Performance Control Of Ba₄Nd_28/3Ti₁₈O₅₄ Microwave Dielectric Ceramics With Tungsten Bronze Structure

With the rapid development of mobile communication technology,people put forward higher requirements for microwave components,and the importance of microwave dielectric ceramics as a key material is self-evident.Ba_6-3xNd_8+2xTi₁₈O₅₄ceramics belong to tungsten bronze structure Ba_6-3xLn_8+2xTi₁₈O₅₄（Ln is lanthanide）ceramic system.It has been widely studied by researchers because of its good comprehensive microwave dielectric properties.However,this system still has the problems of low quality factor and high temperature coefficient of resonant frequency.Based on the above problems,the properties of Ba₄Nd_28/3Ti₁₈O₅₄ ceramics were controlled by B-site substitution and A/B site co-substitution based on x=2/3,and the relationships between microwave dielectric properties and crystal structure,micro morphology and Raman spectrum are discussed.This article first uses(Al_1/2Ta_1/2)⁴⁺to perform B site substitution on the Ba₄Nd_28/3Ti₁₈O₅₄ ceramic system to explore its influence on the microwave dielectric properties,the formula is Ba₄Nd_28/3Ti_18-x(Al_1/2Ta_1/2)_xO₅₄（0≤x≤2.0）.Studies have shown that the upper limit of the solid solution of(Al_1/2Ta_1/2)⁴⁺in the ceramic system is about x=1.5.At the substitution point of x=2.0,the micro morphology changes obviously and a second phase appears.With the increase of the substitution amount x,theε_r of the ceramic sample decreases continuously due to the influence of the ionic polarizability,the Q×f of the ceramic sample increases significantly,and the TCF shift in negative direction.When x=2.0,the ceramic sintered at 1400?C for 4h has the best microwave dielectric properties:ε_r=70.41,Q×f=10500GHz,TCF=+13.1ppm/℃。Considering that the TCF of Ba₄Nd_28/3Ti₁₈O₅₄ ceramic system has not been adjusted to within±10ppm/℃,we continue to use Bi³⁺to perform A site substitution on the basis of(Al_1/2Ta_1/2)⁴⁺B site substitution,and explore its influence on the microwave dielectric properties,the formula is Ba₄(Nd_1-yBi_y)_28/3Ti₁₇(Al_1/2Ta_1/2)O₅₄（0.05≤y≤0.2）.Because Bi₂O₃has the effect of sintering aid,with the increase of the replacement amount y,the sintering temperature of the ceramic sample gradually decreases from 1350℃to 1300℃.As the value of y increases,theε_r of the ceramic continues to increase,and the value of Q×f continues to decrease.TCF first decreased and then increased.When y=0.15,the ceramic sintered at 1325℃for 4h has the best microwave dielectric properties:ε_r=89.02,Q×f=5844GHz,TCF=+8.74ppm/℃。.Although the introduction of Bi³⁺adjusts the TCF value to within±10ppm/℃,at the same time the Q×f value of Ba₄Nd_28/3Ti₁₇(Al_1/2Ta_1/2)O₅₄ ceramics has dropped more severely,so this experiment uses Sm³⁺replace Bi³⁺for A site substitution on the basis of the previous part of the experiment,and explore the influence on microwave dielectric properties.The formula is Ba₄(Nd_1-zSm_z)_28/3Ti₁₇(Al_1/2Ta_1/2)O₅₄（0.05≤z≤0.4）.Studies have shown that Sm³⁺can solid dissolve into the crystal lattice of ceramics.As the value of z increases,ε_rcontinues to decrease,Q×f first increases and then decreases,and TCF shifts to the negative direction.When y=0.4,ceramic sintered at 1400℃for 4h has the best microwave dielectric properties:ε_r=73.79,Q×f=9653GHz,TCF=+7.47ppm/℃。...