The effect of SnO2 addition on the high-frequency dielectric properties of Ba2Ti9O20 ceramics has been investigated using terahertz time-domain spectroscopy, far-infrared (FIR) reflectivity, and Raman-scattering measurements. The dielectric constants determined from the terahertz and FIR spectra are smaller than that taken in the microwave frequency region. In contrast, the increase of the dielectric loss with increasing frequency is due to some resonance modes above 1 THz. Importantly, our data clearly show that the SnO2 (2.4 mole %) addition degraded the dielectric properties of Ba2Ti9O20 ceramics, which is ascribed to the deterioration on the coherency of lattice vibrational characteristics for these materials.
