| It is observed in the shock-wave experiments that there is a sudden electrical conductivity increase and the optical transparence loss of Al2O3 under 131.2Gpa, as well as the electrical conductivity in crease of MgO under 90 Gpa. In order to understand these phenomena, in this paper, combined with CASTEP software, First Principles methods is used to stimulate how vancancies and interstitial atoms affect the electronic band gap structure and optical properties of Al2O3 and MgO under high pressure. We also want to give some possible physical mechanisms to explain the phenomenons observed by shock-wave experiments.The main work and results of these parts are as follows:1,Based on first principles simulation different point defects of Al2O3 (VO0,VO+1,VO+2,VAl0,VAl-1,VAl-2,and oxygen interstitial atoms) are calculated in different situation to simulate how these defects affect the electrical and optical properties of Al2O3. Concluded by the calculation results, we get these cunclusion: 1, +2 price of oxygen vacancy minght be an an origin which causes the transparency loss at visible light range. 2,With the increase of +2 oxygen vacancy concentration, there would be an upset of the conductivity and the blue shift of the optical absorption.3,The interstitial neutral oxygen atom unlikely formed in the material, because it will make the model structure unstable. 4, under certain conditions, the aggregation of vacancy concentration is also possible to cause the conductivity increase.2, we calculate the band gap of ideal MgO within 105GPa, and how the oxygen vacancy affect the band gap of MgO under the pressure of 90GPa. The results showed that: 1, the increase of pressure is not responsible for the increase of electrical conductivity. 2, neutral oxygen vacancy may be one physical mechanism for the experimental phenomena.
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