Preparation And Properties Of Microwave Dielectric Ceramics With Low Dielectric Constant

As a new type of functional ceramics,microwave dielectric ceramics are widely used in microwave devices such as resonators,filters,dielectric antennas.With the rapid development of science and technology,the demand for information is increasing.In order to improve the transmission rate of information and reduce the propagation delay time of devices,low dielectric microwave dielectric ceramics have attracted more and more attention and research.In microwave dielectric ceramics with low dielectric constant,silicate system has lower dielectric constant than other dielectric ceramics because of its unique tetrahedral structure and strong covalent bond.In this paper,several different silicate systems have been investigated,and the relationship between complex chemical bond theory and microwave dielectric properties has been emphatically studied.In this thesis,Ca₂MgSi₂O₇ ceramics were prepared by solid-state reaction method.The effects of different holding time of paraffin removal on the microwave dielectric properties were studied and the optimum holding time of paraffin removal could reduce dielectric loss by an order of magnitude,reaching 1.24×10^-4.Then Sr₂MgSi₂O₇,CaCoSi₂O₆ and CaMg_1-xNi_xSi₂O₆?0?x?0.12?ceramics were prepared under the optimum holding time of paraffin removal.The relationship between chemical bond parameters and microwave dielectric properties was further analyzed using complex chemical bond theory.For Ca₂MgSi₂O₇,Sr₂MgSi₂O₇ and CaCoSi₂O₆ ceramics,dielectric constant,quality factor and resonant frequency temperature coefficient were related to bond ionicity,lattice energy and bond energy,respectively.The dielectric constant and quality factor increase with the increase of bond ionicity and lattice energy,and the increase of bond energy could stabilize the system and made the resonant frequency temperature coefficient close to zero.For CaMg_1-xNi_xSi₂O₆?0?x?0.12?ceramics,the dielectric constant and quality factor were consistent with the variation trend of polarizability and packing fraction,respectively.The resonant frequency temperature coefficient was affected by the total bond valence of Si-O bond.In microwave dielectric properties,within the scope of this study,CaCoSi₂O₆ceramics had the lowest dielectric constant,which could be reduced to about 6 at the optimum sintering temperature.The quality factors of Ca₂MgSi₂O₇ ceramics and Sr₂MgSi₂O₇ ceramics were 8016 GHz and 22530 GHz,respectively.For CaMg_1-xNi_xSi₂O₆?0?x?0.12?ceramics,the quality factor could be further increased to 56050GHz when x=0.10.