Decreased order-disorder transition temperature and enhanced phonon scattering in Ag-alloyed Cu3SbSe3

Cu3SbSe3 is a promising thermoelectric material with ultralow lattice thermal conductivity, especially at temperatures above 450 K at which the order-disorder transition of copper ions takes place. To investigate whether the high-temperature disordered phase can be extended to lower temperature, a series of Ag-alloyed Cu3-xAgxSbSe3 (x = 0, 0.1, 0.2 and 0.3) polycrystalline samples were synthesized and characterized in this work. It was found that the Ag-alloying shifts the order-disorder transition temperature to lower ones, which is beneficial to the thermoelectric application of Cu3SbSe3. For thermal transport, Ag-alloying is effective in suppressing lattice thermal conductivity in the copper-ions-ordered region, while in the copper-ions-disordered region, Ag-alloying barely has any effect on lattice thermal conductivity, as the phonon scattering is dominated by the liquid-like behavior of copper ions. Although Ag and Cu atoms have the same valence electron number, the carrier concentration is slightly increased after Ag-alloying, which suppresses the bipolar effect and increases the Seebeck coefficient at high temperatures. Finally, a maximum zT of 0.34 is obtained at 652 K for the sample Cu2.7Ag0.3SbSe3, which is 161% higher than that of the pristine sample.