Phase stabilization in the light actinides and binary alloys

From a phenomenological analysis of phase stabilization in the binary actinide alloy systems, U-Pu, U-Np-Pu and U-transition metals, the existence of a relatively stable electronic complex with the configuration (5f nd) is deduced. It must be formed by itinerant 5f and nd electron states with n=3, 4, 5, 6 and v should be a fractional number since only band states are involved. The stability of the complexes should depend on temperature. In alpha-Pa, equal numbers of 5f and 6d states in the valence electron system result: (i) in a (5f6d)* supercomplex which correlates with the unique crystal structure of alpha-Pa and (ii) with metal properties which rather resemble those of alpha-Th than that of alpha-U. The alleged properties of the complex are discussed and compared with the thermal behavior of alpha-Pa and of the alpha-U on approaching the alpha/beta transition temperatures and Pa should play a key role for understanding the temperature effects in the light actinide series. In a following paper, the literature on fabrication and properties of Pa metal is critically reviewed for the comparison of relevant properties between alpha-Th, alpha-Pa and alpha-U. (C) 2002 Elsevier Science B.V. All rights reserved.