First-principles Study On The Electronic And Magnetic Properties Of Double Perovskite Oxides With Strong Electronic-Correlation

Perovskite-type compounds are one of the most abundant minerals on the earth,and quite a few materials with practical application value(such as piezoelectric,ferroelectric materials,magnetic materials,catalytic materials,superconducting materials and various functional materials)are inorganic or organic perovskite compounds.With the development of the high-speed computing technology and the theoretical study,it has become a hot spot to investigate the electrical and magnetic correlated interaction of perovskite-type compound and its related physical and chemical properties by first-principles theoretical investigation.Therefore,this study is to systematically explore the crystal structure,magnetic coupling and electronic structure of different double perovskite oxides by implementing first-principles calculations,and the influence of possible antisite defects on the physical properties was discussed.This study mainly includes the following aspects:(1)The crystal structure,magnetic coupling and electronic structure of B-site ordered double perovskite oxide Pb2CoTeO6 have been systematically studied.The first-principles calculation results show that the compound is an antiferromagnetic semiconductor in the low-temperature stable phase P21/n structure.The Te ion at B'site has no cell magnetic moment(?0?B),and the magnetic coupling is determined by B-site sublattice Co(?)-Co(?).The electronic distribution is confirmed to be Pb2+2Co2+Te6+O2-6,in which Co2+with 3d7 electronic configuration splits into t2g and eg orbitals(t2g5eg2)in the high-spin state.This study provided an way for the straightforward understanding of the multiple spin-state of Co and its inextricable effects on magnetic and electronic properties.(2)The crystal structure,magnetic coupling and electronic structure of B-site ordered and disordered double perovskite oxides Pb2FeOsO6 have been systematically studied.The results of first-principles calculations show that ordered Pb2FeOsO6 in Fm 3 m space group is a ferrimagnetic semiconductor with a narrow bandgap.With the introduction of B-site antisite defects,the lattice structure still maintains the original crystal framework,but the internal atomic arrangement and magnetic coupling are reconstructed.As increasing the B-site disordering concentration,it worth noting that the saturation magnetic moment of the compound sharply decreases.This study provided an intuitive explanation for the effect of B-site antisite defects on the electronic and magnetic properties of doubler perovskite,and the close relationship between ionic ordering and physical properties has also been detailed discussed.(3)The d-d electronic correlation interaction,magnetic coupling and electronic structure of ordered 134-type perovskite LaMn3Rh4O12 have been systematically studied.The results of first-principles calculations show that the compound is a semiconductor material with antiferromagnetic properties,the ground state magnetic configuration is G-type-antiferromagnetic coupling,and the charge composition is La3+Mn3+3Rh3+4O2-12.The diamagnetic host perovskite LaRhO3 is transformed into antiferromagnetic semiconductor(La0.25Mn0.75)RhO3 by introducing Mn3+at A-site in the ratio of 75%.This study detailed investigated the enhancement of the magnetic order of the perovskite system by A-site introduced magnetic ions,providing an alternative method for beneficial modification of traditional ABO3 perovskites.(4)The magnetic properties,electronic structure and charge distribution of ordered 134-type perovskite CeCu3Cr4O12 with anomalous chemical valence at A-site have been systematically studied.The magnetic analysis shows that CeCu3Cr4O12 is a ferrimagnetic half-metal with an integral saturation magnetic moment of 7.00 ?B f.u.1(Slater-Pauling rule),and the effective magnetic coupling is mainly contributed by the A'-site Cu and B-site Cr(Cu(?)-Cr(?)).The charge distribution of the compound is Ce(4-?)+Cu2+3Cr(3.5+?)+4O2-12.The A-site Ce is approaching but insufficient to+4 oxidation state,and a small quantity of 4f itinerant electrons of Ce was found.This study gave the first half-metal material in the Perovskite-type compounds with CeCu3B4O12(B=transition metals)structure,opening up the way for subsequent experimental and theoretical researches.