Validity of the Ehrenfest relation for a system with more than one order parameter

Abstract

The relation ΔCp Δκ = TV(Δα)2 is shown to be obeyed under the same assumptions that Davies and Jones used to derive the weaker condition ΔCp Δκ ≥ TV(Δα)2. This means that if a material is found experimentally not to obey the above equality, then it is not describable by an order‐parameter theory. A prescription is given which allows one to determine within the context of order‐parameter theory whether the glass transition of a given material is basically thermodynamic or kinetic in origin.