Low lattice-thermal conductivity in a cage-structured compound YbCu9Sn4 with divalent Yb ions

•Physical properties of a cage-structured compound YbCu9Sn4 are reported in detail.•YbCu9Sn4 exhibits universal relationships of Fermi liquids.•Specific heat reveals the prominent rattling behavior of Yb ion.•Low lattice thermal conductivity due to rattling is observed.

Polycrystalline sample of YbCu9Sn4 has been prepared and the physical properties have been investigated. Magnetic susceptibility shows a weak diamagnetism, indicating the Yb ions are in the nonmagnetic Yb2+ state. Electrical resistivity shows a normal metallic behavior and Seebeck coefficient is as small as the order of 1 μV/K. Specific heat reveals the prominent contribution of Einstein mode at low temperature with the Einstein temperature of 67 K. Lattice thermal conductivity is found to be as small as 2.7 W/Km below room temperature. These results demonstrate that the Yb ions inside the Cu–Sn cage exhibit rattling, which reduces the lattice thermal conductivity of YbCu9Sn4.