Formation of nanodomain structures during polarization reversal in congruent lithium niobate implanted with ar ions

We present the experimental study of the formation of self-similar nanodomain structures during polarization reversal in single-crystalline congruent lithium niobate (CLN) implanted by Ar ions. The formed dense surface nanodomain structure with charged domain walls differs drastically from the growth of the hexagonal domains in unimplanted CLN. The lack of wall shape stability during sideways domain wall motion was revealed. The analysis of the domain structure images in the bulk, obtained by Raman confocal microscopy, revealed the main stages of the domain structure evolution starting at unimplanted polar surface and consisting of nanodomain chain elongation, merging of isolated domains, and domain widening. The switching current data has been fitted by modification of Kolmogorov-Avrami formula for switching in a linearly increasing field. The observed experimental facts have been attributed to formation of an amorphous thin surface layer and increase of the bulk conductivity resulting from oxygen out-diffusion under radiation heating in vacuum during ion implantation. The formation of the experimentally obtained abnormal domain shapes has been explained while taking into account the step generation at the domain wall in the bulk during switching in a low electric field.