Persistence of 5:3 plates in RE5(SixGe1-x)4 alloys

Studies of RE 5 (Si x Ge 1-x ) 4 alloys, where RE equals rare earth, have revealed a second-phase having a thin-plate morphology in essentially every alloy examined, independent of exact composition and matrix crystal structure. Identified as having a composition approximating Gd 5 (Si x Ge 1-x ) 3 and a hexagonal crystal structure in the Gd-based system, it has been suggested that the observed thin-plate second phases seen in this family of rare earth alloys are all most likely of the form RE 5 (Si x Ge 1-x ) 3 . A number of interesting observations suggest that the formation of these second-phase plates is somewhat unusual. The purpose of this article is to investigate the stability of this second phase in Gd- and Er-based compounds. The stability was investigated as a function of thermal cycling and large-scale composition fluctuations. The results of scanning and transmission electron microscopy (SEM, TEM) studies indicate that the RE 5 (Si x Ge 1-x ) 3 phase is extremely stable once it forms in a RE 5 (Si x Ge 1-x ) 4 matrix.