Structural Analysis of Orthorhombic Hafnia by Neutron Powder Diffraction

Abstract

The crystal structure of orthorhombic HfO2 synthesized at 600°C and 6 GPa was investigated by a time‐of‐flight neutron powder diffraction experiment. Rietveld analysis of these data revealed that the space group of this phase is Pbca. The refined lattice parameters are a0= 1.00177, b0= 0.52276, and c0= 0.50599 nm. The structure is derived from a distorted fluorite (CaF2) structure by a b‐glide parallel to the a‐axis. The hafnium atom is in seven‐fold coordination. The structure of orthorhombic HfO2 is found to be the same as that of an orthorhombic ZrO2, which occurs under high pressure above 3 GPa.