High-pressure U3O8 with the fluorite-type structure.

Abstract: A new high-pressure phase of U3O8, which has a fluorite-type structure, forms at pressures greater than ~8.1GPa that was confirmed by in situ x-ray diffraction (XRD) measurements. The fluorite-type U3O8 is stable at pressures at least up to ~40GPa and temperatures to 1700K, and quenchable to ambient conditions. Based on the XRD analysis, there is a huge volume collapse (>20%) for U3O8 during the phase transition and the quenched high-pressure phase is 28% denser than the initial orthorhombic phase at ambient conditions. The high-pressure phase has a very low compressibility comparing with the starting orthorhombic phase. [Copyright &y& Elsevier]