Single crystals of hafnia stabilized with yttrium, neodymium, holmium and erbium 0.25 mm in size were formed in hydrothermal solutions by spontaneous nucleation in 20 M KOH at 750 degrees C. Positive transport conditions were established at 650 degrees C using a single crystal of cubic zirconia as a substrate for growth of yttrium stabilized hafnia at a rate of 0.084 mm/week. During the study single crystals could only be formed with high concentrations of the stabilizer dopants by this method. This is the lowest synthesis temperature reported for any single crystal growth method of this refractory material. (C) 2009 Elsevier B.V. All rights reserved.