Effect of non-stoichiometry on the structure and microwave dielectric properties of BaMg₂V₂O₈ ceramics

Abstract

The effect of the A-site non-stoichiometry on the crystal structure, microstructure and microwave dielectric properties of Ba_1+xMg₂V₂O₈ ceramics was investigated in this work. The X-ray diffraction results show that the BaMg₂V₂O₈ solid solution was formed in the composition range of −0.02 ≤ x ≤ 0.02 while a secondary phase Ba₃V₂O₈ started to appear at x ≥ 0.04, as confirmed by scanning electron microscopy and energy dispersion spectrum. The introduction of a slightly excessive Ba²⁺ into the matrix lattice could enhance the quality factor (Q × f) owing to the improved sinterability while overmuch Ba²⁺ would deteriorate Q × f due to the presence of the high-loss Ba₃V₂O₈ phase. The maximum Q × f value of 192,840 GHz was obtained at x = 0.01. The temperature coefficient of the resonant frequency (τ_f) changed little as −0.02 ≤ x ≤ 0.02 and then monotonically increased up to a positive value as 0.02 < x ≤ 0.52. Near-zero τ_f value was obtained at x = 0.44 owing to the formation of the composite between the secondary-phase Ba₃V₂O₈ and the matrix-phase BaMg₂V₂O₈. In general, excellent microwave dielectric properties of ε_r = 12.4, Q × f = 192,840 GHz, τ_f = −35.9 ppm/°C and ε_r = 13.7, Q × f = 92,580 GHz, τ_f = −5.3 ppm/°C were achieved in Ba_1.01Mg₂V₂O₈ ceramics sintered at 915 °C for 4 h and Ba_1.44Mg₂V₂O₈ ceramics sintered at 930 °C for 4 h, respectively.