Preparation And Properties Of Eu-and Ce-doped Tungsten Bronze Niobate Ceramics

With the rapid development of electronic information technology,the requirements for miniaturization,low cost,multi-functionality and stability of electronic devices have become higher and higher,which requires economical and excellent ceramic materials.As an important functional material,the material with tungsten bronze structure exhibits excellent dielectric,ferroelectric and nonlinear optical properties,and has been widely used.The complex crystal structure of tungsten bronze materials greatly enriches the possibilities for the adjustment and optimization of properties.Unfortunately,although there are many studies on the electrical and nonlinear optical properties of tungsten bronze structural materials at present,most of the researches are focus on single properties,and there are few reports on systematic investigation of multiple properties.At the same time,few researches have been done on luminescence properties of tungsten bronze structural materials.Thus,in the thesis,the effects of Eu-and Ce-doped on preparation,structure,dielectric properties,ferroelectric,optical properties the relationship between them of filled and unfilled tungsten bronze ceramics were investigated in the thesis.Firstly,Eu-doped Ba4La2T14Nb6O30:xEu3+(BLTN)ceramics were prepared by solid-state reaction method.Tungsten bronze single phase was synthesized for all samples.But it displays poor sinterability.At 1 kHz,the dielectric constant of BLTN ceramics can reach 450 or more.And the Eu-doped BLTN ceramic samples show better dielectric constant tenperature stability.At the same time,Eu-doped BLTN ceramics show better luminescence properties.When the excitation wavelength is 390 nm,the intensity of emission peak henhances with the increase of Eu3+ concentration.It is found that no concentration quenching occurs.Secondly,Sr0.5Ba0.5Nb2O6(SBN50):xEu3+ ceramics were prepared by solid-state reaction.The Sr0.5Ba0.5Nb2O6 single phase was synthesized in SBN50^xEu3+ ceramics.However,with the increasing of Eu3+ concentration,the micromorphology of the grains varies significantly from equiaxial to columnar.The dielectric constant of ceramics increases with increasing of Eu3+ concentration:at 1 kHz,the dielectric constant increases from 1148(undoped)to 2004(x=0.06).Eu-doped SBN50:xEu ceramic exhibited excellent luminescence properties.However,the RT ferroelectric properties of Eu-doped samples have degraded.Last,the Ce-doped SBN50 ceramics were prepared by solid-state reaction method and some samples were annealed in H2 atmosphere.XRD shows that the Sr0.5Ba0.5Nb2O6 phase is successfully synthesized in SBN50 ceramics.Compared to the undoped ceramics sample,the dielectric constant of Eu-doped ceramics increases.As the doping concentration increasing,the Curie temperature of the ceramic decreases.At 100 kHz,when the doping concentration changes from 0 to 0.04,the Curie temperature of the sample decreases from 120? to 25?.And the phase transition exhibits the characteristics of diffuse and relaxation.The phase of the annealed sample did not change,but the density increased obviously;and the dielectric constant also increased greatly.At 1 kHz,the dielectric constant of the Ce-doped(x=0.02)sample increased from 1944(unannealed)to 6657(annealed).At the same doping concentration,the Curie temperature of the Ce-doped SBN50 ceramics is lower than that of the samples before annealing,and both the samples shows the diffuse phase transition.