Colossal permittivity in BaTiO3-0.5wt%Na0.5Ba0.5TiO3 ceramics with high insulation resistivity induced by reducing atmosphere

The donor-acceptor co-doping grain-fine BaTiO3-0.5wt%Na0.5Ba0.5TiO3 (BT-0.5wt%NBT) ceramics are obtained by conventional solid-state reaction method and sintered in different atmospheres. The dielectric properties are sensitively influenced by the sintering atmosphere, which the colossal permittivity can be activated and increased by enhanced atmospheric reducibility with the increase of H-2 content. However, the excessive H-2 content can make a significant deterioration in dielectric loss and insulation resistivity. The impedance spectra, XPS and EPR measurements indicate that sintering atmosphere can effectively regulate the concentration and distribution of charge carriers (delocalized electrons, oxygen vacancies and defects), which induce the interfacial polarization and hopping polarization. When sintered in 0.1% H-2/N-2, the sample possesses a relatively good comprehensive performance with colossal permittivity (epsilon(gamma) > 4 x 10(4)), ultra-low dielectric loss (tan delta =0.0218) and high insulation resistivity (p(nu) > 10(11)Omega.cm), which related to the moderate values of resistance and conduction activation energy for the grain boundaries.