Effect of high pressure on the structure of barium disilicate glass-ceramics

Abstract

A systematic study of crystallization of barium disilicate at high pressures and temperatures was undertaken. Two groups of samples were submitted to nucleation at 710°C, and then submitted to a crystal growth at either 860°C or 960°C respectively. Both groups were heat treated at 1 atm, 2.5 GPa, 4 GPa, and 7.7 GPa. The diffraction results show that at atmospheric pressure, the phases formed are, monoclinic Ba6Si10O26, orthorhombic low-Ba2Si4O10, and monoclinic high-Ba2Si4O10 depending on the temperature treatment. In contrast, at 7.7 GPa orthorhombic BaSiO3, monoclinic phase Ba6Si10O26 and coesite formed when treated at 860°C, whereas monoclinic Ba6Si10O26 is predominantly formed when treated at 960°C. At 2.5 and 4 GPa orthorhombic low-Ba2Si4O10 formed when treated at 960°C. The high frequency Raman modes are strongly affected by the different pressure and temperature treatments. The shifts and formations of distinct vibrations modes are discussed as function of pressure.