Bi deficiencies induced high permittivity in lead-free BNBT–BST high-temperature dielectrics

• A plateau of high permittivity ∼5000 is obtained in Bi deficient BNBT–BST ceramics.
• Neutral defect complexes between cation and oxygen vacancies play an important role.
• The dielectric properties are enhanced after the re-oxidation of the Bi deficient ceramics.

The electric and dielectric properties of (Bi0.5−yNa0.5)0.94−xBa0.06(Bi0.2Sr0.7□0.1)xTiO3 (BNBT–BST) ceramics, derived from the morphotropic phase boundary (MPB) of the parent matrix 0.94(Bi0.5Na0.5)TiO3–0.06BaTiO3 (BNT–BT), are studied. The pseudocubic structures are formed without apparent secondary phases for all the compositions. The Bi deficiency displays significant effect on the dielectric permittivity of BNBT–BST ceramics. A plateau of high permittivity ∼5000 in the temperature evolution is formed with small variation, indicating the potential use for the high-temperature dielectrics. The bulk conductivity, calculated from the complex impendence (Z′/Z″), is conducted to learn the influence of the oxygen vacancies on the dielectric response in different atmospheres. After the re-oxidation of the Bi deficient BNBT–BST ceramics, the operational temperature range is broadened with 10% variation in permittivity from 50 °C to 300 °C.