First-Principles Calculation of Defect Formation and Positron Annihilation States in Bi_2Te_3

摘要

Defect formation energy in Bi_2Te_3 thermoelectric material was calculated using a first principles approach based on the Density Functional Theory (DFT). For vacancy-type defect, the Tel vacancy (V_(Te1)) is the most stable defect with low formation energy in both Bi-rich and Te-rich conditions, which indicates that the Te1 vacancies have higher probability to be formed. For antisite defects, the formation energy of Bi_(Te1) is much lower than that of Bi_(Te2) in Bi-rich condition, while in Te-rich condition it is beneficial for Te_(Bi) with lower formation energy. Positron wave function distribution and positron lifetimes of different annihilation states in Bi_2Te_3 were also calculated using the atomic superposition (ATSUP) method. The positron bulk lifetime in Bi_2Te_3 is about 231 ps, and for the neutral vacancy-type defects without relaxation, the positron lifetimes of V_(Bi), V_(Te1) and V_(Te2) are 275 ps, 295 ps and 269 ps, respectively.