Low-temperature heat capacity of GeO2 and B2O3 glasses: thermophysical and structural implications

The heat capacities of rapidly quenched B2O3 and GeO2 glasses have been measured by adiabatic calorimetry from less than 10 to 350 K. The residual entropies at 0 K obtained from these new results and ancillary data are 11.2 +/- 0.8 and 6.6 +/- 1.1 J/mol K for B2O3 and GeO2 glasses with fictive temperatures of 980 and 543 K, respectively. On a g atom basis, both of these entropies are similar to the low value found previously for SiO2 glass. For B2O3, this is likely due to the small contribution of boroxol groups to the topological entropy of the glass. The importance of the Boson peak increases in the order SiO2, GeO2, B2O3 which corresponds to the order of decreasing glass transition temperatures. Some implications about short- and medium-range order are finally drawn from these results and the differences between the glass and crystal phases of the three oxides. (C) 2003 Elsevier Science B.V. All rights reserved.