Preparation And Modification Research On SrTiO₃-based Microwave Dielectric Ceramics

As a type of new functional ceramic materials, microwave dielectric ceramics (MWDC) have been widely used in the field of microwave communication. And in the field of new functional ceramic, MWDC is one of the hot material researches recently. Because perovskite-type materials have the properties of high permittivity and high structure adjustability, in this paper, SrTiO3is used for substrate material, and CeO2、MgO and Bi2O3are used for modified oxides, solid phase method is used to preparing the ceramic samples for experiments, and changes in crystal structures and microstructures of materials have been analyzed, the effects on oxides to dielectric properties and sintering behaviors of SrTiO3material have been Studied. The paper main research contents are as follows:To study crystal structure change on microwave dielectric properties, SrTiO3and Ce&Mg are used for the research subject and adulterate elements, the relationships between tolerance factor and temperature coefficient have been analyzed. The chemical formula of materials designed in this work is (1-x)SrTiO3-xCe(Mg1/2Ti1/2)03. The results show that a small number of Ce&Mg-doped into SrTiO3together change the crystal structure from the cubic to the tetragonal phase. And with the increasing of Ce&Mg content, the cell volume decreases gradually until Ce&Mg content is closed to their solid solubility limit (~20mol%). Calculate the tolerance factors and find it decreases gradually with the doping amounts. Also, the temperature coefficient of the ceramic decreases obviously. And the permittivity and dielectric loss decrease along with the increasing of the doping amounts. When near the solid solubility limit, the temperature coefficient is270ppm/℃, permittivity is108and QXf is1846GHz。To improve the microwave dielectric properties of Sr0.4Ce0.4TiO3(SCT) ceramic and make the temperature coefficient as small as possible, CeO2is used for the modified oxide and the SCT-Ce ceramics have been prepared. The results show that permittivity (εr) of ceramics decreases with the increasing of CeO2content, Qxf product increases gradually and temperature coefficient of resonant frequency decreases linearly. The smallest τf is211ppm/℃when material has high permittivity, and at this time, εr is86, Q X f is12493GHz. When CeO2content is up to90mol%, near-zero temperature coefficient ceramic (~1.7ppm/℃) was achieved, and permittivity(εr) and Qxf are about32and20750GHz respectively, which has identified as middle permittivity microwave dielectric ceramic.To lower the sintering temperature of SCT-Ce ceramics, regard0.1SCT-0.9Ce ceramic as the research object and add Bi2O3as the sintering aid, it finds that a small number of Bi2O3-added0.1SCT-0.9Ce ceramic makes the sintering temperature decreased by120℃。The highest relative density (98%) was achieved when Bi2O3content is about0.5wt%. However, the dielectric properties of ceramics change obviously: with the increasing of Bi2O3content, permittivity increases a little; temperature coefficient changes unobviously, but the value of number is higher than without Bi2O3; and Qxf product decreases significantly.