Atomic-level theoretical and experimental study of lattice dislocations in perovskites

该项目旨在通过原子模拟、电子结构计算和透射电子显微镜研究混合离子-共价键陶瓷氧化物材料中位错的结构和能量学。我们将研究钙钛矿化合物中位错核和相关的平面缺陷(层错、反相和晶界)的结构和成分特征，即SrTiO3，BaTiO3和PbTiO3。采用第一性原理密度泛函理论计算扩展缺陷的性质，具有较高的精度和可靠性。这些结果将进一步验证静电和排斥离子-离子相互作用的经验解析势。有了这样的势，将对由大量原子组成的位错核模型进行原子模拟，以便将针对金属位错核的连续介质理论和原子模拟方法应用于具有普遍离子键的陶瓷材料的模拟。应特别注意正确处理长程弹性和电气边界条件。用电子显微镜研究了钛酸锶中位错核的原子结构和化学成分。这些结果将为原子模拟提供重要的参考。我们希望我们提出的研究将大大提高对钙钛矿材料中位错的科学理解，并将有助于阐明位错对电活性器件功能性质的影响。

The project aims to investigate the structure and energetics of dislocations in ceramic oxide materials with mixed ionic-covalent bonding by means of atomistic simulations, electronicstructure calculations, and transmission electron microscopy. We will study structural and compositional features of dislocation cores and related planar defects (stacking faults, antiphase and grain boundaries) in perovskite compounds, namely SrTiO3, BaTiO3 and PbTiO3. First-principles density functional theory will be used to calculate properties of the extended defects with high accuracy and reliability. These results will serve further to validate empirical analytic potentials for electrostatic and repulsive ion-ion interactions. With such potentials, atomistic simulations of dislocation-core models consisting of large numbers of atoms will be carried out in order to adapt and apply approaches of continuum theory and atomistic simulation developed for dislocation cores of metals to simulations of ceramic materials with prevalent ionic bonding. Special care will be given to correct handling of long-range elastic as well as electrical boundary conditions. The atomistic structure and chemical composition of dislocation cores in SrTiO3 will be studied by transmission electron microscopy. These results will serve as an important reference for the atomistic simulations. We expect that our proposed investigations will significantly improve the scientific understanding of dislocations in perovskite materials and will help to clarify the influence of dislocations on functional properties of electro-active devices.