ErNi2.23Al2.77 and YbNi2.31Al2.69 – i3 superstructures of the CaCu5 type

Abstract The title compounds have been synthesized by reaction of the elements in sealed tantalum crucibles in a muffle furnace using special annealing sequences. The crystal structures of YbNi 2.31 Al 2.69 ( R 1 = 0.0100 for 212 F 2 values and 18 variables) and for ErNi 2.23 Al 2.77 ( R 1 = 0.0154 for 255 F 2 values and 18 variables) were refined from single crystal X-ray data. They belong to the YNi 2 Al 3 type ( i 3 superstructure of CaCu 5 ) with the following crystallographic parameters: space group P 6 / m m m $P6/mmm$ , Pearson symbol hP 18, Z = 3, a = 8.2723(12), c = 4.0672(8) Å, V = 241.03(8) Å 3 for YbNi 2.31 Al 2.69 and a = 8.9109(13), c = 4.0669(8) Å, V = 279.66(8) Å 3 for ErNi 2.23 Al 2.77 . The crystal chemical discussion is supported by electronic structure calculations.