  By using quantitative information about the radiation diffuse-scattering
intensity of the disordered f.c.c. substitutional alloy the Fourier component
of mixing energies of atoms may be estimated. We have to use the measurement
data of the diffuse-scattering intensities at the corresponding
reciprocal-space points k of the disordered phase and then determine the
parameter w(k). The statistical thermodynamics of the nonideal solid solution
is determined by these energy parameters {w(k)}. Therefore, one can obtain the
configuration free energy of an alloy, F = U - TS (U - internal energy, S -
entropy), and then determine its fundamental thermodynamic characteristics,
including not only its phase diagram, but also the concentration-dependent
order-disorder transformation temperature, temperature and concentration
long-range order parameter dependences, chemical activity, heat capacity etc.
Some thermodynamic properties are calculated within the framework of the
statistical-thermodynamic approach for f.c.c.-Ni-Fe alloy. The
diffuse-scattering intensity values are taken from data in the literature.
