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A1: Low temperature materials
Layered structure offers a large platform for exploring high-performance layered thermoelectric materials such as Bi2Te3 and CsBi4Te6, however, challenge remains in the lattice thermal conductivity reduction especially along the in-plane direction. Here we present the thermal properties and lattice dynamics study of a novel layered compound Bi14Rh3I9, which is alternately stacked by graphene-analogue intermetallic layer and insulating layer recently found as a weak 3D topological insulator with a small band gap.[1] Our thermal property characterizations indicate that compared with layered Bi2Te3 and CsBi4Te6 this compound possesses much lower lattice thermal conductivity (0.37 W/m K along in-plane and 0.28 W/m K cross-plane directions at room temperature), almost approaching the amorphous limit. Lattice dynamics calculations reveal that the insulating layers composed of weakly coupled one-dimensional polyhedral chains play an essential role in depressing lattice thermal conductivity. The low frequency vibrational modes of one-dimensional chains can effectively hinder phonon propagation especially for in-plane phonons and the underlying mechanism is relevant to the flattened acoustic branches and large lattice anharmonicity. This study suggests that materials with weakly coupled one-dimensional polyhedral chains might possess extremely low lattice thermal conductivity.
[1] Bertold Rasche, Anna Isaeva, Michael Ruck, Sergey Borisenko, Volodymyr Zabolotnyy, Bernd Büchner, Klaus Koepernik, Carmine Ortix, Manuel Richter, and Jeroen van den Brink, Nat. Mater. 12, 422–425 (2013).