Structure And Multiferroicity Of Bismuth Ferrite Based Ceramics Modified By Magnetic Element Replacement

Multiferroic materials have unique properties and great application value in multifunctional devices.In recent years,BiFeO₃ has become a research hotspot in the field of condensed matter physics and material science,and BiFeO₃ is the most important single-phase room temperature multiferroic material.In this paper,BiFeO₃based ceramics was taken as the research object,and the effects of magnetic elements on their structure and properties are systematically studied by introducing magnetic elements.The main conclusions are as follows.Firstly,Mn₂O₃ substituted 0.84BiFeO₃-0.06Sm FeO₃-0.1CaTi O₃ ceramics were prepared by standard solid state reaction sintering method.Structural refinement shows that all samples are rhombohedral R3c structure and have a small amount of Bi₂Fe₄O₉.With the increase of manganese substitution,the grain size decreases gradually.DSC analysis showed that the endothermic and exothermic peaks exhibit obvious thermal hysteresis behavior,indicating that it is a first-order ferroelectric transition.At the same time,an obvious dielectric anomaly was found at the phase transition temperature.The leakage current increases with the increase of manganese content,which can be attributed to the increase of oxygen vacancy.The magnetic properties of all samples were enhanced,and the best magnetic properties were obtained at x=0.03,M_r=51.9emu/mol.In addition,the magnetoelectric coupling performance is improved,and the linear magneto-electric coefficient exhibits a maximum value ofα_ME=0.38 m V/cm Oe when x=0.03.Therefore,the addition of Mn at the position of Femay destroy the spin cycloid structure and enhance the magnetoelectric coupling effect of BiFeO₃.Subsequently,Mn₂O₃ substituted Bi_0.88Sm_0.12Fe_1-xMn_xO₃ ceramics were studied.Bi_0.88Sm_0.12Fe_1-xMn_xO₃ ceramics were by rapid liquid phase sintering.XRD and TEM analysis showed that all samples have rhombic rhombohedral R3c structure,transition phase Pna2₁ and a small amount of orthorhombic phase Pbnm,in which R3c phase accounts for about 70%.DSC analysis showed that the substitution of Mn ions reduced T_N almost linearly.The dielectric constant increased with the increase of Mn ion substitution（ε′）and dielectric loss（tanδ）The addition of Mn ions increased the conductivity,and the hysteresis loop gradually became"round"with the increase of applied electric field When x=0.03,the maximum piezoelectric coefficient d₃₃=38.7p C/N,indicating that the addition of an appropriate amount of Mn ions can improve the electrical properties of BiFeO₃ based ceramics.The replacement of Mn enhanced the magnetism and obtained the maximum residual magnetization at x=0.05,M_r=28.4emu/mol.Therefore,the substitution of magnetic element Mn can improve the Multiferroicity of BiFeO₃ based ceramics.Finally,the structure and properties of Bi_0.88Sm_0.12Fe_0.97（M）_0.03O₃(M=Mn,Cr,Co,Mn_0.5Cr_0.5,Mn_0.5Co_0.5,Cr_0.5Co_0.5)ceramics modified by multiple magnetic ions were studied.XRD refinement results showed that all samples are rhombohedral R3c phase,transition phase Pna2₁ and a small amount of orthogonal phase orthorhombic Pbnm.The addition of Cr not only improves the dielectric constant,but also reduces the dielectric loss,and improve the dielectric properties of BiFeO₃ based ceramics.The ferroelectric properties of Mn_0.5Cr_0.5 sample are the best because the content of R3c/Pna21 two-phase coexistence region is the most.The piezoelectric coefficient of Mn_0.5Co_0.5 sample is the largest,d₃₃=41.0 p C/N,which showed that Mn/Co co-doping and Mn/Co co-doping can improve the electrical properties of BiFeO₃ based ceramics.The magnetic properties of Co substituted samples are significantly improved,and the maximum residual magnetization M_r=110.8 emu/mol,which may be the result of the large difference in ion radius between Co²⁺（0.74nm）and Fe³⁺（0.64nm）,the spin cycloid is suppressed,and there is a strong exchange coupling between spins.