Structural and electronic properties of oxygen vacancy in lead-free KTa1−xNbxO3: Comparative first-principles calculations

Abstract

The structural and electronic properties of (0) and (+2) charged oxygen vacancies (Vo0 and Vo+2) in KTN are investigated through first-principles density functional calculations. We have tested three exchange–correlation functionals local-density approximation (LDA), the Perdew–Burke–Ernzerhof (PBE) generalized-gradient approximation (GGA), and Wu–Cohen (WC) GGA. WC leads to excellent improvements of geometry predications of KTN (with Vo) over LDA and PBE, although they all underestimate the band gap. We find that Vo0 state is metallic, in good agreement with the conclusion of Vo in KNbO3, and there is a defect peak 0.23eV below the Fermi level which is related to the infrared absorption. The charged Vo state plays an essential role in the displacements of Ta and O ions. We have shown that Vo+2 state of KTN is the most stable in practice, and Vo0 state may be obtained by introducing extra electrons to Vo+2. The results of our calculations indicate that Vo plays an essential role in the metal–insulator transitions in KTN and hence studying Vo is necessitate and significant for devices design.