Electronic Structure of Actinide Hydrides Studied by Photoelectron Spectroscopy

Actinide hydrides constitute an interesting class of materials. From Np on, cubic dihydrides and hexagonal trihydrides exist, very similarly to the rare earths. Uranium only forms the trihydride UH3 (the dihydride is missing), while Th forms a tetragonal dihydride and a complex cubic higher hydride Th4H15. These differences are related to the 5f electrons which, from Np on, are localized in the hydrides, resulting in the rare-earth like behavior. The localization-delocalization threshold is thus shifted to the lighter actinides, and lies between U and Np. It is instructive to compare the evolution of the cohesive energy of metals and hydrides (Fig. 1). While for the metals, 5f localization takes place between Pu and Am, as seen by the sudden drop in density, the hydrides always have an even lower density and do not show any density change between Pu and Am. It is thus concluded that AmH3, PuH3 and NpH3 have localized 5f states. Only UH3 has an increased density, and this may now be taken as indication for participation of the f-states in bonding. And indeed, UH3 is an itinerant ferromagnet and it has an enhanced low temperature specific heat compared to the a-metal. All thisis consistent with formation of a narrow U-5f-band.

GOUDER Thomas;  ELOIRDI Rachel; 

2005-08-30

University of Vienna

JRC30379

https://publications.jrc.ec.europa.eu/repository/handle/JRC30379,