The performance of traditional semiconductors as thermoelectric materials is often hindered by high lattice thermal conductivity, which counteracts otherwise favorable electronic properties. In this work, we identify ${\mathrm{LiTiTe}}_2$-type semiconducting compounds, a family of stable ternary derivatives of the nickel arsenide-structure of those traditional semiconductors, as a platform that effectively resolves this issue. These materials exhibit exceptionally low lattice thermal conductivities, competitive with state-of-the-art group IV-VI compounds. This strong phonon suppression arises from a complex bonding hierarchy that lowers the frequency of acoustic phonons and enhances anharmonic scattering. Crucially, the reduced crystal symmetry inherent to the ${\mathrm{LiTiTe}}_2$ structure-type induces an orbital energy splitting in the vicinity of the valence band maximum. We establish a direct correlation between this splitting and the peak power factor, validating it as an effective descriptor for screening high-performance thermoelectric materials. Orbital energy splitting tuned within the thermal activation window maximizes the power factor, suggesting that a finite splitting optimizes the balance between density-of-states enhancement and the mitigation of detrimental interband scattering. Guided by this principle, we identified ${\mathrm{NaBiS}}_2$ as a prime candidate that possesses both an intrinsically low thermal conductivity and natural band convergence. This synergy leads to an excellent figure of merit approaching 1.0 for $p$-type variant at high temperatures, based on a comprehensive scattering model that includes four-phonon processes and multiple electronic scattering mechanisms. Furthermore, we demonstrate that this splitting is tunable; applying hydrostatic pressure can effectively eliminate residual splitting, providing a direct pathway to engineer band convergence. This work introduces the engineering of orbital energy splitting as a new and powerful design strategy for discovering and optimizing advanced thermoelectric materials.

Close

PrevNext

View figure in article

• Thermoelectric effects
• Thermoelectrics
• Density functional theory