The role of Bi vacancies in the electrical conduction of BiFeO3: a first-principles approach

Abstract

We employ first-principles methods to study the mechanism controlling the electrical conduction in BiFeO₃ (BFO). We find that under oxygen-rich conditions, Bi vacancies (V_Bi) have lower defect formation energy than O vacancies (V_O) (−0.43 eV vs. 3.35 eV), suggesting that V_Bi are the acceptor defects and control the conductivity of BFO, making it a p-type semiconductor. In order to obtain further insight into the conduction mechanism, we calculate the effect of donor (Sn⁴⁺) and acceptor (Pb²⁺) impurities in BFO. Results indicate that Sn impurities prefer to substitute Fe sites to form shallow donor defects, which compensate the acceptor levels derived from V_Bi. Meanwhile, Pb atoms favour the substitution of Bi sites to form acceptor defects, reducing the overall concentration of holes (h⁺). Theoretical findings were later surveyed by current–voltage characteristics of Sn- or Pb-doped BFO nanofibers. This study is of general interest in carrier transport in charge compensation semiconductors, and of particular relevance within the context of defect-mediated conductivity in BFO.