Influence of Humidity on Local Polarization Reversal in a Rb:KTP Single Crystal

The influence of the relative humidity on the domain growth during local switching by a conductive tip of a scanning probe microscope has been studied in Rb:KTP single crystals. The abnormal formation of the elongated hexagonal domains during the local switching in an axial-symmetric field has been attributed to the anisotropy of the domain wall velocity. The increase and subsequent decrease in a hexagonal domain aspect ratio as a function of the pulse duration for high humidity have been attributed to the influence of the high-resistivity water layer. We assume that the domain elongation by the fast walls is limited by the water layer representing the series resistance, which depends on the wall position, while the domain widening by the slow walls is limited by their mobility. The computer simulation of the spatial distribution of the electric field has demonstrated that the appearance of a water meniscus decreases the field close to the tip and increases it far from the tip. This result has allowed explaining the published alternative effects of humidity on the domain size: (1) decrease in size for small domains and (2) increase in size for large ones. The obtained results highlight the necessity of humidity control for domain engineering.