Local symmetry and polarization in relaxor-based ferroelectric crystals

Piezoelectric;Relaxor-ferroelectric single crystal;Morphotropic phase boundary;Symmetry;Convergent beam electron diffraction;Nanodomain structure;Transmission Electron Microscopy (TEM)

Kim, Kyou Hyun

关键词: Piezoelectric;    Relaxor-ferroelectric single crystal;    Morphotropic phase boundary;    Symmetry;    Convergent beam electron diffraction;    Nanodomain structure;    Transmission Electron Microscopy (TEM);   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/45292/Kyou%20Hyun_Kim.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Relaxor-ferroelectric single crystals, such as (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT), have the potential to transform technologies of medical imaging, actuation, and sensors, due to their extraordinary high piezoelectric effect. It has been suggested that polarization rotation driven by external electric fields is responsible for the large piezoelectric response. Polarization rotation is accompanied by a change in crystal symmetry and/or orientation. However, the nature of symmetry in PMN-xPT and other relaxor-ferroelectric crystals, despite extensive study by x-ray and neutron diffraction, is still controversial. Extensive studies have suggested the crystal symmetry varies on the nanoscopic scale and understanding the nature of local symmetry and its variations is thus critical to correlate the structure with polarization properties. In this thesis, the symmetry is measured based on the size of the crystal volume and the volume position in PMN-xPT single crystals. The study is enabled by the use of probes of different length scales to examine the symmetry of PMN-xPT single crystals. Local symmetry recorded by different probes is measured using quantitative convergent beam electron diffraction analysis (CBED) and transmission electron microscopy (TEM). Symmetry in CBED patterns is correlated with polarization direction with help of simulations. Furthermore, local symmetry fluctuation is observed using a new CBED method developed during this research. The technique enables the quantification of local symmetry development.