A transmission electron microscopy study of the (Sm,Pr)5Co19 phase

Transmission electron microscopy has been used to characterize the rhombohedral 5:19 phase (R bar 3m) in a stoichiometric (Sm0.75Pr0.25)5Co19 alloy. In some regions, strain-induced contrast was observed in the 5:19 phase. By contrast analysis, this strain contrast was associated with a displacement vector of the type (1)/(3) [01 bar 10]. In other regions where the strain-induced contrast was significantly reduced, faults with the crystal structure of hexagonal (Sm,Pr)2Co7(2:7H) phase (P63/mmc) were observed. The formation of the faults is believed to release elastic energy within the 5:19 phase. In the interface regions between the 5:19 phase and the minor component hexagonal 2:7H phase, it was found by lattice imaging that the 5:19 and 2:7H plates are superimposed with a common c direction. The orientation relationship between the 5:19 and 2:7H phases is given by [0002]2:7H parallel[0003]5:19R and [11 bar 20]2:7H parallel[11 bar 20]5:19R