Crystal-chemical features of thermal polymorphism of actinides

Abstract

Crystal-chemical analysis of the structure of actinide crystals existing at atmospheric pressure was performed on the basis of Voronoi–Dirichlet (VD) tessellation. The analysis shows that the second moment of inertia of the VD polyhedron (G3) and displacement of the atomic nucleus from the center of gravity of its VD polyhedron (D_А) can be used as descriptors to reveal the occurrence of bonding 5f interactions between the metal atoms in the actinide sublattices of the crystal structures. All the phase transitions occurring on heating of Th, Pa, U, Np, and Pu metals are accompanied by a regular decrease in G₃ of actinide atoms in the range from 0.0810 to 0.0785.