Mixed-phase effect of a high Seebeck coefficient and low electrical resistivity in Ag2S

Abstract

Improvement of thermoelectric performance is very challenging work because the thermoelectric properties, the Seebeck coefficient, electrical resistivity, and thermal conductivity, are generally correlated with each other via a common physical quantity called as carrier concentration. In this study, we successfully achieved separately control the thermoelectric properties of polycrystalline Ag₂S using the spatial-phase separation into the low- and high-temperature phase under the bottom heating and top measurement configuration. We experimentally confirmed that the Seebeck coefficient was determined by the low-temperature phase at the top surface but the electrical resistivity was dominated by the high-temperature phase lying below the low-temperature phase. As a result, the high Seebeck coefficient (~-650 μVK^-1) and low electrical resistivity (~ 2 mΩcm) were simultaneously observed in a broad temperature range (390 ~ 440 K). This experimental fact suggests a new concept in the thermoelectric materials and devices.