Influence of mechanical activation on functional properties of barium hexaferrite ceramics

Abstract

© 2018 Elsevier Ltd and Techna Group S.r.l. Barium hexaferrite ceramics were prepared using mechanically activated mixtures of iron and barium titanate. The 60:40 mass% Fe:BaTiO3 powder mixtures were mechanically activated for different times (100–240 min) and sintered at 1100 and 1200 °C in order to determine the influence of mechanical activation of the precursor on the magnetic and dielectric properties of the resulting barium hexaferrite ceramics. The final product contained 84–89 mass% of Ba2Fe22.46O38Ti1.54 phase, with higher content corresponding to longer mechanical activation of the precursor. XRD and Raman measurements indicated that the remainder of the sample consists of leftover BaTiO3 and hematite, which was formed by the oxidation of iron during mechanical activation and sintering in air. Magnetic properties of samples sintered at 1200 °C are superior to those sintered at 1100 °C, which can be attributed to higher Ba2Fe22.46O38Ti1.54 phase content. The position of the Curie temperature in 350–420 °C temperature region is consistent with 0.8:1 ratio of Ti to Ba. Maximum magnetization was observed for samples activated for 120 min. Dielectric properties of samples sintered at 1200 °C showed a dependence on frequency, with a significant drop in relative permittivity with an increase in frequency in the low-frequency region, and relatively constant values of relative permittivity in the high-frequency region. The tangent loss showed a decrease with increase in frequency, where peaks corresponding to the resonance of the electron hopping frequency with the external field were observed in the samples corresponding to the longer mechanical activation. Dielectric properties showed relatively small changes for samples activated longer than 150 min.