Transparent ultra-low expansion lithium aluminosilicate glass-ceramics: Crystallization kinetics, structural and optical properties

beta-quartz solid solution phase in the Li2O-Al2O3-SiO2-P2O5 (LAS) glass system has been precipitated by controlled heat-treatment of the parent glass prepared by melt-quench technique. Detailed crystallization kinetics of LAS glass was studied which facilitated in determination of an optimized heat-treatment protocol in order to synthesize highly transparent glass-ceramics of extremely low thermal expansion coefficient. The crystallization kinetic studies indicated a bulk nucleation with linear growth event in the LAS glasses. The LAS glass-ceramics (GCs) containing the beta-spodumene crystalline phase shows extremely low to negative thermal expansion coefficient (K-1) ranging from -0.0029 x 10(-6) to 0.3227 x 10(-6) measured in the temperature range 223 to 423 K. The glass-ceramics exhibited visible light transmittance of nearly 90%, such high transparency was possible by restricting average crystal size to nanometric scale through controlled crystallization. Microstructural characterization of the heat-treated GCs using FESEM and TEM showed nano-crystalline spherical particles of 2-3 nm, which provided a rationale for its high transparency.