High-pressure structural evolution in Yttria-Stabilized Zirconia: Pressure as a composition-preserving route towards structural purification

Yttria-stabilized zirconia (YSZ) is a technologically important oxide ceramic whose properties are closely linked to phase stability and structural symmetry. Therefore, the structural evolution of two selected compositions of YSZ, with 3mol% (3YSZ) and 8mol% (8YSZ) of Y 2 O 3 , have been investigated under pressure using in-situ synchrotron X-ray diffraction (XRD) and Raman spectroscopy in a diamond anvil cell up to 40 GPa (at room temperature). The close crystallographic relation between the observed structures and the relatively large difference in the atomic numbers of Y/Zr and O, imposes the simultaneous study using both techniques, aiming to fully elucidate the structural evolution under pressure. The results reveal that for both 3YSZ and 8YSZ, pressure promotes higher-symmetry structures. Under initial compression, the minority at ambient conditions monoclinic phase (m-phase) gradually transforms towards the tetragonal phase (t-phase), a transition that is concluded for both 3YSZ/8YSZ at ≈ 10 GPa. At higher pressures, the solely remaining tetragonal phase of 3YSZ transforms to the pseudo-cubic tetragonal phase (t”-phase), which retains tetragonal symmetry but exhibits cubic lattice parameters. With further pressure increase, the t”-phase transforms to the cubic fluorite-type phase (c-phase) above 28 GPa. Likewise, for 8YSZ the coexistence of t- and t”-phases continues up to 31 GPa, where both transform towards c-phase. Upon pressure release, all observed transitions are fully reversible with negligible hysteresis, with the exception of the practical disappearance of the monoclinic phase at ambient conditions. Our study underscores the significance of simultaneously performing and analyzing the results of both XRD and Raman spectroscopy studies in relevant crystallographic systems and delivers structural evolution insights in defect-stabilized oxide ceramics under high pressure. Moreover, it provides pressure as a composition-preserving route for suppressing the monoclinic phase (m-phase) towards a ”structural purification” in YSZ, as well as other related stabilized ceramic systems.