The Electronic Structure And Optical Properties Of（Mg₀.97,Fe₀.03）O Ferropericlase At Pressure Conditions Of The Earth’s Lower Mantle

(Mg, Fe)O ferropericlase is a main mineral in the Earth’s lower mantle. It is great important for exploring its physical properties at pressure-temperature conditions corresponding to the lower mantle. In recent years, the radiative thermal conductivity of ferropericlase has become a key topic in the high pressure science. In order to obtain the information in radiative thermal conductivity of the lower mantle, the optical-absorption spectrum and refractive-index data at the lower-mantle conditions is needed. The electronic structure and optical properties of(Mg0.97, Fe0.03)O ferropericlase crystal without and with Mg and O ionic vacancy point-defect at pressure conditions of the Earth’s lower mantle are studied using the first-principles calculations.This paper consists of four chapters. The background, significance, research status, problems and ideas are introduced in chapter 1. Research methods and the software are illustrated in Chapter 2. The electronic structure and optical properties of(Mg0.97, Fe0.03)O ferropericlase crystal without and with Mg and O ionic vacancy point-defect under high pressures are presented in Chapter 3. The summary and prospects of the full text are carried on in Chapter 4.In this paper, the main results are as follows:1. The electronic structure of(Mg0.97, Fe0.03)O ferropericlase crystal without and with Mg and O ionic vacancy point-defect are investigated up to 80 GPa. The density of state and electronic density difference data show that the vacancy point-defect and spin transition have great influence on the electronic structure.2. The optical-absorption spectrum of(Mg0.97, Fe0.03)O ferropericlase crystal without and with Mg and O ionic vacancy point-defect are investigated up to 80 GPa. The optical-absorption data show that the perfect-crystal results are similar to the predictions from the crystal field theory etc: the pressure-induced spin transition of iron in ferropericlase causes the large blue-shift of its optical-absorption spectrum, leaving the near-infrared region transparent. However, when there are point defects in ferropericlase, the calculated optical-absorption results are completely inconsistent with predictions from the crystal field theory etc: the spin transition causes the enhancement in the optical absorption at the near-infrared region.3. The refractive-index of(Mg0.97, Fe0.03)O ferropericlase crystal without and with Mg and O ionic vacancy point-defect are calculated up to 80 GPa. In perfect crystal the effects of pressure, wavenumber, and spin-transition on the high-pressure refractive-index of(Mg0.97, Fe0.03)O ferropericlase are slight, but the point defect affect strongly on them.4. The reflectivity and loss function of(Mg0.97, Fe0.03)O ferropericlase crystal without and with Mg and O ionic vacancy point-defect are calculated up to 80 GPa. The results show that the vacancy point-defect and spin transition affect strongly on them.Above-mentioned results are not only important for exploring high-pressure optical properties of lower-mantle ferropericlase, but also show that high-pressure optical-absorption spectrum measurements could be a good approach for probing iron spin state.