Phase Formation Mechanism And Properties Of Ba₂Ti₉O₂₀ Based Microwave Dielectric Ceramics Prepared By Solid State Method

In recent years,with the rapid development of microwave communication industry,the advantages of microwave dielectric ceramic materials have been continuously explored.BaO-TiO₂ series microwave dielectric ceramic materials are widely concerned due to its medium dielectric constant and low dielectric loss.The dielectric properties of Ba₂Ti₉O₂₀-based ceramics were excellent:?_r⁴0;Q⁸000;?_f^±2ppm.So far,as a microwave dielectric material,Ba₂Ti₉O₂₀-base ceramics have not been completely developed.In this thesis,Ba₂Ti₉O₂₀0 based ceramics are selected as the research object.The phase formation mechanism and micro-structure evolution of ceramic in the process of solid-phase sintering have been studied in detail.Further,the relationship between microwave dielectric properties of Ba₂Ti₉O₂₀0 ceramic and densification,micro-morphology and the crystal structure was explored.The phase formation mechanism and micro-structure evolution of Ba₂Ti₉O₂₀0 ceramics by reaction sintering were researched.Single-phase ceramics Ba₂Ti₉O₂₀0 were prepared by reaction sintering method using TiO₂ and BaCO₃ as raw materials and sintered for 10h at1150^oC.The formation behavior of Ba₂Ti₉O₂₀0 phase was analyzed from the perspective of diffusion,and the activation energy needed for the completion of the process was calculated to be about 386.17kJ/mol.Combined with the analysis of SEM and EDS,it is also revealed that the pore of Ba₂Ti₉O₂₀0 grain may be caused by the absence of oxygen element.Besides,we also found that the local inhomogeneous distribution of barium element on the surface of Ba₂Ti₉O₂₀0 grain resulted in the enrichment of titanium element,which would lead to the roughness of the ceramic surface.The effects of dopants MgO,Sm₂O₃ and ZnNb₂O₆ on the microwave dielectric properties of Ba₂Ti₉O₂₀-base ceramics were studied from the aspects of densification,crystal structure and micro-structure.The results show that doping MgO can effectively improve the micro structure of Ba₂Ti₉O₂₀-base ceramics and optimize the microwave dielectric property.Ba₂Ti₉O₂₀-0.1 wt%MgO ceramics were sintered at 1300^oC for 4 hours in air atmosphere.It has excellent microwave dielectric properties:?_r=40.67,Q×f=33552?6.2GHz?,?_f=0 ppm.Doping Sm₂O₃ can not only replace Ba²⁺at A-site in Ba₂Ti₉O₂₀0 lattice by Sm³⁺,but also improve the dielectric properties of Ba₂Ti₉O₂₀0 based ceramics by refining the grains and enhancing grains uniformity.Ba_1.99Sm_3.98/3Ti₉O₂₀0 ceramic with excellent microwave dielectric properties were prepared in air at 1280^oC for 4 hours.The microwave dielectric properties of Ba_1.99Sm_3.98/3Ti₉O₂₀0 ceramic were?_r=38.93,Q×f=26871?6.4GHz?,?_f=2.06ppm.Similarly,ZnNb₂O₆ can also refine Ba₂Ti₉O₂₀0 grains effectively to improve the densification and the uneven micro-morphology,so as to improve the microwave dielectric properties of ceramic materials.Furthermore,the lattice distortion caused by the substitution of B-site Ti⁴⁺by Zn²⁺,Nb⁵⁺and[Zn_1/3Nb_2/3]⁴⁺with slightly larger radius also plays a positive role in improving the microwave dielectric properties of ceramic materials.Ba₂[Zn_1/3Nb_2/3]_0.3Ti_8.7O₂₀0 ceramic with excellent microwave dielectric properties were prepared in air at 1300^oC for 4 hours.The microwave dielectric properties were?_r=39.3,Q×f=43897?6.36GHz?,?_f=7.08 ppm.