Lattice vibrations and local order in substitutional solid solutions. II

The nearest neighbour effect on the mean vibrational state is investigated in solid solutions. It is shown that the possibility of A-B pair bond affection in the closest surrounding of the bond is accounted for, when linear, parabolic or some more complicated dependence of the states of A and B atoms on the relative proportions of both types in their first coordination shell is used. The expression is deduced for the mean vibrational state of atoms in the solid solution under the assumption that the dependence of A and B atom states on the number of unlike atoms in the first coordination shell is given as a polynomial ofi-th order. In the case of the parabolic approximation it follows that the structure of the solid solution (i.e. degree of order) is given by atom interactions, which result in configurations with maximum lattice cohesion. There is no assumption about the nature of atom interaction in the present paper. Therefore the results combined with experimental data can serve as a criterion of availability of different physical models and help in a better understanding of atomic bonds in metal systems.