Abstract
Owing to the intrinsic high thermoelectric performance, Ag(2)Se is a promising alternative for traditional near-room temperature Bi(2)Te(3)-based materials. In this study, a Na(2)SO(3) solution has been used as the transient liquid during the modified cold sintering process to induce a hierarchical structure, including micropores, nanopores, sub-nanopores, and additional nanoscale Na(2)SO(3) residuals. Such a hierarchical structure contributes to an ultralow lattice thermal conductivity of 0.18 W m(-1) K(-1) at ≈300 K in the Ag(2)Se-30%Na(2)SO(3). Additionally, extra Se vacancies further optimize the carrier concentration to ≈5.6 × 10(18) cm(-3), leading to a high power factor of ≈25 µW cm(-1) K(-2) at ≈300 K in the Ag(2)Se-30%NS. Consequently, due to the synergistic effects of high power factor and low lattice thermal conductivity, an ultrahigh room-temperature figure of merit of 1.04 in the Ag(2)Se-30%Na(2)SO(3). The study demonstrates that introducing transient liquid solutions in the modified cold sintering process can effectively achieve specific structural engineering and high thermoelectric performance.