Invited Paper AC+MI+SA+TF-MoA1
Structural and Electronic Relationships Between the Lanthanide and Actinide Elements

Monday, October 28, 2013, 2:00 pm, Room 102 C

The similarity and difference between the solid state properties of the 4f and 5f transition

metals are pointed out. The heavier 5f elements show properties which have direct

correspondence to the early 4f transition metals, suggesting a localized behaviour of the

5f electrons for those metals. On the other hand, the fact that Pu metal has a 30% lower

volume than its neighbour heavier element, Am, suggests a tremendous difference in the

properties of the 5f electrons for this element relative to the heavier actinides. This change

in behaviour between Pu and Am can be viewed as a Mott transition within the 5f shell

as a function of the atomic number Z. On the metallic 5f side of the Mott transition (i.e.,

early actinides), the elements show most unusual crystal structures, the common feature

being their low symmetry. An analogous behaviour for the lanthanides is found in cerium

metal under compression, where structures typical for the light actinides have been observed

experimentally. A generalized phase diagram for the actinides is shown to contain features

comparable to the individual phase diagram of Ce metal. The crystal structure behaviour of

the lanthanides and heavier actinides is determined by the number of 5d (or 6d) electrons

in the metallic state, since for these elements the f electrons are localized and nonbonding.

For the earlier actinide metals electronic structure calculations – where the 5f orbitals

are treated as part of the valence bands – account very well for the observed ground state

crystal structures. The distorted structures can be understood as Peierls distortions away

from the symmetric bcc structure and originate from strongly bonding 5f electrons occupying

relatively narrow 5f states.