Effect of Al2O3 addition on the formation of perovskite-type NaNbO3 nanocrystals in silicate-based glasses

The crystallization behavior of 30Na2O–25Nb2O5–(45 − x) SiO2–xAlO1.5 (x = 0, 2.5, and 5) (mol%) glasses was examined and the effect of Al2O3 addition on the formation of perovskite-type NaNbO3 crystals was clarified. It is found from X-ray diffraction analyses and transmission electron microscope observations that NaNbO3 nanocrystals are formed in all glasses and the size of NaNbO3 crystals decreases with the substitution of Al2O3 for SiO2. A crystallized (heat-treated at 684 °C for 5 h) glass with x = 5, which contains NaNbO3 nanocrystals with an average size of 50 nm, shows good optical transparency in the wavelength region of 500–2000 nm and a small hysteresis loop in the polarization–electric field curve. The lines containing NaNbO3 crystals were patterned on the surface of NiO-doped glass with x = 5 by irradiations (power: 1.3–1.4 W, scanning speed: 10 μm/s) of Yb:YVO4 fiber laser (wavelength: 1080 nm). The formation mechanism of NaNbO3 nanocrystals in aluminosilicate glasses was also discussed.