Hydrogen in U-T alloys: Crystal structure and magnetism of UH3-V

Abstract

U-V alloys with variable phase composition were prepared using ultrafast cooling. 15 at.% V is not sufficient to suppress entirely the orthorhombic α-U type of phase and higher alloying concentrations lead to a segregation of pure vanadium. The alloys are stable with respect to H2 exposure at pressures of 105 Pa. Nevertheless hydrogenation proceeds slowly at high H2 pressures. Resulting hydrides exhibit a common β-UH3 structure. This is unusual among the U-T systems, which yield either α-UH3 or nanocrystalline β-UH3 structures. The UH3-V system is ferromagnetic with the Curie temperatures monotonously increasing with the V concentration to TC = 190 K for 15 at.% V. Magnetic moments remain on the level of 1.0 μB/U. The results prove that the increase of TC in alloyed U hydrides of the UH3-T type does not depend on particular structure details or type of the T element, although the latter modifies somewhat the maximum TC values achieved. The situation can be understood assuming that the substitution of U by T provides an enhanced H/U ratio, while the U-H interaction is a prominent element of the 5f moments formation and ordering.