The solubility of Fe, Cr and Nb in ZrO2 by thermal treatment of the corresponding oxides at 1300°C is reported. Doping zirconia with these elements has considerable effect on thermal expansion, on the temperature of the monoclinic - tetragonal transition and on the volume-change accompanying it. It is shown that such impurities strongly influence properties which are important for the use of ZrO2 as a ceramic material. © 1990.