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

摘要

The densification, grain growth and microstructure development of Li-ferrite (Li_(0.50)Fe_(2.50)O_4) ceramics, doped with Bi_2O_3 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 (Li_(0.50)Fe_(2.50)O_4) requires high temperature (1200 deg C). High temperature sintering resulted in undesirable high dielectric loss tangent, due to the formation of Fe~(2+) ions. To reduce the sintering temperature of (Li_(0.50)Fe_(2.50)O_4), Bi_2O_3 was selected as sintering aid because of its relatively low melting point (approx 820 deg C). The densification behavior and slow grain growth rate of (Li_(0.50)Fe_(2.50)O_4) were greatly improved by the addition of Bi_2O_3, because a liquid phase sintering occurred during the sintering process at high temperature due to the low melting point of Bi_2O_3. It is found that 1 percent Bi_2O_3 is able to promote full densification of (Li_(0.50)Fe_(2.50)O_4) at a temperature of as low as 850 deg C. Comparatively, the effect of Co on the densification and grain growth behavior of (Li_(0.50)Fe_(2.50)O_4) ceramics is much less significant.