La2O3 doped nanocrystalline zirconia (ZrO2) has been prepared by chemical co-precipitation method for various dopant concentrations, varying from 3 to 30 mol%. Structural phases have been characterized by X-ray diffraction technique. All the as-synthesized samples were found to be in monoclinic phase. Annealing of the samples at different temperatures from 400 to 1000 degrees C stabilized ZrO2 either partially or fully the tetragonal/cubic phases. When they were annealed at 1200 degrees C, the monoclinic phase appeared again with a new cubic pyrochlore structured La2Zr2O7 at the expense of stabilized tetragonal phase. Formability of the tetragonal/cubic phase has been influenced by the dopant concentration and the annealing temperature. Sample with 8 mol% La2O3 has been stabilized completely in tetragonal/cubic phase after annealing at 900 degrees C for 1 h. Smallness of the grain in these nanocrystalline materials may also have assisted in the formation of La2O3-ZrO2 solid solution. (c) 2005 Springer Science + Business Media, Inc.