The Regulation And Performance Of Filled Tungsten Bronze Niobate Ceramics

Due to the rapid development of communication and electronic technology,these function,miniaturization,low cost and high performance of electric devices are increasing demand.Therefore,to explore the materials with excellent properties,economic and multifunction is the important issue of modern electronic industry.The tungsten bronze ceramics are widely applied in the electric field because of their excellent properties,such as dielectric properties,ferroelectric properties and non-linear electric-optic properties.Recently,Ba4Sm2Fe2Nb8O30(BSFN)ceramics has been reported room temperature multiferroic.However,it exists controversy in the multiferroic.Thus,in the present thesis,BSFN ceramics have been investigated through conventional sintering,microwave sintering and the template grain growth with Sr2KNb5O15 added.(1)BSFN dense ceramics with tetragonal filled tungsten bronze structure have been prepared by microwave sintering and conventional sintering methods.The major phase of tetragonal tungsten bronze phase,secondary phase of BaFe12O19 and columnar grains are observed in the BSFN ceramics prepared by the conventional sintered method.The microwave-sintered BSFN ceramics exhibits the higher denstiy and tungsten bronze single phase,which exhibits equal-axial grains.It is more important that the excellent dielectric properties and obvious multiferroics are achieved for the BSFN ceramics prepared by the microwave sintering.These room temperature multiferroic properties are as following,lager polarization Pr of 2.16?C/cm2,small coercive electric field Ec=6.56kV/cm,lager remanent magnetization Br of 0.43emu/g and coercive magnetic field Hc=2930Oe(2)The best synthetic conditions of SKN template with salt methods:the salt is KCl,the molar ratio of SrNb2O6 and Nb2O5 is 1,the weight ratio of salt to oxide sources was 1.5,The synthesis temperature is 1150? and the soaking time is 4h.The template for the length to diameter ratio of 3-15 is the single-phase Sr2KNb5O15 with pure tungsten bronze phase.the density and shrinkage of Ba4Sm2Fe2Nb8O30 ceramics decrease slightly with the content of Sr2KNbsO15 rising.the dielectric constant of BSFN ceramic increases gradually,while the curie temperature decreasing.when the content of Sr2KNbsO15 is 5%,the ferroelectric properties superior to the one prepared by conventional sintered,but its ferroelectric properties is reducing.(3)The BSFN ceramics with tetragonal tungsten bronze structure had been prepared by template grain growth,but it contains a small amount of impurity phase niobate strontium oxide.the microstructure of the BSFN ceramic has good orientation degree of the rod-shaped grain alignment,compared with conventional sintering methods.the peak dielectric constant value is near quadruple of that conventional sintered sample and the dielectric loss is also declined.the BSFN ceramics exhibits better ferroelectric properties synthesized by template grain growth,Although the coercive field is slightly superior to the ceramics of conventional sintered,but the residual polarization were increased from 1.25?C/cm2 to 2.12 ?C/cm2.