Enhancement of thermoelectric properties in rapidly synthesised β-Cu2Se using optimized Cu content and microwave hybrid heating

To our knowledge, this is the first study to successfully synthesise high-temperature-phase copper selenide (β-Cu2Se) at room temperature using rapid microwave hybrid heating (MHH). Controlling the starting Cu/Se ratio is the critical parameter for adjusting the content of α- and β-phases in the as-synthesised sample. The relatively low Cu composition causes impurities to form in the Cu3Se2 phase, deteriorating the thermoelectric (TE) properties of the Cu2Se material. The β phase formation at room temperature promotes electrical conductivity. The thermal conductivities of the Cu2.0Se samples were 0.5–0.8 Wm⁻¹K⁻¹ at 303–673 K. A strong electronic-phonon interaction may potentially couple electronic thermal conductivity (κe) and lattice thermal conductivity (κL), resulting in incomplete separability of κL and κe in the β-Cu2.0Se sample. The Cu2.0Se exhibited a ZT value of 0.65 at 523 K because of its considerably lowered thermal conductivity.