Structure of HfO2 modified with Y, Gd, and Zr at ambient conditions and high pressures

Abstract

High-resolution and high-pressure X-ray diffraction measurements were performed to determine the effects of 5% Y, 3% Gd, and 50% Zr substitution on the crystal structure and polymorphism of HfO2. High-resolution experiments at ambient pressure show a mixture of monoclinic and cubic fluorite phases in 5% Y:HfO2 and 3% Gd:HfO2, while 50% Zr:HfO2 formed a monoclinic, single-phase solid solution. Crystallographic refinement using the Rietveld method indicates that Y and Gd substitute for Hf in both the monoclinic and cubic phases. High-pressure X-ray diffraction was performed in situ up to 31 GPa and shows that the pressure-induced phase transitions were reduced with the addition of either Y, Gd, or Zr relative to the transition pressures in undoped HfO2. The pressure-induced changes in lattice parameter, relative volume, and spontaneous strain are reported.