First principle study of intrinsic point defects in Zintl-phase thermoelectric Eu2ZnSb2

Abstract

Zintl phase compound Eu2ZnSb2, containing an intrinsic 50% Zn atom vacancy, is a potential mid-temperature p-type thermoelectric (TE) material with the low thermal conductivity. Understanding the intrinsic point defect plays a vital role in optimizing the TE properties, however, it keeps unknown so far for the Eu2ZnSb2 compound. In this work, we applied density functional theory to investigate the intrinsic point defect of Eu2ZnSb2. Phase diagram analysis shows that EuZn11, Eu11Zn6Sb12 and Eu16Sb11 may exist as the secondary phase during the grown environment of Eu2ZnSb2. Among all vacancy, substitution, and interstitial defects, Zn vacancy (VZn) is found to have the lowest formation energy of ∼0.14 eV near CBM with a −2 charge state, suggesting Zn vacancy is the p-type dominant defect in Eu2ZnSb2. Calculated electronic localization function (ELF) shows that in the VZn structure, the change of the electron distribution only occurs near the Zn vacancy. In addition, VZn only changes its neighbor structure slightly. These results suggest that VZn is an isolated point defect behaving as −2 charge state, which agrees with our defect formation energy calculation. This intrinsic point defect study is beneficial for developing effective point defect strategy to optimize TE properties of Eu2ZnSb2.