Dielectric properties of Y2O3 donor-doped Ba0.8Sr0.2TiO3 ceramics

• 0.27Y2O3-BST ceramics is of dielectric constant>110,000 and loss<0.15 in −40–140 °C.
• Unipolar charge in semiconductive grain plays a major contribution.
• XPS result confirms a state of e-Ba2+, the site responsible for electron hopping.

Ba0.8Sr0.2TiO3 ceramics doped with Y2O3 from 0 to 0.10 mol% exhibit normal ferroelectric phase transition, while the ceramics doped with Y2O3 from 0.20 to 0.30 mol% show a giant dielectric constant behavior with loss less than 0.15 at 1 kHz from −40 °C to 140 °C, which is suggested due to semiconductive grain and the Maxwell–Wagner effect by structure disordering in grain boundary. The analyses of unipolar charge for the semiconductive grain indicate three kinds of dielectric processes: thermally stimulated process of unipolar hopping, dispersion process of dielectric constant with frequency, and phase transition process accompanied with disappearance of giant dielectric constant in cubic phase. The XPS results confirm that some of the barium ions are in low energy state to form e-Ba2+ and to provide hopping sites for electrons. The ceramics doped with Y2O3 from 0.50 to 0.75 mol% recover the normal ferroelectricity. The possible mechanics are relevant to binding effect of cation vacancies on electrons.