In contrast with other metals, actinide elements from protactinium through plutonium exhibit, at atmospheric pressure, low-symmetry crystal structures and small compressibility, as an effect of the 5f-electron character in their bonding. Americium and heavier actinides have fully localized 5f electrons and more symmetrical close-packed crystal structures, similar to those observed in lanthanides.  However, upon compression, changes in the 5f occupancy and the hybridization with spd states destabilize the crystal structure and give rise to a rich polymorphism not observed elsewhere in the Periodic Table. Here, I will present some of the most significant results obtained at the Institute for Transuranium Elements in the framework of a collaboration with Dick Haire, which has been ongoing for more than three decades, including high-pressure x-ray diffraction characterization of allotropic phases in Pa, Am, Cm, Bk, Cf, and Es, studies of electronic spectra in Am and Cm, superconductivity in Am, and magnetism in Cm.

Living under pressure: Experimental studies of actinide metals at ITU and ORNL

245th National Meeting (2013)

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