Far-infrared study of BaTi₄O₉ microwave dielectric ceramics

In this work, lattice vibrations in BaTi₄O₉ ceramic were investigated using far-infrared spectra (FIRS), which were transformed by Kramers-Kronig relations into the real and imaginary parts of permittivity spectra. Curve fitting of reflectance spectra shows that 32 vibration modes were observed, among which transverse vibrations at lower frequencies (stretching and bending vibration modes involving A-site cations and TiO₆ octahedra) account for most dielectric loss. An evaluation of dielectric constants and quality factors using an extrapolation method was accomplished. The calculated dielectric constants agree well with the measured ones, while the calculated dielectric losses are about half the measured ones, indicating that noneigen elements such as defects and pores exist and play an important role in BaTi₄O₉ ceramics. A multimode behavior of vibration modes involving Ba-sites was proposed as the origin of dielectric loss.