Magnetic And Magnetoelectric Properties Of Doped Ba_0.8Sr_0.2TiO₃ Ferroelectric Ceramics

The BaTiO₃ based perovskite ferroelectric materials have many applications in energy storage,microwave equipment and other electronic devices because of its non-toxic,high dielectric constant and low dielectric loss.It is known that the properties of BaTiO₃ can be regulated by Sr doping,with the ferroelectric-paraelectric phase transition temperature gradually moving towards higher temperatures at increased mole ratio of Ba/Sr,so as to regulate the peoperties of material's properties.In addition,there will further broaden the application of Ba_xSr_1-xTiO₃ material with introducing magnetic ions into Ba_xSr_1-xTiO₃matrix to induce multiferroic.However,it can be seen from the present researches that the magnetism is usually weak for Ba_xSr_1-xTiO₃materials when the content of magnetic ions is low,and there are little reports concerning magnetoelectric coupling.We choose Ba_0.8Sr_0.2TiO₃(BST)ceramics with room-temperature ferroelectricity as matrix material,and try to induce magnetism and magnetoelectric effect with different magnetic ions and different method of doping.In this paper,we investigate the microstructure,ferroelectricity,dielectricity,magnetism and magnetodielectric effect of the unsaturated Fe ion doped at A/B site and rare earth element B site doped Ba_0.8Sr_0.2TiO₃ ferroelectric ceramics prepared by traditional solid phase method,and discuss the intrinsic mechanism.The main contents are as follows:1.The structure and properties of a special unsaturated Fe-doping Ba_0.8Sr_0.2TiO₃based ceramics were investigated.The doped ceramic samples that the component ratio of A/B site is slightly modulated are prepared,which are Ba_0.8Sr_0.2Ti_0.9Fe_0.1O₃(BSTF)?Ba_0.8Sr_0.18Ti_0.9Fe_0.1O_3-?(BSVTF)and Ba_0.8Sr_0.18Ti_0.92Fe_0.1O_3-?(BSFTF).The structure characterizations exhibit that ferroelectric tetragonal phase and paraelectric cubic phase coexist in the doped ceramics with the cubic phase being dominant.The ceramic samples exhibit poor room temperature ferroelectricity,but appear obvious room temperature ferromagnetism and magnetodielectric effect as well as dipole glass and spin glass at low temperature.It is considered that Fe ions not only mainly replace Ti sites,but also partially occupies Sr sites and produces variable valence.As more Fe ions enter into Sr sites,ferroelectricity,ferromagnetism and magnetodielectric effect increase slightly,which is related to the increase of dipoles formed between oxygen vacancies and low-valent Fe ions off-center at Sr-sites,as well as the enhancement of ferromagnetic interaction between non-equivalent Fe ions.This work manifests the uncommonly used unsaturated Fe-doping as an effective method for tailoring the electric and magnetic properties and realizing magnetoelectric coupling in traditional ferroelectrics.2.The properties of rare earth element Dy doped Ba_0.8Sr_0.2TiO₃ ceramics were studied.X-ray diffraction and Raman spectra reveal that paraelectric cubic phase and ferroelectric tetragonal phase coexist in the doped ceramics Ba_0.79Dy_0.01Sr_0.2TiO₃(BDST1)and Ba_0.78Dy_0.02Sr_0.2TiO₃(BDST2)with tetragonal phase playing a dominant part.BDST1 and BDST2 exhibit excellent room temperature ferroelectricity with phase transition temperature is 332 K and 338 K respectively.Dielectric relaxation behaviors appear at high temperature,which are originated from dipole interaction and double-ionized oxygen vacancies.The doped samples also exhibit room temperature ferromagnetism and enhanced magnetodielectric effect,which probably results from Dy 4f-O 2p orbital hybridization state and RKKY interaction related with Dy 4f-Ti 3d.Compared with pure BST ceramics(whose weak magnetism derived from low-valent Ti ions),the doped samples exhibit slightly weak ferroelectricity,while enhanced ferromagnetism and the different temperature dependence of magnetization and magnetodielectric behaviors.This work manifests that rare earth element doping is also a feasible way to induce the ferroelectricity and magnetoelectric coupling effect in ferroelectric materials.