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

Abstract

Single crystals of Sc 5 Rh 6 Sn 18 were grown from Sn-flux. The crystal structure (SG: I4 1 /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 Sc 5 Ir 6 Sn 18 (space group I4 1 /acd) type of structure. The performed structural studies suggest also the presence of local domains with broken average translational symmetry. Analysis of the chemical bonding situation reveal highly polar Sc2-Sn1, Sn-Rh and Sc2-Rh bonds, two-and three-center bonds involving Sn-atoms as well as ionic nature of Sc1 bonding. The thermopower of Sc 5 Rh 6 Sn 18 is isotropic, small and negative (i.e. dominance of electron-like charge carriers). Due to structural disorder, the thermal conductivity is lowered in comparison with regular metallic systems.

Conventional isotropic s -wave superconductivity with strong electron-phonon coupling in Sc5Rh6Sn18

“…The synthesis and complete structural characterization of the octahedral crystals with a base of about 1 × 1 cm 2 and a height of about 1 cm (see Fig. 1 in [24]), on which the here-reported properties were measured, as well as the electronic structure and chemical bonding of Sc 5 Rh 6 Sn 18 are discussed in Ref. [24].…”

“…1 in [24]), on which the here-reported properties were measured, as well as the electronic structure and chemical bonding of Sc 5 Rh 6 Sn 18 are discussed in Ref. [24]. The performed diffraction studies showed Sc 5 Rh 6 Sn 18 [space group: I4 1 /acd, a = 13.5529(2) Å, c = 27.0976(7) Å] crystallizes with the Sc 5 Ir 6 Sn 18 type of structure [22].…”

“…1 in Ref. [24] was cooled from above T c in an applied field of 10 and 50 mT normal to the largest face of the respective crystal. In ZF experiments the Earth's magnetic field was compensated with accuracy better than 30 mG by three orthogonal Helmholtz coils around the spectrometer along the x, y, and z axes [26].…”

“…The temperature dependence of the electrical resistivity ρ of Sc 5 Rh 6 Sn 18 shows a sc transition at T res c = 5.2 K. The derivative of the electrical resistivity measured along the c axis is presented in Fig. 3(a) for different values of B c. The observed transitions are broad (full width at half maximum of 0.2-0.4 K), which is most likely due to structural disorder [24]. An increase of the magnetic field leads to a continuous lowering of T c , and for B = 9 T no indication of superconductivity is observed for temperatures above 0.4 K. Identical behavior of ρ(T ) is observed when measuring in a magnetic field perpendicular to the c axis [B ⊥ c; not shown in Fig.…”

“…Such controversial reports on 5:6:18 stannide SCs as well as our recent combined high-resolution x-ray diffraction and transmission electron microscopy study [24], which indicates locally broken translational symmetry (i.e., the possible presence of microscopic noncentrosymmetric domains) in the complex crystal structure of Sc 5 Rh 6 Sn 18 [24], prompted us to perform additional physical property investigations of this compound. In the present work we report on magnetic susceptibility, electrical resistivity, specific heat capacity, and μSR spectroscopy measurements.…”