We use high-resolution synchrotron x-ray powder diffraction and density-functional theory (DFT) to investigate the phase stability, equations of state (EOSs), and mechanical hardness of zirconia $\left({\text{ZrO}}_2\right)$ up to $\sim 54$ and 160 GPa, respectively. For the equilibrium phase at ambient conditions (MI), we provide an experimental EOS that is comparable to results obtained from room-pressure Brillouin scattering experiments and bulk modulus-volume systematics but different from previous high-pressure experiments. The experimental second-order Birch-Murnaghan EOS parameters of ${\text{MI-ZrO}}_2$ are: ambient-pressure volume $\left(V_0\right)$ of $35.15\left(\pm 0.03\right){\text{Å}}^3/\text{f}\text{.u}\text{.}$ with an ambient-pressure bulk modulus $K_0$ of $210\left(\pm 28\right)\text{GPa}$. For the high-pressure OI phase, we find that the $K_0=290\left(\pm 11\right)\text{GPa}$, which is 19%–32% higher than previously determined, and $V_0=33.65\left(\pm 0.07\right){\text{Å}}^3/\text{f}\text{.u}\text{.}$ The small volume decrease of 3.4% across the $\text{MI}\to \text{OI}$ transition at $\sim 10\text{GPa}$ is associated with a 38% increase in the bulk modulus consistent with our DFT calculations that predict a $\sim 36\mathrm{\%}$ and 39% increase in $K_0$ for the generalized gradient and local density approximations, respectively. In contrast to the EOS of MI and OI, we find that our experimental EOS for the high-pressure OII phase is in good agreement with previous measurements. The large volume decrease across the $\text{OI}\to \text{OII}$ phase transition as obtained from both our experiments and calculations is $\sim 10\mathrm{\%}$. Our estimates, using scaling relations, indicate that this phase, while dense and quenchable, may have a comparatively low mechanical hardness of $\sim 10\text{GPa}$.

• Received 28 December 2009

DOI:https://doi.org/10.1103/PhysRevB.81.214102