Hydrothermal Synthesis Of BiFeAO₃?A=Zn,Ga? Powders: Local Electronic Structure Study

BiFeO₃ is known as hopeful multiferroic materials,because of its antiferromagnetic behavior with Néel temperature of 380 Co and Curie temperature of 810 Co.However,there are several issues in BiFeO₃ have to be solved.The big leakage of current is the most disadvantages due to a few ofFe2+ ions and oxygen vacancies existing.At the same time,it is hard to prepare pure BiFeO₃ owing to the thermodynamic instability with the high temperature.The secondary phases of Bi2Fe4O9 and Bi25FeO40 are always generated in the short time.Until now,several researches have been done by the different ways to overcome the disadvantages of BiFeO₃.In another words,substitution by divalent or rare-earth ions at A-B-site of BiFeO₃?viz.,Bi-site andFe-site?in which the improvement in the multiferroic properties is obtained effectively.In this paper,we have chosen Zn2+ and Ga3+ ions as doping element and studied the BiFe_1-xAxO₃?A = 0,0.025,0.05,0.1 and 0.15?compounds.This compound BiFe_1-xAxO₃ was prepared by hydrothermal route.In order to investigate the local electronic structure and valance states ofFe and Bi ions,we usedFe K-edge and BiL₃-edge X-ray absorption fine structure spectroscopy test for the BiFe_1-xAxO₃ compounds.In addition,the effect of Zn2+ and Ga3+ doping on structural,morphological,optical and magnetic properties was studied.The following main results were obtained:1.Multiferroic compounds BiFe_1-xZnxO₃ with 0 ? x ? 0.1 were prepared using the hydrothermal route.Structural studies were done by X-ray diffraction,which revealed that samples belong to rhombohedral perovskite space group R3 c.Scanning electron microscopy showed that the decreased slightly in average grain size with increasing Zn content.TheFe K-edge and BiL₃-edge X-ray absorption fine structure spectra measurement indicated that theFe and Bi ions retained its +3 valence states.On the other hand,the local electronic structure of the center atoms ofFe and Bi were modified by Zn substitution.Fourier transform infrared measurement showed that the characteristic vibrations of the achieved BiFe_1-xZnx O₃ compounds.Magnetic hysteresis loop analysis showed maximum Mr for the x = 0.025.This enhancement magnetization was stems from the anti-ferromagnetic interaction ofFe3+-O-Zn2+.2.The compounds of BiFe_1-xGa_xO₃ with 0 ? x ? 0.15 were synthesized by the hydrothermal method.X-ray diffraction analysis revealed that with Ga doping on the B-site of BiFeO₃ leads to in a structural transition from rhombohedral?R3c space group?to orthorhombic?Pbnm space group?symmetry.The Scanning electron microscope measurement showed grain size reduction of Ga doped BiFeO₃ compared with un-doped BiFeO₃.The X-ray absorption near-edge structure spectra revealed that theFe K and BiL₃-edge absorption spectra shifted to higher energy site with increasing Ga content.An X-ray absorption near-edge structure spectrum also revealed that Ga substitution can affect the local electronic structures of Bi andFe atoms in BiFe_1-xGa_x O₃ samples.In Fourier transform infrared spectra,the obvious change in transmission band implies the evidence for structural transition from rhombohedral to orthorhombic with the Ga substitution.The magnetization hysteresis measurement indicated that BiFeO₃ is transformed from antiferromagnetic to weak ferromagnetic by Ga substitution.The enhancement of the weak ferromagnetism primarily results inFe3+-O2--Ga3+ exchange interaction.