Abstract
The effect of microstructure on ferroelectric domain nucleation in epitaxial bismuth ferrite was probed at a single atomically-defined defect: an artificially fabricated model bicrystal grain boundary (GB). Switching Spectroscopy Piezoresponse Force Microscopy is used to map the variation of local hysteresis loops at the grain boundary and its immediate vicinity. We found the influence of the GB on nucleation to be relatively weak, resulting in a slight shift of the negative nucleation bias to higher (negative) voltages. The mesoscopic mechanisms of grain boundary effect on local polarization switching are studied in detail using phase field modeling, elucidating the complex mechanisms governed by the interplay between ferroelectric and ferroelastic wall energies, depolarization fields, and interface charge. The combination of phase field modeling and SS-PFM allows quantitative analysis of mesoscopic mechanisms for polarization switching, and hence suggests a route for optimizing materials properties through microstructure optimization.