Planar faulting in R2Co17 intermetallic alloys was studied by using high-resolution X-ray diffraction techniques. In the case of light rare-earth elements, the Th2Zn17 rhombohedral structure was found while, for heavy rare-earth atoms, the Th2Ni17 structure prevailed. For intermediate rare earths, the R2Co17 structure exhibited planar disorder. The occurrence of planar faulting was associated with the interlayer distance in the structure. A correlation was found between interlayer distance and stacking order. A simple qualitative explanation was given for the energy preference for one particular type of stacking order. Planar disorder did not introduce new nearest-neighbor environments for the rare-earth atoms, apart from those already found in the hexagonal and rhombohedral variants, but merely changed the probability of occurrence of each neighborhood. Simple stacking fault models were expected to prove to be insufficient for explaining the observed planar disorder.

Planar Faulting in Rare Earth–Cobalt 2:17 Alloys. R.Lora-Serrano, E.Estevez-Rams, A.Penton-Madrigal, J.Fidler, R.Grossinger, J.C.Tellez: Solid State Communications, 2002, 122[1-2], 105-9