Pressure-induced structures of Si-doped HfO₂

The effect of hydrostatic pressure on the structure of Si-doped HfO₂ (Si:HfO₂) was studied by using a diamond anvil cell in combination with high-energy X-ray diffraction at a synchrotron source. Diffraction data were measured in situ during compression up to pressures of 31 GPa. Si:HfO₂ with 3, 5, and 9 at. % Si were found to undergo a monoclinic to orthorhombic transition at pressures between 7 and 15 GPa. Whole pattern analysis was carried out using nonpolar (Pbca) and polar (Pca2₁) crystallographic models to investigate the symmetry of the observed high-pressure orthorhombic phase. Rietveld refinement results cannot discriminate a reliable difference between the Pbca and Pca2₁ structures as they nearly equally model the measured diffraction data. The pressure dependent lattice parameters, relative volume, and spontaneous strain are reported.