Published online by Cambridge University Press: 21 February 2011
Energetics and structure of germania doped silica prepared from high temperature melts and by flame hydrolysis were investigated using transposed temperature drop and solution calorimetry. Heat contents (H973-H298) are similar for first and second drops for the flame hydrolysis preforms reflecting the effect of temperature of deposition (1073 K) in creating a relaxed structure which is not easily rearranged. Heats of solution, at 973 K in molten lead borate, of fused glasses along the SiO2-GeO2 binary show ideal heats of mixing between the endmembers. This'indicates that fused glasses behave in a simple manner, with ideal substitution of Ge for Si in the tetrahedral framework. Flame hydrolysis samples (preform and annealed glasses) also show ideal heats of mixing. This suggests that the flame hydrolysis materials are energetically very similar to their bulk-melted counterparts. This insensitivity of energetics to preparation conditions is consistent with our previous studies on silica prepared at various temperatures [1].