Defect-Controlled Electronic Structure and Phase Stability in Thermoelectric Skutterudite CoSb₃

Controlling extrinsic defects to tune the carrier concentration of electrons or holes is a crucial point with regard to the engineering application of thermoelectric semiconductors. To understand the defect-controlled electronic structure in thermoelectric materials, we apply density functional theory (DFT) to investigate the defect chemistry of dopants M (M = O, S, Se, or Te) in CoSb₃. DFT predicts that the breakage of Sb₄ rings induced by these dopants produces the unexpected (n- or p-type) conductivity behavior in CoSb₃. For example, energetically dominant O interstitials (O_i) chemically break Sb₄ rings and form O-4Sb five-membered rings, leading to the charge neutral behavior of O_i. While S interstitials (S_i) collapse Te-3Sb four-membered rings within Te doped CoSb₃ leading to p-type conduction behavior, Se substitution on Sb (Se_Sb) breaks the Se-Te-2Sb four-membered ring, resulting in a charge neutral behavior of the Se_Sb+Te_Sb complex defect. Furthermore, the solubility limits of M dopants (M = S, Se, or Te) are also calculated to provide essential information about single-phase material design. This study provides new insight into understanding the complicated chemical structure in doped CoSb₃, which is beneficial for devising effective doping strategies for the development of high-performance bulk thermoelectric materials.