Transparency of LiTaO3-SiO2-Al2O3 glass-ceramics in relation to their microstructure

Abstract

The glasses with various compositions in the LiTaO3-SiO2-Al2O3 system were heated from room temperature to temperatures ranging from 750° to 1050° C at a rate of 5° C min−1. From the glasses in the LiTaO3-SiO2 system no transparent glass-ceramic was obtained even when their LiTaO3/SiO2 mole ratios were as high as 2.33. The diameter and number of the LiTaO3 crystal grains precipitated in the glasses were 5–15 μm and 108–1010 grains cm−3, respectively. On the contrary, transparent glass-ceramics were obtained from the glasses containing Al2O3; their compositions covered a fairly large area in the LiTaO3-SiO2 -Al2O3 system, which encompasses the compositions with the LiTaO3/SiO2+AlO1.5 mole ratio as low as 0.25. The diameter and number of the LiTaO3 crystal grains precipitated in the transparent glass-ceramics were as small as 10–20 nm and as many as 1016–1018 grains cm−3, respectively. High nucleation rates of the LiTaO3 crystals in the Al2O3-containing glasses were interpreted in terms of structural inflexibility induced in the glass-network by the addition of Al2O3 to the LiTaO3-SiO2 system.