Tetragonal Phase in the System ZrO2-Y2O3

Precipitates of the high-ZrO2 tetragonal distorted-fluorite phase in the system ZrO2-Y2O3 appear to be quite different from those observed in other well-studied partially stabilized zirconias Mg-PSZ. In this paper, we discuss the nature of the tetragonal phase in Y2O3 partially stabilized zirconia Y-PSZ single crystals. We note that three versions of the phase diagram exist, which differ in detail mainly at the high-ZrO2 region our work thus also sheds light on the subsolidus phase equilibria in this system. Scott 4 described a metastable nontransformable high-Y2O3-content tetragonal ZrO2 solid solution t-ZrO2, which he and other workers suggested formed from the cubic ZrO2 solid solution c-ZrO2 via a displacive phase transformation the nontransformability relates to its reluctance to undergo the stress-assisted martensitic transformation to monoclinic symmetry found in lower-Y2-O3-content t-ZrO2. JES