CEO(1.5)-STABILIZED TETRAGONAL ZRO2

Ceria-stabilized tetragonal zirconia polycrystals show high toughness and high resistance to the low-temperature ageing degradation. However , ceria is less effective in stabilizing tetragonal zirconia compared to yttria and other trivalent oxides. The tetravalent oxide of CeO2 ca n be easily reduced to the trivalent CeO1.5, but phase separations occ ur leading to the destabilization of the tetragonal phase or the stabi lization of the cubic phase. A procedure of high-temperature sintering and low-temperature reduction has been developed for preparing CeO1.5 -stabilized tetragonal zirconia. It was found that 9 mol % CeO1.5 coul d stabilize the tetragonal zirconia to room temperature and that the s tability region in the CeO1.5-ZrO2 system was extended to the lower do pant content region. The CeO1.5-stabilized tetragonal zirconia had a l ower tetragonality and lower transformability compared to the CeO2-sta bilized tetragonal zirconia with the same dopant mole percentage. The changes in the phase composition, tetragonality and stability caused b y the reduction of CeO2 to CeO1.5 have been discussed in relation to t he changes of oxygen stoichiometry, which is considered of the first-o rder importance in the stabilization of polymorphous zirconia.