Fe-doped zirconium oxide produced by self-sustained high-temperature synthesis: Evidence for an Fe-Zr direct bond

The local structure of iron in Fe-doped cubic ZrO2 produced by combustion synthesis was studied by Mossbauer spectroscopy and Fe-K edge extended x-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES). Iron was found to be in its II oxidation state and to occupy two different sites of the fluorite ZrO2 structure, both associated with some amount of disorder. One of the sites has been identified with the regular Zr position in 0,0,0, thus giving rise to substitutional Fe-Zr('') (i.e., Fe atoms occupying the regular Zr position, with a net 2-charge, with respect to the lattice) defects, while the other site has been identified with the normally empty position at 1/2, 1/2, 1/2, thus giving rise to interstitial Fe-i(..) (i.e., Fe atoms occupying an interstitial position, with a net 2+ charge, with respect to the lattice) defects. For this last site, there is a short Fe-Zr distance (2.64 Angstrom). This result, coupled to the quite small value of the Debye-Waller factor for this distance, gives evidence of a direct Zr-Fe metal-to-metal bond.