Thermoelectric properties of Ag-added KSr₂Nb₅O₁₅-based ceramics: A combined experimental and computational study

Strontium potassium niobate-based ceramics with different amounts of nanosized Ag particles as a secondary phase were synthesized via a solid-state reaction. The influence of Ag content on thermoelectric performance was examined with first-principles calculations. With increasing Ag content, the Seebeck coefficient increases, but the associated increase in effective mass decreases both the carrier concentration and electron transport capability. The incorporation of Ag introduces multidimensional defects, such as vacancies, dislocations, strain fields, mass fluctuations, and grain boundaries, which collectively yield multiscale scattering, such as Umklapp scattering, point defect scattering, and grain boundary scattering, thus yielding a pronounced reduction in thermal conductivity. Under the synergistic coupling of electronic transport and phonon transport, the sample with the lowest Ag content achieves the highest ZT values, with theoretical and experimental values reaching 0.230 (1100 K) and 0.133 (1073 K), respectively, and the corresponding average ZT values are 0.076 and 0.052, respectively. Although increasing the Ag content reduces the thermal conductivity, it also decreases the power factor, which severely affects the thermoelectric transport performance. This finding indicates that simply pursuing a high content of a nanosized secondary phase is not necessary to achieve the optimal ZT. Nevertheless, an optimal composition with high ZT was obtained, and the thermoelectric properties of strontium potassium niobate-based ceramics with appropriate Ag contents were significantly enhanced.