[en] The production of tetragonal zirconia polycrystalline (TZP) ceramics and identification of factors controlling the stability of the tetragonal phase in the ZrO₂.TiO₂ system gas been investigated. In this binary system, it was not possible to retain tetragonal zirconia polycrystals at room temperature for compositions sintered above 1200⁰C. A decrease in the martensitic transformation temperature of zirconia was observed with titania addition, but the effect was insufficient to retain the tetragonal phase at room temperature. In solid solution, TiO₂ additions act to suppress ZrO₂ densification, this leading to grain growth when attempts are made to attain higher densities. The use of fine powders, fast firing or sintering in reducing conditions altered densification but was not able to retain a final grain size sufficiently small to avoid spontaneous tetragonal up and down monoclinic transformation on cooling. (author)