Synthesis and properties of AxV2Al20 (A = Th, U, Np, Pu) ternary actinide aluminides

Abstract Polycrystalline samples of A x V 2 Al 20 ( A = Ce, Th, U, Np, Pu; 0.7 ≤ x ≤ 1.0) actinide intermetallics were synthesized using the arc-melting method. Crystal structure studies were performed by means of powder x-ray diffraction and the Rietveld refinement method. All studied compounds crystallize in the CeCr 2 Al 20 -type structure (space group Fd-3m, no. 227) with the actinide or Ce atom located in the oversized cage formed by Al atoms. Comparison of the crystallographic results with the reported data for LnV 2 Al 20 (Ln = lanthanides) counterparts reveals distinctly different behavior of the lanthanide- and actinide-bearing compounds. This difference is suggested to be caused by fairly localized character of the 4 f electrons, whereas itinerant character of the 5 f electrons is likely seen for U- and Np-containing phases. Magnetic susceptibility and specific heat measurements did not reveal any magnetic ordering in U 0.8 V 2 Al 20 , Np 0.8 V 2 Al 20 and Pu 0.8 V 2 Al 20 down to 2.5 K. A small anomaly in low-temperature specific heat of Ce 0.8 V 2 Al 20 , U 0.8 V 2 Al 20 , and Np 0.8 V 2 Al 20 is observed, likely arising from a low-energy Einstein mode.