Mossbauer Studies Of BiFeO₃ Multiferroic Materials Doped With Eu,Zn And Sr

Bismuth ferrite is one of the few multiferroic materials that exhibits ferroelectricity and ferromagnetism at room temperature.BiFeO₃is one of the most attractive.Although BiFeO₃ has excellent performance,its application potential has not yet been fully exploited,because there are some issues that hinder its applicability,for instance,the high leakage current,weak ferroelectric behaviour and small remnant polarization.Moreover,the presence of large spatial spin cycloid structure with a period of 62nm means loss of macroscopic magnetization and suppression of linear magnetoelectric effect.Therefore,breaking the spatially modulated spin structure in BiFeO₃ is the key to releasing ferromagnetism and exhibiting magnetoelectric effects.Among numerous methods for enhancing its properties,the most studied one is the ion-doping approach.BiFeO₃ can be modified by using transition elements,rare earth elements or alkaline earth metal elements to enhance the ferromagnetism and ferroelectricity.The purpose of this research is to improve the multiferroic of BiFeO₃ by ion-doping approach.The doping elements we use are Eu,Zn and Sr.In this study,XRD and Mossbauer spectroscopy were used to characterize the prepared bismuth ferrite samples.?1?Bi_1-xEu_xFeO₃?x=0,0.10?was prepared by a rapid sintering method.Both synthetic samples contained a small amount of impurity Bi₂Fe₄O₉.XRD and Mossbauer spectroscopy showed that the content of impurity in Bi_0.9Eu_0.1FeO₃ increased slightly compared with the undoped samples.And there was a slight crystal distortion in Bi_0.9Eu_0.1FeO₃.Mossbauer spectroscopy studies found that only Fe³⁺exists in the undoped BiFeO₃.While the oxygen vacancies due to substitution of different valences ions make Fe²⁺and Fe³⁺coexist in Bi_0.9Eu_0.1FeO₃.The internal magnetic field H_int increased from 472kOe of BiFeO₃ to 479kOe of Bi_0.9Eu_0.1FeO₃.?2?BiFe_1-xZn_xO₃?x=0,0.05,0.10,0.15,0.20,0.25?,Bi_1-xSr_xFeO₃?x=0,0.05,0.10,0.15?and Bi_1-xSr_xFe_1-xZn_xO₃?x=0,0.05,0.10,0.15?were also successfully prepared using the sol-gel auto-combustion method.The replacement of iron ions by zinc ions makes the structure of bismuth ferrite more unstable and the phases more complex.The Mossbauer spectra?MS?of BiFe_1-xZn_xO₃?x=0,0.05,0.10,0.15?are fitted with a sextet and a doublet,but BiFe_1-xZn_xO₃?x=0.20,0.25?are fitted with only one paramagnetic doublet.This doublet is attributed to the Bi₂₅FeO₄₀ phase.There could be two probable causes for the absence of sextet:one is that there has been already a phase transition from a magnetic phase to a non-magnetic phase when Zn concentration are more than 20%.Another is that Zn ion has successfully been substituted for Fe,and then destroy the magnetism of samples and magnetic sextet.The introduction of Sr²⁺can inhibit the formation of impurity phases during the synthesis of BiFeO₃.Bi_1-xSr_xFeO₃?x=0,0.05,0.10,0.15?are fitted with a sextet and a doublet.The possible reason for the presence of Fe²⁺in the sample is that the charge compensation promotes the formation of oxygen vacancies.XRD shows that there is a new impurity(Bi₂O_2.3)in Bi_0.85Sr_0.15Fe_0.85Zn_0.15O₃.Mossbauer study shows that there has been a new impurity in Bi_0.90Sr_0.10Fe_0.90Zn_0.10O₃.There are some Fe³⁺transformed into Fe²⁺and Fe⁴⁺in Bi_0.95Sr_0.05Fe_0.95Zn_0.05O₃.This disproportionation is related to the oxygen vacancies introduced by ion-doping.?3?The introduction of Sr²⁺can inhibit the formation of impurity phase during the synthesis of bismuth ferrite.The Mossbauer spectra of Bi_1-xSr_xFeO₃?x=0,0.05,0.10,0.15?are fitted from a sextet and a doublet.The possible reason for the presence of Fe²⁺in the sample is that charge compensation promotes the formation of oxygen vacancies.?4?XRD shows that Bi_0.85Sr_0.15Fe_0.85Zn_0.15O₃ has added a new impurity Bi₂O_2.3.Mossbauer spectrum studies show that a new impurity has been generated in Bi_0.90Sr_0.10Fe_0.90Zn_0.10O₃.Fe³⁺is transformed into Fe²⁺in BSFO,which is related to the oxygen vacancy introduced after doping.