Dielectric Properties Optimization Of Ba-Nd-Ti Based Microwave Dielectric Ceramics With A Tungsten Bronze-structure

With the rapid development of information technology and the advent of the 5G era,high-performance microwave dielectric ceramics have achieved unprecedented development and have aroused interest internationally.High dielectric microwave dielectric ceramics have attracted great attention due to their promising applications in the miniaturization,integration,and high performance of microwave devices.Tungsten bronze-structured Ba_6-3xLn_8+2xTi₁₈O₅₄（BLT,Ln=La,Nd,Sm,Pr）solid solutions have excellent and adjustable microwave dielectric properties,and their dielectric properties can be effectively tailored with the change of the Ln ions and the x value.For example,its dielectric constant（ε_r）can be varied between 70 and140,and it can obtain a near-zero temperature coefficient of resonant frequency（τ_f）by compositional tailoring.Therefore,they have promising applications in mobile and wireless communications.In this work,the Ba_6-3xNd_8+2xTi₁₈O₅₄（BNT）ceramic materials were prepared by the conventional solid-state reaction method.When the value of x is 0.67,the material has the best microwave dielectric properties,and the basic composition of BNT Optimal microwave dielectric properties;In addition,by introducing composite doping ions(Al_0.5Nb_0.5)⁴⁺to the Ti site,the phase compositions,microstructures,microwave dielectric properties,oxygen vacancy,and Ti valence were studied;Then,by adding Nd Al O₃to further adjust its temperature coefficient to achieve the purpose of near zero,through the study of its performance and structure changes to establish the relationship between macroscopic properties and microstructure;Finally,the Bi_0.5Na_0.5Ti O₃substitution was used to increase the dielectric constant,and the internal factors of the performance change were explained by characterizing the phase composition,microstructures and microwave dielectric properties.The main work and results are as follows:1.In order to improve the microwave dielectric properties of the materials,composite ions(Al_0.5Nb_0.5)⁴⁺was selected for doping at Ti sites.Ba₄Nd_9.33(Al_0.5Nb_0.5)_xTi_18-xO₅₄（BNANT x=0,0.4,0.8,1.2,1.6）were prepared by the solid-state reaction method.Because the(Al_0.5Nb_0.5)⁴⁺average ion radius is small,and Al³⁺can effectively suppress the reduction of Ti⁴⁺and the generation of oxygen vacancies,thereby improving the performance of the materials.By analyzing its phase composition,micro-morphology,element valence,oxygen vacancy and microwave dielectric properties,the effect of composite ions on the performance control of BNT-based ceramics was studied.The results showed that when(Al_0.5Nb_0.5)⁴⁺is selected for doping,the optimal microwave dielectric properties are obtained at x=1.2:ε_r=80,Q×f=10245 GHz,τ_f=18 ppm/℃.2.Although the(Al_0.5Nb_0.5)⁴⁺doping can improve the microwave dielectric properties of ceramic samples,a near-zeroτ_fwas not obtained.Therefore,Nd Al O₃was used as a compensator,and samples of（1-y）Ba₄Nd_9.3(Al_0.5Nb_0.5)_1.2Ti_16.8O₅₄+y Nd Al O₃（BNANT+NA y=0.4,0.45,0.5,0.55,0.6,0.65）were prepared.Because Nd Al O₃has a high quality factor and negative temperature coefficient,it can effectively tailor the microwave dielectric properties of BNANT ceramics.A series of properties such as phase analysis,microstructures,and microwave dielectric properties of the doped ceramics were characterized to study the effect of different substitution amounts on their properties.The results show that the optimal microwave dielectric properties were obtained when y=0.55:ε_r=70,Q×f=13680 GHz,τ_f=-2 ppm/℃.3.Bi_0.5Na_0.5Ti O₃was introduced to increase the dielectric constant of BNANT ceramics.Samples of（1-z）Ba₄Nd_9.33(Al_0.5Nb_0.5)_1.2Ti_16.8O₅₄+z Bi_0.5Na_0.5Ti O₃（BNANT+BN z=0,0.2,0.4,0.6,0.8）were prepared.Because Bi has a higher polarizability,the dielectric constant of the material were increased effectively.Through the characterization and analyses of its phase compositions,microstructures,and element valence,the influence of the doping amount on microwave dielectric properties was studied.The results show that the optimal microwave dielectric properties are obtained at z=0.4:ε_r=83,Q×f=9200 GHz,τ_f=16ppm/℃.