Stabilization of Metastable Face-Centered Cubic Cobalt and the Tetragonal Phase of Zirconia by a Carbon Shell: Reaction under Autogenic Pressure at Elevated Temperature of CoZr2(acac)2(OiPr)8

Spherical Co and ZrO2 particles in the size range of 11-16 nm, exhibiting at room temperature metastable phases, fcc for cobalt and tetragonal for zirconia, were synthesized, by the reaction under autogenic pressure at elevated temperature (RAPET) technique. The tetragonal phase in ZrO2 was obtained without doping the ZrO2 with trivalent impurities. Using high -resolution transmission electron microscopy and selected area energy-dispersive X-ray analysis it is manifested that a carbon shell of ~4 nm thickness is formed on the surface of Co and ZrO2 nanocrystallites. This carbon shell is responsible for stabilizing the high-temperature metastable phases at room temperature. These two products were obtained by the dissociation of CoZr2(acac)2(OiPr)8 at 700 C under its autogenic pressure.