Effect of Bi2O3–B2O3 as a sintering aid in microstructure and dielectric properties of Fe2Mo3O12 electroceramic

Abstract

Molybdates from A2Mo3O12 family have been widely investigated due to its low sintering temperature, low thermal expansion coefficient, and low dielectric loss. Fe2Mo3O12 (FMO) is an oxide from this family and widely used in the catalytic field. The aim of this work is to evaluate the influence of the Bi2O3–B2O3 as a sintering aid in the microstructure and dielectric properties of FMO. The diffraction results showed that the FMO with the monoclinic structure phase was obtained after the calcination process (650 °C). Mössbauer spectroscopy showed the formation of Fe2O3 after the sintering process at 800 °C. The scanning electron-microscopic image demonstrates an increase of the grain as a function of sintering aid concentration. The samples were analyzed using the impedance spectroscopy at radiofrequency with temperature variation. The Nyquist diagram obtained in this temperature range was fitted from an equivalent circuit with three R-CPE associations, corresponding to the morphology of the electroceramics. For dielectric properties in the microwave, all the samples showed values of εr lower than 10. Values of Q x f above 14,132.35 GHz were achieved. The thermal stability was evaluated by the temperature coefficient of resonant frequency (τf). The lowest τf values of − 6.55 ppm/°C and − 4.35 ppm/°C (near-zero) were measured to FMO and FMO mixed with 7.5 wt % Bi2O3–B2O3, respectively. Based on these results, FMO can be used to low-permittivity ceramic for low-temperature co-fired ceramics (LTCC) applications, antenna substrate, and millimeter-wave range.