A Chemical Understanding of the Band Convergence in Thermoelectric CoSb₃ Skutterudites: Influence of Electron Population, Local Thermal Expansion, and Bonding Interactions

N-Type skutterudites, such as Yb_xCo₄Sb₁₂, have recently been shown to exhibit high valley degeneracy with possible band convergence, explaining the excellent thermoelectric efficiency of these materials. Using a combined theoretical and experimental approach involving temperature-dependent synchrotron diffraction, molecular orbital diagrams, and computational studies, the chemical nature of critical features in the band structure is highlighted. We identify how n-type doping on the filler site induces structural changes that are observed in both the diffraction data and computational results. Additionally, we show how chemical n-type doping slightly alters the electronic band structure, moving the high-valley degeneracy secondary conduction band closer to the primary conduction band and thus inducing band convergence.