Milling effect on the microwave properties of Ba2Ti9O20 investigated by EMP technique

The effects of milling process on the microstructure and microwave properties of Ba2Ti9O20 materials were systematically investigated by the evanescent microwave probe (EMP) technique. It was found that although the reaction kinetics of Ba2Ti9O20 materials was markedly enhanced by the high-energy-milling (HeM) process, the quality factor of the materials decreases with the duration in HeM process. SiO2-contamination due to the HeM milling process (with Si3N4 media) is presumed to be the main cause. In this study, SiO2-doped Ba2Ti9O20 sample was adopted to enhance and trace the SiO2 effect during HeM process. The EMP investigation on the microwave dielectric properties of the local region for the Ba2Ti9O20 samples indicates that lossy Si/Ti-containing phases were expelled by the Ba2Ti9O20 grains, which is especially obvious in the as-sintered sample surface. Si-contamination induced the abnormal grain growth phenomenon, which, in turn, degrades the microwave dielectric quality factor of the Ba2Ti9O20 materials.