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Citation - WoS: 139
Citation - Scopus: 140
CaXH₃ (X = Mn, Fe, Co) perovskite-type hydrides for hydrogen storage applications
(Wiley, 2020) Surucu, Gokhan; Gencer, Aysenur; Candan, Abdullah; Gullu, Hasan H.; Isik, Mehmet
Hydrogen storage is one of the attractive research interests in recent years due to the advantages of hydrogen to be used as energy source. The studies on hydrogen storage applications focus mainly on investigation of hydrogen storage capabilities of newly introduced compounds. The present paper aims at characterization of CaXH3 (X: Mn, Fe, or Co) perovskite-type hydrides for the first time to understand their potential contribution to the hydrogen storage applications. CaXH3 compounds have been investigated by density functional theory studies to reveal their various characteristics and hydrogen storage properties. CaXH3 compounds have been optimized in cubic crystal structure and the lattice constants of studied compounds have been obtained as 3.60, 3.50, and 3.48 angstrom for X: Mn, Fe, and Co compounds, respectively. The optimized structures have negative formation enthalpies pointing out that studied compounds are thermodynamically stable and could be synthesized experimentally. The gravimetric hydrogen storage densities of X: Mn, Fe, and Co compounds were found in as 3.09, 3.06, and 2.97 wt%, respectively. The revealed values for hydrogen storage densities indicate that CaXH3 compounds may be potential candidates for hydrogen storage applications. Moreover, various mechanical parameters of interest compounds like elastic constants, bulk modulus, and Poisson's ratio have been reported throughout the study. These compounds were found mechanically stable with satisfying Born stability criteria. Further analyses based on Cauchy pressure and Pugh criterion, showed that they have brittleness nature and relatively hard materials. In addition, the electronic characteristics, band structures, and associated partial density of states of CaXH3 hydrides have been revealed. The dynamic stability behavior of them was verified based on the phonon dispersion curves.
Citation - WoS: 10
Citation - Scopus: 11
Low Temperature Thermoluminescence of Gd₂o_{3< Nanoparticles Using Various Heating Rate and t_{max< - t_{exc< Methods}}}
(Elsevier, 2019) Delice, Serdar; Isik, Mehmet; Gasanly, Nizami M.
Thermoluminescence (FL) measurements for Gd2O3 nanoparticles were carried out for various heating rates between 0.3 and 0.8 K/s at low temperatures (10-280 K). TL spectrum exhibited two observable and one faint peaks in the temperature region of 10-100 K, and four peaks in the temperature region of 160-280 K. Heating rate analysis was achieved to understand the behaviors of trap levels. It was seen that the peak maximum temperatures and TL intensities of all peaks increase with increasing heating rate. This behavior was ascribed to anomalous heating rate effect. T-max - T(exc )analysis was accomplished for TL, peaks at relatively higher temperature region to reveal the related traps depths. T-max - T-exc plot presented a staircase structure indicating that the TL glow curve is composed of well separated glow peaks. Mean activation energies of trapping centers corresponding to these separated peaks were found as 0.43, 0.50, 0.58 and 0.80 eV.
Citation - WoS: 21
Citation - Scopus: 20
Nonlinear Optical Absorption Characteristics of Pbmoo₄ Single Crystal for Optical Limiter Applications
(Elsevier, 2022) Pepe, Yasemin; Isik, Mehmet; Karatay, Ahmet; Gasanly, Nizami; Elmali, Ayhan
Molybdate materials take great interest due to their photocatalytic and optoelectronic applications. In this report, PbMoO4 single crystal, one of the member of molybdate materials, is grown by Czochralski technique and the change of nonlinear absorption characteristic depending on the input intensity was reported. Linear absorption analysis revealed the band gap energy and Urbach energy as to be 3.12 and 0.52 eV, respectively. Nonlinear absorption characteristics of the PbMoO4 single crystal was examined with the open aperture (OA) Z-scan experiments at 532 nm excitation wavelength under various input intensities. Fitting results of the OA Z-scan experiments indicated that PbMoO4 single crystal has nonlinear absorption (NA) behavior, and NA coefficient (beta(eff)) increased from 7.11 x 10(-8) to 1.96 x 10(-7) m/W with increasing input intensity. This observation was associated with the increase of the contribution of the free carrier absorption to the NA with the generation of more excited electrons with increasing input intensity. At the 532 nm excitation wavelength (2.32 eV), the dominant mechanisms were revealed as one photon and free carrier absorptions. The optical limiting threshold of the PbMoO4 single crystal was obtained to be 4.91 mJ/cm(2). The reported results indicated that PbMoO4 single crystal can be a good optical limiter in the visible wavelength region due to its effective NA behavior.
