A sphere-packing model for the prediction of lattice parameters and order in σ phases

Abstract

A model is presented for the determination of the unit-cell size for ordered and disordered binary σ phases from a geometry assuming spherical atoms. The basis of the calculations is the assumption of an average radius of the atoms occupying each of the five crystallographic sites in the unit cell. The model is then used to predict the changes in lattice parameters produced by fast-neutron irradiation and by the addition of a third element in some ternary a phases. The calculated parameters are compared with experimental results.