Electrical properties of bismuth ferrites:Bi2Fe4O9 and Bi25FeO39

Bi2Fe4O9 was prepared by solid-state reaction and the electrical properties measured by impedance spectroscopy. After annealing in O2 at 900 °C, Bi2Fe4O9 is an electrically-homogeneous insulator. Its high frequency permittivity is constant (∼14.1) over the temperature range 300–400 °C and shows no evidence of incipient ferroelectricity at lower temperatures. On annealing in N2 at 900 °C, the pellets gradually decompose.

Bi25FeO39 was prepared by both solid-state reaction and mechanosynthesis. It showed a modest amount of mixed conduction of both oxide ions and holes. Impedance analysis showed a complex response that best fitted an equivalent circuit consisting of a parallel combination of long-range conduction and short range dielectric relaxation elements.

The electrical conductivity of both Bi2Fe4O9 and Bi25FeO39 is less than that of BiFeO3 prepared by solid-state reaction, which indicates that any leakage conductivity of BiFeO3 is not due to the possible presence of small amounts of these secondary phases.