  A formalism for the vacancy formation energies in random alloys within the
single-site mean-filed approximation, where vacancy-vacancy interaction is
neglected, is outlined. It is shown that the alloy configurational entropy can
substantially reduce the concentration of vacancies at high temperatures. The
energetics of vacancies in random Cu-0.5Ni-0.5 alloy is considered as a
numerical example illustrating the developed formalism. It is shown that the
effective formation energy is increases with temperature, however, in this
particular system it is still below the mean value of the vacancy formation
energy which would correspond to the vacancy formation energy in a homogeneous
model of a random alloy, such as given by the coherent potential approximation.
