Temperature-tuned bandgap characteristics of Bi 12 TiO 20 sillenite single crystals
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Temperature-tuned bandgap characteristics of Bi12TiO20 sillenite single crystals M. Isik1,*
, S. Delice2, N. M. Gasanly3, N. H. Darvishov4, and V. E. Bagiev4
1
Department of Electrical and Electronics Engineering, Atilim University, 06836 Ankara, Turkey Department of Physics, Hitit University, 19040 Çorum, Turkey 3 Department of Physics, Middle East Technical University, 06800 Ankara, Turkey 4 Institute of Physical Problems, Baku State University, 1148 Baku, Azerbaijan 2
Received: 7 October 2020
ABSTRACT
Accepted: 15 November 2020
Bi12MO20 (M: Si, Ge, Ti, etc.) compounds are known as sillenites having fascinating photorefractive characteristics. The present paper reports the structural and optical characteristics of one of the members of this family, Bi12TiO20 single crystals, grown by Czochralski method. X-ray diffraction pattern of the crystal presented sharp and intensive peaks associated with planes of cubic crystalline structure with lattice constant of a = 1.0142 nm. The optical properties were studied by means of room temperature Raman and temperature-dependent transmission experiments at various temperatures between 10 and 300 K. Raman spectrum indicated peaks around 127, 162, 191, 219, 261, 289, 321, 497 and 537 cm-1. The analyses of transmittance spectra indicated the increase of direct bandgap energy from 2.30 to 2.56 eV as temperature was decreased from room temperature to 10 K. The temperature-dependent bandgap characteristics of Bi12TiO20 were analyzed by means of Varshni and O’Donnell-Chen models. The analyses under the light of these models resulted in absolute zero bandgap energy of Eg(0) = 2.56(4) eV, rate of change of bandgap energy of c = – 1.11 9 10-3 eV/K and average phonon energy of hEphi = 8.6 meV.
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Springer Science+Business
Media, LLC, part of Springer Nature 2020
1 Introduction The compounds formulated as Bi12MO20 (M: Si, Ge, Ti, etc.) are known as sillenites and have been a significant research interest especially due to their fascinating photorefractive characteristics [1–3]. These sillenites have a wide range of usage areas like photocatalytic applications, water-splitting, optical data
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https://doi.org/10.1007/s10854-020-04904-4
processing devices, optical computing and high-sensitive photo-detectors [4–8]. Among the sillenites, Bi12TiO20 (abbreviated as BTO) is one of the most studied compounds due to its various outstanding characteristics like high electro-optical coefficients, low optical activity, high photosensitivity in visible red range, high dielectric constant, excellent electrooptical and photo-electric properties [9–12]. These
J Mater Sci: Mater Electron
characteristics of BTO make it favorable in holographic interferometry applications [13], waveguides [14], optical information processing, phase conjugation and amplification of weak light signals applications [15]. The photocatalytic properties of BTO have been utilized to reveal its possible industrial applications. In Ref. [16], it was shown tha
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