Temperature-induced transformation in a Pu-2at. % Al alloy

The delta phase stabilized with 2 at.% aluminum transforms to a monoclinic ..cap alpha..' phase at low temperatures by a thermally activated nucleation and displacive/diffusionless mechanism. The ..cap alpha..' phase is an expanded monoclinic lattice suggesting a valence change in the ..cap alpha..-Pu atoms as a result of trapping smaller, trivalent aluminum atoms. The transformation sequence appears to be directly delta ..-->.. ..cap alpha..'. The ..cap alpha..' product is plate-like, resembling a lenticular martensite