Citation - WoS: 28
Citation - Scopus: 30
Composition-tuned band gap energy and refractive index in GaS_xSe_1-x layered mixed crystals
(Elsevier Science Sa, 2017) Isik, Mehmet; Gasanly, Nizami
Transmission and reflection measurements on GaSxSe1-x mixed crystals (0 <= x <= 1) were carried out in the 400-1000 nm spectral range. Band gap energies of the studied crystals were obtained using the derivative spectra of transmittance and reflectance. The compositional dependence of band gap energy revealed that as sulfur (selenium) composition is increased (decreased) in the mixed crystals, band gap energy increases quadratically from 1.99 eV (GaSe) to 2.55 eV (GaS). Spectral dependencies of refractive indices of the mixed crystals were plotted using the reflectance spectra. It was observed that refractive index decreases nearly in a linear behavior with increasing band gap energy for GaSxSe1-x mixed crystals. Moreover, the composition ratio of the mixed crystals was obtained from the energy dispersive spectroscopy measurements. The atomic compositions of the studied crystals are well-matched with composition x increasing from 0 to 1 by intervals of 0.25. (C) 2016 Elsevier B.V. All rights reserved.
Citation - WoS: 8
Citation - Scopus: 9
Experimental and Theoretical Investigation of the Mechanical Characteristics of Sillenite Compound: Bi₁₂geo_20<
(Elsevier Science Sa, 2021) Surucu, Gokhan; Isik, Mehmet; Gencer, Aysenur; Gasanly, Nizami
The present study reports the mechanical and elastic characteristics of Bi12GeO20 (BGO) compound by experimental nanoindentation measurements and density functional theory (DFT) calculations. X-ray diffraction pattern of BGO was plotted and revealed diffraction peaks were associated with Miller indices of cubic crystalline structure with lattice constant of a = 10.304 angstrom. Two- and three-dimensional representations of Young's modulus, linear compressibility, shear modulus and Poisson's ratio were presented according to DFT calculations. The calculated elastic constants pointed out the mechanically stable and anisotropic behavior of the BGO. The hardness and Young's modulus ranges of the BGO calculated from DFT studies were found as 3.7-6.3 GPa and 61.7-98.9 GPa, respectively. Hardness and Young's modulus of BGO single crystal were also obtained by analyzing force-dependent nanoindentation experimental data. It was observed that hardness and Young's modulus decrease with increase of load in the low applied loads and then reaches saturation in the high applied loads. This behavior is known as indentation size effect. True hardness value was determined from proportional specimen resistance model as 4.1 GPa. The force independent region presented the Young's modulus as 114 GPa. (C) 2021 Elsevier B.V. All rights reserved.
Citation - WoS: 1
Citation - Scopus: 1
Characterization of Pbmo_0.3w_{0.7< Crystal: a Potential Material for Photocatalysis and Optoelectronic Applications}
(Wiley-v C H verlag Gmbh, 2024) Isik, Mehmet; Gasanly, Nizami Mamed
PbMo0.3W0.7O4 semiconductor crystal, which contains the balanced ratios of Mo and W, is grown for the first time by Czochralski method. The structural and optical properties of the crystal are investigated in detail in the present study. Structural analysis shows that crystal has tetragonal structure like PbMoO4 and PbWO4 compounds. The optical characteristics are studied by transmission, Raman, FTIR and photoluminescence methods. The bandgap energy is found to be 3.18 eV, and the positions of the conduction and valence bands are determined. The vibrational characteristics are studied by means of Raman and FTIR spectroscopy techniques. Photoluminescence spectrum presents three peaks around 486, 529, and 544 nm which fall into the green emission spectral range. Taking into account the properties of the compound, it is stated that PbMo0.3W0.7O4 (or Pb(MoO4)(0.3)(WO4)(0.7)) has the potential to be used in water splitting applications and optoelectronic devices that emit green light.
Citation - WoS: 4
Citation - Scopus: 3
Exploring the Thermal Stability of Sb2se3 for Potential Applications Through Advanced Thermal Analysis Methods
(Amer Chemical Soc, 2025) Altuntas, Gozde; Isik, Mehmet; Surucu, Gokhan; Parlak, Mehmet; Surucu, Ozge
Antimony selenide (Sb2Se3) is a promising material for energy applications, including photovoltaics, thermoelectrics, and photodetectors, due to its favorable electronic properties, availability, and low toxicity. However, its thermal stability, crucial for device efficiency and reliability, has been less explored, leaving a gap in understanding its high-temperature suitability. This study evaluates the thermal stability of Sb2Se3 using thermogravimetric analysis (TGA), differential thermal analysis (DTA), and differential scanning calorimetry (DSC). The results show that Sb2Se3 remains stable up to 500 degrees C, with two significant weight loss stages: 1.75% between 500 and 610 degrees C, and 3.50% between 610 and 775 degrees C, indicating decomposition processes. Activation energies for the decomposition phases were determined as 121.8 and 57.2 kJ/mol using the Coats-Redfern method. Additionally, an endothermic phase transition was observed between 599 and 630.6 degrees C via DSC analysis. These findings demonstrate Sb2Se3's potential for high-temperature energy applications, providing essential insights for optimizing its use in solar cells, thermoelectric devices, and other technologies.
