Microstructure and microwave dielectric properties of Ba4Sm9.33Ti18O54 ceramics containing columnar crystals

The tungstenbronze-type-like Ba6−3xSm8+2xTi18O54 [x=2/3, Ba4Sm9.33Ti18O54 (BST)] is known as an excellent microwave dielectric material. In this study, Ba4Sm9.33Ti18O54 powder having needle-like or columnar shapes were prepared by NaCl–KCl molten salt route at 1100 °C. By this method. The derived BST columnar crystals were then added to calcined BST powder to form oriented ceramics. The columnar crystals acted as seeds for anisotropic grain growth within the specimens. For up to 10 wt.% seed crystals, the specimens demonstrated nearly equivalent εr and Q·f values to the specimens prepared without seed particles. In contrast, τf increased monotonously with an increasing amount of seed crystals. It is noteworthy that τf=0 ppm/°C was expected in BST specimens prepared with 5 wt.% of columnar crystals. The relationship between microstructure development and dielectric properties is discussed.