High-pressure and high-temperature induced phase transition and thermoelectric property modulation in CoSbS

Paracostibite (CoSbS) has received significant attention as a thermoelectric material due to its earth-abundant, low-toxicity, and cost-effective constituent elements, as well as its potential application in power generation. In this work, both the conventional orthorhombic and distinct cubic CoSbS compounds were facilely synthesized using the high-pressure and high-temperature method. It was found that cubic CoSbS exhibits a higher solid solubility of Ni at the Co site compared to the orthorhombic sample. The high-density point defect NiCo in cubic CoSbS results in enhanced phonon scattering, thereby sharply suppressing phonon thermal conductivity. First-principles calculations show that the cubic structure of CoSbS exhibits higher band degeneracy and greater band dispersion compared to the orthorhombic structure, resulting in superior electrical transport properties. As a result, an enhanced figure of merit zT ∼ 0.37 was obtained at 773 K for cubic Ni0.1Co0.9SbS, which is approximately 16% higher than that of the orthorhombic sample prepared by the same method. These results indicate that employing high-pressure and high-temperature synthesis techniques offers a practical and controllable approach to modulate the crystal structure and thermoelectric performance of CoSbS.