Synergetic Optimization of Electrical and Thermal Transport Properties by Cu Vacancies and Nanopores in CuSe.

In this study, a series of CuInSe (-0.3 ≤ ≤ 0.2 and 0 ≤ ≤ 0.05) samples were prepared by melting and the spark plasma sintering method. X-ray diffraction measurements indicate that the Cu-deficient samples ( = -0.3 = 0 and = -0.2 = 0) prefer to form the cubic phase (β-CuSe). Adding excessive Cu or introducing In atoms into the CuSe matrix triggers a phase transition from the β to α phase. Positron lifetime measurements confirm the reduction in Cu vacancy concentration by adding excessive Cu or introducing In atoms into CuSe, which causes a dramatic decrease in carrier concentration from 1.59 × 10 to 5.0 × 10 cm at room temperature. The samples with In contents of 0.01 and 0.03 show a high power factor of about 1 mW m K at room temperature due to the optimization of the carrier concentration. Meanwhile, the excess Cu content and doping of In atoms also favor the formation of nanopores. These pores have strong interaction with phonons, leading to remarkable reduction in lattice thermal conductivity. Finally, a high ZT value of about 1.44 is achieved at 873 K in the CuInSe ( = 0 and = 0.01) sample, which is about twice that of the Cu-deficient sample (CuSe). Our work provides a viable insight into tuning vacancy defects to improve efficiently the electrical and thermal transport performance for copper-based thermoelectric materials.