Examination of Lone s ² Pair in Cu‐Sb‐Se Ternary Semiconductors with Wannier‐orbital Analysis

Abstract The ternary compound CuSbSe ₂ exhibits lower lattice thermal conductivity, relative to its analogous counterpart Cu ₃ SbSe ₄ . Such anomaly is attributed to the presence of lone s ² pair electrons in CuSbSe ₂ . In this work, the proposed lone pair effects are carefully examined by first‐principles calculations combined with Wannier‐orbital analysis. It is revealed that the Sb atom exhibits the similar electron configuration both in Cu ₃ SbSe ₄ and CuSbSe ₂ . Moreover, the Wannier‐function calculations indicated that the Sb‐5 s orbital is strongly distorted in CuSbSe ₂ , rather than in Cu ₃ SbSe ₄ . These observations are just in contradiction to the explanation of the lone s ² pairs. Based on the reasonable reproducing of experimental lattice thermal conductivity, the calculations and analysis disclose that the anomalous low thermal conductivity of CuSbSe ₂ is due to the reduced p ‐ p bonding strength between Sb and Se, originating in the structural distortion.