Inelastic Neutron Scattering in Epoxy Resins: The Phonon-Fracton Density of States and the Specific Heat

Abstract

Inelastic neutron-scattering experiments have been used to determine the density of states, $G\left(E\right)\mathrm{}$, of thermal excitations in epoxy resins. The results show that, over part of the range, $G\left(E\right)\mathrm{}$ increases with an energy ($E$) dependence which is higher than $E^2$. This is in accord with the predictions of the phonon-fracton model of Derrida, Orbach, and Wu. Calculations of the low-temperature specific heat using the measured density of states are in reasonable agreement with experiment, but it is shown that these calculations are very sensitive to the values of $G\left(E\right)\mathrm{}$ below $E=1\mathrm{}$ meV.