Impedance spectroscopy studies of bulk electrical conduction in A-site acceptor (K)-doped BaTiO₃

BaTiO₃ ceramics with different acceptor concentrations of potassium at A-site Ba_1-x K _x TiO_3-x/2 (BKT) were prepared by solid-state processes. The solution limit of potassium in BKT is determined to be 1 mol%. Furthermore, electrical conduction behaviours were investigated in the temperature range of 300-800 C by analysing impedance spectra and were found extremely depending on processing and measurement conditions. When annealed at 800 C and measured in an atmosphere of dry N ₂, BKT is a mixed oxide ion/electron conductor and its ionic transference number decreases with increasing temperature. But when annealed at 800 C and measured in an atmosphere of dry air and O₂, BKT is a p-type semiconductor with a transition from a trapped holes' conduction to activated holes' conduction as temperature increases. On exposure of BKT to an atmosphere of wet N₂, BKT is a proton conductor in the temperature of 300-550 C; however, it reverts to a p-type semiconductor above 550 C as water is lost from the sample.