Positional ordering in the light ER-Ga systems (ER=rare earth element)

摘要

Crystal data and results of structure refinement, using powder X-ray diffraction and Rietveld analysis, for ∈-ordered structures near 75 at./100 Ga are reported. The structures are based on the AIB_2-type with deviation from stoichiometry due to pairwise substitution of rare earth (RE) atoms By gallium. Weak reflections which are forbidden in the AIB_2-type structure were observed and Indicate the existence of positional ordering of Ga_2-type structure were observed and Indicate the existence of positional ordering of Ga_2 pairs located in the basal planes preserving the Hexagonal symmetry (S.G.P6/mmm).