The ionic and electronic conductivities of nonstoichiometric BaTiO3 (undoped, Ca-doped, and Zr-doped BaTiO3-delta) ceramics were investigated through high temperature equilibrium conductivity (HiTEC) and in-situ impedance measurements at various equilibrium conditions with different oxygen partial pressures over a temperature range of 950-1050 degrees C. Contribution of mobile oxygen vacancies on the electrical conductivity has been determined by HiTEC measurement as a function of oxygen partial pressure; the electrical conductivity with mobile oxygen vacancies shows a broad transition from p-type to n-type, and thereby there is an increase of the minimum conductivity at the n-p transition point. Through combining in-situ impedance spectroscopy measurements with the HiTEC measurements, it was confirmed clearly that the mobile oxygen vacancy contributes to the total conductivity, and the oxides become mixed conductors around the n-p transition regime (minimum electronic conductivity regime). It was found that Warburg impedance can be observed at the condition of t(ion)/t(electronic) greater than or similar to 0.05 in the temperature range of 950-1050 degrees C and pO(2) range of 0.95-10(-16) atm. The ionic conductivity varied with the concentration of extrinsic oxygen vacancies and dopants, and the activation energy for mobility of oxygen vacancy in Ca-doped BaTiO3-delta was found to be 1.04 +/- 0.05 eV using the two techniques in a very good agreement. (C) 2013 Elsevier B.V. All rights reserved,