Thermoelectric properties of S-doped Cu2Se materials synthesized by high-pressure and high-temperature method

High-pressure technique is an effective route to synthesize thermoelectric materials and tune transport properties simultaneously. In this work, S-doped copper–selenium compounds ( Cu 2 Se 1 − x S x $({\mathrm{\text{Cu}}}_2{\mathrm{\text{Se}}}_{1-x}{\mathrm{\text{S}}}_x$ , 0 ≤ x ≤ 0 . 0 5 ) $0\le x\le 0.05)$ were successfully synthesized by high-pressure and high-temperature (HPHT) technology in just 30 min. Cu 2 Se 1 − x S x ${\mathrm{\text{Cu}}}_2{\mathrm{\text{Se}}}_{1-x}{\mathrm{\text{S}}}_x$ samples show layered morphology composed of abundant pores and lattice defects. The appropriate S introduction ( x = 0 . 0 1 $x=0.01$ and 0.03) can effectively enhance Seebeck coefficient and reduce the thermal conductivity of Cu 2 Se ${\mathrm{\text{Cu}}}_2\mathrm{\text{Se}}$ . Compared with the pure Cu 2 Se ${\mathrm{\text{Cu}}}_2\mathrm{\text{Se}}$ sample, Cu 2 Se 0 . 9 7 S 0 . 0 3 ${\mathrm{\text{Cu}}}_2{\mathrm{\text{Se}}}_{0.97}{\mathrm{\text{S}}}_{0.03}$ exhibits a 30% lower thermal conductivity, but the decline of power factor by the distinctly increased electrical resistivity at high temperature results in a smaller zT at temperature > 6 5 0 $>650$  K. The variations of thermoelectric properties are resulted from the competitive effects between S-doping and actual composition change (Cu:S). It indicates that S-doping is not so effective in improving the zT value of Cu 2 Se ${\mathrm{\text{Cu}}}_2\mathrm{\text{Se}}$ materials by high-pressure synthesis.