Rational design, two-step synthesis of Cu2GeS3 crystal with enhanced thermoelectric performance by Te alloying

Currently, Cu 2 GeS 3 has been obtained through solid-state reaction. However, the pure phase Cu 2 GeS 3 synthesized still faces challenges due to the low boiling point of the sulfur element. Herein, we have prepared pristine Cu 2 GeS 3 by a two-step method. Firstly, the pure phase GeS 2 was synthesized by solvothermal method and then used the freshly as-synthesized GeS 2 as raw material to react with copper powder to fabricate pure phase Cu 2 GeS 3 . Further, the thermoelectric properties of Cu 2 GeS 3 crystal have been explored. At room temperature, the electric resistance value measured by multimeter was ~ 2634 Ω for intrinsic Cu 2 GeS 3 crystal, which exceeded the instrument (electrical conductivity/Seebeck coefficient) test range of 0–2000 Ω, so there is no relevant report in the thermoelectric field about Cu 2 GeS 3 crystal. In order to improve its conductivity, Cu 2 GeS 3 crystal is alloyed with a small amount of Te powder to obtainable Cu 2 GeS 3− x Te x samples, which have obvious thermoelectric properties. By adjusting the content of Te, finally, the electrical conductivity of the Cu 3 GeS 2.6 Te 0.4 sample reached 364.20 S m −1 and the figure-of-merit ZT max value of ~ 0.12 were obtained at 816 K.