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

Single crystals of Sc5Rh6Sn18 were grown from Sn-flux. The crystal structure (SG: I4(1)/acd, a = 13.5529(2) angstrom, c = 27.0976(7) angstrom) 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 I4(1)/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.