Scandium–copper–indides deriving from the ZrNiAl and MnCu2Al type structures

Abstract Phase analytical studies in the Sc–Cu–In system led to samples of the solid solutions ScCu1–x–y In1+x and ScCu2–x In which were studied by X-ray powder diffraction. At room temperature the compounds ScCu1–x–y In1+x crystallize with the ZrNiAl type, space group P 6 ‾ $\overline{6}$ 2m. Exemplarily, the structure of ScCu0.76In1.17 was refined from single crystal X-ray diffractometer data, revealing strong anisotropic displacements for the scandium atoms and a mixed occupied Cu/In site. Superstructure formation is observed at low temperatures. The ScCu0.78In1.14 and ScCu0.76In1.16 structures were refined from diffraction data recorded at 90 K. Both compounds adopt the HfRhSn type, space group P 6 ‾ $\overline{6}$ 2c, a klassengleiche subgroup of index 2; doubling of the subcell c axis. The Cu/In filled trigonal Sc6 prisms are strongly distorted in the superstructure, resulting from pairwise dislocation of the Cu/In atoms from ideal positions within an equidistant chain to shorter (311.0 pm) and longer (392.8 pm) Cu/In–Cu/In distances. Single crystal data of the Heusler phases ScCu1.95In and ScCu1.94In show small degrees of copper vacancies.