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.

**Present address: Augsburg University, Universitätsstrasse 1, 86159 Augsburg, Germany

***On leave from A.I. Ioffe Physical-Technical Institute, Politekhnicheskaya 26, 194021 St. Petersburg, Russian Federation.

Keywords:

• Soft mode
• permittivity
• reflectivity
• Sr_1-xBa_xTiO₃ ceramics

Acknowledgments

The work was supported by the Grant Agency of the Czech Republic (projects No. 202/06/P219 and 202/04/0993) and by an exchange program between the German Academic Exchange Service (DAAD) and the Academy of Sciences of the Czech Republic (D5-CZ7/04-05). One of the authors (T. O.) acknowledges financial support of the L'Oreal Czech Republic for Women in Science Scholarship Program.

Notes

**Present address: Augsburg University, Universitätsstrasse 1, 86159 Augsburg, Germany

***On leave from A.I. Ioffe Physical-Technical Institute, Politekhnicheskaya 26, 194021 St. Petersburg, Russian Federation.