-induced pressure and temperature on the optical absorption of MgO are mainly in the short-wavelength region. At a wavelength of532nm, the calculated refractive-index of perfect-MgO decreases faintly with increasing pressure below～0.8GPa, but it increases weakly with increasing pressure between～0.8GPa and100GPa.3. The Vo+2-induced heterogeneous absorption within～300-700nm should be a possible origin causing shock-experimental observations, based on this result, we may infer further that the interpretation of the transparency loss of shocked Al2O3is reasonable. Other, Vo+2induces the obvious increase in refractive-index and effects of Vo+2on it could reinforce with increasing shock-pressure according to the viewpoint that the defect concentration should increase with increasing shock-pressure. However, the effect of VMg-2is slight.