Thermoelectric properties, crystal and electronic structure of semiconducting RECuSe₂ (RE = Pr, Sm, Gd, Dy and Er)

Highlights: • Crystal and electronic structure of monoclinic and trigonal RECuSe₂ phases. • Thermoelectric properties of the RECuSe₂ phases. • Temperature stability of the RECuSe₂ phases. - Abstract: The ternary RECuSe₂ phases have been prepared and structurally characterized. They adopt either a monoclinic structure (P2₁/c, z = 4) for lighter rare earths (RE = Pr, Sm and Gd) or Cu-disordered trigonal structure for heavier rare-earths (P3^¯m1, z = 1, RE = Dy and Er). The resistivity and Seebeck coefficient measurements on GdCuSe₂, DyCuSe₂ and ErCuSe₂ indicate that the studied phases are p-type semiconductors with relatively small activation energies (0.045–0.11 eV). However, their electrical resistivities are too high (0.45–220 Ω cm at room temperature) to make them competitive thermoelectric materials. Electronic structure calculations indicate presence of a band gap in the RECuSe₂ phases