Origin and characteristics of internal fields in LiNbO3 crystals

Abstract

We report the presence of an in-built internal field in Z-cut LiNbO3 crystals of 3.35KV/mm in the direction of the polarization in a virgin crystal. Upon polarization reversal under an electric field, the internal field tends to realign along the new polarization direction. At room temperature, this realignment process was incomplete even after many days, while on annealing at 250°C for 2 min followed by cooling down, ∼ 80% recovery was observed (from + 3.35 KV/mm to −2.14 KV/mm). A change in the infrared absorption spectrum of OH− ions in LiNbO3 crystal was also observed upon polarization reversal at room temperature. Upon annealing above 200°C for a few minutes followed by cooling to room temperature, the shape of the spectrum partially recovers to that of the virgin crystal at room temperature, indicating a strong correlation between OH− ions and internal field in LiNbO3 crystals. We also show that 180° domains in a polarization reversed LiNbO3 crystal can be observed by light microscope, suggesting structural changes in the regions close to domain walls.