The annealing effect on the structural perfection of Fe-doped LiNbO 3 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 Li 2 CO 3 and Nb 2 O 5 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 À and CO 3 2À ionic defects. Grain boundaries and CO 3 2À ionic defects were successfully removed, while the concentration of OH À ions was considerably reduced by post-growth thermal annealing at elevated temperatures.

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