Multiferroic and optical studies on the effects of Ba²⁺ ions in BiFeO₃ nanoparticles

Single phase Ba²⁺ ions doped BiFeO₃ nanoparticles have been successfully synthesized with varied concentration (0.0 ≤ x ≤ 0.2) using the auto combustion method. The structural properties of Bi_1−xBa_xFeO₃ (x-0.0, 0.1 and 0.2) nanoparticles reveal the formation of highly crystalline rhombohedrally distorted perovskites without undergoing any structural phase transformation analyzed via Rietveld refinement. The Pauling’s equation confirmed that Ba²⁺ ions doped BiFeO₃ ceramics have much more negative enthalpy of formation (ΔH _f ) than undoped BiFeO₃. A reduction of particle size has been observed up to x = 0.1 and then after increases, whereas the band gap shows a reverse trend. Magnetic and ferroelectric transition temperatures are found to be slightly shifted towards the lower temperature up to x = 0.1 and then higher temperature side which could be attributed to the particle size effect. Ba²⁺ doped BiFeO₃ ceramic with concentration x = 0.2 exhibit larger magnetization as compared to others at room temperature, but these magnetization curves were not saturated. Remnant polarization is found to decrease from 7.693 to 5.141 µC/cm² along with the doping of Ba²⁺ ions. The on-site d-to-d crystal field excitations of Fe³⁺ ions associated with ⁶A_1g–⁴T_1g or ⁶A_1g–⁴T_2g electronic energy levels, Fe₁3d–Fe₂3d inter-site electron transfer and inter-atomic O 2p–Fe 3d electronic energy levels are observed by the means of absorption spectroscopy.