Achieving low thermal conductivity and high quality factor in sextuple-doped TiS2

Transition-metal dichalcogenide TiS₂ stands out as a sustainable candidate for room- and medium-temperature thermoelectric materials due to its affordability, non-toxicity, eco-friendly nature and use of non-critical elements. However, its light element compositional nature results in a large thermal conductivity, which is the main limitation of the thermoelectric performance of TiS₂. Here, we report a multi-element doping strategy by incorporating equivalent (Se, Zr) elements and introducing higher-valence (Nb, Ta) and lower-valence (Y, La) elements in pairs to minimize its lattice thermal conductivity, ${\kappa }_{\text{lat}}$. The findings indicate a nearly 50 % decrease in ${\kappa }_{\text{lat}}$ across the entire temperature range, attributed to the presence of strong point-defect scattering after multi-element doping. Additionally, we observed a reduced dependency of ${\kappa }_{\text{lat}}$ on temperature in multi-element doped TiS₂, as point defects can effectively scatter phonons at room temperature. As a result, the multi-element doped TiS₂ attained its highest ZT value of approximately 0.4 at 625 K. Incorporating higher-valence and lower-valence elements in pairs proves to be an effective method for decreasing lattice thermal conductivity without compromising too much of its large Seebeck coefficient.