A mean-field free energy is formulated in k-space and applied to order-disorder reactions in
substitutional solid solutions whose average lattice is i'. cc or bcc The different symmetry
properties of the harmonic and anharmonic contributions are described. The dynamics of
concentration fluctuations and the early-stage kinetics of decomposing solutions are
governed mainly by the harmonic terms whose basic properties are related to the special
points of the first Brillouin zone. Useful predictions can be made about short-range order …