The Bragg-Williams theory for the $A{B}_3$ alloy is interpreted analogously to van der Waals theory to calculate relaxation of the long-range order. This theory is related to the relaxation experiment of Collins and Teh for ${\mathrm{Ni}}_3$Mn, and the investigation of the first-order nature of the order-disorder transition by Beers and Guttman for an alloy close to this composition.

• Received 10 December 1973

DOI:https://doi.org/10.1103/PhysRevB.11.2069