STRUCTURAL-ANALYSIS OF ORTHORHOMBIC HAFNIA BY NEUTRON POWDER DIFFRACTION

The crystal structure of orthorhombic HfO2 synthesized at 600 degrees C and 6 GPa was investigated by a time-of-flight neutron powder diffra ction experiment. Rietveld analysis of these data revealed that the sp ace 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 (CaF2) structure by a b-glide parall el 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 o rthorhombic ZrO2, which occurs under high pressure above 3 GPa.