Research On The Preparation And Properties Of B₂O₃-P₂O₅-SiO₂ Based Microwave Dielectric Ceramics

Silica oxide-based microwave dielectric ceramics have excellent dielectric properties,but the use of silicon oxide-based ceramics is limited because of the high sintering temperature and the complex phase transition in the sintering process.Microwave dielectric ceramics based on B₂O₃-P₂O₅-SiO₂?BPS?take silica as raw material,B₂O₃-P₂O₅ as sintering aid and reinforced ceramic matrix in the form of BPO₄ grain precipitation.BPS ceramics have the advantages of low sintering temperature,low dielectric constant?e_r?,and low dielectric loss.Therefore,they have broad application prospects as microwave dielectric substrate materials.BPS-based microwave dielectric ceramics were prepared by solid-state sintering by using SiO₂,H₃BO₃ and NH₄H₂PO₄ as raw materials.The effects of pre-sintering temperature,heating rate and holding time on the pre-sintered green body were systematically studied,and the appropriate pre-sintering process was formulated.The kinds of SiO₂ raw materials,the ratio of SiO₂ to BPO₄ in formula of raw material and sintering temperature on the microwave dielectric properties of BPS ceramics were systematically studied.The influence of ternary system ZnO-B₂O₃-SiO₂?ZBS?glass and multielement system Li₂O-MgO-ZnO-B₂O₃-SiO₂?LMZBS?glass as sintering aids on the low-temperature sintering properties of BPS,the compatibility between BPS ceramics and Ag particles,and the adjustment of frequency-temperature coefficient of BPS ceramics by CaTiO₃ were also discussed.The main research work and results are as follows:?1?For different types of SiO₂ source as diatomite and cristobalite SiO₂ powder,Preparation of porous low dielectric constant BPS ceramics from Diatomite for its porosity of structure.Optimum comprehensive dielectric properties were obtained When H₃BO₃-NH₄H₂PO₄?mol ratio 1.05:1?was added 10wt%and sintered at 340? for 2 hours to presinter synthesis,and sintered at 1000? for 2h,the porous ceramics were prepared with a bulk density of 1.81g/cm³ and a porosity of 56.42%.The dielectric properties of the ceramics weree_r=2.21,Q×f=5758GHz,t_f=-14.61ppm/?;The dielectric loss of BPS ceramics was reduced by using cristobalite SiO₂ powder as SiO₂ source to prepare compact ceramics.Optimum dielectric properties were obtained When H₃BO₃-NH₄H₂PO₄?mol ratio1.05:1?was added 30wt%and sintered at 850? for 2 hours to presinter synthesis,and sintered at1000? for 2h,the BPS ceramics were prepared with a bulk density of 2.31g/cm³,and the dielectric properties of the ceramics weree_r=3.97,Q×f=16040GHz,t_f=-24.72ppm/?;?2?ZBS and LMZBS glass sintering additives have different effects on the sintering properties and microwave dielectric properties of BPS ceramics.The experimental results show that the densification sintering of BPS ceramics can be achieved at 900? by adding 4wt%of ZBS glass.The microwave dielectric properties of BPS ceramics aree_r=4.0,Q×f=16702GHz,t_f=-24ppm/??BPS ceramics with 4wt%LMZBS addition can be densified and sintered at 900?.The microwave dielectric properties of BPS ceramics aree_r=4.04,Q×f=22600GHz,t_f=-22ppm/?;?3?On the basis of adding 4wt%LMZBS as sintering aids,the frequency-temperature coefficient of BPS ceramics is obviously improved by doping a certain amount of CaTiO₃.The frequency-temperature coefficient of BPS ceramics sintered at 900? for 2h is nearly zero when the addition is 3wt%,and its dielectric properties are as follows:?_r=4.26,Q×f=19600GHz,?_f=-5.74ppm/?.