The Modification Of Bi-ion Substituted Zr_0.8Sn_0.2TiO₄ Based Microwave Dielectric Ceramic

In recent years,high speed of communication system and the miniaturization of electronic components have led to the rapid development of the wireless communication industry.In this context,the requirements for related microwave devices in the industry are becoming more stringent,requiring microwave dielectric materials with higher dielectric constant,quality factor and good temperature stability.At present,many commercial high dielectric microwave materials are titanate-based ceramics,such as（Zr,Sn）TiO₄,BaTi₄O₉,etc.The Zr_0.8Sn_0.2TiO₄（ZST）ceramic have been widely used due to the high dielectric constant and near zero temperature coefficient.However,the sintering temperature of ZST ceramic is high and it is difficult to compact without sintering aid,which restricts its application in practical production.Previously,many studies have investigated the sintering aid modification of ZST ceramic.In this thesis,bi-ion substitution sintering of Zr_0.8Sn_0.2TiO₄（ZST）ceramic is studied.The solid phase sintering method is used in the experiment.Starting from the preparation process of ZST ceramic,the influence of substitution on the sintering characteristics and dielectric properties of materials is investigated,and the chemical effects in crystals caused by substitution are studied.The experimental results are as follows:（1）The effects of two different ball-milling dispersants on the phase composition,microstructure and microwave properties of ZST ceramic sintered samples are investigated.Deionized water and ethanol are selected as dispersant.The properties of the pre-calcined powder and the sintered samples obtained by using the two dispersants are compared.The ethanol molecules can form a chain structure with each other and be connected to the oxide through its hydroxyl group,which enhances the viscosity of the ethanol solution and causes the agglomeration of the oxide particles when dispersed in the ethanol solution.Agglomerated particles stratify and settle,which affects the sintering characteristics and microwave dielectric properties of ZST.ZST ceramics can achieve better microwave performance at lower sintering temperatures using deionized water as the dispersant:ε_r=40,Q×f=33700 GHz,τ_f=+3.5 ppm/°C.（2）According to the size of the ion radius,(Zn_1/3Nb_2/3)⁴⁺is selected to substitute Zr⁴⁺in Zr_0.8Sn_0.2TiO₄.The doping material system is Zr_0.8-x(Zn_1/3Nb_2/3)_xSn_0.2TiO₄.The best microwave dielectric properties are obtained by the substitution of 5 mol%of Zr⁴⁺（ε_r=39,Q×f=46000 GHz,τ_f≈0 ppm/°C）,as the substitution amount continues to increase the dielectric loss gradually increases.After the incorporation of divalent and pentavalent cations,in order to maintain the local electrical neutrality of the crystal,the electronic compensation mechanism is excited to generate chemical defects such as oxygen vacancies.The free electrons are trapped by the oxygen vacancies and shared by the surrounding Ti⁴⁺,resulting in the reduction reaction of Ti⁴⁺which affects the microwave dielectric properties of the material.（3）According to the size of the ion radius,(Al_1/2Nb_1/2)⁴⁺is selected to substitute Ti⁴⁺in Zr_0.8Sn_0.2TiO₄.The doping material system is Zr_0.8Sn_0.2Ti_1-x(Al_1/2Nb_1/2)_xO₄.The best microwave dielectric properties can be obtained by the substitution of 20 mol%of Ti⁴⁺（ε_r=36,Q×f=43600 GHz,τ_f≈0 ppm/°C）,as the substitution amount continues to increase the dielectric loss gradually increases.When 80 mol%of Ti⁴⁺was substituted,the system still maintains a single phase and good temperature stability.After the incorporation of trivalent and pentavalent cations,in order to maintain the local electrical neutrality of the crystal,the electronic compensation mechanism is excited to generate chemical defects such as oxygen vacancies.The free electrons are trapped by the oxygen vacancies and shared by the surrounding Ti⁴⁺,resulting in the reduction reaction of Ti⁴⁺which affects the microwave dielectric properties of the material.