Citation - WoS: 2
Citation - Scopus: 2
Analysis of Optical Constants and Temperature-Dependent Absorption Edge of Gas_0.75se_{0.25< Layered Crystals}
(Pergamon-elsevier Science Ltd, 2017) Isik, Mehmet; Gasanly, Nizami
GaS0.75Se0.25 single crystals were optically characterized through transmission and reflection measurements in the wavelength range of 450-1000 nm. Derivative spectrophotometry analyses on temperature dependent transmittance spectra showed that band gap energies of the crystal increase from 239 eV (T=300 K) to 2.53 eV (T=10 K). Band gap at zero temperature, average phonon energy, electron phonon coupling parameter and rates of change of band gap energy with temperature were found from the temperature dependences of band gap energies under the light of different models reported in literature. Furthermore, the dispersion of room temperature refractive index was discussed in terms of single effective oscillator model. The refractive index dispersion parameters, namely oscillator and dispersion energies, zero-frequency refractive index, were determined as a result of analyses. (C) 2017 Elsevier Ltd. All rights reserved.
Citation - WoS: 2
Citation - Scopus: 2
Temperature-Tuned Band Gap Energy and Oscillator Parameters of Gas_0.5se_{0.5< Single Crystals}
(Elsevier Gmbh, Urban & Fischer verlag, 2016) Isik, Mehmet; Tugay, Evrin; Gasanly, Nizami
Temperature-dependent transmission and room temperature reflection measurements were carried out on GaS0.5Se0.5 single crystal in the wavelength range of 380-1000 nm to investigate its optical parameters. The analysis of the temperature-dependent absorption data showed that direct and indirect band gap energies increase from 2.36 to 2.50 eV and 2.27 to 2.40 eV, respectively, as temperature is decreased from 300 to 10 K. The rates of change of the direct and indirect band gap energies with temperature was found around -7.4 x 10(-4) eV/K from the analysis of experimental data under the light of theoretical relation giving the band gap energy as a function of temperature. The absolute zero value of the band gap energies were also found from the same analysis as 2.50 eV (for direct) and 2.40 eV (for indirect). Wemple-DiDomenico single effective oscillator model, Sellmeier oscillator model and Spitzer-Fan model were used for the room temperature reflection data to find optical parameters of the crystal. (C) 2016 Elsevier GmbH. All rights reserved.
Citation - WoS: 9
Citation - Scopus: 14
Bifunctional Praseodymium-Doped Sns2 Thin Films for Photocatalytic and Antibacterial Applications
(Elsevier, 2024) Ech-Chergui, Abdelkader Nebatti; Bennabi, Farid; Isik, Mehmet; Khane, Yasmina; Garcia, Francisco Jose Garcia; Kadari, Ali Sadek; Amrani, Bouhalouane
This paper introduces a novel application of bifunctional Pr-doped SnS2 thin films, demonstrating their efficacy in both photocatalytic degradation of dye and antibacterial activities. The thin films were fabricated using an eco-friendly spray-coated method, encompassing undoped and Pr-doped SnS2 variations. The study comprehensively examines the structural, morphological, chemical, photocatalytic, and antibacterial characteristics of these films. The crystal structure of both undoped and Pr-doped SnS2 thin films exhibited hexagonal patterns, prominently favouring the growth in (1 0 1) orientation. Notably, an increase in crystallite size was observed with higher levels of Pr-doping. Raman spectroscopy analysis highlighted a distinct peak at 315 cm -1, corresponding to the A1 g vibrational mode associated with Sn-S bonds along the c-axis of the structure. Employing X ray Photoelectron Spectroscopy (XPS), the presence of essential components - Sn, S, and Pr - within the fabricated thin films was confirmed, consistent with experimental values of undoped and Pr -doped SnS2-x compositions. Importantly, the XPS analysis confirmed the integration of the Pr3+ oxidation state within Pr -doped SnS2 films. The photocatalytic degradation and antibacterial activities of the films were investigated. Notably, the photocatalytic potential of the synthesized materials against Congo Red exhibited a direct correlation with the Pr3+ doping percentage, indicating enhanced pollutant degradation with increasing doping levels. Similarly, the antibacterial performance against Escherichia coli displayed improvement with increasing Pr -doping content, highlighting the promising antimicrobial capabilities of the films. This study presents an innovative avenue to address both organic pollutant degradation and microbial control. By harnessing the attributes of Pr -doped SnS2 thin films, this research introduces a promising strategy for sustainable material applications in environmental purification and improvement in public health.

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