Effect of powder, chemistry and morphology on the dielectric properties of liquid-phase-sintered alumina

Dielectric properties of liquid-phase-sintered alumina (LPS) ceramics prepared using commercial powders of different particle size distribution and impurities (Na2O) content were studied. So far as the particle size distribution of the commercial powder is concerned, LPS ceramics, those derived from powders of both medium (3.1–8.4 μm) and coarse (70–100 μm) grades, showed similar dielectric loss, whereas it was higher in the case of LPS derived from the reactive powders (<1 μm). While considering the impurity levels of the powders, higher Na2O content (0.57 wt.%) in the powder showed significantly higher dielectric loss compared to that of the lower Na2O content (<0.2 wt.%). Furthermore, the MgO/(CaO+BaO+KNaO) ratio in the chemical composition of the LPS within the range of 0.4–1.8 was found to influence the dielectric properties in the frequency range of 102–107 Hz. The dielectric loss in the frequency band of 102–103 Hz was found to be higher in the case of the LPS with a MgO/(CaO+BaO+KNaO) ratio of 1.6. Besides the starting powder and the chemical composition, the orientation of alumina platelets arising out of fabrication route (e.g. tape casting) was also found to have a profound influence on the dielectric properties. A higher loss was observed in the tape cast specimen.