Effects Of Eu Substituting Positions And Concentrations On Luminescent, Dielectric And Magnetic Properties Of SrTiO₃ Ceramics

With the intensive development of functional materials and devices, researchers expect to develop a material or a device to realize more and more functions. A multifunctional material is typically a composite or hybrid of several distinct material phases, in which each phase performs a different but necessary function. Besides each phase of the material performs an essential function, multifunctional materials promise more weight-efficient, volume-efficient performance flexibility than traditional multicomponent integrated systems, which are emerging as a new interdisciplinary research field..In the past few years, ABO₃-like compounds with the perovskite-type structure, such as BaTiO₃, SrTiO₃(STO), CaTiO₃ and their solid solutions, have drawn a great deal of attention due to their attractive ferroelectric and dielectric properties. Moreover, it has been demonstrated that the dielectric and ferroelectric properties can be changed by doping rare-earth (RE) elements in the materials. For example, room-temperature ferroelectricity was observed in Pr-doping STO, unlike the paraelectric characteristic in pure STO. [JAP 97(2005)104109]. Most recently, Bassoli et al [JAP 103(2008)014104] reported the dielectric enhancement behavior in Yb³⁺:CaTiO₃ ceramics. Compared with that of the pure samples, the dielectric constant of the ceramic, in which Yb³⁺ ion substituted both Ca²⁺ and Ti⁴⁺, was increased of about one order of magnitude, while the dielectric loss kept up in a low range. On the other hand, ever since a red-emitting phosphor STO:Pr³⁺ was developed in 1996, RE-doped STO (BaTiO₃, CaTiO₃)has been regarded as a potential choice of phosphors for flat panel display. Therefore, RE element doped STO can be considered as the potential multifunction materials.In this thesis, the structural, luminescent, dielectric and magnetic properties of multifunction Eu³⁺ doped STO ceramics were investigated at room temperature. Three different charge compensation mechanisms were realized in Eu³⁺ doped STO ceramics by changing the Sr/Ti ratio to force Eu³⁺ on the Sr site, on Ti site, or on both sites. It was found that the multifunction properties of the samples strongly depended on the substituting positions of Eu ions in STO. The photoluminescence intensities and dielectric constant for both Sr and Ti sites substituted samples were obviously higher than those for Sr or Ti site substituted samples. Such behaviors were mainly ascribed to the different charge compensation mechanisms and local symmetric environment around Eu3+ ions. A linear magnetization-magnetic field behavior revealed the paramagnetic nature of Eu3+ doped STO, which was sensitive to Eu doping concentrations. Our results show that multifunctional luminescent/dielectric/magnetic properties are realized in Eu-doped STO ceramic. The above conclusions were published on APPLIED PHYSICS LETTERS.