The electronegative filling in skutterudites not only broadened the scope of filling atoms, but also facilitated the preparation of p-type skutterudites. However, the introduction of a single sulfur atom in the Co₄Sb₁₂ cannot be achieved without charge compensation through the traditional equilibrium method. In the present study, the dual occupations of S-atoms by self-charge compensation were shown as the most stable forms under high pressure, and a series of p-type S_yCo₄Sb_12-2yS_2y skutterudites was successfully prepared by high-pressure-high-temperature (HPHT) method. The electronic structures and transport properties of as-obtained materials were investigated, and the related mechanisms were explored. The results suggested that the presence of S-impurities led to flattening of the electronic band that led to a higher Seebeck coefficient. The S-doped Co₄Sb₁₂ displayed lower elastic modulus, elastic constant, and Debye temperature, thus indicating the chemical bond softening in skutterudites. The thermal conductivities of S_yCo₄Sb_12-2yS_2y compounds reduced monotonously with the increase in S-content. This study provides a new and promising avenue for optimizing the thermoelectric properties of p-type Co₄Sb₁₂.

High-pressure and high-temperature (HPHT) synthesis provides an effective way to tune the band structure of materials and improve their electronic properties. To investigate the influence of synthesis pressure on electronic properties, Mg_1.97Al_0.03Si samples were synthesized using the HPHT method. The maximum effective mass 0.92m_e is obtained for the sample prepared with the synthesis pressure of 3 GPa, leading to the biggest Seebeck coefficient –201.3 μV/K at room temperature. Meanwhile, the 3 GPa sample obtains the higher electron carrier concentration and electrical conductivity, resulting in nearly overall enhancement of power factor. The Density Functional Theory (DFT) calculations evidences that the Conduction Bands Minimum (CBM) can be tuned effectively by applied pressure and the convergence of the CBM leads to a larger effective mass of DOS, which are beneficial to the enhancement of power factors. These results indicate that high-pressure is a powerful tool to tune Mg_1.97Al_0.03Si band structures.