Ionic conductivity was directly measured in undoped BaTiO3−δ, at 550 to 1000C, with the aid of a modified electron-blocking cell. The modified cell could eliminate or greatly suppress or circumvent the haunting annoying artefacts associated with gas leak, reaction of a sample with an electron-blocking electrode or sealing glass, and large interfacial resistances in a conventional 2-probe electron-blocking cell. The ionic conductivity of undoped BaTiO3−δ in the stoichiometric regime (δ ≈ 0) could best be represented, depending on temperature range, as:

T > 1073K:     σ (S/cm) = (6.6 x 105)/T exp[-1.58(eV)/kT]

T < 1073K:     σ (S/cm) = (1.20 x 107)/T exp[-1.83(eV)/kT]

It was indicated that association (with an association enthalpy of 0.25eV) occurred between carrier O vacancies and the charge compensating acceptor species, whether extrinsic or intrinsic, below 1073K. The higher temperature result was in good agreement with those obtained indirectly from the identical quality specimens. The chemical diffusivity was determined from the temporal change of the cell voltage under a galvanostatic condition and was also in satisfactory agreement with the earlier study.

Ionic Conductivity of Undoped BaTiO3−δ with Electron Transfer Suppressed. L.X.He, D.K.Lee, H.I.Yoo, M.Martin: Solid State Ionics, 176[9-10], 2005, 929-35