Explanation for the conductivity difference of half-Heusler transparent conductors: Via ionization energy

To further understand the less-studied half-Heusler transparent conductors, we have considered four 18-electron ABX compounds (TaIrGe, TaIrSn, ZrIrSb, and TiIrSb) to focus on their carrier effective masses and ionization energies. The novelty of this work lies in two aspects: (i) we discover that hole-killer defects are more likely to form in TaIrGe than in ZrIrSb, which leads to a lower concentration of the holes in TaIrGe. This is the fundamental reason for the conductivity of TaIrGe being much lower than that of ZrIrSb; (ii) we propose that the hole effective mass near the sub-valence band maximum (Sub-VBM) could be used to forecast the potential transport performance of the materials. The obtained results show that the transport performance of TaIrGe & TaIrSn is potentially more promising than that of TiIrSb and ZrIrSb. Besides, this work firstly studies the mechanical properties of the considered ABX compounds, offering strong evidence that TaIrGe, TaIrSn, ZrIrSb, and TiIrSb could be potentially flexible and ductile TCMs.