Pressure dependence of the refractive index of monoclinic and yttria-stabilized cubic zirconia

The pressure dependence of the refractive index of monoclinic and yttria-stabilized cubic zirconia was measured up to 3 and 8 GPa, respectively, using an interferometric method with the diamond-anvil cell. The experimental results show a practically linear behavior for both crystalline structures. For cubic zirconia, the refractive index remains practically constant under pressure, while for the biaxial monoclinic phase, one component of the refractive index decreases and the other component increases with pressure, despite the rather isotropic lattice compression in the corresponding crystalline directions. The behavior of the electronic polarizability of the oxygen ion was investigated through the Lorentz-Lorenz relation, yielding the following Mueller parameters: for the cubic phase ${\mathrm{\Lambda }}_0$=1.02, and for the monoclinic phase ${\mathrm{\Lambda }}_0$=1.05 for the component nearly parallel to the b direction, and ${\mathrm{\Lambda }}_0$=0.85 for the component in the direction of the projection of the ‘‘a’’ axis on the sample plane. In the case of monoclinic zirconia, the behavior of the polarizability under pressure is about 20% more anisotropic than the compression of the respective lattice parameters, indicating a distinct effect of the interatomic interactions over the oxygen ions for the two directions under consideration.