报告题目：Probing Mesoscopic Dynamic Phenomena in Ferroelectric Materials via Advanced Piezoresponse Force Microscopy

报 告 人：Qian Li (美国橡树岭国家实验室)

报告时间：2016年12月29日（周四）10：00

报告地点：物理系三楼报告厅C302

报告摘要：Ferroelectric materials show a hierarchy of structure and associated dynamic behavior, and thus obtaining deep insights into them necessitates probing at various length/time scales. The prevalence of piezoresponse force microscopy (PFM), a scanning probe modality, has largely fulfilled the task of mesoscopic imaging of ferroelectric domains. PFM can also be adapted to probe a range of locally/globally induced dynamic phenomena that are closely tied in with material functionalities, for instance, polarization switching, phase transitions and ion migration activities. In this talk, I will first present my development of a near-field ultrasound elastic spectroscopy based on multi-frequency PFM and its case studies of morphotropic phase transitions in BiFeO₃thin films, which led to the first observations of highly spatially-confined lattice elastic softening behavior due to the phase instabilities. In the second part, I will explore the coupling mechanism between oxygen vacancy transport and polarization evolution in Pb(Zr,Ti)O₃thin films, which may provide a revised explanation for the tip-pressure induced ferroelectric switching phenomena currently attributed to flexoelectricity. Apart from PFM, my talk will emphasize the combination of phase-field modeling in understanding those complex mesoscale phenomena, and also briefly illustrate our recent initiative of correlative mesoscale structural characterization using full-field X-ray Bragg diffraction imaging.