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Origin of Fe substitutions in Nd 2 Fe 17 − δ <…

1998; American Physical Society; Volume: 57; Issue: 10 Linguagem: Inglês

10.1103/physrevb.57.5711

1095-3795

Er. Girt, Z. Altounian,

Hydrogen Storage and Materials

In ${\mathrm{Nd}}_{2}{\mathrm{Fe}}_{17\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}{X}_{\ensuremath{\delta}}$ ($X=\mathrm{Al},$ Si, Ti, V, Cr, Mn, Co, Ga, Nb, Mo, W, and $\ensuremath{\delta}=0, 0.5$) the $X$ atoms substitute for Fe without changing the crystal structure. Neutron-diffraction measurements show that Al, Si, Co, and Ga tend to substitute for Fe with a strong preference for the $18h$ sites while Ti, V, Cr, Mn, Nb, Mo, and W tend to substitute for Fe with a strong preference for the $6c$ sites. This substitution can be understood by considering a model which includes contributions from the enthalpy of solution of the $X$ atom at each Fe site, the elastic energy due to the differences in the volume of the site and the volume of the $X$ atom, and a structural-dependent contribution reflecting the difference in the average number of valence electrons at each Fe site.