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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Nanocrystals of magnetite (Fe 3 O 4 ) were prepared by sol-gel technique. The prepared nanocrystals were characterized for phase by powder X-ray diffraction (XRD) of the samples annealed at successively higher temperature. The magnetite phase was formed during the annealing of the synthesized powder at 400 °C for a few hours. The Fourier transform infrared spectroscopy (FTIR) was performed to analyze the functional groups in the material. The energy dispersive X-ray diffraction (EDAX) was performed for chemical composition analysis. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques were used to analyze the morphology of nanocrystals and for estimating their average size. The results confirm the formation of Fe 3 O 4 nanocrystals of the sizes ~20-50 nm.