Ionic conductivity of undoped BaTiO3−δ with electron transfer suppressed

Ionic conductivity has been directly measured on “undoped” BaTiO3−δ over a temperature range of 550 to 1000 °C with the aid of a modified electron-blocking cell. The modified cell could eliminate or greatly suppress or circumvent the haunting annoying artifacts associated with gas leak, reaction of a sample with an electron-blocking electrode or sealing glass, and large interfacial resistances in a conventional two-probe electron-blocking cell. The ionic conductivity of undoped BaTiO3−δ in the stoichiometric regime (δ≈0) may best be represented depending on temperature range as: σ ion / Scm − 1 = ( 6.6 × 10 5 / T ) exp ( − 1.58 eV / k ⁢ T ) for T ≥ 1073 K ; σ ion / Scm − 1 = ( 1.20 × 10 7 / T ) exp ( − 1.83 eV / k ⁢ T ) for T < 1073 K . indicated that association (with an association enthalpy of 0.25 eV) occurs between carrier oxygen vacancies and the charge compensating acceptor species, whether extrinsic or intrinsic, at temperatures below 1073 K. The higher temperature result is in good agreement with those obtained indirectly from the identical quality specimens. The chemical diffusivity has been determined from the temporal change of the cell voltage under a galvanostatic condition and is also in satisfactory agreement with the earlier study.