Study On Microstructure And Microwave Properties Of Two New Silicon-based Ceramics

With the rapid development of mobile communications and Internet of Things,people have higher requirements on signal bandwidth.The high frequency of equipment has become an inevitable requirement for the design and development of microwave devices,and those low dielectric constant microwave dielectric ceramics with high performance are the basis of microwave device and microwave circuit board design.In this paper,the traditional solid-state sintering method is used to synthesize low dielectric constant silicalite Ca₂(Al_1–xMg_x)(Al_1–xSi_1+x)O₇ series microwave dielectric ceramics,olivine(Mg_1-xLi_0.5xY_0.5x)₂SiO₄ and Mg_2-xY_xSiO_4-xN_x series microwave dielectric ceramics.Through the analysis methods of bulk density,X-ray diffraction,scanning electron microscopy,vector network analyzer,impedance analyzer,etc.,the interrelationships between the sinterability,microstructure and microwave dielectric properties are studied,and the relationship between different components and microwave performance is also explored.As x increases,Ca₂(Al_1–xMg_x)(Al_1–xSi_1+x)O₇ series ceramics obtain a single-phase material in each component according to XRD analysis,but the peak near 31.3° begins to shift toward a low angle.The cell volume obtained by Rietveld refinement of XRD data also increases with increasing x.Since the average ion polarizability of the substitutional ions Mg²⁺ and Si⁴⁺ is larger than that of the substituted Al³⁺,the relative permittivity also increases with the increase of x.In the low-frequency dielectric spectrum,it is seen that as the temperature increases,?_r gradually increases,and the difference of ?_r at different frequencies also increases.With the change of x,the Q*f value first decreases and then increases.The Ca₂(Al_1–xMg_x)(Al_1–xSi_1+x)O₇ series ceramics obtain the best microwave performance??_r=8.09,Q*f=23938GHz,and?_f=-51.46 ppm/??at x=0. For the(Mg_1-xLi_0.5xY_0.5x)₂SiO₄ series ceramics,the XRD analysis shows that the phase of the sample changes with the change of x due to the difference in the radius of between Y³⁺ions,Li⁺ions and Mg²⁺ions.With the increase of the doping,the Mg₂SiO₄ phase of the sample will change to the LiYSiO₄ phase,and the change of the ionic radius will be accompanied with the obvious peak shift and the change of the peak intensity during the transition.Relative permittivity and temperature coefficient of resonance frequency have a linear relationship with x.By substituting for Mg2+ions,the sintering temperature of the sample is from 1475? to 1125?,and better sintering characteristics and microwave performance??_r=8.5,Q*f=55831 GHz?@12.6 GHz?,?_f=-38.7 ppm/??are obtained at x=0.5,1125?.For the Mg_2-xY_xSiO_4-xN_x series ceramics,it is found by XRD analysis that there is a small amount of Y₂SiO₅ phase present.The relative dielectric constant and temperature coefficient of resonance frequency of the samples have a linear relationship with x,but the sintering temperature of the sample does not change much with doping,and they are all around 1500?.The Q*f value decreases with the change of x due to the occurrence of Y₂SiO₅ heterophase,and the range changes from68236GHz to 109656GHz.