Viscous liquids and the glass transition. V. Sources of the excess specific heat of the liquid

The possibility that the excess ’’configurational’’ specific heat ΔCp of liquids above the glass transition temperature Tg might contain contributions either from changes in vibrational frequencies with configurational state, from changes in the anharmonicity of vibrations, or from the influence of changes in configurational state on the thermodynamic contributions of molecular rearrangement processes that also give rise to secondary relaxations below Tg is investigated with the use of calorimetric data on six quenched and annealed glasses. It is concluded that at least half of ΔCp arises from these sources, the greater part of this either from anharmonicity or from the molecular rearrangement processes.