Ternary selenides A2Sb4Se8 (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 K2Sb4Se8 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 Bi2Te3 and PbTe. The lattice thermal conductivity kappa(latt) of K2Sb4Se8 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.