Optical spectra of triglycine sulfate crystals in the range of 7–33 eV and its changes at phase transition

Abstract

Pseudo-dielectric functions ⟨ε₁(E)⟩ and ⟨ε₂(E)⟩ of triglycine sulfate (TGS) crystal have been obtained in the range of 7–33 eV for different temperatures close to ferroelectric phase transition by spectral ellipsometry using the synchrotron radiation source BESSY II. These dielectric functions ε₁(E) and ε₂(E) have also been calculated from first principles using CASTEP CAmbridge Serial Total Energy Package code together with the band structure and density of electronic states of the crystal. Experimental and theoretical dielectric functions agree satisfactorily. A characteristic decrease of temperature dependences of the dielectric losses tgδ(T) and related values just below the phase transition temperature T _c have been found and discussed.

Keywords:

• ferroelectrics
• TGS crystals
• band structure
• dielectric functions

AMS Subject Classifications:

• 82D45
• 82-08
• 78A10

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 Synchroton and Free Electron Laser Science under the contract R II 3-CT-2004-506008 (1), and by the Bundesministerium fur Bildung und Forschung (BMBF) under the contract number 05 KS4KTB/3. The calculations presented were performed on the computers of ICM (Warsaw University) and WCSS (Technical University of Wroclaw). We also want to thank the BESSY GmbH for help and support.