Colossal dielectric permittivity in (Al plus Nb) co-doped Ba0.4Sr0.6TiO3 ceramics

Stimulated by the outstanding colossal permittivity behavior achieved in trivalent and pentavalent cations co-doped rutile TiO2 ceramics, the co-doping effects on the dielectric behavior of Ba0.4Sr0.6TiO3 ceramics were further explored. In this work, (Al + Nb) co-doped Ba0.4Sr0.6TiO3 ceramics were synthesized via a standard solid state ceramic route. The structural evolution was analyzed using X-ray diffraction patterns and Raman spectra. Dense microstructures with no apparent change of grain morphology were observed from the scanning electron microscopy. A huge enhancement of dielectric permittivity was obtained with 1 mol% (Al + Nb) doping and excellent dielectric performances (epsilon(r) similar to 20,000, tan delta similar to 0.06 at 1 kHz) were achieved after further heat treatment. The formation of electron pinned defect dipoles localized in grains may account for the optimization of dielectric behaviors and the corresponding chemical valence states were confirmed from the XPS results.