中文摘要：

采用密度泛函理论研究了钛酸铅和钛酸钡的晶格振动性质和电子结构。结果表明立方相钛酸铅和钛酸钡的铁电不稳定性来源于Ti3d和O2p之间的轨道相互作用。钛酸铅和钛酸钡的铁电相变序的差异来自于两者不同的四方应变。在钛酸铅中，Pb6s轨道与O2p轨道形成有效的共价键，导致较大的四方应变，并使其四方相铁电不稳定性消失；而钛酸钡中Ba主要以离子形式存在，其四方相四方应变较小，其四方相仍可以发生低温铁电相变。

英文摘要：

The vibrational properties and electronic structures of PbTiO3 and BaTiO3 crystals were investigated by density functional theory. The calculation result indicates the ferroelectric instabilities of cubic PbTiO3 and BaTiO3 are derived from the hybridization between the Ti3d and O2p orbitals. The difference in the ferroelectric phase transition sequence of PbTiO3 and BaTiO3 is from their different tetragonal strain. For PbTiO3, the Pb6s, orbital bends with O2p orbital effectively, which results in large tetragonal strain and stabilizes its tetragonal phase. For BaTiO3, the barium atom is strongly ionic, and its tetragonal strain is rather small, and it can still undergo other low - temperature ferroelectrie phase transition.