Low temperature sintering and microwave dielectric properties of (Mg3 − xZnx)(VO4)2 ceramics

This paper describes the effects of Zn substitution for Mg on the microwave dielectric properties of (Mg3 − xZnx)(VO4)2 ceramics. As for the XRPD patterns of (Mg3 − xZnx)(VO4)2 ceramics sintered at the sintering temperature of 750 °C, no secondary phase was detected over the whole composition range. However, in the case of the sample sintered at 850 °C, the Zn4V2O9 and Zn2V2O7 compounds were identified by using XRPD; this result was attributed to the decomposition of Zn3(VO4)2 phase. From crystal structure analysis, it was found that the atomic distances of M(1)O (M = Mg and Zn) and M(2)O in MO6 octahedra increased, though that of VO in VO4 tetrahedron decreased. Moreover, the slight tilting of M(2)O6 octahedron was observed by the Zn substitution. As for the covalency of cation–oxygen bond, the covalency of MO bond in M(1)O6 and M(2)O6 octahedra decreased because of the increase in the atomic distance of MO, whereas that of VO increased with increasing the Zn addition. However, as a result, the slight decrease in the covalency of cation–oxygen bond was recognized because the variation in the covalency of MO bond is predominant in this crystal structure. The dielectric constants of the samples range from 4.4 to 11.1. The decrease in the covalency may be related to the difference in the dielectric constant of each composition. The maximum Q · f value of bulk densities is effected by varying the chemical composition of (Mg3 − xZnx)(VO4)2 ceramics and it shifts toward lower sintering temperature with an increase in x within the temperature region of 800–1050 °C. The temperature coefficient of resonant frequency (τf) of the samples decreased with increasing of Zn, and then a variation in τf value was attributed to the tilting of M(2)O6 octahedron caused by Zn substitution for Mg.