Influence of the sintering process on microstructures and microwave properties of Ca5Ni2Mg2V6O24 ceramics

A new low-temperature sintered microwave ceramic Ca 5 Ni 2 Mg 2 V 6 O 24 (CNMVO) was synthesized by a solid-state reaction method. The effect of sintering process on microstructures and microwave properties of CNMVO ceramics was investigated in detail. XRD results and EDS analyses show that CNMVO ceramics sintered at 850–925 °C are the uniform solid solution with a stable cubic garnet structure. The CNMVO ceramic sintered at 875 °C has the highest Q × f value and is accompanied by the volatilization of vanadium observed by SEM . TG curves demonstrate that the increase of heating rate weakens the vanadium loss. According to the Raman spectra , the Q × f value reaches the maximum value at a heating rate of 2 °C/min, because of the highest cation ordering degree and the densest packing fraction caused by the properly deficient vanadium. As a result, the Ca 5 Ni 2 Mg 2 V 6 O 24 ceramic sintered at 875 °C with a heating rate of 2 °C/min exhibits the best microwave properties: ε r  = 8.07, Q × f = 60,613 GHz, and τ f  = −32 ppm/°C.