Preparation And Properties Research Of Ca₅Ni₄?VO₄?₆ Microwave Ceramics

The rapid development of microwave components places higher requirements on microwave dielectric ceramics:proper dielectric constant,high quality factor,and low temperature coefficient of resonant frequency.In this paper,the garnet Ca₅Ni₄?VO₄?₆microwave ceramics with low permittivity are taken as the research object and synthesized by the solid-state reaction method.Then attempts to improve the microwave performance of Ca₅Ni₄?VO₄?₆ ceramics through non-stoichiometry and B-site ion substitution.XRD,SEM,Raman and other methods were used to systematically study the changing law of crystal phase composition,micromorphology,lattice constant,ionic bonds,packing fraction and cation ordering degree,thus analyzing the inner connection with microwave properties.This paper has researched the following main content:Effects of the non-stoichiometric V and Ni on the microwave properties of Ca₅Ni₄?VO₄?₆ ceramics were firstly studied.When vanadium is absent,the presence of NiO phase will increase the sintering temperature,which results in low dielectric constant and quality factor.Excessive vanadium will reduce the relative density and decrease the quality factor.The effects of non-stoichiometric Ni are essentially opposite to V for Ca₅Ni₄?VO₄?₆ ceramics.Therefore,it is found that the non-stoichiometric V and Ni cannot improve the microwave properties of Ca₅Ni₄?VO₄?₆ ceramics.Effects of B-site ion substitution on the microwave properties of Ca₅Ni₄?VO₄?₆ceramics were studied afterwards.Mg substitution will not change the garnet structure but form a solid solution.Mg substitution will increase the unit cell volume,thus reducing the dielectric constant;moderate Mg substitution will increase the B-site ionic bond strength and bond valence,thereby improving the quality factor,while reducing the B-site ionic bond length and ameliorating?_f.Ca₅Ni₂Mg₂?VO₄?₆ ceramics sintered at875?exhibit excellent microwave properties:?_r=9.6,Q×f=60613 GHz,and?_f=-32 ppm/?.The sintering process of Ca₅Ni₂Mg₂?VO₄?₆ ceramics was researched subsequently.Increasing the sintering temperature will lead to the appearance of V⁴⁺and then increase the lattice constant,which results in the decrease of packing fraction and the reduction of quality factor.The change in heating rate will affect the quantity of vanadium volatilization.A proper heating rate can increase the packing fraction and cation order degree,which will ameliorate the quality factor.The optimal sintering temperature of Ca₅Ni₂Mg₂?VO₄?₆ ceramics is 875?,and the optimal heating rate is2?/min.After Zn substitution,the ceramics still keep a garnet structure and the lattice constant increases.Zn substitution increases the dielectric constant.When the amount of Zn substitution is 2,it will lead to exceeding the solid solution and accompanied by the precipitation of the second phase.The quality factor is affected by both packing fraction and relative density;Zn substitution moves the?_f in the negative direction.Ca₅Ni_3.2Zn_0.8?VO₄?₆ ceramics sintered at 845?have good microwave dielectric properties:?_r=9.94,Q×f=39074 GHz,and?_f=-62 ppm/?.