Microstructure and dielectric properties of Ba<i><sub>x</sub></i>Y<sub>26</sub>Si<sub>16</sub>O<sub>71+</sub><i><sub>x</sub></i> (<i>x</i> ≈ 10.2) ceramics prepared using a planetary ball mill

BaCO3, Y2O3 and SiO2 powders weighed at Ba:Y:Si molar ratios of x:26:16 with x = 9.0–14.0 were mixed in a planetary ball mill, compacted, and calcined at 1300 °C for 12 h. The calcined compacts were reground in a planetary ball mill and recompacted to form disk-shaped powder compacts that were then heated at 1600 °C for 2 h. X-ray diffraction measurements revealed that the ceramic disks were mainly composed of the tetragonal oxide, BaxY26Si16O71+x (x ≈ 10.2), with some secondary phases. A ceramic disk with the highest relative density of 96 % respect to the theoretical density of the tetragonal oxide was obtained at x = 10.8. The granular and elongated grains of the tetragonal oxide were contained in a matrix of fine oxide grains. The relative dielectric constant (εr) and dielectric loss (tan δ) measured for the ceramic disk at frequencies of 10 Hz and 1 MHz were 5410 and 0.07, and 380 and 0.44 at 25 °C, and 7000 and 0.08 and 3830 and 0.334 at 325 °C, respectively.