Structural evolution, low-firing characteristic and microwave dielectric properties of magnesium and sodium vanadate ceramic

A low-firing microwave dielectric ceramic with the composition of NaMg4V3O12 was prepared by a solid state reaction method. NaMg4V3O12 ceramic could be indexed as a tetragonal phase and the unit cell parameters were calculated as a=b=6.894 Å, c=19.308 Å. Room temperature X-ray diffraction data shown that the ceramic displayed an obvious peak variations. After sintered at 830 °C for 4 h, the ceramic could be well densified and exhibited good microwave dielectric properties with a relative dielectric constant (εr) of 9.53, quality factor (Q×f) of 32,820 GHz (at ~11 GHz), and temperature coefficient of resonator frequency (τf) of −90 ppm/°C. With increasing the sintering temperatures, the curve of the relative dielectric constant exhibits a similar trend to that of the relative density. The Q×f values were related to the average grain size. Due to the decline of the average grain size, the Q×f values decrease above 830 °C. The variation of τf values was attributed to microstructure variations with increasing the sintering temperatures. Moreover, an X-ray photoelectron spectroscopic analysis illustrated that the mass percentages of vanadium element in the sample (sintered at 830 °C) are 96.34% for vanadium (V) and 3.66% for vanadium (IV).