Debye temperature, anharmonic thermal motion and oxygen non-stoichiometry in yttria stabilized cubic zirconia

The temperature dependence of the Debye-Wailer factors of a 9.4 mol% Y2O3 stabilized cubic ZrO2 ceramic was studied in the range 4-1923 K using neutron powder diffraction. It was found that the data could not be modelled on a harmonic Debye-like model with an additive static disorder component but are significantly anharmonic. The anharmonic thermal motion in this material is not confined to the usual fluorite third-order term for the anion. It is shown that the temperature variation of the Debye-Waller factors is well modelled by an isotropic fourth-order anharmonic vibration of both the cation and anion each with its own additive static disorder component. The Debye temperature was determined its approximately 963 K which is much higher than the only known previous measurement. There is evidence that the sample became non-stoichiometric during the measurements. The oxygen content appears to follow an extrapolation of the ZrO2-x lower phase boundary of the Zr-O phase diagram.