Application of the cluster variation method to ordering in an interstitialsolid solution: the gamma-Fe[N]/gamma '-Fe4N1-x equilibrium

The tetrahedron approximation of the cluster variation method (CVM) was app lied to describe the ordering of N atoms on the fee interstitial sublattice of gamma-Fe[N] and gamma'-Fe4N1-x. A Lennard-Jones potential was used to d escribe the dominantly strain-induced interactions, caused by the misfittin g of the N atoms in the interstitial octahedral sites. The gamma-Fe[N]/gamm a'-Fe4N1-x miscibility gap, short-range ordering (SRO), and long-range orde ring (LRO) of nitrogen in gamma-Fe[N] and gamma'-Fe4N1-x, respectively, and lattice parameters of gamma and gamma' were calculated. For the first time , N distribution parameters, as calculated by CVM, were compared directly t o Mossbauer data for specific surroundings of Fe atoms.