Structural Analysis of Orthorhombic Hafnia by Neutron Powder Diffraction

Abstract

The crystal structure of orthorhombic HfO 2 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 a 0 = 1.00177, b 0 = 0.52276, and c 0 = 0.50599 nm. The structure is derived from a distorted fluorite (CaF 2 ) structure by a b ‐glide parallel to the a ‐axis. The hafnium atom is in seven‐fold coordination. The structure of orthorhombic HfO 2 is found to be the same as that of an orthorhombic ZrO 2 , which occurs under high pressure above 3 GPa.