The High-pressure Phase Transition Of Fecr₂o₄ And Density-functional Theory Investigation On Each Phase Of Fecr₂o₄

Density function theory, as we know, can deal multi-electron system with single-electron system. Binding energy, lattic constants, bulk modules werepresented based on density function theory of semiconductor and metal materials.These results were in a very good agreement with experiments. Theory calculation was an important achievement in electronic theory. A lots of experiments data were obtained and the large,quick computers were also developed in recent years.The calculations by simulating are becoming more and more powerful, and the theory resulted the research of energy band from develop qualitative universal disciplinarian to the complex band structure of typical materials. There is much arithmetic based on density function theory. Such as LCAO-TB,OPW,PWP,LAPW and LMTO, etc. The PWP was used in this thesis.In this thesis, the main research works can be divided into four parts:(1)The electronic structural models of three phases of FeCr2O4 crystals have been established. The plane-wave pseudopotential method within generalized gradient approximation was used to investigate three phases of FeCr2O4 crystals.We optimized their structures and obtained the equilibrium lattic constants and volume. The imitated result and experimental value is suitable basically, which explains that our method is reasonable and the conclusion gotten is accurate and reliable. The stability of three-phase crystal:CT is the most unstable phase and Spinel is most stabilized phase.(2) The high-pressure phase transition of FeCr2O4 has been computed by means of plane wave pseudo-potential method (PWP) with GGA. The total energies as functions of volume indicated the transition pressures which has a same quantity level with experimental value, this maybe because Simulated temperature is chosen for 0℃while the temperature is 2000℃in experiment. At the same time, it indicates that the effect of temperature is significant in phase transition. Moreover, we analyze and compare the electronic populations and band feature of three phases of FeCr2O4 crystals.(3)The plane-wave pseudopotential method within generalized gradient approximation was used to calculate and analyze the band structural, DOS,PDOS of the phases of Spinel,CF and CT. The results show that the Spinel phase is a narrow Narrow-Gap Semiconductor material.In the vicinity of Fermi surface, the conduction bands of CF, CT move upward, which result in this two phases show some metal features. In the aspect of band, Cr 3p electron has played a significant role.(4) The plane-wave pseudopotential method within generalized gradient approximation was used to calculate and analyze the optical properties of Spinel, CF and CT phase. There are two optical response districts in each phase of FeCr2O4, one is high energy district, and the other one is low energy district. The calculation results show that Spinel and CT all have five inherent frequencies while CF phase has only three, which is due to relatively simple optical response districts of CF phase.