LAUSR

Abstract A powder neutron scattering study of atom substitution in Nd2(Fe1-xCox)14B, Y2(Fe1-xCox)14B and Ce2(Fe1-xCox)14B compounds is presented. Compared to previous studies, this one benefits from the considerable progress made in neutron diffraction measurements and their analysis during the last 15 years. The normalization of the occupancy values to those expected from a random distribution permits to reveal small deviations from random distribution. On all crystallographic sites some preferential occupancy is evidenced, the extent of which depends on the Co versus Fe content. A statistical model quantitatively describing site occupancies is proposed, which allows us to study the extreme cases of very dilute substitutions. Steric considerations primarily determine atom substitution, more particularly Fe-substitution in Co-rich compounds. The enthalpy of mixing must also be considered to describe Co preferential occupancies more exactly.