Two New Np--Ga Phases: Alpha -NpGa sub 2 and Metastable M-NpGa sub 2

摘要

Following an earlier study of metastable Np-rich Np--Ga alloys, rapidly quenched Np--Ga alloys with 63 to 80 at. pct. Ga were prepared and studied. Two new NpGa sub 2 phases, both with an AlB sub 2 type structure, were found: alpha -NpGa sub 2 , with a = 4.246A, c = 4.060A, c/a = 0.956, and m-NpGa sub 2 , with a = 4.412A, c = 3.642A, c/a = 0.825. While m-NpGa sub 2 was observed only in very fast quenched (splat cooled) samples and appears to be metastable, alpha -NpGa sub 2 is probably an equilibrium phase. In a splat cooled alloy with 75 at. pct. Ga, another, unidentified, metastable phase was observed. Crystal chemical discussions of atomic volumes, interatomic distances and axial ratios are given; the volume difference between the two forms of NpGa sub 2 is correlated with a valence change of Np. (ERA citation 01:016575)