Order-Disorder Phenomena

Abstract

The thermodynamics of the order-disorder transition in β brass is explored by making the assumption that the energy difference between the disordered and ordered state has the form E0—BT2. Such a law suggests itself if the coupling of the thermal expansion to the order-disorder transformation is emphasized and the effect of short range order is neglected. The constant B is shown to be related to the lattice vibrations of both the ordered and disordered phases. A very rough estimate of B was obtained from electrical resistivity measurements, the assumption being made that the connection between the resistivity and the vibrational frequency, ρ∝T/MΘ2, holds. A heat capacity versus temperature curve, which was calculated on the basis of a nonconstant energy of disordering and which also includes the effect of lattice vibrations, is shown to agree well with the experimental one. The usefulness of the form E0—BT2 is not confined to β brass and the same expression may be applied to systems other than solid-solid.