【摘要】 弛豫铁电体PMN(Pb(Mg1/3Nb2/3)O3)和PMN-xPT(Pb(Mg1/3Nb2/3)O3-xPbTiO3)由纳米畴结构组成。在弛豫铁电体PMN中B位有序的模型,以及有序畴和极化微区的关系是长期悬而未决的科学问题。本文采用纳米束电子衍射和能谱分析结合的手段确定了B位有序的杂乱位置模型;在有序畴和无序基体之间的成分波动最剧烈,有序无序界面可能是极化中心的位置;电子衍射和高分辨像还发现了片状反铁电畴结构,这种结构与铁电有序相互竞争,使得PMN中局部结构的相互竞争更加复杂。在PMN-xPT中准同型相界附近的单斜相的本质一直存在异议,X光衍射、中子衍射以及偏光显微镜只能给出宏观的结果,不能给出纳米尺度的结构信息,本文利用会聚束电子衍射,成功的解决了这一问题,确定单斜相MC具有多层次的畴结构,在纳米尺度具有四方对称性,而在宏观尺度由于平均效应具有单斜对称性。文中还讨论了采用电子显微学方法研究铁电体时,遇到的技术难点及相应的解决方法。更多还原

【Abstract】 Relaxor ferroelectrics PMN(Pb(Mg-1/3 Nb-2/3)O-3) and PMN-xPT(Pb(Mg-1/3 Nb-2/3)O-3-xPbTiO-3) are composed of nanodomains.It remains a puzzle about the model of the B-site ordered structure and the relationship between ordered domains and disordered matrix.In this paper nano-beam electron diffraction(NBED) and energy dispersion spectrum(EDS) are used to claim the random site model,there exists large composition fluctuation across the interface between ordered domain and disordered matrix,and the interface may be the center of polar cluster.Sheet-like local anti-ferroelectric ionic displacements are found according to the selected area electron diffraction(SAED) and high resolution electron microscopy(HREM),such anti-ferroelectric ordering may be a competing mechanism with the ferroelectric ordering.In PMN-PT it is unclear whether the monoclinic phase is a real phase or a mixed phase,X-ray diffraction,neutron diffraction and polarized light microscopy can provide the macroscopic information but not the structure information on the nanometer scale,the convergent beam electron diffraction(CBED) was used to determine that the monoclinic M-C phase composed of hierarchical domain structure is tetragonal in nanometer scale while appears as monoclinic symmetry in micrometer scale due to an average effect.It is also discussed about the technical difficulties and the corresponding solutions while studying ferroelectrics with analytical electron microscopy.更多还原