Electron microscopy examination of R5T4 alloys, where R = Ho, Yb and Gd, and T = Si, Ge, Ga and Sb

Optical and electron micrographs reveal that R5(SixGe1–x)3-type compounds, existing as thin plates, are prevalent in R5(Six,Ge1–x)4 compound systems. The purpose of this research is an attempt to improve understanding of the formation of these thin plates by extending microstructural examination to other R5(SixGe1–x)4 systems where formation of R5(SixGe1–x)3 compounds may face additional constraints. Ho5(Si0.8Ge0.2)4, Ho5Ge4, Yb5Ge4, Gd5Ge3.5Sb0.5, Gd5Ge3Ga and Gd5Ge3Sn alloys were examined by X-ray powder diffraction, scanning and transmission electron microscopy and energy dispersive spectroscopy. R5(SixGe1–x)3-type thin plates were observed in all alloys studied except for the Sb substituted system, which may be related to deviation of the valence electron concentration from normal R5(SixGe1–x)4 systems. Calculations of lattice misfit based on various assumptions indicate that the formation of thin plates is less sensitive to small lattice distortion than initially believed, and also appears fairly insensitive to slight composition variations.