Fabrication and dielectric properties of phase-pure Ba2Ti9O20 microwave resonators

The thermal processing schedules necessary to form phase pure Ba2Ti9O20, with and without substitutional solid solution were investigated. Undoped compositions formed the compound most easily under rapid (500 degrees C/min) heating rates, where diffusional agglomeration of the TiO2 batch constituent was minimized. The compound formed most easily with minor (0.82%) substitutions of SnO2 and ZrO2 for TiO2. The solubility of Sn in Ba2Ti9O20 was higher than that of Zr. Extended heat treatment (16 vs. 6 h at 1390 degrees C) resulted in volitalization of grain boundary liquid phase, leading to a more porous and slightly degraded resonators. The effects of dopant concentrations and soak periods at 1390 degrees C on dielectric constants and temperature-dependent quality factors are reported.