Research Of Preparation And Dielectric Properties Of MgZrNb₂O₈ Microwave Dielectric Ceramics

As the key electronic material of 5G base station,microwave dielectric ceramics have the necessary demand for practical production and application with appropriate dielectric constant,low loss,near zero resonant frequency temperature coefficient and low sintering temperature.MgZrNb₂O₈ ceramics has been widely studied by many scholars for its relatively high microwave dielectric properties and low cost.This thesis also takes this system as the research object and systematically analyzes the effects of complex ion substitution and glass doping on the microwave properties and crystal structure of the material.The specific research contents are as follows.1.The effects of(Mg_1/3Ta_2/3)⁴⁺complex ions on phase composition,crystal structure and microwave properties of ceramics were systematically studied.As the substitution amount of(Mg_1/3Ta_2/3)⁴⁺complex ions increases gradually,the ceramic forms a solid solution without the formation of the second phase,and the dielectric constant increases gradually.The quality factor shows a trend of first increasing and then decreasing,and the resonant frequency temperature coefficient decreases all the time.The optimum microwave dielectric properties of Mg Zr_0.96(Mg_1/3Ta_2/3)_0.04Nb₂O₈ ceramics sintered at1340℃ for 4 hours areε_r=25.42,Q×f=65,950 GHz,τ_f=-61.04 ppm/℃.2.Zr⁴⁺ion was replaced by(Al_1/2Ta_1/2)⁴⁺ion.As the substitution amount of complex ions gradually increases,the ceramics form solid solution.According to the Rietveld refinement results and the complex chemical bond theory,the relationship between the microstructure and the microwave dielectric properties is analyzed.The optimum microwave dielectric properties of Mg Zr_0.8(Al_1/2Ta_1/2)_0.2Nb₂O₈ ceramics were obtained at1340℃ for 4 hours:ε_r=24.77,Q×f=59,234 GHz,τ_f=-54.17ppm/℃.3.The B site was replaced by(Ti_1/2W_1/2)⁵⁺complex ion.As the number of ion substitution increases gradually,the ceramic forms a solid solution without the formation of a second phase.The reasons for the continuous decrease of dielectric constant were analyzed by using the theoretical dielectric polarization,the reasons for the first increasing and then decreasing of the quality factor were systematically analyzed by using the atomic packing fraction and B site average lattice energy.The variation trend of the temperature coefficient of resonant frequency was systematically analyzed by Nb site average bond energy.Finally,MgZrNb_2-x(Ti_1/2W_1/2)_xO₈（x=0.06）ceramics were sintered at 1360℃ for 4 hours to obtain the best microwave dielectric properties:ε_r=24.91,Q×f=66,246 GHz,τ_f=-56.72 ppm/℃.4.The sintering temperature of MZN ceramics was reduced by using ZB glass with low melting point as combustion aid.The whole process was systematically analyzed by means of phase composition and microscopic morphology.ZB glass formed a lot of liquid phase in ceramics,which accelerated the densification process of ceramics,and successfully reduced the sintering temperature of MZN from 1340℃ to 950℃.Although the generated second phase Zn₄O（BO₂）₆ and third phase Zn₃（BO₃）₂ deteriorate the ceramic properties to a certain extent,MgZrNb₂O₈+30wt.%ZB still exhibits excellent properties at 950℃ sintering temperature for 4h:ε_r=20.39,Q×f=38,412 GHz,τ_f=-74.21 ppm/℃.