A study of the effect of annealing on Fe-doped LiNbO₃ by HRXRD, XRT and FT–IR

The annealing effect on the structural perfection of Fe-doped LiNbO₃ single crystals has been studied by high-resolution X-ray diffractometry (HRXRD), X-ray topography (XRT) and Fourier transform infrared (FT–IR) spectroscopy. The single crystals, prepared by mixing Li₂CO₃ and Nb₂O₅ powders in the molar ratio 48.6:51.4 with 0.05 mol% of iron at 1415 (1) K, were grown by the Czochralski (CZ) method along the [001] direction in air and poled during crystal growth by the application of a DC field. Two low-angle (tilt angle ∼1 arc minute) structural grain boundaries were observed in as-grown specimens. FT–IR spectra revealed that these crystals contain OH⁻ and CO₃²⁻ ionic defects. Grain boundaries and CO₃²⁻ ionic defects were successfully removed, while the concentration of OH⁻ ions was considerably reduced by post-growth thermal annealing at elevated temperatures.