A novel cage for actinides: A 6 W 4 Al 43 ( A = U and Pu)
We report on synthesis and characterization of the compounds A 6W4Al43 (A = U and Pu), that form in the hexagonal Ho6Mo4Al43 caged-structure family. The A ions reside within W/Al cages where the A–A nearest neighbors form dimers between adjacent W/Al cages, with U–U and Pu–Pu distances of 3.3892 and 3.4080 , respectively. While the W/Al networks provide environments similar to those of other cage-like materials (e.g. filled skutterudites), the atomic displacement parameters from single crystal x-ray diffraction measurements show that the A-ions do not exhibit rattling behavior. We find that there is site interchange disorder on one of the W/Al sites. Magnetic susceptibility measurements show that U6W4Al43 displays anisotropic Curie–Weiss behavior where it fits to the data yield an effective magnetic moment near 2.0 /U. At low temperatures the magnetic susceptibility deviates from the Curie–Weiss temperature dependence and eventually saturates to a constant value. In contrast, Pu6W4Al43 displays nearly temperature independent Pauli paramagnetism for all temperatures, as would be expected if the 5f-electrons are delocalized. The electrical resistivity for U6W4Al43 increases slightly with the decreasing temperature, suggesting that it is dominated by f-electronic hybridization effects and disorder scattering that originates from the W/Al site interchange. Specific heat measurements for U6W4Al43 further reveal an enhanced electronic Sommerfeld coefficient that is consistent with a moderately enhanced charge carrier effective mass. Together these measurements expose these materials as hosts for unstable f-electron magnetism, where the novel cage-like structures control the phenomena through the spacing between the A ions. Through this combination of mild magnetism, the low cost elements of the Al–W cages, and chemical tunability that has been shown for related materials in the same structure, the A 6W4Al43 compounds emerge as promising nuclear waste-forms for transuranics, while the wider family of materials makes an appealing environment for studying f
- Research Organization:
- Energy Frontier Research Centers (EFRC) (United States). Center for Actinide Science & Technology (CAST); Florida State Univ., Tallahassee, FL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- DOE Contract Number:
- SC0016568
- OSTI ID:
- 1566673
- Journal Information:
- Journal of Physics. Condensed Matter, Vol. 31, Issue 16; ISSN 0953-8984
- Publisher:
- IOP Publishing
- Country of Publication:
- United States
- Language:
- English
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