VIBRATIONAL DENSITY-OF-STATES AND STRUCTURAL ORIGIN OF THE HEAT-CAPACITY ANOMALIES IN CA3AL2SI3O12 GLASSES

The low-temperature heat capacity, C-p, of the crystalline and glassy forms of the mineral grossular Ca3Al2Si3O12 are distinctly different. The effect has been linked to differences in coordination of Al and th e resulting structural roles of the ion in each phase. Inelastic neutr on-scattering measurements for the glassy phase reveals an excess dens ity of states below 30 meV and C-p, calculated from the vibrational de nsity of states agree with thermodynamic measurements. Static neutron- scattering data confirm that Al is tetrahedrally coordinated in the gl ass as distinct from octahedral coordination in the crystal. (C) 1998 Elsevier Science B.V. All rights reserved.