Ferroelectric crystals with periodic laminar domains

Publisher Website
Google Scholar
Abstract
This paper reviews our researches on the growth, the characterization and the physical properties of ferroelectric crystals with periodic laminar domains. The growth of LiNbO3 and LiTaO3 crystals with periodic laminar domains has been achieved in Czochralski growth system. The melt was doped with solutes such as yttrium, indium or chromium. Either eccentric rotations or applying electric current pulses with reversed polarities was used to induce the growth striations in the growing crystals. Two kinds of domain walls, the smooth vs. the rough have been found with electron microscopic observations. The determination of solute concentration variation along the growth axis shows that there are sharp minima and broad maxima which correspond to the smooth and the rough domain walls. The mechanism for the formation of periodic laminar domains has been discussed. Components of a 3rd rank tensor such as nonlinear optical or piezoelectric coefficient may change sign across a ferroelectric domain wall. For these physical properties, ferroelectric crystals with periodic laminar domains may be regarded as the superlattices with periods in the micron range. These micron superlattices have interesting physical properties, for their reciprocal vectors may participate some wave processes such as nonlinear optical or acoustic processes, ensuring the conservation of k vectors. We have demonstrated experimentally that micron superlattices of LiNbO3 and LiTaO3 have excellent nonlinear optical properties as expected theoretically. For quasi-phase-matching may be realized by adjusting the growth parameters so that the periods of these superlattices equal to the coherence lengths of the corresponding nonlinear optical processes. An order of magnitude enhancement of frequency doubling output for YAG laser has been achieved in LiNbO3 by utilizing the largest nonlinear optical coefficient d 33; and significant frequency doubling output has been achieved in LiTaO3 which is a positive uniaxial crystal phase unmatchable by birefringence, usually considered unfit for nonlinear optical applications. Generalization of these concepts to other wave processes may be envisaged and experiments in these directions are in progress.