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

Abstract

We investigated the thermoelectric properties of the layered ternary selenides A₂Sb₄Se₈ (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 A₂Sb₄Se₈ (A = K, Rb and Cs) are greater than those of the well-known thermoelectric materials Bi₂Te₃ and PbTe. The lattice thermal conductivity κ_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 A₂Sb₄Se₈ (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.