Effects of excess Bi on structure and electrical properties of BiFeO₃ thin films deposited on indium tin oxide substrate using sol–gel method

As a kind of potential unleaded multiferroic material, BiFeO₃ (BFO) is expected to be used instead of Pb(Zr,Ti)O₃ in high density ferroelectric random access memories. Bi_1+xFeO₃ (x = 0, 5, 10, 15 and 30 %) thin films deposited on indium tin oxide/glass substrate were successfully fabricated using sol–gel method, spin coating and layer by layer technique. The XRD and SEM analysis indicated that the orientation of BFO thin films is sensitive to the content of excess bismuth. Both sense surface and suppression of impurity phases were realized in the BFO_x=10% thin films. Adding appropriately excess Bi can cover the volatilization of Bi₂O₃ during the thermal treatment. Leakage current density and P–E hysteresis loop demonstrate that x = 10 % is the best excess Bi content. BFO_x=10% thin films has a minimum current density of 7.8 × 10⁻⁹A/cm² at applied electric field of 600 kV/cm, a maximum remnant polarization 71.18 μC/cm² with a coercive field of 412.52 kV/cm at measured electric field value of 1213 kV/cm, and a largest dielectric constant 208 with a relatively lower dielectric loss of 0.042 at applied frequency of 10⁵ Hz, of which the current conduction mechanisms are Ohmic conduction and grain boundary limited conduction.