Formation mechanism and sintering behavior of Ba2Ti9O20

The reaction mechanism of a mixture of BaTi4O9 and TiO2 was investigated. It was found that the development of Ba2Ti9O20 was not via the direct reaction of BaTi4O9 and TiO2 at the interface, but by nucleation from the matrix of BaTi4O9 inserted by the Ti species in the limited temperature range of 1200–1300°C. It is suggested that the formation of Ba2Ti9O20 is via nucleation and growth. Moreover, it was observed that twinning existed in the remaining BaTi4O9 grains during the formation processes, which is due to the fact that the retained BaTi4O9 grains were stressed by the surrounding Ba2Ti9O20 grains. Possible explanations for the difficulty in preparing Ba2Ti9O20 are proposed. A sample with a high-density (about 99% theoretical density) and fine-grained uniform microstructure could be achieved and the dielectric properties are dielectric constant 39, Q 5863 at 7.3 GHz, and the temperature coefficient of resonance frequency 5 ppm/°C.