Over the years, the fact that the quaternary diamond-like thermoelectric materials show much lower carrier mobilities than ternary compounds remains mysterious. In this work, by adopting first-principles defect chemistry and electrical transport calculations, the fundamental origin of the difference on carrier mobility between quaternary and ternary diamond-like compounds is addressed, exemplified by Cd₂Cu₃In₃Te₈. The results of defect chemistry show that the main intrinsic defects in quaternary compound Cd₂Cu₃In₃Te₈ are substitutional defects, i.e., Cd_In and Cd_Cu, differing from the copper vacancy defect in ternary Cu-based compound such as CuInTe₂. The low defect formation energies in Cd₂Cu₃In₃Te₈ result in high defect concentrations, which is caused by the similar atomic radii and electronegativities between CdIn and CdCu. Further calculations show that the low-energy defects are mainly located around the valence band maximum in Cd₂Cu₃In₃Te₈. The electrical transport calculations, considering both the acoustic phonon scattering and ionized impurity scattering, demonstrate that mainly due to the higher concentration of the ionized defects, the mobility of the quaternary Cd₂Cu₃In₃Te₈ is much lower than that of ternary CuInTe₂. Our work sheds light on the intrinsic defects in quaternary diamond-like compounds and their influence on charge transport.

多年来，四元类金刚石热电材料显示出比三元化合物低得多的载流子迁移率这一事实仍然是个谜。在这项工作中，通过采用第一性原理缺陷化学和电输运计算，解决了四元和三元类金刚石化合物之间载流子迁移率差异的根本原因，例如 Cd ₂ Cu ₃ In ₃ Te ₈。缺陷化学结果表明，四元化合物Cd ₂ Cu ₃ In ₃ Te ₈的主要本征缺陷是取代缺陷，即Cd _In和Cd _Cu，不同于CuInTe ₂等三元Cu基化合物中的铜空位缺陷。_{Cd 2} Cu ₃ In ₃ Te ₈中的低缺陷形成能导致高缺陷浓度，这是由 Cd In 和 Cd Cu 之间相似的原子半径和电负性引起的。进一步计算表明，低能缺陷主要位于Cd ₂ Cu ₃ In ₃ Te _{8的价带最大值附近。}. 考虑声子散射和电离杂质散射的电输运计算表明，主要由于电离缺陷浓度较高，四元 Cd ₂ Cu ₃ In ₃ Te ₈的迁移率远低于三元 CuInTe ₂ . 我们的工作揭示了四元类金刚石化合物的内在缺陷及其对电荷传输的影响。