Far Infrared Spectroscopy of Sr_1-xBa_xTiO₃(0.01 ≤ x ≤ 0.2) Ceramics

Abstract

We report on lattice dynamics and far infrared dielectric response of Sr 1−x Ba x TiO 3 ceramics with small concentration of Ba (0.01 ≤ x ≤ 0.2). Reflectivity spectra were obtained on cooling down to 5 K by Fourier transform interferometer in the 25–650 cm− 1 frequency range and by coherent-source submillimetre technique in the 30–40 cm− 1 range and fitted by the factorized model of the dielectric function. Fitted permittivity was compared with the dielectric data measured in the 10 2 –10 6 Hz frequency range. Splitting of the soft TO1 phonon into E and A 1 components, indicating the ferroelectric transition, was observed for x ≥ 0.05. In addition to the soft mode dispersion, low-frequency dielectric relaxation was observed in the vicinity of the permittivity maximum, indicating a crossover into order-disorder regime with relaxor ferroelectric features.