Manifestation of phase transformations in optical spectra of Na_0.5Bi_0.5TiO₃ crystals between 25°C and 350°C

Abstract

The pseudo dielectric function ⟨ε⟩ (E) = ⟨ε ₁⟩ (E) + i⟨ε ₂⟩ (E) of sodium bismuth titanate Na_0.5Bi_0.5TiO₃, has been obtained in the spectral range of electronic excitations (2–9.5 eV) by spectroscopic ellipsometry using the synchrotron radiation source BESSY II. The spectrum contains a broad absorption band at 4.2–4.5 eV. The temperature dependence in the range of 25–350°C is presented by the related susceptibilities ⟨χ ₁⟩ (T) and ⟨χ ₂⟩ (T) at 5 eV. A clear peculiarity in the temperature behavior of ⟨χ ₁⟩ (T) and ⟨χ ₂⟩ (T) between 180 and 320°C has been revealed and discussed. In this range an extremum-like temperature dependence of intensity of the light reflected from the sample surface, has been revealed and can be explained by the diffraction of light on the grid of the elastic domain structure of the sample.

Keywords:

• ferroelectrics
• Na_0.5Bi_0.5TiO₃ crystals
• electronic excitations
• dielectric functions

Acknowledgements

This work was supported by the European Community - Research Infrastructure Action under the FP6 “Structuring the European Research Area” Programme through the Integrated Infrastructure Initiative “Integrating Activity on Synchrotron and Free Electron Laser Science” under the contract R II 3-CT-2004-506008 (1), by European Community through the “NanoCharM” project under the Seventh Framework Programme (FP7) and by the German Federal Ministry of Education and Research (BMBF) under the contract number 05 KS4KTB/3. We also want to thank the BESSY GmbH for help and support.