Compositional tuning of weighted mobility and phonon scattering in Ti(S_1-xSe_x)₂: a strategy for high-performance thermoelectric materials

Transition metal dichalcogenides are promising thermoelectric materials due to the potential for manipulating their electronic and thermal properties through strategic alloying. Recent studies, such as the solid-solution alloying of TiSe₂ with TiS₂ demonstrate improved thermoelectric performance despite a reduction in electronic transport properties. This enhancement is attributed to a significant (~ 60%) reduction in lattice thermal conductivity. However, the effect of TiSe₂ alloying in electronic band parameters and phonon scattering of Ti(S_1-xSe_x)₂ alloys for x in the range from 0 to 0.5 has not been studied. Herein, we investigate the impact of solid-solution alloying on the electronic and thermal transport properties of Ti(S_1-xSe_x)₂ alloys using the Single Parabolic Band (SPB) model and the Debye–Callaway (D–C) model, respectively. The SPB model analysis reveals a moderate decrease in the theoretical maximum power factors of the alloys due to a density-of-states effective mass decrease with increasing x. The D–C model confirms that the substantial reduction in lattice thermal conductivity in the alloy originates from strong point defect phonon scattering in Ti(S_0.5Se_0.5)₂ (x = 0.5), where the maximum disorder occurs. Despite the decrease in weighted mobility with increasing x, the concurrent suppression of lattice thermal conductivity exerts a more dominant influence. This interplay results in the highest theoretical maximum zT at x = 0.4 according to theoretical calculations. Identification of the alloy composition with the highest thermoelectric quality factor is essential in designing transition metal dichalcogenide alloys with high thermoelectric performance.