Thermoelectric modulation by intrinsic defects in superionic conductor AgxCrSe2.

AgCrSe₂ materials have shown the potential to be the promising thermoelectric materials due to the intrinsic ultralow lattice thermal conductivity enabled by the fluid-like motion of Ag ions in crystal structures. However, what important role the Ag point defects can play in promoting liquid-like conduction still remains a mystery. Moreover, understanding the electronic transport properties, specifically for clarifying the contribution of various impurity states, is of critical importance for improving the thermoelectric performance of AgCrSe₂. Here, the thermoelectric properties of AgCrSe₂ with various Ag content have been systematically investigated. It is found that the carrier concentration can be modulated in a broad range by inducing deep level impurity states, enabling a transition from degenerate semiconductor to nondegenerate one and a reliable evaluation on the thermoelectric transport properties. The single parabolic band model gives a good clarification regarding the increased electronic performance. Furthermore, the enhancement of the liquid-like effect triggered by the Ag vacancies contributes to the ultralow lattice thermal conductivity (∼0.25 W m⁻¹ K⁻¹). Eventually, a maximum figure of merit zT of ∼0.6 is realized in Ag_0.97CrSe₂ at 750 K. The present findings may shed light on the improvement of thermoelectric performance in AgCrSe₂ materials. [ABSTRACT FROM AUTHOR]