Local polarization switching in the presence of surface-charged defects: Microscopic mechanisms and piezoresponse force spectroscopy observations

Thermodynamic description of probe-induced polarization switching in ferroelectrics in the presence of well-localized surface field defects and their effect on local piezoresponse force spectroscopy measurements is analyzed. Corresponding analytical expressions for the free energy, activation energy, nucleation bias, and nucleus sizes are derived. Both numerical calculations and analytical expressions demonstrate that well-localized field defects significantly affect domain nucleation conditions. The signature of the defects in reproducible piezoresponse hysteresis loop fine structure are identified and compared to experimental observations. Deconvolution of piezoresponse force spectroscopy measurements to extract relevant defect parameters is demonstrated. Proposed approach can be extended to switching in other ferroics, establishing a pathway for the understanding of the thermodynamics and kinetics of phase transitions at a single-defect level.