Investigation On The Novel Niobate-tantalate-based Microwave Dielectric Ceramics With Medium Permittivity

With the rapid development of microwave devices to high frequency,broadband,miniaturization,low power consumption and high temperature stability,the microwave dielectric ceramics with series of medium permittivity and high quality factor have become a new research hotspot in the field of functional materials.The microwave components made of it are widely used in the satellite communication,mobile base stations,and other fields.General formula for the M²⁺M⁴⁺?Nb,Ta?₂O₈niobate-tantalate-based ceramics is a kind of new medium permittivity microwave dielectric material,and has excellent microwave dielectric properties.But it is also lack of relatively systematic research of this system.In this paper,the phase composition,crystal structure,chemical bond characteristic of M²⁺M⁴⁺?Nb,Ta?₂O₈microwave dielectric ceramics were further studied.It also established the connection between the microstructure and microwave dielectric properties,improving the theory of dielectric response.Through the collaborative ion substitution technology,it developed a series of high-performance and engineering application value of microwave dielectric ceramics with medium permittivity.The carried out research works of this paper are as follows:The crystal structure and lattice vibration mode of the niobate Zn ZrNb₂O₈ceramic were studied.It revealed the influence of mechanism between the the microstructure characteristics and macroscopic dielectric properties.Complex dielectric crystal chemical bond theory was introduced,by analyzing all kinds of chemical bonding properties in Zn Zr Nb₂O₈ system,at the same time the crystal structure stability of ZnZr Nb₂O₈ system was characterized by the ionic chemical bonds and lattice energy,providing a new method of dielectric response mechanism for this system.As the theoretical basis,by studying the collaborative ions substitution(that is,A-site Ni²⁺and B-site Ta⁵⁺)of Zn ZrNb₂O₈ system,it maked the quality factor?Q×f value?of ZnZrNb₂O₈ system improving nearly doubled,developed the(Zn_0.94Ni_0.06)ZrNbTaO₈ system with excellent microwave dielectric properties:?_r=27.88,Q×f=128,951GHz,?_f=-39.9ppm/?.The influence factors of structure stability and intrinsic dielectric loss of the tantalate AZrTa₂O₈?A=Zn,Mg?microwave dielectric ceramics was investigated,improving the structure of wolframite and related theory of microwave dielectric properties.The study found that the changes of temperature coefficient of resonance frequency??_f?and bond valence of A-site(Zn²⁺and Zr⁴⁺)of ZnZrTa₂O₈ system were the same.As the bond valence of A-site increased,the?_f value of ZnZrTa₂O₈ system moved to the positive direction.And it had the opposite trend of bond valence of B-site(Ta⁵⁺),while the?_f value of MgZrTa₂O₈ system was consistent with the bond valence of B-site.The Q×f value of tantalate AZrTa₂O₈?A=Zn,Mg?system increased with increasing the packing fration.Two kinds of high-Q microwave dielectric ceramics were prepared by conventional solid-state reaction route,the microwave dielectric properties of ZnZrTa₂O₈ as follows:?_r=32,Q×f=110,700GHz,t_f=-32ppm/?,and for MgZrTa₂O₈ as follows:?_r=29.5,Q×f=140,900GHz,?_f=-44.3ppm/?.In order to improve the temperature stability of resonance frequency of M²⁺M⁴⁺?Nb,Ta?₂O₈ microwave dielectric ceramics,this research studied the phase change process of three kinds of niobium-tantalate-based?1-x?ZnZrNb₂O₈-xTiO₂,MgZr_1+xNb₂O_8+2x and Zn_1-xMn_xTiTa₂O₈ systems,revealing the mechanism of the influence of structure phase transition on the temperature stability of resonance frequency.And it then discussed to realize the accurate control of?_f value through the complex phase design,such as ion doping structure modulation means,developing a series of near-zero?_f values of microwave dielectric ceramics.In order to make the M²⁺M⁴⁺?Nb,Ta?₂O₈ microwave dielectric ceramic system meet the requirements of low temperature co-firing ceramic?LTCC?technology,this study selected the near-zero?_f value of niobate 0.3Zn ZrNb₂O₈-0.7TiO₂ system,and investigated the low temperature sintering characteristics through mutual-doping of B₂O₃ and CuO with low melting point.Then this paper also studied the co-firing behavior of the ceramic powder and Ag electrode by a series of process such as the tape casting,electrode printing,laminating,isostatic pressing,and cutting.The results showed that the low-sintered material had good matching with LTCC technology.As the niobate CuZrNb₂O₈ has inherent low-temperature sintering,the microwave dielectric properties of CuZrNb₂O₈ were investigated sintered at 920?:?_r=28.7,Q×f=28,800GHz,?_f=-77.3ppm/?.This peper also studied the structure of CuZrNb₂O₈ system using X-ray diffraction,X-ray photoelectron spectroscopy and Raman scattering spectra,establishing the related mechanism of microstructure and microwave dielectric properties CuZrNb₂O₈ system.In order to lower the cost of microwave dielectric ceramics with medium permittivity,two kinds of titanate Li Ni_0.5Ti_0.5O₂ and CoZnTiO₄ were prepared by conventional solid-state reaction route.The microwave dielectric properties of rock-salt structure LiNi_0.5Ti_0.5O₂ as:?_r=19.25,Q×f=51,290GHz,?_f=-20.1ppm/? and the spinel structure CoZn TiO₄ as:?_r=17.31,Q×f=97,571GHz,?_f=-36.4ppm/?,both of them belong to the cubic crystal system.The price of raw materials is cheap,and easy to mass production.