Fe-substitution in Nd 2Fe 17-δX δC 0.3 (X = Al, Ti, V, W and δ = 0, 0.5)

Abstract

Neutron diffraction results on Nd 2Fe 17-δX δC 0.3 (δ = 0, 0.5) show that C occupies exclusively the 9e site in agreement with the an elastic continuum model calculation which shows that the elastic energy required for C to access the 9e and 18g sites is 1.7 and 14.0 kJ/mol, respectively. Al preferentially substitutes for Fe in the 18h site while Ti, V and W preferentially substitutes for Fe in the 6c site in agreement with the results obtained for the carbon-free compounds. Al has a higher affinity towards Nd than Fe thus occupies the Fe site which has the highest fraction of its Wigner-Seitz cell surface shared with Nd. However, Ti, V and W have a higher affinity towards Fe than Nd and those elements substitute for Fe sites with the highest fraction of the Wigner-Seitz cell surface shared with Fe. Due to the high Ti affinity towards C we find that C does not enter the 2–17 structure preferring to form TiC.