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Subject: Defects in solids

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    Article
    Citation - WoS: 7
    Citation - Scopus: 6
    Temperature-Dependent Structural Transition, Electronic Properties and Impedance Spectroscopy Analysis of Tl2ingas4< Crystals Grown by the Bridgman Method
    (Elsevier Sci Ltd, 2018) Qasrawi, A. F.; Alkarem, Qotaibah A.; Gasanly, N. M.
    In this work, we report the temporary structural modifications associated with the in situ heating of the Tl2InGaS4 crystals in the temperature range of 300-420 K. The analysis of the X-ray diffraction patterns revealed the temperature-independent possible phase transformations between the monoclinic and triclinic phases. The temperature analysis of the lattice parameters, crystallite size, strain, dislocation density and stacking faults has shown a temporary enhancement in the crystallinity of this compound above 375 K. Significant increase in the grain size accompanied to decrease in the strain, defect density and stacking faults was observed above this temperature. The scanning electron microscopy imaging has shown that the crystals are layer structured with high quality layers of thicknesses of similar to 12 nm. In addition the energy dispersive X-ray analysis has shown that the crystal comprise no detectable impurity. Moreover, the room temperature optical characterizations has shown that the Tl2InGaS4 exhibit an energy band gap of 2.5 eV. The temperature dependent electrical resistivity measurements indicated highly resistive crystal with activation energy values of 0.84 and 0.19 eV above and below 375 K, respectively. On the other hand, room temperature impedance spectroscopy analysis in the frequency domain of 10-1800 MHz has shown that the crystal exhibits negative resistance and negative capacitance effects below and above 1580 MHz. The crystals are observed also to behave as band stop filter with notch frequency of 1711 MHz.
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    Article
    Citation - WoS: 22
    Citation - Scopus: 23
    Temperature Effects on the Structural and Optical Properties of the Tlinse2xs2(1-x)< Mixed Crystals (x=0.3)
    (Elsevier Science Sa, 2017) Omar, A.; Qasrawi, A. F.; Gasanly, N. M.
    In this work, we have studied the temperature effects on the recrystallization process and on the energy band gap of the TlInSe(2)xS(2(1 - x)) mixed crystals at the critical composition (x = 0.3) where structural phase transition from tetragonal to monoclinic takes place. Remarkable effect which included permanent recrystallization process, enlargements in the monoclinic crystallite size, decreases in the compressing strain and in the dislocation density as well as in the stacking faults and in the energy band gap with increasing temperature were observed. In addition, the temperature dependent energy band gap of the crystal which is investigated in the same temperature range that was used for the recrystallization process revealed that the recrystallization process is associated with energy band gap narrowing. (C) 2017 Elsevier B.V. All rights reserved.