Crystal structure of the compound ScCo2Si2: single crystal investigation

Abstract

For the first time, the complete single crystal structure study of the compound ScCo 2 Si 2 was performed. It belongs to the CeGa 2 Al 2 structure type, Pearson’s symbol tI 10,139, space group I 4/ mmm , lattice parameters a =3.7775(3) c =9.6208(11) Å. The compound was prepared by arc-melting of the initial elements with the purity of not less than 99.9 % under argon followed by annealing in silica tubes at 800 °C for 350 h. Single crystals for structural examination were selected under a microscope from the broken alloys obtained. X-ray diffraction data of one of the irregularly faceted single crystals obtained at a temperature of 300(2) K by means of single crystal X-ray diffractometer Bruker D8 Venture with monochromatized Mo K α-radiation. The structure is refined using the program SHELXL, version 2018/3 (full-matrix least-squares refinement with anisotropic atomic parameters), R 1 = 0,0247, wR 2 = 0,0614 for 57 unique reflections with I o > 2 σ(I o ) and 8 refined parameters. Coordinates of atoms are the following: 2Sc at 2 а 0 0 0; 4Co at 4 d 0 1/2 1/4; 4Si at 4 e 0 0 z , z =0.3776(2). Coordination numbers of Sc, Co and Si atoms are 20, 12 and 9, respectively. The interatomic distances, with the exception of Co–Si, are longer than the sum of the metal radii of the corresponding atoms. Co–Si distances (2.2525(9) Å) are smaller than the sum of the radii of these atoms (2.42 Å) and indicate a significant interaction between Co and Si in the structure. Currently known three scandium ternary compounds ScM 2 Si 2 (M=Co, Ni, Cu) are members of complete series of compounds RM 2 Si 2 (R=rare earths) isotypic with CeGa 2 Al 2 . Crystal chemical analysis of scandium intermetallic compounds of stoichiometric composition ScM 2 X 2 (M= d -element; X= p -element) was performed. Scandium occupies a special place among rare earths and shows crystal chemical affinity both with rare earths and Zr and Hf. Keywords : ternary silicides, rare earth elements, single crystal, crystal structure.