Effect of oxygen vacancy and A-site-deficiency on the dielectric performance of BNT-BT-BST relaxors

There is an urgent need for dielectrics to suit multitudinous burgeoning applications with high-temperature dielectric stability. Here the intrinsic defect and polarization mechanism are investigated in A-site-deficient 0.66(Bi0.5Na0.5)TiO3-0.06BaTiO3-0.28(BixSr1–3x/2▯x/2)TiO3 (BNT-BT-BST) relaxors where strontium vacancies (VSr′′) are designed to compensate the negative charge shortage when Sr2+ is substituted by Bi3+ (BiSr•). Incremental Bi3+ is conducive to the polarization in nano-regions at high temperatures resulting in an enhancement of the temperature stability of dielectric permittivity. It reveals a strong defect induced disorder accompanied with slightly increased dielectric loss due to the partial reduction of Ti4+. Furthermore, the existing oxygen vacancies confirmed by X-ray photoelectron and atmosphere dependent ac impedance spectroscopies are suppressed effectively when sintering at O2 for BNT-BT-BST to the benefit of maintaining stable dielectric properties. Remarkably high energy storage density and efficiency are achieved simultaneously under relatively low electric fields. This work not only provides promising candidates in Bi0.5Na0.5TiO3 (BNT) based relaxors but also demonstrates an effective route considering the importance of oxygen vacancies in the optimization for dielectric applications.