The effect of Ag+ on the thermoelectric properties of Sm3+- and Ti4+- co-doped KSr₂Nb₅O₁₅ ceramics: a combined first-principles and experimental study on synergistic optimization of thermal and electrical transport

Strontium potassium niobate-based ceramics doped with different concentrations of Ag⁺ were prepared in this work, aiming to regulate the synergistic interplay between electronic and thermal transport. Ag⁺ doping increases the carrier concentration, leading to a corresponding enhancement in the Seebeck coefficient and a significant improvement in electronic transport. Concurrently, a low thermal conductivity of 1.938 W m⁻¹ K⁻¹ was obtained at 1073 K, representing a 24% reduction compared to the undoped sample. The synergistic effect of a higher power factor and a relatively lower thermal conductivity resulted in a thermoelectric figure of merit (ZT) of 0.202 at 1073 K for the Sm_0.04K_0.86Ag_0.1Sr₂Nb_4.96Ti_0.04O₁₅ ceramic, which is 71% higher than that of its Ag⁺-free counterpart. Furthermore, both the computational model KSmAg₂Sr₈Nb₁₉TiO₆₀ and the experimental composition Sm_0.04K_0.66Ag_0.3Sr₂Nb_4.96Ti_0.04O₁₅, which possess higher Ag⁺ content, exhibited the highest. This work provides ideas for simultaneously enhancing electrical transport and suppressing thermal conductivity in oxide thermoelectrics, and improving the thermoelectric performance of strontium potassium niobate-based ceramics.