Hole conduction and nonlinear current-voltage behavior in multiferroic lanthanum-substituted bismuth ferrite

Polycrystalline Bi_1-xLa_xFeO₃ (BLF, x = 0.05-0.2) were prepared by solid state reaction and followed by annealing in O₂, air and N₂. The electrical properties of BLF ceramics were investigated by impedance spectroscopy and it is found that the conduction is dominated by p-type conduction. The conductivity of samples varies by several orders of magnitude, depending on the oxygen partial pressure during the annealing process. Activation energy (E_a) increases from ∼0.5 eV for O₂/air-annealed samples to ∼0.9 eV for the N ₂-annealed samples, and E_a shows a slightly increase with the increment of La doping amount. Besides, all the samples exhibit nonlinear current (I)-voltage (V) characteristics, and the threshold field voltage is much higher for the N₂-annealed samples than for the O ₂-annealed samples. The nonlinear coefficient increases with the increase of oxygen partial pressure and temperature as well as the decrease of the La doping amount. The intrinsic electrostatic barrier at the domain walls rather than grain boundaries is responsible for the nonlinear behavior.