High‐Pressure Phase Transitions in Zirconia and Yttria‐Doped Zirconia

Raman spectroscopy has been utilized to characterize the phase transformations and transition pressures in pure and doped zirconia containing 3, 4, and 5 wt% Y 2 O 3 . The pressure‐induced transformations were investigated to over 6 GPa (at room temperature) using a diamond anvil pressure cell. Pure zirconia single‐crystal samples transformed to a “new” tetragonal phase (different from the one obtained at high temperatures at atmospheric pressure) at about 4 GPa. The pressure transformation, like the temperature transition, was reversible and exhibited an approximately 0.45‐GPa hysteresis at room temperature. The 3 and 4 wt% Y 2 O 3 crystals underwent a monoclinic ( P 2 1/b ) to tetragonal ( P 4 2 nmc ) phase transition similar to that observed at high temperatures. This phase change was found to be irreversible on releasing the pressure. The 5 wt% Y 2 O 3 at atmospheric pressure consists of a tetragonal modification in a disordered cubic matrix; a gradual, but reversible, disordering transformation of the tetragonal precipitate takes place with pressure.