Research On Preparation And Modification Of 0.65CaTiO₃-0.35LaAlO₃-based Microwave Dielectric Ceramics

In order to further miniaturize microwave device and improve the performance of microwave components,it is very important to develop new high-quality factor,middle-dielectric constant and low sintering temperature microwave dielectric ceramics.the 0.65CaTiO₃-0.35LaAlO₃?CTLA?perovskite solid solutions is a newly reported ceramic with excellent dielectric properties.0.65CaTiO₃-0.35LaAlO₃ ceramics had the best microwave dielectric properties:?_r=44,Q×f=30000 GHz,?_f=-2×10-6/?.the sintering temperature of CTLA ceramic is higher than 1450?,production cost is high,and the microwave dielectric properties also need to be improved.At present,the most effective tow methods to improve the sintering property and dielectric properties of microwave dielectric are adding appropriate oxide or glass frit doping and using ultrafine powder prepare ceramics.While improving some properties of microwave dielectric ceramics,it often affects other properties,especially when the sintering temperature is reduced,the quality factor of ceramics will be greatly reduced.Therefore,the object of the research mentioned above is CTLA ceramic.The effects of Y³⁺ doped on the microstructure and microwave dielectric properties of CTLA ceramic were systematically studied.This research approached the influence of cell structure parameters such as ionic bond,inclination and distortion degree of oxygen octahedron value and tolerance factor on microwave dielectric properties.The preparation of CTLA nano-ceramic powder by polymer precursor method was studied,the sintering temperature of CTLA ceramics was reduced by starting with nano powder prepared by liquid phase method.Based on the preparation technology of polymer precursor method,the effect of Ce³⁺ doped on the dielectric properties of CTLA ceramics was studied,and the changes of the order degree and micro structure of the cations in different Ce³⁺ doped amount were studied.Through the above modification methods,materials with excellent microwave dielectric properties and low sintering temperature were obtained.Firstly,the best microwave dielectric properties of CTLA ceramics was ?_r=45.92.Q×f=37774 GHz,?_f=-2.3×10-6/? when the ceramics were sintered at 1270? for 3 h and sintered at 1480? for 5 h by conversional solid-state reaction method.In order to adjust the temperature coefficient of resonator frequency of CTLA ceramic,Y³⁺ion was selected as doping element to prepare the 0.65CaTiO3-0.35(La_i-xY_x)AlO₃?CTLYA-x,x=0,0.02,0.04,0.06,0.08?microwave dielectric ceramics by conventional solid-state reaction method.The effects of Y³⁺ion doping on the micro crystal structure and dielectric properties were investigated.The results revealed that a single orthorhombic phase for all the compositions can form and the unit cell volume increases linearly with the doping content x.Y³⁺ion dopant can increase the quality factor and improve the temperature coefficient of resonant frequency of CTLA ceramics.When x=0.02,the optimal microwave dielectric properties of ?_r=45.8,Q×f=38957 GHz,and ?_f=4×10-6/? for the CTLYA-0.02 ceramics could be obtained,which sintered at 1500?for 5 h.Secondly,in order to reduce the sintering temperature of CTLA ceramic,CTLA ceramic powders were prepared by polymer precursor method,the process principle of polymer precursor method was analyzed,and the effect of liquid phase reaction conditions on polymer stability was studied.CTLA ceramic powders were obtained by calcining the polymer at different temperatures.When n?EG/EDTA?=2:1,n?EDTA/metal-ion?=1:1,precursor solution pH is 6,the CTLA nano-ceramic powder was synthesized at 950?.CTLA ceramics made from this powder have optimal microwave dielectric properties:?_r=41.8,Q×f=34151 GHz,and ?_f=-5.8×10-6/?,which calcined at 950? and sintered at 1325? for 3 h.Finally,in order to reduce the sintering temperature of CTLA ceramics and further improve its dielectric properties.The 0.65CaTiO3-0.35(La_1-xCe_x)AlO₃?CTLCA-x,x=0,0.1,0.2,0.3,0.4?microwave dielectric ceramic was successfully synthesized by the polymeric precursor method.The effects of Ce³⁺ion doping on the micro crystal structure and dielectric properties were investigated.When x=0.2,the optimal microwave dielectric properties of ?_r=42.7,Q×f=39159 GHz,and ?_f=-7×10-6/? for the CTLCA-0.2 ceramics could be obtained,which sintered at 1325? for 3 h.