Mixed-phase effect of a high Seebeck coefficient and low electrical resistivity in Ag <sub>2</sub> S
Gareoung Kim, Dogyun Byeon, Saurabh Singh, Keisuke Hirata, Seongho Choi, Masaharu Matsunami, Tsunehiro Takeuchi
Abstract
Abstract The improvement of thermoelectric performance is very challenging, because the thermoelectric properties, the Seebeck coefficient, electrical resistivity, and thermal conductivity are generally correlated with each other via a common physical quantity known as carrier concentration. In this study, we successfully achieved separate control of the thermoelectric properties of polycrystalline Ag 2 S using spatial-phase separation into low- and high-temperature phases using a configuration based on bottom heating and top measurement. 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, a high Seebeck coefficient ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>∼</mml:mo> <mml:mo>−</mml:mo> <mml:mn>650</mml:mn> <mml:mi>μ</mml:mi> <mml:mrow> <mml:mtext>V</mml:mtext> </mml:mrow> <mml:mrow> <mml:msup> <mml:mrow> <mml:mtext>K</mml:mtext> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> ) and low electrical resistivity ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>∼</mml:mo> <mml:mn>2</mml:mn> <mml:mrow> <mml:mtext>m</mml:mtext> <mml:mi mathvariant="normal">Ω</mml:mi> <mml:mtext> </mml:mtext> <mml:mtext>cm</mml:mtext> </mml:mrow> </mml:math> ) were simultaneously observed over a broad temperature range (390 ∼ 440 K). This experimental discovery suggests a new concept for thermoelectric materials and devices.