Theory of reconstructive transformations in actinide elements : packing of nonspherical atoms and macroscopic symmetries

Atomistic and macroscopic mechanisms explaining the formation of the structures in crystals of eleven actinide elements are given, and shown to correspond to a small number of irreducible degrees of freedom of the parent bcc structure. The causes of the rich polymorphism and idiosyncratic structures found in U, Np, and Pu are assigned to a close packing of ovaloid atoms. The incommensurate structure found in [alpha]-U is interpreted in this framework.