Effects of additives on the microstructure and dielectric properties of Ba₂Ti₉O₂₀microwave ceramic

Preparation of dense and phase-pure Ba₂Ti₉O₂₀is generally difficult to achieve using a solid-state reaction, due to the presence of several thermodynamically stable compounds in the vicinity of the desired composition. This work investigated the effects of various additives (TiO₂, MnO, and ZrO₂) on the densification, microstructural evolution, phase stability, and dielectric properties of Ba₂Ti₉O₂₀. Ceramics with theoretical density of ≥95% were achieved in all cases after sintering at 1300 °C. A pure Ba₂Ti₉O₂₀phase was obtained by treating the material with TiO₂additions (≤5.6 wt.%) and sintering at temperatures ranging between 1200 and 1350 °C. Ba₂Ti₉O₂₀is a nonstoichiometric compound that can accommodate an excess amount of TiO₂. As the temperature was increased, pure Ba₂Ti₉O₂₀partially decomposed and formed a mixture of BaTi₄O₉and Ba₂Ti₉O₂₀. The ceramic with excess TiO₂sintered at 1390 °C possessed a higher permittivity and a lower quality factor due to the larger grain size and lower density. For ceramic with the addition of ZrO₂(≤6 wt.%), pure Ba₂Ti₉O₂₀phase was obtained after sintering between 1200 and 1390 °C, and the quality factor was improved. The decomposition temperature of the Ba₂Ti₉O₂₀phase was greater than 1390 °C. For sintering temperatures ≥1350 °C, the extent of Ba₂Ti₉O₂₀phase decreased with MnO additions. As the MnO content reached 0.5 wt.%, only BaTi₄O₉and TiO₂phases existed, suggesting a decrease in the decomposition temperature of Ba₂Ti₉O₂₀with the addition of MnO. The microwave properties of the ceramics degraded significantly at the sintering temperature of 1390 °C.