ORIGIN OF FERROELECTRICITY IN PEROVSKITE OXIDES
ORIGIN OF FERROELECTRICITY IN PEROVSKITE OXIDES
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DOI：
10.1038/358136a0
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发表时间：
1992-07-09
期刊：
影响因子：
64.8
通讯作者：
COHEN, RE
中科院分区：
文献类型：
--
作者：
COHEN, RE
铁电材料具有可切换的宏观极化特性。大多数技术上重要的铁电体是具有钙钛矿结构的氧化物。然而，它们铁电行为的起源尚不清楚，并且对为什么相似但化学性质不同的钙钛矿应该表现出非常不同的铁电行为的理解也不完全。铁电体对化学、缺陷、电边界条件和压力的高度敏感性源于远程库仑力（有利于铁电态）和短程斥力（有利于非极性立方结构）之间的微妙平衡。为了准确地模拟跃迁，需要综合电荷畸变和共价效应的总能量技术。本文报告了两种铁电性钙钛矿（BaTiO3和PbTiO3）的电子结构计算结果，并证明钛的3d态和氧的2p态之间的杂化对于铁电性是必不可少的。两种材料的不同铁电相行为也很清楚：在PbTiO3中，铅态和氧态杂交，导致稳定四方相的大应变，而在BaTiO3中，钡和氧之间的相互作用完全是离子的，有利于菱形结构。
FERROELECTRIC materials are characterized by a switchable Macroscopic polarization. Most technologically important ferroelectrics are oxides with a perovskite structure. The origin of their ferroelectric behaviour is unclear, however, and there is incomplete understanding of why similar, but chemically different, perovskites should display very different ferroelectric behaviour. The great sensitivity of ferroelectrics to chemistry, defects, electrical boundary conditions and pressure arises from a delicate balance between long-range Coulomb forces (which favour the ferroelectric state) and short-range repulsions (which favour the nonpolar cubic structure). To model the transition accurately, total-energy techniques are required which incorporate the effects of charge distortion and covalency. Here I report results of electronic-structure calculations on two classic examples of ferroelectric perovskites, BaTiO3 and PbTiO3, and demonstrate that hybridization between the titanium 3d states and the oxygen 2p states is essential for ferroelectricity. The different ferroelectric phase behaviour of the two materials is also clear: in PbTiO3, the lead and oxygen states hybridize, leading to a large strain that stabilizes the tetragonal phase whereas in BaTiO3 the interaction between barium and oxygen is completely ionic, favouring a rhombohedral structure.