Development of magneto-dielectric materials based on Li-ferrite ceramics. I. Densification behavior and microstructure development

Abstract

The densification, grain growth and microstructure development of Li-ferrite (Li0.50Fe2.50O4) ceramics, doped with Bi2O3 as sintering aid and Co as magnetic property modifier, were studied. The primary objective of the present study was to develop magneto-dielectric materials, with matching permeability and permittivity, as well as low magnetic and dielectric loss tangents, for miniaturization of HF (3-30 MHz) antennas. Due to its poor densification, fully sintering of pure Li0.50Fe2.50O4 requires high temperature (1200 °C). High temperature sintering resulted in undesirable high dielectric loss tangent, due to the formation of Fe2+ ions. To reduce the sintering temperature of Li0.50Fe2.50O4, Bi2O3 was selected as sintering aid because of its relatively low melting point (∼820 °C). The densification behavior and slow grain growth rate of Li0.50Fe2.50O4 were greatly improved by the addition of Bi2O3, because a liquid phase sintering occurred during the sintering process at high temperature due to the low melting point of Bi2O3. It is found that 1% Bi2O3 is able to promote full densification of Li0.50Fe2.50O4 at a temperature of as low as 850 °C. Comparatively, the effect of Co on the densification and grain growth behavior of Li0.50Fe2.50O4 ceramics is much less significant. © 2007 Elsevier B.V. All rights reserved.