Preparation And Properties Research Of Ca₅Mn₄?VO₄?₆ Microwave Ceramics

The requirement for miniaturization,integration and modularization of devices are becoming increasingly urgent.Low Temperature Co-fired Ceramic?LTCC?technology is widely used in the manufacture of key components because of its high integration,miniaturization and high frequency characteristics.Therefore,microwave dielectric ceramics with low dielectric constant and high quality factor under low sintering temperature attract much attention due to their great potential value in application.In this paper,Ca₅Mn₄?VO₄?₆ microwave dielectric ceramic was prepared by traditional solid-state reaction method at 875°C,and then the performance of this cermic was optimized by non-stoichiometry and ion substitution methods.To correlate the ceramic phase composition,unit cell volume,packing fraction,bond valence,distortion,micromorphology,elemental composition,cation ordering degree,Raman shift with Microwave dielectric properties,the test methods such as XRD,SEM,EDS,Raman spectroscopy had been carried out.The main work of this paper as follow:Firstly,the effect of V nonstoichiometry on the dielectric properties of Ca₅Mn₄V_6+xO₂₄ microwave dielectric ceramics was studied.XRD results and SEM images showed that Ca₅Mn₄V_6+x+x O₂₄?-0.15?x?0?samples were proved to be single Phase,but a small amount of vanadium-rich phase appeared at x=0.05.Due to the V-vacancy,the ceramic grains were becoming tightly packed and the cation ordering degree was improved.Ca₅Mn₄V_5.9O₂₄ ceramic sample exhibited excellent microwave dielectric properties:?_r=11.5?Q×f=39141GHz and?_f=-74.9ppm/°C.Secondly,on the basis of V content of 5.9,the effects of Ca²⁺and Mn²⁺ions nonstoichiometry on the microwave dielectric properties of Ca₅Mn₄V_5.9O₂₄ ceramic were studied systematically.The study found that the relative density reduced whether Ca²⁺and Mn²⁺ions were insufficient or excessive,leading to the decrease of quality factor.Hence,the samples had the best microwave dielectric properties when both Ca²⁺and Mn²⁺ions were in stoichiometry.The substitution of Mg²⁺and Zn²⁺ions for Mn²⁺ions had been studied to investigate the effect of B-site substitution on the crystal structure,morphology and dielectric properties of Ca₅Mn₄?VO₄?₆.First,the substitution of Mg²⁺ions did not change the crystal structure of Ca₅Mn_4-xMg_x?VO₄?₆ ceramics in the range of 0?x?2.The unit cell volume and dielectric constant of Ca₅Mn_4-xMg_x?VO₄?₆ ceramics were gradually decreasing with the content of Mg²⁺ions increases.Meanwhile,the optimal sintering temperature of the ceramic system reduced with Mg²⁺ions content increased,and then resulting in the decrease of the average grain size.With increasing Mg²⁺contents,the quality factor increased due to the adding of the packing fraction and?_f value moved towards the positive direction because of the increase of the Mn/Mg-O bond valence.Finally,the Ca₅Mn_2.4Mg_1.6?VO₄?₆ ceramic sintered at 860°C exhibited excellent microwave dielectric properties:?_r=10.9?Q×f=60444GHz and?_f=-76.5ppm/°C.Secondly,The addtion of Zn content resulted in the decreasing of the optimal sintering temperature and?_f value,and leaded to the adding of dielectric constant.The Q×f value was mainly affected by packing fraction and the impurity phase.Hence,The maximum Q×f value was obtained when x=0.4.Ca₅Mn_3.6Zn_0.4?VO₄?₆ceramic sintered at 835°C to obtain good microwave dielectric properties:?_r=11.55?Q×f=39259Ghz and?_f=-85.5ppm/°C.