Structural and vibrational properties of cage-type Sc₅Ru₆Sn₁₈ superconductor under pressure using synchrotron X-ray diffraction and Raman spectroscopy

We report detailed structural investigations of cage-type quasi-skutterudite compound Sc₅Ru₆Sn₁₈ using synchrotron single-crystal and powder x-ray diffraction. Single-crystal x-ray diffraction studies at ambient temperature revealed that the Sc₅Ru₆Sn₁₈ compound has a tetragonal symmetry in the I4₁/acd space group setting with a = 13.58 Å and c = 27.14 Å, similar to other R₅Rh₆Sn₁₈ (R = Y, Sc, Lu) cage-type compounds. The electrical resistivity ρ(T) revealed the presence of a sharp superconducting (SC) transition at T_c = 4.07 K. The ρ(T) of Sc₅Ru₆Sn₁₈ above T_c shows a smooth decrease with decreasing temperature without any evident anomalies. Systematic temperature dependent synchrotron x-ray powder diffraction (XRPD) studies covering 400–110 K shows that the Sc₅Ru₆Sn₁₈ system remain in the tetragonal I4₁/acd structure in this temperature range without any anomalous behaviour in the unit-cell parameters. High-pressure (HP) synchrotron XRPD revealed a smooth reduction in the unit-cell parameters up to ∼7 GPa which can be well described by a third-order Birch-Murnaghan equation providing the bulk modulus of the system to be ∼102.6 GPa. This system is found to several Raman modes below 300 cm⁻¹. We could follow the pressure evolution of four Raman modes, all of which show a smooth hardening with pressure up to ∼7 GPa. Our results call for systematic HP studies of the SC properties of the title system.