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2024-11-23 18:10

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Conference: Bucharest University Faculty of Physics 2022 Meeting

Section: Solid State Physics and Materials Science, Optics, Spectroscopy, Plasma and Lasers

Title:

Dielectric and optical properties of triglycine sulphate crystals

Authors:

Oana Diana Baban, Ciceron Berbecaru

Affiliation:

University of Bucharest, Faculty of Physics, Atomistilor 405, Magurele, Ilfov, Romania

E-mail

berbecaru2ciceron@yahoo.com ; oanadiana_98@yahoo.com

Keywords:

triglicin sulphate, permittivity and losses, absorbance, optical bandgap, phonons

Abstract:

Quality TGS crystals were grown from aqueous solution at a constant 44 oC temperature in static regime by slow solvent evaporation. Cleaved (perpendicular on ferroelectric b axis) and polished plates were used in order to investigate for electrical and optical properties. Permittivity and losses were measured on a large temperature range, from room temperature (TC) till 70 oC, crossing up and down Curie temperature (TC), at three selected frequencies. Optical transmittance of TGS crystal was also measured in UV-VIS region. Permittivity show increased values with temperature increasing, with maxims at TC. Beyond TC, for further increase of temperature, dielectric constant show decreasing values in paraelectric region. Non reproducible values of permittivity were registered in the ferroelectric phase while in paraelectric region these are reproducible. Losses with higher values at RT start to decrease toward TC with small maxims at TC and decreased values in paraelectric region. Also non-reproducible values of losses were registered in the ferroelectric phase with increased values after cooling the sample from paraelectric to ferroelectric phase. Both, permittivity and losses shows strong frequency dependencies. It was concluded that the ferroelectric domains evolution with the temperature and frequencies and associated relaxations processes are responsible for this behavior, [1],[2]. Our sample shows a very good transmittance of about 0.8 in the UV-VIS region beyond the edge of the fundamental band-gap in UV. Correction for reflectance was used in order to investigate the region of the identified indirect optical transitions with associated tail of absorbance curve. The band gap of the TGS crystal was found to be 4.9 eV with energies of absorbed and emitted phonons of about 0.2 eV and 0.15 eV. It was concluded that phonons involved in the optical transitions could be associated with internal vibrations of structural groups of TGS crystal, [3],[4],[5].

References:

[1] C. BERBECARU, Temperature and frequency investigations of the electrical parameters in the TGS ferroelectric transition, Phys. Status Solidi C 7, No. 5, 1440– 1443 (2010).

[2] M. S. Pandian et al., Device-relevant properties of [010]-oriented undoped TGS single crystals grown above and below the phase transition temperature, J Mater Sci: Mater Electron 32, 15778–15788 (2021).

[3] A. K. ABASS et al., Indirect Electronic Transitions in Single Crystals of Triglycine Sulfate, phys. stat. sol. (a) 89, 225-229 (1985).

[4] A. Abu El-Fadl, Effect of divalent-ions-doping on the absorption spectra and optical parameters of triglycine sulphate crystals, J. Phys. and Chem. of Solids 60, 1881–1893 (1999)

[5] P. O. CERVENKA et al., THE FERROELECTRIC PHASE TRANSITION AND DIELECTRIC ANOMALY IN TRI-GLYCINE SULFATE, Ferroelectrics, Vol. 11, pp. 511-517 (1976).