Ternary Ag₂Se_1–<i>x</i>Te_<i>x</i>: A Near-Room-Temperature Thermoelectric Material with a Potentially High Figure of Merit

Abstract

Discovering high-performance near-room-temperature thermoelectric materials is extremely imperative to widen the practical application in thermoelectric power generation and refrigeration. Here, ternary Ag₂Se_1-<i>x</i>Te_<i>x</i> (<i>x</i> = 0.1, 0.2, 0.3, 0.4, and 0.5) materials are prepared via the wet-mechanical alloying and spark plasma sintering process to investigate their near-room-temperature thermoelectric properties. From density functional theory calculation and single-parabolic-band modeling study, we found that the reduced contribution of Se 4p orbitals to the total density of states decreases the carrier effective mass with increasing Te content, which should enhance the theoretically maximum <i>zT</i>. These calculation results are also verified by the experimental results. Meanwhile, complex microstructures including dislocations, nanograins, high-density boundaries, Te_Se substitution, lattice distortions, and localized strain have been observed in ternary Ag₂Se_1-<i>x</i>Te_<i>x</i>. These complex microstructures strengthen phonon scattering and in turn lead to ultralow lattice thermal conductivity in the range of 0.21-0.31 W m^-1 K^-1 in ternary Ag₂Se_1-<i>x</i>Te_<i>x</i> at 300 K. Although the increased deformation potential suppresses the carrier mobility, benefiting from the engineered band structures and ultralow lattice thermal conductivity, a high <i>zT</i> of >1 can be potentially obtained in the ternary Ag₂Se_1-<i>x</i>Te_<i>x</i> with appropriate carrier concentration. This study indicates that ternary Ag₂Se_1-<i>x</i>Te_<i>x</i> is a promising candidate for near-room-temperature thermoelectric applications.