Linear microstructural features in R5(Si,Ge)4-type alloys: Difficulties in identification

A brief review of the current literature concerning compounds based upon the R5(SixGe1−x)4 structure reveals that essentially all examined alloys contain “linear features” similar to those first observed by Szade et al. on the surface of Gd5Si4, Gd5Si2Ge2 and Gd5Ge4 samples. Attempts to characterize these features, using a variety of techniques, have proven to be a difficult task. Rather than becoming clearer and better understood, discrepancies in the reported data have resulted in much confusion. A series of comprehensive experiments involving optical, scanning and transmission electron microscopy, X-ray diffractometry, magnetization, and heat capacity measurements have been performed in an attempt to clarify the situation. These experiments, coupled with a critical examination of published data, allow certain misconceptions and apparent contradictions to be understood and explained. Of major importance is the discovery that the volume fraction of the linear feature present is far lower than what one may estimate on the basis of etched samples. The results of this study support previous data that show the linear features are a second phase of composition R5(SixGe1−x)3, and reveal the various difficulties associated with proper identification of this phase due to its small size scale and low volume percentage.