Crystal structure, chemical bonding, and electrical and thermal transport in Sc5Rh6Sn18

Abstract

Single crystals of Sc₅Rh₆Sn₁₈ were grown from Sn-flux. The crystal structure (SG: I4₁/acd, a = 13.5529(2) Å, c = 27.0976(7) Å) was studied by high-resolution X-ray diffraction on powder and single crystal material as well as by TEM. All methods confirm it to crystallize with a Sc₅Ir₆Sn₁₈ (space group I4₁/acd) type structure. The performed structural studies also suggest the presence of local domains with a broken average translational symmetry. An analysis of the chemical bonding situation reveals highly polar covalent Sc2–Sn1, Sn–Rh and Sc2–Rh bonds, two- and three-centre bonds involving Sn-atoms as well as the ionic nature of Sc1 bonding. The thermopower of Sc₅Rh₆Sn₁₈ is isotropic, small and negative (i.e. dominance of electron-like charge carriers). Due to structural disorder, the thermal conductivity is lower in comparison with regular metallic systems.