Observation of the poling process in ferroelectric ceramics using piezoresponse force microscopy

Evolution of the domain structure in bulk polycrystalline PZT during poling was studied using Piezoresponse Force Microscopy (PFM). For the study, two different experimental methods were employed. First, a trapezoidal PZT specimen was subjected to electric field so as to produce a wide variation of electric field intensity in the specimen. PFM images were then acquired from several different areas that have experienced different field strengths. Histograms of pixel intensity show a distinct difference in the pattern of piezoresponse signal between poled and unpoled areas. The presence of non-180° domain structure in the scanned area significantly affects the histogram pattern. At high levels of electric field the presence of mainly 180° domain structures leads to a bi-modal M-shaped histogram. To illustrate the evolution of the non-180° domain structure, in-plane poling was conducted with the electric field level increased in steps, and the domain evolution process was observed by PFM after each step. The resulting images demonstrate that non-180° domain structures gradually disappear from the specimen surface during the poling process. The PFM data can be exploited to study domain evolution in bulk ferroelectric materials via both qualitative observation and statistical analysis.