Study On Preparation And Properties Of BaTiO₃-BiFeO₃-LaFeO₃ Ternary Multiferroics Materials

With the development of science and technology,there are increasing requirements of miniaturization,which requires the development of new materials with two or more than two kinds of functions.Multiferroic material is one of the typical representative materials.There are two or more than two kinds of ferroics properties,namely,ferroelectric,ferromagnetic or iron elasticity.There is a coupling effect between the different ferroics properties of the material.Up to now,the research on the multiferroic materials can be seen that there are only few monophasic materials in nature and laboratory.BiFeO3(BFO)is the only one single-phase multiferroic material which presents a ferroelectric and weak ferromagnetic under the condition of room temperature,while ferroelectric Curie(TC)1123 K and antiferromagnetic Neel temperature(TN)583 K,so it has a great application prospect.However,there are still two obstacles about BFO in the present practical application.On the one hand,the ferroelectricity of BFO is not strong and exists serious leakage,especially Fe valence change and the oxygen vacancy in the preparation process(bismuth can volatile easily and to produce a impurity phase of Bi2Fe4O9 and Bi25FeO40),because of this,cause the low resistivity and limit its application in piezoelectric or magnetoelectric functional materials;On the other hand the spiral magnetic structure of BFO showed very weak ferromagnetic under the low magnetic field.These problems have a great relationship with the structure of BFO itself.How to design new materials based on BFO and develop new manufacturing methods is a challenging and important research topic in this field.This research is to design the ternary solid solution to improve multiferroic BFO,with ferroelectric BaTiO3(BTO)to form solid solution to improve its ferroelectricity,with magnetic LaFeO3(LFO)to form solid solution to improve the ferromagnetism.(1)The(1-x)BTO-xBFO powders were prepared by sol-gel method,and the suitable preparation technology was 750?,pH value was 6,citric acid content was 0.48 times of the metal cation.The(1-x)BTO-xBFO ceramics were prepared by the method of lamination burying method.The research shows that the ceramics are single phase at the temperature range of 1000-1300?,and with the increase of temperature,the crystallinity of the ceramic is higher and higher.By increasing the BFO concentration,it was not appeared the second phase,and the change of tetragonal to cubic phase exists at around x=0.04.XRD and TEM electron diffraction pattern proved this point,and at the same time the properties also has anomalies.At the sintering temperature of 1100? and the frequency of 1 kHz,the dielectric constant of x=0 was 1000,while,the dielectric constant of x=0.04 was increased to 3500,it was increased by 3.5 times.The remnant polarization 2Pr of x=0.01 was 0.436 ?C/cm2 while the 2Prof x=0.04 was 4,540 ?C/cm2,it was increased more than 10 times.With the increase of BFO components,the leakage current of(1-x)BTO-xBFO(x=0-0.07)ceramic has a minimum value 10-9-10-10 A/cm2 at x=0.02 and maximum value 10-4-10-6 A/cm2 at x=0.05.With the increase of BFO components,the magnetization of the product gradually increases.But even in the magnetic field of 10 kOe,the system is not saturated.At the magnetic field increased from 0 to 2000 Oe,the magnetoelectric coupling coefficient was stable.With the increase of frequency,the magnetoelectric coupling coefficient has been increased,with frequency increased to 100 kHz,the magnetoelectric coupling coefficient were increased to 85 mV/cm·Oe.(2)In the(1-x)[0.96BTO-0.04BFO]-xLFO(x=0.1-0.5)ternary solid solution system,using the same process conditions to prepare the required solid solution ceramics.With the increase of LFO components,the crystal structure of the system was still tetragonal.The average grain size of the binary solid solution was 4 ?m.but with the increase of LFO components,the average grain size was decreased to 1?m and a lot of pores.At the frequency of 1000 kHz,the dielectric constant of the ternary solid solution was stable at about 500,which were decreased compared to the binary solid solution.With the increase of LFO components,the leakage current was increases,and the maximum value is obtained at x=0.4,which is about 10-5-10-6 A/cm2.The leakage current of the ternary solid solution system is relatively large,and the effect of the composition on the ferroelectric property of the system is measured at low temperature.In the test temperature of-30?,with the increase of LFO content,the remnant polarization and saturation polarization of the ternary solid solution system was decreased,and the 2Pr has a maximum value 0.472 ?C/cm2 at x=0.1.With the increase of LFO content,the remnant magnetization and saturation magnetization of the ternary solid solution system was improved,and the remant magnetization has a maximum value 0.8 emu/g at x=0.4.At the magnetic field increased from 0 to 2000 Oe,the magnetoelectric coupling coefficient was stable between 40 and 60 mV/cm·Oe.With the increase of frequency,the magnetoelectric coupling coefficient has been increased,with frequency increased to 100 kHz,the magnetoelectric coupling coefficient were increased to 95 mV/cm·Oe.