Defect Oxygen in NaNbO3 and Its Fatigue Behavior

Abstract

Oxygen vacancies are among the most critical defects governing the performance and reliability of lead-free ferroelectric perovskites. This work presents a systematic first-principles investigation of oxygen vacancy effects in sodium niobate (NaNbO₃), with a particular focus on their role in ferroelectric fatigue. Using density functional theory calculations, the evolution of the electronic structure was examined through total density of states (DOS) for supercells containing up to 10 oxygen vacancies. Results reveal progressive introduction of Nb-d derived defect states within the band gap, upward shift of the Fermi level, and non-monotonic changes in the band gap, consistent with n-type doping and partial Nb reduction. Formation energy calculations demonstrate that neutral oxygen vacancies exhibit moderate stability under oxygen-rich conditions (≈ 4.6-5.2 eV per vacancy), but become significantly more favorable under reducing environments relevant to device operation. Theoretical considerations of charged vacancies further highlight their importance in domain-wall pinning and leakage current enhancement.