Preparation And Co-Doping Of BiFeO₃ Cermacis And Flim By Sol-Gel Process

Multiferroics are materials possessing a spontaneous polarization and magnetization.Of particular interest is BiFeO₃,which exhibits the coexistence of ferroelectric and antiferromagnetic orders up to quite high temperature(T_c=1103 K, T_N=673 K).Recently,it has been reported that both epitaxial and polycrystalline BiFeO₃ thin films with reasonably high resistivity show large polarizations.For example,(001)oriented thin films BiFeO₃ display a polarization of 90μC/cm², comparable to the very popular ferroelectrics system,PbZr_xTi_1-xO₃(PZT),which provides an altemative choice of a Pb-free ferro/piezoelectric material.BiFeO₃ presents opportunities for potential applications in information storage and spintronics.In this paper,we studied the sol-gel method of BiFe_1-xCo_xO₃ ceramics and BiFe_1-xCo_xO₃ film.The main results and conclusions in this thesis can be summarized as following:1.BiFeO₃ gel is prepared by sol-gel method.Then BiFeO₃ ceramics is produced by rapid annealing process.Compared to the traditional solid-state sintering process, The method is more simple and convenient for preparation of pure BiFeO₃ ceramics. The structural,ferroelectrical and ferromagnetic properties of the prepared single-phase BiFeO₃ ceramics were investigated.2.The BiFe_1-xCo_xO₃ ceramics has been successfully prepared by sol-gel method. The structure and properties BiFeO₃ ceramics with Co substitution also have studied. Rhombohedral phase was confirmed via x-ray diffraction analysis and no impure phases were observed in BiFeO₃ ceramics.For BiFe_1-xCo_xO₃ ceramics,when x is over 0,minor Bi₂₅FeO₄₀ were observed.The ferroelectrical properties of the BiFe_1-xCo_xO₃ ceramics were investigated.3.BiFeO₃ films were deposited on indium tin oxide(ITO)/glass substrates at different annealing temperatures from 500℃to 600℃by sol-gel process.Phase pure(110) preferred oriented BiFeO₃ films were prepared at annealing temperature of 500℃and 550℃.Randomly oriented BiFeO₃ films were prepared at annealing temperature of 600℃,which have minor Bi₂Fe₄O₉.The remnant polarizations of the BiFeO₃ film is 0.86μC/cm² under annealing temperatures of 500℃.For BiFeO₃ films under annealing temperatures of 550℃and 600℃,standard polarization hysteresis loops were not measured successfully because of large leakage current of the sample. The magnetic properties of the BiFeO₃ film under annealing temperatures of 500℃was investigated.4.The BiFe_1-xCo_xO₃(x=0.00 to 0.15)films deposited on ITO/glass substrates were annealed at 500℃,which show(110) preferred orientation.The film with x=0.15 show Bi₂O₃ and Fe₂O₃.The crystal grains were observed finer and the compaction of the films increased through the substitution and which caused higher measuring fields.The remnant polarization under different measuring electric fields for the films with x=0,0.05,0.1 and 0.15 are 0.86μC/cm²,1.72μC/cm²,1.74μC/cm²å’Œ3.54μC/cm².The magnetization results indicate that the magnetization of BiFe_0.9Co_0.1O₃ film is much larger than that of BiFeO₃ film.