The synthesis of Co2+-stabilized zirconia by the nitrate/urea combustion route is investigated. Using seven times the so-called stoichiometric urea proportion allows to obtain for the first time the Zr0.9Co0.1O1.9 solid solution fully stabilized in tetragonal form. The thermal stability in air and the reduction in H-2, H-2-CH4 and H-2-C2H4 atmospheres are studied. The carbon forms obtained upon reduction are investigated. Reduction in H-2-CH4 produces many carbon species including short carbon nanofibers, nanoribbons, hollow particles often forming bamboo structures, carbon-encapsulated Co particles and carbon nanotubes. Reduction in H-2-C2H4 produces 15-30 nm nanofibers. (C) 2007 Elsevier Ltd. All rights reserved.