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.