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 °C to 1290 °C. The prepared ceramics was characterized by very good dielectric properties, such as high dielectric constant (1.5 × 10⁵), low dielectric loss (0.1), and good dielectric temperature stability in the −40 °C to 100 °C range for the sample sintered below 1270 °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 °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.