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 arcmelting 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 = lanthanoids) 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 4f electrons, whereas itinerant character of the 5f electrons is likely seen for U-and Npcontaining 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.

Electronic properties of RX2Al20 (R = La, Ce, Yb, Th, U; X = Ti, V, Cr and Mn) cage compounds

“…Strong V f p interaction leading to delocalization of f electrons is an obvious reason for weak magnetic behavior in many binary and ternary intermetallic aluminides, such as intermediate valence compounds YbAl 3 [63, 64],YbAl 2 [74] or YbPtGe 2 [76] an archetypal spinfluctuator UAl 2 , a weakly temperature-dependent paramagnet UAl 3 [72, 73], 450 classical magnetic Kondo systems CeAl 2 [77], or prototype heavy-fermion materials CeNi 2 Ge 2 [75] and YbPtIn[78]. Comparison between the physical properties observed for the RT 2 Al 20 phases and those reported for the isostructural RT 2 M 20 compounds with M = Zn, Cd, characterized by similar d R−R and d R−T distances leads to final conclusion that the ground-state electronic properties of the whole 1:2:20 family is caused mainly by the f − p hybridization, in line with some previous suggestions[21, 81, 82]. Final exper-imental verification of all these predictions, e.g., by additional spectroscopic investigation is desired to indentify the band structures at Fermi surface in RX 2 Al 20 (R = La, Ce, Yb, Th, U; X = Ti, V, Cr and Mn).…”

“…The nonmagnetic subgroup of aluminides RX 2 Al 20 with R = La, Ce, Yb, U, Th, involving the lightest transition metals X = Ti, V, Cr, shows weakly temperature-independent Pauli paramagnetism or diamagnetism. The magnitude of paramagnetic susceptibility depends on the number of the valence electrons [9,17,21,22,23,24,26,27,28,29,30,31,32]. Electrical resistiv-50 ity and specific heat measurements showed that all these systems are simple metals with no sign of magnetic order at least down to 0.35 K. This indicates that cerium and ytterbium are in tetravalent and divalent states, respectively, whereas the 5f electrons of uranium are strongly itinerant because of their hybridization with the electronic states of ligands.…”

Anomalous rattling and single crystalline properties of the caged compound URu2Al10

“…In terms of actinides, AnT 2 Al 20 aluminides based on Th and U have been found for Ti, Nb, Ta, W, V, Cr and Mn [5,[12][13][14][15][16]. All of these show metallic properties; only UMn 2 Al 20 exhibits an itinerant ferromagnetic order [13,14] carried by Mn atoms, while all the remaining ternaries are Pauli paramagnets down to the lowest measured temperatures.…”

“…All of these show metallic properties; only UMn 2 Al 20 exhibits an itinerant ferromagnetic order [13,14] carried by Mn atoms, while all the remaining ternaries are Pauli paramagnets down to the lowest measured temperatures. Additionally, the An x V 2 Al 20 (An = Th, U, Np, Pu) actinide intermetallics were found not to be superconductors down to 1.9 K [16], although the rattling of the An-atoms inside their Al atom cage is large (their Einstein temperatures are around 20 K). Similar magnetic properties to the above aluminides are also exhibited by some UT 2 Zn 20 ternaries containing T= Fe or Ru [17].…”

Localization‐vs‐Delocalization of 5f Orbitals in Superatom Systems

“…It could not only get larger size particles, but also avoid the high radioactive dust . Moreover, ultra‐high vacuum magnetron sputtering, reverse strike, and arc melting methods are also very common methods for preparing actinides and metal alloys. Consequently, we expect the synthesis of novel actinide‐containing superatom gold clusters to be feasible.…”