Abstract
The effects of the milling process on the characteristics of Ba 2 Ti 9 O 20 materials were investigated. The chemical analyses using transmission electron microscopy (EDAX in TEM) revealed that the SiO 2 species incorporated into the Ba 2 Ti 9 O 20 materials were expelled by the Ba 2 Ti 9 O 20 grains. It induced the dissociation of the Ba 2 Ti 9 O 20 materials near the grain boundaries and degraded the microwave dielectric properties of the materials. The same phenomenon was assumed to be the procedure by which the high-energy-milling (HEM) process using Si 3 N 4 grinding media (Si 3 N 4 -HEM) deleteriously influenced the microwave dielectric properties for the Ba 2 Ti 9 O 20 materials. Utilizing the three-dimensional-milling (3DM) process in place of the Si 3 N 4 -HEM one markedly improved the characteristics of the Ba 2 Ti 9 O 20 materials. The 3DM-processed samples own the same crystallinity as the HEM-processed ones but possess a pronouncedly more uniform microstructure and, therefore, exhibit a superior quality factor [(Q × f) 3DM ≤ 28 500 GHz and (Q × f) HEM ≤ 21,900 GHz] with the same large dielectric constant (K ≤ 38-39), when sintered at the same conditions (1350 °C/4 h). Such a phenomenon is ascribed to the fact that the 3DM process can pulverize the powders efficiently but induce no SiO 2 -contamination. © 2006 IOP Publishing Ltd.