Tb0.67PdAl3 and Gd1.33Pt3Al8 with layers of rare-earth-metal atoms and Al-atom triangles

Abstract

The crystal structures of the ternary compounds Tb0.67PdAl3 (hP14-4.67, P63/mmc, a = 4.394(4), c = 9.372(6) Å) and Gd1.33Pt3Al8 (hR51-14.00, R-3m, a = 4.3090(14), c = 38.54(2) Å) were refined from X-ray single-crystal diffraction data. They contain monoatomic layers stacked along [001] with ordered or disordered distribution of rare-earth-metal atoms and Al-atom triangles. Together with the structures of Y2Co3Ga9, Sc0.67Fe2Si5, Er4Pt9Al24, and ErNi3Al9, they form a family of intergrowth structures built up of three kinds of monoatomic layer. Analyzing the relative positions of the monoatomic layers, some basic stacking rules, which may help to predict new structures, are formulated.