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Content available remote Study of As-Sb-Se chalcogenide glasses by NQR and EPR spectroscopy methods
In this paper experimental results obtained by both 75As NQR and EPR spectroscopy are presented for the three-component system As-Sb-Se. The 75As NQR spectra of glasses of structures (As2Se3)0.78 (Sb2Se3)0.22, (As2Se3)0.75 (Sb2Se3)0.25, (As2Se3)0.5 (Sb2Se3)0.5 have broad lines with two Sb-NQR lines (corresponding to the Sb2Se3 units) and two 75As-NQR lines (corresponding to the As2Se3 units). Differences in the EPR spectra of the different glasses arise because of the different amounts of arsenic and antimony in their structure.
The structure of chalcogenide glassy semiconductors in three-component systems of Ge-As-Se and As-Sb-Se has been studied by means of both NQR (nuclear quadrupole resonance) and EPR (electron paramagnetic resonance) spectroscopy. It is investigated that in the glasses of both systems the value of the electric field gradient at the resonating nuclei grows with increasing concentration of the clusters As2Se3 and Sb2Se3, thereby increasing the NQR resonance frequencies. It appears that for the Ge-As-Se system the structural transition from a two-dimensional to three-dimensional structure occurs at average coordination number $\bar r$ = 2.45. The EPR spectral parameters of glasses depend on the composition, the average coordination number and the temperature, and these are discussed. The effect of ”ageing” for CGS (chalcogenide glassy semiconductors) of As-Sb-Se system due to partial crystallization of the sample is observed from the EPR spectra.
Density functional theory (DFT) calculations are carried out to study the influence of carbon doping (C-dop ing) on the aluminum-27 and nitrogen-14 quadrupole coupling constants (CQ) in a representative model of aluminum nitride nanotubes (AlNNTs). The model includes two perfect and C-doped forms of the (4,4) single-walled armchair AlNNT. To this aim, each of two forms of AlNNT is firstly optimized and then the electric field gradient (EFG) tensors are calculated and converted to CQ. Comparison of the calculated CQ values in two perfect and C-doped forms of AlNNT reveals that the influence of C-doping is significant at the sites of the nearest Al and N nuclei while those nuclei far from the C atoms do not show changes.
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