Study Of Multiferroic Properties Of BiFeO₃ Ceramics Prepared By Microwave Hydrothermal Mothod

The increasingly high demands of development of electronic information technology for miniaturization and multi-functional devices have made the dielectric material attracted widespread attention. Multiferroic material is a class of multifunctional materials which simultaneously possess ferroelectric, ferromagnetic, antiferromagnetic, ferroelastic property and could achieve the coupling between two or more these behaviors. Bi Fe O3(BFO) possesses ferroelectric and antiferromagnetic behavior at room temperature, the Curie temperature and Neel temperature of BFO are 830 oC and 370 oC which incite more and more research passion.In this work, pure BFO powders were successfully synthesized by microwave hydrothermal method, then the obtained BFO powders were calcined under different microwave temperatures and made into pure BFO ceramics via conventional ceramic processing. In order to improve the multiferroic behavior of BFO, the doping in the site of A and B of Bi Fe O3 ceramics were considered. The rare-erath elements of La and Gd substituted Bi, Co or Ga was chose to replace Fe.First, the optimum parameters of microwave hydrothermal method synthesized high pure BFO powders were determined after the analysis of lots of XRD results, drawn: choosing dilute nitric acid as the solvent, 10 M KOH as mineralizer, 0.05mol/L bismuth nitrate and iron nitrate solution was back titrated into KOH solution. The precuesors were transferred into reactors soaking under 200 oC for 10~60min, then the high pure BFO powders were obtained. Using a certain concentration of dilute nitric acid to leach the BFO powders, we can learned that the grain morphology of BFO powders was tetradecahedral after the analysis of SEM images.The acid washed BFO powders were calcined at 550 oC, 650 oC, 750 oC, 800 oC respectively in a microwave muffle-furnace. And the sample calcined at 750 oC exhibited a better antiferromagnetic behavior. Moreover, the dielectric polarization behavior of pure BFO ceramics belongs to Mawell-Wagner model. The leakage current of all samples decreased which the ferroelectric property of BFO was enhanced.The sintering behavior and crystal structure of La-doped BFO ceramics varied with the content of La. The dielectric constant, ferroelectric, antiferromagnetic property of La-doped BFO ceramics increased with increasing the La contents. The complex impadence spectroscopy of all the samples showed that the resistance characteristics of La-doped BFO ceramics became weakened and capacitance characteristics were enhanced.The dopant of Gd can effectively reduce the grain size of BFO ceramics and improve the dielectric constant, ferroelectric and antiferromagnetic behavior of BFO ceramics. From the figure of series of ceramics electric modulus as a function with frequency, we can obtain the conduction mechanism and the distribution of relaxation time of the Gd-doped BFO ceramics.Although the introduction of Co into BFO ceramics would make the dielectric loss of the ceramics increasing with the increasing of Co contents, the magnetic property of the samples was improved and transform antiferromagnetic to ferromagnetic behavior.The introduction of Ga into BFO ceramics would cause the space group structure of Cm appear in BFO ceramics which would make the improvement of piezoelectric properties of the ceramics. And the grain size was reduced in the samples with the increasing of Ga contents. From the spectroscopy of complex impedance and modulus, we found that the capacitance characterisitics were improved with the increasing of Ga.