Field-enhanced bulk conductivity and resistive-switching in Ca-doped BiFeO3 ceramics

The bulk conductivity at room temperature of Ca-doped BiFeO3 ceramics is p-type and increases reversibly by up to 3 orders of magnitude under the influence of a small dc bias voltage in the range ∼3 to 20 V mm(-1). The effect occurs in both grain and grain boundary regions, is isotropic and does not involve creation of filamentary conduction pathways. It is proposed that, by means of capacitive charging and internal ionisation processes under the action of a dc bias, hole creation leads to a more conductive excited state. This gradually returns to the ground state when the dc bias is removed and the holes recombine with electrons trapped at the sample surface. The holes are believed to be created on oxygen, as O(-) ions.