Electrical conductivity of hexagonal Ba(Ti0.94Ga0.06)O2.97 ceramics

Impedance spectroscopy is used to estimate the bulk conductivity, σb, of hexagonal (6H)-Ba(Ti0.94Ga0.06)O2.97 ceramics in air, N2 and 5%H2/95%N2 between 400 and 1000 °C. Isothermal plots of log σb vs log pO2 in the temperature range between 700 and 1000 °C show the presence of a p–n transition with slopes of ∼−1/4 and +1/4 in the n- and p-type regions indicating that the conductivity obeys the ‘extrinsic’ model proposed by Smyth and co-workers for undoped and acceptor-doped cubic BaTiO3-based materials [J. Am. Ceram. Soc. 64 (1981) 556; J. Am. Ceram. Soc. 65 (1982) 167]. The activation energy Ea for oxidation in the p-type region to produce free holes is similar for 6H-Ba(Ti0.94Ga0.06)O2.97 and cubic BaTiO3-based ceramics with an estimated value from σb data of ∼0.8 eV. The band gap for 6H-Ba(Ti0.94Ga0.06)O2.97 ceramics is ∼3.2 eV.