Bi掺杂BaTiO_3陶瓷缺陷性质的第一性原理研究

First Principle Study of Defect Properties of Bi-doped BaTiO_3

采用第一性原理计算了Bi掺杂BaTiO3陶瓷3种不同的晶格缺陷结构,分别为单独的BiBa掺杂缺陷模式(BTB模型),1个BiBa掺杂缺陷与1个VBa钡空位同时存在(BTB1模型),符合化学计量比的BiBa掺杂缺陷与VBa钡空位缺陷模式(BTB2模型)。BTB模型显示缺陷结构是由施主掺杂机制控制的,Bi与周围的O原子形成典型的离子键,Ti 4+被还原成Ti 3+。在BTB1模型中钡空位的存在则影响了Bi在晶格中与O的相互作用,Bi偏离初始的中心位置,与邻近的3个氧原子形成了弱的共价键,而正是由于这些弱的共价键导致缺陷附近的[TiO6]八面体产生较大畸变,削弱了Ti 4+的极化能力,使缺陷附近的[TiO6]八面体极化能力减弱,此时缺陷结构是由Ba2+离子空位补偿机制控制的。而BTB2模型可以看成是BTB模型与BTB1模型的叠加,因此缺陷结构是由施主掺杂机制与Ba2+离子空位补偿机制共同控制的。

A density functional plane-wave pseudopotential method was used to study the defect structure of Bidoped BaTiO3 compounds.Three models of single BiBa impurity （BTB）,a BiBa impurity and a VBa vacancy coexisted （BTB1）,BiBa impurity and VBa vacancy coexisted which conforms to the stoichiometric ratio （BTB2）,were presented.In BTB model,BiBa impurity is charged by donor doping mechanism.Bi forms ionic bond with nearby O atom and part of Ti^4＋ is reduced into Ti^3＋.However,Ba^2＋ vacancy compensation mechanism presents in BTB1 model.Bi forms three valence bonds with nearby O atoms in BTB1 model,which causes large structure distortion and weakening of polarization Ti^4＋.The BTB2 model can be seen as a superposition of BTB model and BTB1 model,so the defect structure is controlled by donor doping mechanism and Ba^2＋ ion vacancy compensation mechanism.