Composition-Dependent Phase Stability in Yttria Stabilized Zirconia: Clues from Lattice Dynamics Calculation*

Yttria-stabilized zirconia (YSZ) is one of the widely-used thermal barrier coating (TBC) materials in gas-turbine engine applications at high operating temperatures. It is well reported that the thermal cycle life of these oxide coatings is highly sensitive to the concentration of yttria introduced in YSZ. In particular, at approximately 3 to 4 mol% of yttria in YSZ, it was proposed that this concentration of yttria yields the longest thermal cycle life and may have strong correlations to its preferred crystal phase (cubic (c) or tetragonal (t)) and mechanical strength. However, a careful and systematic study of the spectroscopic fingerprints of low-yttria YSZ is still lacking, and knowledge gained here will be very useful for the future design of more durable YSZ-based TBCs. Using first-principles density-functional theory calculations, we examine the lattice dynamics of c-YSZ and t-YSZ for low Y₂O₃ mol%, supplementing our structural analysis information with simulated X-ray diffraction and pair distribution function results to explain new inelastic neutron scattering experiments.