Preparation And Properties Research Of Ca₅Mg₄?VO₄?₆ Microwave Ceramics

Microwave dielectric components with excellent performance is indispensable to the rapid development of microwave communication,which put forward higher requirements for microwave dielectric ceramics.The low-temperature co-fired ceramic technology meet the needs above.The Ca₅Mg₄?VO₄?₆ microwave dielectric ceramics studied in this paper have a low intrinsic sintering temperature,they were prepared by the solid-phase reaction method.To improve the microwave dielectric properties of Ca₅Mg₄?VO₄?₆ceramics,two methods were employed:non-stoichiometric ratio of elements and substitution of B-site ions.The phase composition and microscopic morphology of the ceramics were analyzed by XRD and SEM.At the same time,the internal laws of the microwave dielectric properties were studied by the theoretical calculations,such as lattice energy and bond energy.The non-stoichiometric ratio of V or Ca was not detrimental to the microwave dielectric properties of Ca₅Mg₄?VO₄?₆ ceramics.For Ca₅Mg_4+x?VO₄?₆?-0.05?x?0.15?ceramics,the Q×f value at x=0.05 was significantly improved comparing to the stoichiometric one.The specific properties are as follows:?_r=9.93?Q×f=56192GHz??_f=-48.3ppm/?.The tests showed that a slight excess of Mg²⁺ions impaired the growth of grains and no second phase was found.Based on theoretical calculation and analysis,it was found that the increase of the Q×f value was attributed to the reduction in grain size,the elevation in the ordering degree of ions,and the augment in packing fraction and lattice energy.In the study of substitution on B-site,the Q×f value of Ca₅Mg₄?VO₄?₆ ceramics was improved by the Co²⁺ions,and the maximum value was obtained when the element ratio of Co was 1.The specific properties are as follows:?_r=9.65?Q×f=54685GHz??_f=-55.3ppm/?.After the replacement,solid solution was formed,which was a reasonably explanation for the decrease in sintering temperature.In addition,the grain size reduction caused by the substitution was beneficial to the promotion of the Q×f value.Both the Q×f value and the sintering temperature were lowered when replacing Mg²⁺ions by Zn²⁺ions.When the element ratio of Zn is 2,the sintering temperature dropped to 750?.Except the research above,the study of?_r and?_f were carried out.It was showed that the relative density is the primary factor for?_r.When the relative density is lower than94%,it dominated the change of?_r.But when the relative density is higher than 94%,?_r was mainly affected by the ion polarizability per unit volume.As for?_f,it always changed as the bond energy of the V-O bond altered,which was the largest bond energy in ceramics.