SBT材料微结构的TEM研究

本文利用透射电子显微术(TEM)对 SrBi2Ta2O9 (SBT) 材料(单晶、陶瓷及薄膜)的微结构进行了研究. 在(001)取向的SBT单晶材料及多晶陶瓷中观察到90°铁电畴结构.在SBT晶体中观察到大量的条带状四度反相畴界结构和少量的三度反相畴界结构,利用TaO6氧八面体的扭转和四态自旋结构模型,对反相畴界结构的实验观测结果进行了解释.在(001)取向的SBT铁电薄膜中,观察到小角晶界(倾角为8 2°)的位错分解现象,导致不全位错和层错的出现.利用平衡状态下两个不全位错之间的排斥力等于层错的吸引力,估算了小角晶界处的层错能量,大小为0 27～0 29 J/m2.小角晶界位错的分解对(001)取向的SBT铁电薄膜漏电流及耐疲劳特性具有重要的影响.

Microstructures of SBT materials investigated by transmission electron microscopy

In this work, the microstructures of SrBi2Ta2O9 (SBT) materials including (001) oriented single crystal, ceramics, and thin films with (001) orientation, were investigated by transmission electron microscopy. The 90° domain walls in SBT single crystal and ceramics were identified by the 90° rotation relationship in the electron diffraction pattern along the 001] zone axis. They exhibit irregular configurations. The structural planar defects of anti phase boundaries (APBs) in the SBT single crystal were also observed, which exhibit ribbonlike morphologies. Four fold vertices formed by joint of four APBs are observed as predominant singularities, and are explained by a four state spin clock model. Some three fold vertices are also observed since both threefold and fourfold vertices are energetically allowed in the present model. Dissociation of grain boundary dislocations (GBDs) in the SBT thin films with (001) orientation was also examined. Small angle (8 2°) 001] tilt grain boundaries with a boundary plane close to the (110) plane exhibit partial GBDs separated by stacking fThe dissociated grain boundary structures have twice the number of GBDs and interdislocation core channel width smaller than that Frank's geometrical rule predicts. The edge dislocations at small angle tilt grain boundary are deleterious to the leakage current of SBT films since the edge dislocation cores can providepinning centers for the space charges in SBT films, resulting in high leakage current and poor fatigue resistance characteristics.