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Serge Desgreniers and Ken Lagarec, Laboratoire de
physique des solides densesUniversity of Ottawa, Ottawa-Carleton
Institute of Physics, Ottawa, Canada [Phys. Rev. B, Vol 59, 8467(1999)]
Zirconium dioxide and hafnium dioxides quenched at room conditions from high pressure have yielded ultra dense, low compressibility crystalline forms of matter. These materials are of interest for their potentially large hardness (resistance to deformation). The x-ray measurements below complement the optical, electrical, and transport properties measured in the home laboratory to give a more complete picture about the properties that describe these unusual materials.
Angle dispersive x-ray diffraction is a key technique to study the structural modifications in dense materials. At the left are the Debye rings from the x-ray diffraction pattern of hafnium oxide at a pressure of 1.2 GPa in a diamond anvil cell, taken at the CHESS B2 station. The spacing of the rings depends on the actual distance between atoms, a value that changes in response to the pressure generated in the diamond anvil cell.
The relative volume change with pressure (equation of state) has been obtained from the Debye ring pattern above for the dense phases of hafnium oxide. The high density phase, retrieved at room conditions from a pressure exceeding 70 GPa, presents a relatively high bulk modulus (B0=340 GPa) with a relative volume reduced to 0.87.
Other studies of dense oxides, as potentially ultrahard materials are underway. The ability to perform diffraction measurements at CHESS is a key aspect to the success of the understanding of strong atomic bonding in dense oxides and how it translates into hardness.