The effect of Na and Ag doping – alone and in combination – on SnS1−xSex nanostructured thermoelectric materials

Abstract

In this study, Na-doped and Ag-doped as well as (Na, Ag) co-doped SnS_0.9Se_0.1 nanoparticles were synthesized via a wet chemical route, and the structures and thermoelectric properties of their hot-pressed sintered bodies were systematically investigated. Nanostructuring significantly reduced the lattice thermal conductivity, and all samples exhibited a pronounced suppression of heat transport compared to bulk SnS. The electrical conductivity was markedly enhanced by Na doping, and the SnS_0.9Se_0.1:Na sample achieved a maximum ZT of 0.14 at 658 K. In contrast, (Na, Ag) co-doped samples showed limited increases in carrier concentration and electronic properties comparable to those of the Ag-only doped sample. Atom probe tomography analysis revealed the formation of Na-rich clusters and Ag non-uniformly distributed near nanograin boundaries, along with Ag and Na distributed throughout the matrix. The solute concentrations of Na and Ag in the matrix were measured to be 0.15 at% and 0.096 at%, respectively, and charge compensation between them was confirmed to suppress the carrier enhancement effect of Na doping. These findings demonstrate that the interplay between dopant spatial distribution and defect chemistry critically governs the electronic transport properties of SnS-based thermoelectric materials, providing new insights for microstructural control and doping strategies.