Electrical Properties of Ca-Doped BiFeO₃ Ceramics: From p-Type Semiconduction to Oxide-Ion Conduction

The conductivity of Ca-doped BiFeO 3 ceramics varies by many orders of magnitude, depending on the oxygen partial pressure during processing. Bi 1– x Ca x FeO 3–( x /2)+δ ceramics are mixed oxide ion/electron conductors at 800 °C, but the electron conduction can be suppressed; when sintered and cooled in N 2 from 800 °C, they are oxide ion conductors with activation energy ∼0.82–1.04 eV and conductivity ∼1 × 10 –5 S cm –1 at 300 °C, comparable to that of 8 mol % yttria-stabilized zirconia. When heated in O 2 at 125 bar, however, they are mainly p -type semiconductors with conductivity ∼1 × 10 –3 –4 × 10 –5 S cm –1 at room temperature and activation energy ∼0.27–0.40 eV. The oxygen stoichiometry varies over the range 0 < δ < ∼0.016, depending on processing conditions. The semiconductivity is attributed to mixed valence Fe with < ∼3.2% Fe 4+ .