Improved ferroelectric properties and band-gap tuning in BiFeO3 films via substitution of Mn
Multiferroic BiFe1−xMnxO3 (x = 0, 0.04, 0.08, 0.12) films have been prepared on Pt/Ti/SiO2/Si and ITO/glass substrates via the solution-gelation technique. The impacts of Mn doping of BFO thin films on the structure, morphology, leakage current, ferroelectric properties and optical band gap have been systematic investigated. From the XRD patterns, all samples match well with the perovskite structure without an impurity phase and the thin films exhibit dense and smooth microstructure. A leakage current density of 1.10 × 10−6 A cm−2 which is about four orders of magnitude lower than that of pure BiFeO3 was observed for the 8% Mn doped BFO thin film at an external electric field <150 kV cm−1. An increase in the remnant polarization with Mn substitution was observed, with a maximum value of ∼19 μC cm−2 for the 8% Mn-substituted film. Moreover, optical absorption spectra indicate that the doping of Mn has an effect on the energy band structure. Compared with pure BiFeO3, Mn doped thin films present an intense red shift as shown in the UV-visible diffuse absorption together with the decreased direct and indirect optical band gaps. In addition, this work gives insight into the relationship between ferroelectric remnant polarization and band-gap and finds that the optical band gap decreases with the increase of residual polarization.