Low-Temperature Heat-Capacity Differences between Glasses and Their Crystals

Abstract

It is suggested that the low‐temperature heat‐capacity difference between glasses and their crystal may be computed by considering the simple process, C x (V x ) ⇒(a) C x (V g ) ⇒(b) C g (V g ) , where Cx (Vx ) is the constant volume heat capacity of the crystal at its equilibrium volume at normal pressures, Vx, Cx (Vg ) is the heat capacity of the substance of identical structure as the crystal but of a volume, Vg , equivalent to that of the glass, and Cg (Vg ) is the constant volume heat capacity of the glass. Estimates are made of the change in heat capacity due to step (a) (the change in heat capacity at constant crystal structure due to a volume change) and to step (b) (the change in heat capacity due to disordering at constant volume) for a one‐dimensional model of a glass and crystal. These suggest that step (a) contributes more to the heat‐capacity difference than does step (b). Contributions to step (a) from a three‐dimensional Debye model show reasonable agreement with experiment.