Study On Structures And Microwave Dielectric Properties For Two Types Of New Silicate Ceramic

As a novel multi-functional basic material,microwave dielectric material are widely used in communication system equipment as an electronic basic component,such as dielectric resonator,filter,microwave substrate,substrate etc.Silicon-based microwave dielectric ceramics with advantages of low loss,tunable resonant frequency temperature coefficient and low dielectric constant,meet the market demand for miniaturization,high frequency and low cost of communication equipment,and have attracted the attention of research teams at home and abroad.In this paper,the microstructure and microwave dielectric properties of two kinds of new low-dielectric-constant silicate materials are studied.By means of XRD,SEM,Raman,and vector network analyzers,the effects of sintering process,microstructure and defects on the microwave dielectric properties of materials were analyzed.The main contents are listed as follows:?1?The apatite structure silicate ceramics Ca_1-xSr_xLa₄Si₃O₁₃ were synthesized by solid-phase method.The XRD and rietveld refinement shows that CaLa₄Si₃O₁₃ is a hexagonal crystal structure belonging to the space group P63/m?176?.The SiO₄ tetrahedron forms the basic skeleton of the crystal,and the Ca and La ions occupy the same crystal lattice position,forming two different coordination polyhedral structures with the O atom.Raman spectroscopy shows that the CaLa₄Si₃O₁₃ crystal cell is composed of SiO₄ tetrahedral functional groups,La-O and Sr-O polyhedron,and the vibrational spectra of oxygen vacancies are detected.According to the data of density and SEM,when the CaLa₄Si₃O₁₃ ceramic sintered at 1400 ? for 4 hours,the density is the largest with the clear grain surface and uniform size.After a certain amount of Sr ions are doped,the diffraction angle shifts.With the different content of Sr ion doping,the optimal sintering temperature of ceramic samples is also different.The curves of Q×f and dielectric constant at different sintering temperatures are strongly correlated with the density characteristic curves.When the Ca_1-xSr_xLa₄Si₃O₁₃ ceramics were sintered at 1400? for 4 hours,excellent microwave dielectric properties were obtained impure phase CaLa₄Si₃O₁₃ ceramic:re =14.5,Q×f = 31100GHz?at 9.05GHz?,?_f=–21ppm/?.Although the doping of Sr ions did not improve the microwave performance of CaLa₄Si₃O₁₃,it provided a new idea for the improvement of theperformance of apatite structural ceramics.?2?Two trisilicates AY₂Si₃O₁₀?A=Sr and Ba?were synthesized by the solid phase method.The XRD and rietveld refinement results show that the diffraction pattern of SrY₂Si₃O₁₀ matches with ICSD 167613 and is a triclinic structure,belonging to the space group.The Si-Si-Si bond angle in the [Si₃O₁₀]^8- trimer is 133.5 degrees.The diffraction pattern of Ba Y₂Si₃O₁₀ is matched with ICSD 240470,which is a monoclinic structure,belonging to the P21/m space group.The Si-Si-Si bond angle is96.1 degrees.The radius of A ions affects the extrusion force of trimer [Si₃O₁₀]^8-,which results in different spatial structures of the two trisilicates.When the SrY₂Si₃O₁₀ ceramics were sintered at 1425? for 4h,the density was the highest,the porosity was the smallest,the crystallites were clear,the size was uniform,and the microwave performance was the best:re =9.3,Q×f = 64,100GHz?at 14.1GHz?,?_f=-31ppm/?.When BaY₂Si₃O₁₀ was sintered at 1425? for 4 h,the density was the largest,but the Q×f decreased slightly.This was related to the grain size uniformity and the existence of liquid phase in the sample.The BaY₂Si₃O₁₀ ceramics exhibited good microwave dielectric properties:re =9.3,Q×f =64100GHz?at 14.1GHz?,?_f=-31ppm/? when the sintered at 1400 ? for 4h.