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A highly efficient facile method was used to synthesize Cu 2 Te via spark plasma sintering (SPS) of highenergy ball-milled elemental powders, followed by annealing, which dramatically reduced the whole process time. The multiple phase transitions of Cu 2 Te over an extensive temperature range were determined using a combination of high temperature X-ray diffraction (HTXRD) and differential scanning calorimetry (DSC). This merit endows Cu 2 Te with the ability to trigger multiple critical scatterings from room temperature up to 900 K. Microscopic investigation showed that the Cu 2 Te prepared by this rapid method possesses tiny dispersive precipitates, with sizes in the range of 50-100 nm, that could serve as obstacles for the transfer of mid-wavelength phonons. As a result, a ZT value of $0.52 at 1000 K was obtained for the sample annealed for 10 h after SPS.

Doping Sn into the Cu2Te lattice can synergistically enhance the power factor and decrease thermal conductivity, leading to remarkably optimized zTs. The lone pair electrons from the 5s orbital of Sn can increase the DOS near the Fermi level of Cu2Te to promote PF and reduce κe by decreasing the carrier concentration. This study explores a scalable strategy to optimize the thermoelectric performance for intrinsically highly degenerate semiconductors.

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