| AVS 66th International Symposium & Exhibition | |
| Actinides and Rare Earths Focus Topic | Tuesday Sessions |
| Session AC+AS+LS-TuM |
| Session: | Chemistry and Physics of the Actinides and Rare Earths |
| Presenter: | Ladislav Havela, Charles University, Prague, Czech Republic |
| Authors: | L. Havela, Charles University, Prague, Czech Republic V. Buturlim, Charles University, Prague, Czech Republic E. Chitrova, Charles University, Prague, Czech Republic O. Koloskova, Charles University, Prague, Czech Republic P. Minarik, Charles University, Prague, Czech Republic M. Cieslar, Charles University, Prague, Czech Republic M. Dopita, Charles University, Prague, Czech Republic L. Horak, Charles University, Prague, Czech Republic M. Divis, Charles University, Prague, Czech Republic I. Turek, Charles University, Prague, Czech Republic D. Legut, VSB-Technical University of Ostrava, Czech Republic T. Gouder, European Commission - Joint Research Centre |
| Correspondent: | Click to Email |
Although the published U-H binary phase diagram contains only the UH3 phase, a recent progress in sputter deposition synthesis led to the discovery of UH2, which is with its CaF2 structure type analogous to e.g. PuH2 or YH2 [1]. In addition, a high pressure synthesis yielded several U hyper-hydrides (as UH8), which are predicted to be a high-temperature supreconductors [2]. As both UH3 (appearing in two structure modifications, α- and β-UH3) and UH2 allow alloying with selected transition metals, we have a whole spectrum of U-H hydrides and certain general features can be deduced, which have a serious implications for our understanding of actinides in general.
The striking fact that both UH3 phases have, despite very different crystal structure, practically identical size of U moments and magnentic ordering temperature TC ≈ 165 K, which do not change even in the nanostructured state (grain size several nm) is underlined by the fact that both parameters only weakly depend on substantial alloying with Mo and other d-metals. UH2 with substantially larger U-U spacing is a ferromagnet, as well, its TC ≈ 125 K. Structure of all those forms contains identical building blocks, H atoms inside U tetrahedra of invariable size, which are only set up into different patterns. The U-H bonding seems to be therefore an ingredient, which is more important than the conventional U-U spacing. The nature of the bonds is revealed by ab-initio calculations. One general feature is the U-6d hybridization with the H-1s states, which leads to an electron transfer towards H. However, unlike rare-earth trihydrides, UH3 remains metallic, UH2 naturally, too. The 5f states largely released from the 5f-6d hybridization can therefore develop a strong ferromagnetism despite low U-U spacings. The transfer could be traced even in the real space using the Bader analysis.
The ab-initio techniques, which are successful in capturing the equilibrium volumes and U magnetic moments, are so far less successful in description of photoelectron spectra close to the Fermi level, which indicates importance of electron-electron correlations.
This work was supported by the Czech Science Foundation under the grant No. 18-02344S.
[1] L. Havela et al., Inorg. Chem. 57 (2018) 14727.
[2] I.A. Kruglov et al., Sci. Adv. 4 (2018) eaat9776.