Hydrides of actinides, their magnetic, electronic, transport, and thermodynamic properties are discussed within a general framework of H impact on bonding, characterized by volume expansion, affecting mainly the 5fstates, and a charge transfer towards H, which influences mostly the 6dand 7sstates. These general mechanisms have diverse impact on individual actinides, depending on the degree of localization of their 5fstates. Hydrogenation of uranium yields UH2and UH3, binary hydrides that are strongly magnetic due to the 5fband narrowing and reduction of the 5f-6dhybridization. Pu hydrides become magnetic as well, mainly as a result of the stabilization of the magnetic 5f5state and elimination of the admixture of the non-magnetic 5f6component.Ab-initiocomputational analyses, which for example suggest that the ferromagnetism ofβ-UH3is rather intricate involving two non-collinear sublattices, are corroborated by spectroscopic studies of sputter-deposited thin films, yielding a clean surface and offering a variability of compositions. It is found that valence-band photoelectron spectra cannot be compared directly with the 5fnground-state density of states. Being affected by electron correlations in the excited final states, they rather reflect the atomic 5fn-1multiplets. Similar tendencies can be identified also in hydrides of binary and ternary intermetallic compounds. H absorption can be used as a tool for fine tuning of electronic structure around a quantum critical point. A new direction is represented by actinide polyhydrides with a potential for high-temperature superconductivity.

Department of Condensed Matter Physics Faculty of Mathematics and Physics Charles University Ke Karlovu 3 121 16 Prague 2 Czech Republic

Institute of Physics Czech Academy of Sciences Na Slovance 2 182 00 Prague Czech Republic

IT4Innovations VŠB Technical University of Ostrava 17 listopadu 2172 15 708 00 Ostrava Czech Republic

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