SPACE IS CONTINUOUS-CONTINUOUS-DISPLACEMENT TREATMENT OF PHASE-SEPARATING DIAGRAMS

The conventional crystal statistics treats permutation of species plac ed at lattice points of a fixed lattice. The present work removes the fixed lattice restriction and allows displacement of atoms from lattic e points of a fixed reference lattice, This extension responds to the need of taking into account local lattice distortion caused by size di fferences of species in alloys, Because the continuous displacement co ncept had not been studied before in the cluster variation method form ulation, the current series started with the two-dimensional lattices. This work is the first in the series to venture into the three-dimens ional lattices, We use the pair approximation for fcc and work out pha se diagrams of phase-separating systems. The step-by-step formulation of the theory is presented. Numerical computations on a number of mode l systems show asymmetrical phase diagrams, Various future application s are discussed.