Effects of B2O3 addition on sintering behavior and microwave dielectric properties of Mg5Nb4O15 ceramics prepared by the sol–gel method

• Mg5Nb4O15 ceramics were prepared by the sol–gel method.
• B2O3 was dopped to improve the properties of Mg5Nb4O15 ceramics.
• The τf values of Mg5Nb4O15 ceramics were in range of −27.04– −54.64 ppm/°C.
• The εr values was ∼13.4 and Q·ƒ values was ∼55,700 GHz at 1300 °C when 5% B2O3 added.

The correlations of sintering temperatures and the microwave dielectric properties of (1-x)Mg5Nb4O15-xB2O3 (x = 1, 3, 5, and 10 wt.%) compounds were investigated based on the sol–gel method. A suitable amount of B2O3 (5 wt.%) was added to decrease sintering temperatures with little detrimental effect on these dielectric properties of the Mg5Nb4O15 compounds due to the formation of liquid phase. The variations in the dielectric constant (εr) and the quality factor (Q·f) of the pseudobrookite-type Mg5Nb4O15 compounds depending on the amount of B2O3 and the sintering temperature were studied, respectively. With the increase of the x values, the εr and Q·f increased and the optimal microwave dielectric properties with high εr ∼13.4, Q·f ∼55,700 GHz, τf ∼ −50.93 ppm/°C was obtained for (1-x)Mg5Nb4O15-xB2O3 (x = 5 wt.%) sintered at 1300 °C for 4 h.

The aqueous sol–gel route was used to synthesize the B2O3 doped nanosized Mg5Nb4O15 powders. Inexpensive raw materials of Nb2O5 were converted into aqueous Nb–CA solution by corrosive HF. A stoichiometric amount of Mg(NO3)·6H2O and H3BO3 were added to the above solution. The whole process involved complexation of aqueous metal ions by cheap poly functional carboxyl acids such as citric acid and ethylene glycol instead of expensive metal alkoxides. The (1 − x)Mg5Nb4O15 − xB2O3 (x = 1, 3, 5,and 10 wt.%) compounds were sintered with nearly full density when the Mg5Nb4O15 compound with x = 5% sintered at 1300 °C for 4 h with the excellent microwave properties of εr = ∼13.4, Q·ƒ = ∼55, 700 GHz and τƒ = ∼−50.93 ppm/°C, which was comparable with the results of pure samples sintered at 1450 °C by the aqueous sol–gel method.Figure optionsDownload as PowerPoint slide