Theoretical Aspects of the Study on the Thermoelectric Properties of Pnictogen-Dichalcogenide Layered Compounds

Recent experimental studies revealed that BiCh2 (Ch = S, Se) layered compounds, which have been well known as superconductors, also exhibit high thermoelectric performance. We review theoretical investigations on the thermoelectric properties of PnCh2 (Pn = Bi, Sb, As) layered compounds. Their electronic structure shows quasi-one-dimensionality, which is favorable for realizing high power factor. This quasi-one-dimensionality originates from the anisotropy of the px,y orbitals on the PnCh2 square lattice. First-principles calculation suggests that atomic substitution can enhance the one-dimensionality, and thus the power factor. Another important aspect is the lattice instability, which can result in the strong anharmonicity of phonons and the low lattice thermal conductivity.