Investigation of the phase relations in the U-Al-Ge ternary system: Influence of the Al/Ge substitution on the properties of the intermediate phases

X-ray absorption study on the origin of the deviation from Vegard's law for U(Al1−Ge )3 solid solution

“…1 (a). Because they crystallize in the same structure-type with relatively close lattice parameters and similar covalent radii 1 , (r Al = 1.21 Åand r Ge = 1.20 Å [10]), the existence of a total solid-solution as reported by Tyunis et al [6] and later on by Moussa et al [7] is not surprising. Indeed, similar pseudo-binary systems USn 3 -UGa 3 , USn 3 -UAl 3 [11] and UAl 2 -UCo 2 [12] are solid solutions with a complete miscibility and present a conventional evolution of lattice parameters.…”

“…7). Despite some noise at the lowest temperatures in the signal of UAl 3 due to the non-congruent melting of this phase [14,7] inducing the appeareance of porosity and cracks after annealing, the specific heat follows up to about 10 K the expected law for a regular metal:…”

“…A deep knowledge of the local and long range order of the U(Al,Ge) 3 solid solution is thus required to simulate as precisely as possible the reactivity and irradiation behavior of this fuel. But opposite to the case of U(Al,Si) 3 for which numerous data are available in literature [3,4,5], scarce reports are available for the U(Al,Ge) 3 solid solution [6,7].…”

“…However, although the similitude with the other U pseudo-binary system, both Tyunis et al and Moussa et al [6,7] reported that the lattice parameter of the U(Al 1x Ge x ) 3 solid-solution deviates negatively from linearity and thus violate the Vegard's law. A valence instability of uranium or relative size effects of the p-element were evoked, respectively, to explain this observation.…”