Preparation And Study On The Ion Doping Modification Of BiFeO₃ Nanoparticles

BiFeO₃ is a kind of single phase multiferroic material that simultaneously exhibits ferroelectric and magnetic orderings at room temperature.Due to their potential applications in the multifunctional devices,Bi Fe O₃ has attracted extensive studies in recent years.In addition,Bi FeO₃ has been recognized as a visible light-driven photocatalyst because of its suitable band gap and excellent chemical stability.Considering the properties of Bi FeO₃ depends on the particle size and morphology,the fabrication of BiFeO₃ nanoparticles and nanowires has caught much attention.Moreover,appropriate ionic doping is an effective way to modify the physical property of Bi FeO₃.In this thesis work,we synthesized Bi₁-_xPd_xFeO₃,Bi_0.9-_xBa_0.1Rb_x FeO₃ and Bi_0.98Na_0.02Fe₁-_xRu_xO₃ nanoparticles using a facial sol-gel method,and studied the effect of element substitution on its multiferroic and optical properties.First,we selected aliovalent Pd²⁺ions as dopants to substitute Bi³⁺ions and prepared Bi₁-_xPd_x FeO₃?x?28?0,0.005,0.01,0.015?nanoparticles through a sol-gel method.Weak ferromagnetism was observed in the samples at room temperature.The oxygen vacancy concentration is increased with the increase of Pd content.However,with increasing Pd content,the optical band gap of Bi₁-_xPd_xFeO₃ first increases for x?28?0.005 and then decreases for x?28?0.01 and 0.015,respectively.In order to explain this behavior,a phenomenological qualitative model based on the fluctuation of Fe-O-Fe bond angle and the concentration of oxygen vacancy was proposed.Second,we selected alkali metal Ba²⁺ions and univalent Rb¹⁺as dopants to substitute Bi³⁺ions of BiFe O₃,and prepared Bi_0.9-_xBa_0.1Rb_x FeO₃?x?28?0,0.01,0.02?nanoparticles via a sol-gel route.X-ray photoelectron spectroscopy?XPS?analysis indicated that both oxygen vacancy content and leakage current were increased with the increase of Rb content.However,the band gap remains unchanged with Rb substitution.To explain this phenomenon,the combined effects of oxygen vacancy and Fe-O-Fe bond angle were analyzed carefully.Additionally,the optical band gap is narrowed relatively??2.18 eV?,indicating the possible applications as visible-light photocatalytic materials.Finally,alkali metal Na¹⁺ions and tetravalent Ru⁴⁺were chosen as dopants to substitute Bi³⁺ions and Fe³⁺ions of BiFeO₃,respectively,and synthesized Bi_0.98Na_0.02Fe₁-_xRu_xO₃?x?28?0,0.01,0.02?nanoparticles via a sol-gel method.The oxygen vacancy concentration and leakage current density are increased with the increase of Ru content.However,the optical band gap was narrowed gradually in our samples.To better understand this abnormal optical property,the effect of bandwidth was analyzed based on the change of Fe-O bond length and Fe-O-Fe bond angle.The magnetization was increased with Ru substitution.In addition,an exchange bias phenomenon was observed at room temperature,which was explained by introducing a core-shell structure model.