Research On The Properties Of SrTiO₃ And 3C-SiC From First Principle

The dissertation is devoted to the study of electronic structure and related properties of SrTiO₃, thermodynamic properties and thermal transport properties of 3C-SiC from first principles.Electronic structure and related properties of SrTiO₃ were investigated by using a first-principles ultrasoft pseudopotential approach of the plane wave and General Gradient Approximation (WC functional) based upon the Density Functional Theory. Main contents and results obtained in this study divides into three parts as follows: (1) The detailed investigation of the electronic structures including band structure, density of states (DOS) and the Mulliken population analysis of perfect SrTiO₃ has been performed.(2) We also have studied the crystal structures, electronic structures, and formation energies of intrinsic vacancies (VSr, VTi and VO) in bulk SrTiO₃. Through the analysis of the calculation results we can explain well the effect of intrinsic vacancy defect on the semiconducting mechanics.(3) Formation energies of Fe doping Sr site and Ti site in SrTiO₃ were investigated respectively. At the same time, the crystal structures, and electronic structures of SrTi_1-x Fe_xO₃ (x=0,0.125,0.167,0.25) were calculated and we study the great affects of Fe doping SrTiO₃ on elecronic structures, which can help us explain the conductivity mechanics of Fe doping SrTiO₃.Based on density functional perturbation theory (DFPT) and combined with the norm-conserving pseudopotential method, the lattice dynamic simulation of 3C-SiC was presented in this dissertation. The total phonon density of states, partial phonon density of states and phonon dispersion spectrum were obtained. By using the special point sampling method within the first Brillouin zone, the specific heat capacity,the Debye temperature and the average group velocity of phonon were calculated. The anharmonic phonon mean free path was calculated theoretically within anharmonic interaction and by using the Fermi's golden rule scheme combined with the special point sampling method within the first Brillouin zone. Lastly, with two types of the phonon scattering mechanisms (phonon interaction scattering and surface scattering) considered comprehensively, the thermal conductivity of 3C-SiC crystal was achieved. Variations with temperature of the calculated thermal conductivity and the specific heat capacity agreed well with the experimental results.