Generalized model for atomic site preference in crystal and its application in rare-earth alloys

A generalized atomic site preference (ASP) model for crystalline compounds is developed. The ASP state can be characterized quantitatively by the atomic distribution tensor or the ASP tensor. The freedoms and the value ranges of the ASP state parameters are analyzed and determined. Based on the present model, the ASP behaviors of atom Al in LaNi5−xAlx with CaCu5 structure and atom M in SmCo12−xMx (M = Mn or Mo) with ThMn12 structure are simulated by a thermodynamic mean field method and the inversed pair potentials. The calculated results show (1) in LaNi5−xAlx, the site preference degree of Ni on sublattice g decreases with the increasing of Al composition, and all Al atoms occupy sublattice g preferentially; (2) Mn and Mo prefer to locate on sublattice i in SmCo12−xMx alloys. The present results agree well with the experimental results and/or the reported theoretical calculations in literature.