Investigating the Structural Behavior of Transplutoninm Elements to very high Pressure via Synchrotron Radiation: Am0.5Cm0.5 Alloy as an Example

The structural behavior of an Am0.5Cm0.5 alloy has been recently investigated at the High-Pressure-ID30 beamline of the ESRF. The use of synchrotron radiation, diamond anvil cell and 2D detector has allowed us to collect very high quality diffraction patterns up to pressures of 65 GPa. The atmospheric pressure double hexagonal close packed (P63/mmc) structure transforms around 10 GPa to a face centered cubic (Fm3m) phase. Like for pure Am metal1-2), we find that the pressure induced derealization of the 5f electrons in Am0.5Cm0.5 occurs in two distinct stages rather than a single step: at 21 GPa the cubic phase converts to a face centered orthorhombic (Fddd) structure, which transforms into a primitive orthorhombic structure (Pnma) at 45 GPa. The latter phase is stable to at least 65 GPa. Work is presently underway to determine whether the elements Cm and Cf behave similarly under pressure.