Effect of acceptor concentration on the bulk electrical conduction in acceptor (Mg)-doped BaTiO₃

Bulk electrical conductivity of acceptor (Mg)-doped BaTiO₃ ceramics were evaluated via an impedance spectroscopy analysis for materials with Mg concentrations up to 0.6 mol % and over a temperature range of 120-540 °C. At high temperatures beyond 320 °C, the activation energies of the bulk electrical conduction (E_σ) slightly decreased from 1.2 to ∼1.0 eV with an increase in the Mg concentration. However, in the low temperature range below 320 °C, there is a continuous decreased from 1.2 eV and then this saturated to ∼0.4 eV with the increase in Mg concentration. The calculated bulk conductivities based on a defect chemistry model explains conductivity for temperatures above 320 °C. The model demonstrates a predominant electronic conduction in the low concentration range below 0.1 mol % Mg and mixed conduction with ionic and electronic carriers in the intermediate and in high acceptor concentration range of 0.2-0.6 mol % Mg. However, the decrease in E_σ with the increase in Mg concentration in the low temperature range could not be explained by the defect chemical model. Such deviation however could be explained by a transition to hopping conduction between ionized acceptor (Mg ^″ _Ti) and neutral or hole-trapped acceptor (Mg ^× _Ti) with the increase in Mg concentration in the low temperature range.