Charge Carriers and Time Dependent Currents in BaTiO3-Based Ceramic

The following items are treated for BaTiO3-based ceramic and multilayer ceramic (MLC) capacitors: type of charge carrier, mode of transport, and time dependence of conductivity during degradation. For a specific X7R-type ceramic, the charge carrier is verified to be the electron by several independent measurements. Seebeck voltages are negative; Galvanic voltages are zero; leakage currents are constant over long time periods; space charge limited currents are evident. The shapes of complex impedance plots depend on ceramic composition, indicating that grain boundary impedance may be present in some cases and not others. A quantitative model based on ionic movement is presented to account for leakage currents that increase exponentially with time. Evidence for ionic movement for specific Z5U capacitors is reported. Degradation can be reversed by reversing bias polarity or by storage under zero bias.