Anomalous electrical performance of A-site double-bivalent-doped Bi0.49Na0.5TiO3-δ ceramics from nominal oxygen deficiency to excess

Perovskite structural Bi0.5Na0.5TiO3 (BNT) ferroelectrics can exhibit considerable ionic conductivity, giving a new area for the application as oxygen ion conductors. Through acceptor doping and A-site nonstoichiometry, an ionic conductive mechanism associated with well-resolved arcs in the complex impedance spectra is proposed. Different dielectric responses in ceramics can be deduced to probe the electrical inhomogeneities in separative regions, such as bulk, grain boundary, and electrode, regions. Generally, ionic conductivity only arises at the nominal oxygen deficiency composition of BNT based ceramics. Although large current leakage can exist in the BNT ferroelectrics, they overall display an insulative nature and dominate the electronic conductive contribution, and only a large main arc can be identified in the Nyquist plots. In this work, A-site bivalent doped Bi0.49x(SrBa)xNa0.5TiO3-delta and Bi0.49-x(SrCa)xNa0.5TiO3-delta ceramics ranging from oxygen deficiency to excess are investigated. However, anomalous ionic conductive characteristics are achieved at nominal oxygen excess composition. Herein, the polarization and conductive mechanisms are discussed to elucidate the effect of compositions and their phase and microstructure on the AC impedance, dielectric, and ferroelectric performances. The inhomogeneous distribution of oxygen vacancies, resulting from element segregation or distorted phases in the respective electroactive domains, is a crucial issue in the design of BNT based dielectrics or ionic conductors.

Automated summary

This article investigates the influence of A-site doping on Bi0.5Na0.5TiO3 (BNT) ferroelectric materials and finds that ionic conductivity can be achieved through doping and nonstoichiometry. The study also reveals that different dielectric responses can be used to probe the electrical inhomogeneities in the material. Additionally, the effect of composition, phase, and microstructure on AC impedance, dielectric, and ferroelectric performances is discussed.