was proposed. According to this
interpretation, changes in the stiffness of a chemical bond are
mainly produced by changes of the bond lengths, which occur with
compositional variations. Such a relation was found for the Pd-V
and Ni–Al systems using first principles methods [17,18]. A substitution
of an atom of different size produces both bond softening of
the smaller atom and bond stiffening of the larger atom. However,
one of both effects may dominate the vibrational behaviour of the
solid solution giving rise to excess vibrational entropies. Recently,
a simple relationship was presented [19] for estimating the