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

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 degrees C, and then submitted to a crystal growth at either 860 degrees C or 960 degrees 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 degrees C, whereas monoclinic Ba6Si10O26 is predominantly formed when treated at 960 degrees C. At 2.5 and 4 GPa orthorhombic lowBa(2)Si(4)O(10) formed when treated at 960 degrees 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.