Ternary selenides A 2 Sb 4 Se 8 (A = K, Rb and Cs) as an n-type thermoelectric material with high power factor and low lattice thermal conductivity: importance of the conformationally flexible Sb-Se-Se-Sb bridges.

We investigated the thermoelectric properties of the layered ternary selenides A 2 Sb 4 Se 8 (A = K, Rb and Cs) and the lattice thermal conductivity of K 2 Sb 4 Se 8 on the basis of DFT calculations, to find that these selenides are a high-performance n-type thermoelectric material. The Seebeck coefficients and power factors calculated for the electron carriers of A 2 Sb 4 Se 8 (A = K, Rb and Cs) are greater than those of the well-known thermoelectric materials Bi 2 Te 3 and PbTe. The lattice thermal conductivity κ latt of K 2 Sb 4 Se 8 is comparable to that of PbTe, well-known for its low lattice thermal conductivity. In terms of both electronic and phonon structures, the structural parts of the A 2 Sb 4 Se 8 (A = K, Rb and Cs) phases crucial for their thermoelectric properties are the conformationally-flexible Sb-Se-Se-Sb bridges that interlink between their structurally rigid units.