Synthesis of Fe-ZrO2 nanocomposite powders by reduction in H2 of a nanocrystalline (Zr, Fe)O2 solid solution.

The formation of Fe-ZrO2 nanocomposite powders by reduction in hydrogen of a nanocrystalline totallystabilized Zr0.9Fe0.1O1.95 solid solution was investigated by X-ray diffraction (XRD), field-emission-gunscanning electron microscopy (FEG-SEM) and M ossbauer spectroscopy. The reduction of the stabilizedZr0.9Fe0.1O1.95 solid solution and the formation of metallic particles precedes the transformation of zirconiainto the monoclinic phase, which becomes the major zirconia phase upon reduction at 950 ?C. -Feparticles with a size distribution slightly increasing from 10?50 to 20?70nm upon the increase in reductiontemperature are observed and a second population of smaller (<5 nm) -Fe nanoparticles is alsonoticed when the reduction is performed at 1000 ?C. Another metallic phase with a hyperfine field of?200 kOe at RT (?250 kOe at 80 K) is detected, which could account for an Fe/Zr phase. It could be formedby the reduction on an Fe2+-rich transient phase incorporating a small fraction of the Zr4+ ions, formedby a phase partitioning process superimposed to the reduciton processes.