Defect-Controlled Electronic Structure and Phase Stability in Thermoelectric Skutterudite CoSb_3

Abstract

Controlling extrinsic defects to tune the carrier concentration of electrons or holes is a crucial point concerning 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, Te) in CoSb_3. DFT predicts that the breakage of Sb_4-rings induced by these dopants produces the unexpected (n- or p-type) conductivity behavior in CoSb_3. For example, energetically dominant O interstitials (Oi) chemically break Sb_4-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 CoSb_3 leading to a 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 complex defect Se_(Sb)+Te_(Sb). Furthermore, the solubility limits of M dopants (M = S, Se, Te) are also calculated to provide essential information on single-phase material design. This study provides a new insight to understand the complicated chemical structure in doped CoSb_3, which is beneficial for devising effective doping strategies to develop high-performance bulk thermoelectric materials.

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