Enhanced and stabilized n-type thermoelectric performance in α-CuAgSe by Ni doping

Abstract

Ternary selenide CuAgSe has potentially outstanding thermoelectric performance owing to its high electron mobility and low thermal conductivity. It has two phases including the room-temperature semimetallic β phase and the high-temperature (above 470 K) semiconductive α phase. However, as the temperature rises, the common CuAgSe samples are likely to undergo an n-p transition with an abrupt sign reversal of the Seebeck coefficient, which is often caused by the unintentionally off-stoichiometry introduced in the synthesis procedure. Thus, the high-temperature α-phase CuAgSe tends to behave as a p-type thermoelectric material in many previous works. In this study, we propose a strategy to conveniently achieve stabilized n-type conduction in α-CuAgSe by doping Ni at the Cu sites. The thermoelectric transport properties of Cu1-xNixAgSe with x = 0–0.05 have been systematically analyzed. The results show that in all the Ni-doped samples, hole carriers are successfully suppressed in β-CuAgSe through the significant increase in electron concentration, which guarantees the deterministic n-type behavior of α-CuAgSe. Furthermore, Ni doping not only raises the electron concentration of CuAgSe but also dramatically increases the carrier mobility, thus improving its thermoelectric performance. As a result, a zT value around 0.8 at 623 K is obtained in the Cu0·96Ni0·04AgSe sample.