The First-principle Investigations Of Electronic And Magnetic Properties Of Square Planar Coordinated Transition Metal Oxides

In this thesis, we mainly use the first-principle to study electronic properties and magnetic properties for the square planar coordinate oxides.This thesis can be divided into two parts. In the first part of this thesis, we study the electrical and magnetic properties of the phase transition of quasi-one-dimensional chain structure Sr2FeO3 compound under pressure. In the process of compressing, firstly, Sr2FeO3 shows a structural transition from Immm (No.65) to Ammm (No.71) at about 35 GPa. Secondly, it occurs high spin (S=2) to intermediate spin (S=1) transition when about 55GPa, moreover, which is accompanied by an insulator to metal transition and antiferromagnetic to ferromagnetic transition.In the second part of this thesis, we study mainly the structural properties and electrical properties of Sr2CoO2CI2 compound. Firstly, we study the arrangement of Co 3d orbitals due to crystal-field splitting and correlation effect. Secondly, we carry out antiferromagnetic calculation for Sr2CoO2Cl2 and further determine the nature of the crystal structure and electrical properties for high-spin (S=3/2) state. Finally, we can conclude that the distance of Co-Cl affects arrangement of Co 3d orbitals and is the main reason to avoid the Jahn-Teller effect in Sr2CoO2Cl2.