Low Temperature Ionic Conductivity of an Acceptor-Doped Perovskite: II. Impedance of Single-Crystal BaTiO3

Low temperature conductivity mechanisms were identified in acceptor-doped BaTiO3 single crystals equilibrated and quenched from high temperature under different oxygen partial pressures. A range of acceptor ionization states were quenched into samples doped with manganese or iron. Using an appropriate equivalent circuit to interpret impedance spectroscopy data, room temperature conductivity mechanisms in the single crystal samples were identified, and the permittivity/temperature dependence was also shown to be self-consistent with the nature of a first-order ferroelectric phase transition. The primary, low temperature, conduction mechanism in acceptor-doped BaTiO3 was determined to be dominated by the migration of oxygen vacancies. The activation energy for oxygen vacancy migration was experimentally determined to have a value of nearly 0.7 eV. This activation energy represents an intrinsic value for vacancy hopping and confirms our previous work that revealed minimal interaction between acceptor dopants and oxygen vacancies in BaTiO3 in contrast to the well-documented evidence of defect association in SrTiO3.