Greatly reduced leakage current and conduction mechanism in aliovalent-ion-doped BiFeO3

Transport properties of aliovalent-ion-doped ${\mathrm{BiFeO}}_3$ (BFO) thin films have been studied in order to identify the cause of high leakage currents. Doping of $2\text{at.}\%$ ${\mathrm{Ti}}^{4+}$ ions increased the dc resistivity by more than three orders of magnitude. In contrast, doping of $2+$ ions such as ${\mathrm{Ni}}^{2+}$ reduced the dc resistivity by two orders of magnitude. Current–voltage $\left(I–V\right)$ characteristics indicated that the main conduction mechanism for pure and ${\mathrm{Ni}}^{2+}$ doped BFO was space charge limited, which was associated with the free-carriers trapped by the oxygen vacancies, whereas in the ${\mathrm{Ti}}^{4+}$ doped BFO, field-assisted ionic conduction was dominant.