Microwave dielectric imaging of Ba₂Ti₉ O₂₀ materials with a scanning-tip microwave near-field microscope

The dielectric image of Ba₂Ti₉O₂₀, B₂T₉, materials at microwave frequencies was measured using a scanning evanescent microwave probe (EMP) technique. The average dielectric constant evaluated from the dielectric image ( ε _r=26-43) was consistent with the measurements made using a conventional cavity method, which are in the range ε _r=32-38. The dielectric image consists of aggregates of clusters about tens of micron in size, and is totally different from the conventional granular structure for the materials, which contains submicron sized grains. The calcination conditions were observed to impose marked influence on the phase purity and hence the microwave dielectric properties of the sintered materials. EMP-derived dielectric images reveal that the materials containing secondary phases and exhibiting low Q -factor consist of aggregates of clusters with pronounced fluctuated distribution of dielectric constant, whereas the materials of high phase purity and high Q -factor show very mild fluctuation in dielectric constant over the samples.