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First Principles Study On The Effect Of The Vacancies On The Electronic Structure And Optical Properties Of LiF And Al2O3 Under High-pressure

Posted on:2012-12-01Degree:MasterType:Thesis
Country:ChinaCandidate:X HeFull Text:PDF
GTID:2210330374953665Subject:Condensed matter physics
Abstract/Summary:PDF Full Text Request
Optical window materials are used in coherent laser and light spectrum of shock wave experiments, so their optical transparency issues are concerned by people in shock wave experiments. LiF and Al2O3 crystals are used optical window materials in shock wave experiments. so it is very important to develop the technique of experimental in shock wave experiments and give people impetus to the understanding of nature. This paper is divided into two parts, studying on some physical and optical properties of LiF and Al2O3.The main work and results of the first part are as follows:Based on the plane-wave pseudopotential method in the frame-work of the density function theory and the local density approximation of Ceperly and Adler by the parametrization of Perdew and Zunger (LDA-CA-PZ), the electronic structures and optical properties of LiF without and with Li-1 and F+1 vacancies are calculated.The results indicate that:(1) Presence of the vacancy causes defective states within the band gap of LiF.(2) The optical absorption of LiF in the visible-light region is not influenced by the vacancy point-defect (absorption coefficients are still zero).(3) In the ultra-violet region, the weak absorption induced by the Li-1 vacancy, appears within 99-114 nm, and the relative strong absorption, induced by the F+1 vacancy, exists at the range of 99-262 nm.(4) Effects of the Li-1 and F+1 vacancy on reflectivity and loss-function are focused on the ultra-violet region, which is similar to those of optical absorption.And by using ultra-soft pseudo-potential approach of the plane wave based on the Density-functional theory, the refractive index and reflectivity and dielectric function of LiF without and with Li-1 and F+1 vacancies under 102 GPa are also calculated and analyzed. The results indicate that: effects of the Li-1 and F+1 vacancy on reflectivity and loss-function are focused on the ultra-violet region, which is similar to those of optical absorption.The main work and results of the second part of the paper are as follows:(1)The first principles were used to calculate the effect on lattice constants and band gaps and other properties of perfect Al2O3 in three structural phases (Corundum phase and Rh2O3(Ⅱ) phase and CaIrO3 phase under different pressure, and get the relationship between the lattice constants and pressure, at 0K and the same structure phases, with the pressure to increase its lattice constants gradually reduced, it is to say the structure is become more stable. And the band-gap data may be obtained from the corresponding calculated energy-band structures. It is found that Corundum-Rh2O3(Ⅱ) and Rh2O3(Ⅱ)-CaIrO3 transitions in alumina at 0 K cause band-gap different level reductions, respectively. The band gap decreases slightly with pressure in the CaIrO3 phase region but increases in Corundum and Rh2O3(Ⅱ) phase regions.(2) Based on the plane-wave pseudopotential method in the frame-work of the density function theory and the local density approximation of Ceperly and Adler by the parametrization of Perdew and Zunger (LDA-CA-PZ), the author calculate the effect different point defects of Al2O3 (VO0,VO+1,VO+2,VAl0,VAl-1,VAl-2 )on crystal lattice parameters of Al2O3 supercell with 80 atoms under 131.2 GPa pressure. The results indicate that: the lattice parameters of Al2O3 become enhance when point defects exist except the -3 price of Al vacancy.(3)The first principles were used to calculate the effect different point defects of Al2O3 (VO0,VO+1,VO+2,VAl0,VAl-1,VAl-2 )on electronic difference density of states properties of Al2O3 in CaIrO3 structural phases under 131.2 GPa.
Keywords/Search Tags:LiF, Al2O3, first principles, high pressure, vacancy, electronic structure, optical transparency, optical absorption
PDF Full Text Request
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