Ba_(0.5)Sr_(0.5)TiO_3有序构型的第一性原理研究

First-principles study of ordered structures in Ba_(0.5) Sr_(0.5) TiO_3

采用第一性原理计算了Ba0.5Sr0.5TiO3三种有序构型的晶格结构和对应的电子结构,晶格结构的详细分析结果表明BST{100}有序构型为四方相,Ti-O八面体中Ti原子和Ba-Sr平面上的O原子沿[100]方向分别偏心位移0.040和0.065,八面体畸变导致反平行自发极化出现,构型处于反铁电态.BST{110}构型也是四方相,并且(110)和(110)面上的O原子存在0.029偏心移动,但Ti原子仍位于Ti-O八面体中心,构型处于顺电态.而BST{111}构型为立方相,其Ti-O八面体高度对称无畸变,构型为顺电态.态密度结果显示Ti3d和O2p轨道的杂化作用对BST钙钛矿晶体中铁电性的产生起着至关重要的作用,计算结果的综合分析表明A位的局部有序性会导致无序结构BST固溶体的结构相变.

The lattice structures and the electronic structures of different ordered structures in Ba0.5Sr0.5TiO3 are calculated by the first-principles method. The results of geometry structures and overlap populations reveal that the BST{100} ordered structure is tetragonal. The O atoms in Ti-O octahedron parallel to Ba plane and Sr plane are shifted ward Sr plane by 0.065 . And the Ti atom in Ti-O octahedron has a off-center displacement of 0.040 . The off-center displacements of O atoms and Ti atoms result in the distortion of Ti-O octahedron, and the occurrence of antiparallel spontaneous polarization. Therefore the BST{100} ordered structure is in antiferroelectric phase. The O atoms in BST{110} ordered structure also have a off-center displacement of 0.029 , while the Ti atom in Ti-O octahedron is still in-center. This tetragonal structure is in paraelectric phase. The BST{111} ordered structure is in cubic paraelectric phase. The calculated density of states shows that the hybridization between Ti 3d and O 2p plays a primary role in the generation of ferroelectricity. The results of the present work imply that the local order of A site can significantly influences the structural phase transition of disordered BST solid solution.