Investigation On The Electronic And Magnetic Properties Of 1322-type Perovskite Transition Metal Oxides By First-principles Calculations

Perovskite materials have attracted extensive attention in recent decades owing to their flexible crystal structures and rich physical properties.At present,perovskite materials are playing an important role in the fields of superconductivity,ferroelectricity,catalysis,solar cells and so on.The study of magnetic coupling mechanisms and related physical and chemical properties for perovskite materials via first-principles calculations have become hotspots.It can not only theoretically explain the experimental results of perovskite materials,but also play an important role in guiding experimental synthesis.Therefore,this thesis is to systematically explore the thermodynamic stability,electronic structure,and magnetic coupling mechanism of perovskite materials using first-principles calculations.The specific work is mainly divided into the following aspects:(1)The thermodynamic stability,electronic structure and magnetic properties of 1322-type perovskites CaCu3Fe2Ta2O12 and CaCu3Fe2V2O12 were theoretically predicted.Analysis of thermodynamic properties indicates that perovskite should be synthesized experimentally.Analysis of electronic and magnetic properties also clarifies that they are ferrimagnetic semiconductors with a direct bandgap.The electronic structure analysis based on GGA+U method shows that the electronic configuration of perovskite is Ca2+Cu2+3Fe3+2Ta5+2O2-12 and Ca2+Cu2+3Fe3+2V5+2O2-12,respectively.This work also opens up a new avenue for the new optoelectronic applications of AA'3B2B'2O12 perovskites(2)The influence on crystal structure stability and electromagnetic properties of 1322-type perovskite CaCu3Fe2Ru2012,due to the doping of Cu ions at A' site,has been systematically investigated.Analysis of thermodynamic properties confirmed that perovskite materials can be synthesized under high temperature and high pressure conditions.The calculation results of different magnetic configurations based on GGA and GGA+U methods show that the ferrimagnetic of perovskite is derived from Cu(?)Fe(?)Ru(?)magnetic coupling between Cu at A' site,Fe at B site and Ru at B site.This also makes the total magnetic moment of system as high as 7.0 ?B/f.u.,compared to double perovskite Ca2FeRuO6.In addition,Analysis of electronic structure shows that charge combination of perovskite should be Ca2+Cu2+3Fe3+2Ru5+2O2-12.Our study opens up a new avenue to further enhance electrical and magnetic properties of 1322-type AA'3B2B'2O12 perovskite by introducing magnetic ions at A' site(3)The electronic structure and magnetic properties of experimentally synthetic 1322-type perovskite LaCu3Fe2Os2O12 have been systematically studied by GGA+U method.Analysis of magnetic properties indicates that perovskite is a ferrimagnetic material,which is also consistent with experiment.Furthermore,the magnetic configuration of perovskite at the ground state energy is Cu(?)Fe(?)Os(?).The total magnetic moment of system is as high as 11.82 ?B/f.u.,owing to the strong magnetic coupling between Cu at A' site,Fe at B site and Os at B' site.Analysis of electronic structure shows that perovskite LaCu3Fe2Os2O12 has rare semi-metallic properties,which can be excellent candidates for spintronic devices.