Crystallization processes of Li2O–Ga2O3–SiO2–NiO system glasses

Crystallization processes of Li2O–Ga2O3–SiO2–NiO system glasses have been studied by X-ray diffraction, differential calorimetry and optical absorption. Transparent glass-ceramic containing LiGa5O8:Ni2+ as the sole crystalline phase has been obtained from glass with the composition of 13Li2O–23Ga2O3–64SiO2–0.1NiO (in mol%) by the heat treatment in the temperature range from 923 to 953 K. It was revealed that the specific surface area of samples enhances crystallization of LiGaSi2O6 but obstructed that of LiGa5O8. LiGa5O8 grew to nano-sized crystallites dispersed in the glass matrices and did not affect the transparency seriously. In contrast, LiGaSi2O6 grew to crystallites with diameters more than 100 nm on the surface and made the glasses opaque. Optical absorption measurements revealed that doped Ni2+ occupied five-folded trigonal bipyramidal sites in the as-quenched glass matrices but six-folded octahedral sites of precipitated LiGa5O8 in the glass-ceramics. It was confirmed that transparent glass-ceramic containing Ni2+:LiGa5O8 was effectively obtained by the heat treatment at a temperature of 953 K for 10 h.