稀土元素Gd掺杂BiFeO3的第一性原理研究

摘要

采用基于密度泛函理论的局域自旋密度近似加U法(LSDA+U:Hubbard参数)计算了多铁材料BiFeO3铁电相以及稀土元素Gd掺杂BiFeO3材料的能带结构、态密度(DOS)、原子轨道占据数和净电荷分布等,对稀土元素Gd掺杂BiFeO3可能引起的电子结构、介电常数和铁磁性的改变进行了第一性原理研究.计算结果表明:Gd掺杂对材料钙铁矿结构影响不大,BiFeO3铁电性主要来源于Fe原子3d轨道和O原子2p轨道杂化；掺杂Gd后材料中的Fe原子和O原子的共价性减弱,Bi原子和O原子的离子性增强,禁带宽度变窄,绝缘性减弱,铁磁性明显增强；计算得到的光学性质表明材料的静态介电常数有所增加.%The band structure, density of states (DOS) , Mulliken charge population etc. Of ferroelectric (FE) BiFeO3 and rare-earth-element Gd doped BiFeO3 have been studied by first-principles calculations within the local spin density approximation plus Hubbard U (LSDA+U) approach. Our result turns out that the perovskite structure of BiFeO3 is not significantly affected by Gd doped. The ferroelectric stability of BiFeO3 is found to be attributed to the hybridization between 3d orbit of Fe and 2p orbit of O atom. And the strength of covalent bonds between Fe atom and O atom becomes weaker while the strength of ionic bonds between Bi and O becomes stronger. Meanwhile the insulativity becomes weaker since the band gap of Gd doped BiFeO3 is narrower than that of ferroelectric BiFeO3. However, the fer-romagnetism improved significantly. Furthermore, the absorption coefficient and dielectric function were calculated and the corresponding numerical results show that the static dielectric constant of Gd doped BiFeO3 is higher than that of pure BiFeO3.