Colossal dielectric constant of NaNbO3 doped BaTiO3 ceramics

BaTiO3 ceramics doped with 0.40 mol% NaNbO3 were prepared using a traditional approach by sintering at temperature of 1250 degrees C to 1290 degrees C. The prepared ceramics was characterized by very good dielectric properties, such as high dielectric constant (1.5 x 10(5)), low dielectric loss (0.1), and good dielectric temperature stability in the 40 degrees C to 100 degrees C range for the sample sintered below 1270 degrees C. The dielectric characteristics obtained with XPS confirmed that Ti4+ ions remain in the state without any change. The huge increase in dielectric constant in NaNbO3 doped BaTiO3 samples occurs when large amount of Ba2+ ions are excited to a high energy bound state of Ba2+ - e or Ba+ to create electron hopping conduction. For samples with the content of NaNbO3 higher than 0.40 mol%, or sintering temperature higher than 1280 degrees C, compensation effect is dominated by cation vacancies with sharply decreasing dielectric constant and increased dielectric loss. The polaron effect is used to explain the relevant mechanism of giant dielectric constant appearing in the ferroelectric phase.