Band structure and optical spectra of ferroelectric triglycine sulphate

Abstract

First-principal calculations of the band structure, density of electronic states, and dielectric functions of the triglycine sulphate crystal (TGS) together with the corresponding experimental dielectric functions in the range of 4–10 eV have been presented. Calculations have been performed in the frame of density functional theory using the CASTEP code. The experimental dielectric functions ε′(ω) and ε″(ω) have been obtained for different temperatures by ellipsometry using the synchrotron radiation source BESSY II. The theoretical dielectric functions ε′(ω) and ε″(ω) of TGS crystal agree satisfactorily with corresponding experimental dependencies. The character and magnitude of temperature changes of dielectric functions in the vicinity of phase transition point depend on the crystal orientation and photon energy. The greatest maximum-like temperature changes of dielectric functions observed at the phase transition point are detected for the photon energy ω ≈ 9.5 eV.

Keywords:

• Ferroelectrics
• TGS
• Band structure
• Dielectric function

Acknowledgments

The calculations presented were performed on the computers of ICM (Warsaw University) and WCSS (Technical University of Wroclaw). The authors further gratefully acknowledge the support by BESSY (Berlin).