Yazar "Ozkendir, O. Murat" seçeneğine göre listele

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    Boron activity in the inactive Li2MnO3 cathode material
    (Elsevier, 2019) Ozkendir, O. Murat; Harfouche, Messaoud; Ulfat, Intikhab; Kaya, Cigdem; Celik, Gultekin; Ates, Sule; Aktas, Sevda
    Boron substituted Li2MnO3 cathode materials have frequently been studied and found to be inactive. In this reseach, crystal and electronic properties of the Li-ion cathode material with boron substitution having general formula; Li(2)Mn(1-x)BxO(3) (where x has values of 0.00, 0.05, 0.10, 0.15 and 0.20, respectively) were studied. The study revealed that, with the substitution of boron atoms in the manganese coordinates in the Li2MnO3 cathode materials, boron atoms acted as a landmark for the parent oxides by forming LiBO2 crystal domains. In the studied samples, boron atoms were determined as the key to construct new crystals and to restrict the excess of oxygen in the materials. Beyond the boron coordinations, the manganese atoms formed a cubic LiMn2O4 crystal structure which was reported to have good electrochemical properties. With the formation of the LiMn2O4 crystal, the substituted samples became a polycrystalline material with Li2MnO3- LiBO2- LiMn2O4 crystals. The obtained structure in the cathode materials have similarity with the general formula xLi(2)MnO(3)center dot(1-x)LiMn2O4 which had been reported to have good intercalation and electrochemical properties.
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    Crystal and electronic structure study of the Li2Mn1-xNdxO3 battery cathode
    (Elsevier Science Inc, 2019) Celik, Gultekin; Aktas, Sevda; Ates, Sule; Ozkendir, O. Murat; Klysubun, Wantana
    Neodymium substituted Li2MnO3 samples were prepared by the solid-state reaction method. The crystal and electronic structure properties of the prepared samples were investigated by x-ray based techniques. According to the analysis, it was determined that Nd atoms did not sit in to the Cr coordinations in Nd substituted samples and built up a different crystal structure. To support the analysis of the crystal structure study of the samples, electronic structure properties of the Nd substituted samples were studied via the collected data by x-ray absorption fine structure (XAFS) spectroscopy from the Mn K-edge. The results of the data analysis revealed that due to the misfit with the ionic radii and also the oxidation states, substituted neodymium atoms built up isolated crystal domains in Li8Mn5Nd18O39 cubic crystal structure. The symmetry in Mn K-edge absorption data of the sample both in parent Li2MnO3 and Nd substituted samples confirmed that Mn coordinations has not been influenced by the Nd substitution.
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    Electronic and crystal structure analyses of boron doped LiFeO2 cathode material by the XAFS spectroscopy
    (Elsevier, 2022) Gunaydin, Selen; Harfouche, Messaoud; Ozkendir, O. Murat
    The influence of boron substitution in LiFeO2 (LFO) material on crystal and electronic structure properties has been investigated by x-ray absorption fine structure (XAFS) spectroscopy with the general formula LiFe1_xBxO2 where x has values of 0.00, 0.05, and 0.10. The study revealed that boron has a key role in oxide materials due to its high effect on the oxygen regions and provides better performance values by reducing the excess oxygen in the material. The electronic structure properties were investigated by x-ray absorption near-edge spectroscopy (XANES). In this study, a new analysis method has also been applied for crystal properties determination like the Rietveld method for the first time and named Inverse EXAFS Fitting . For the crystal structure study, extended XAFS (EXAFS) analyses were processed in reverse mode to determine the crystal lattice properties as an alter-native way to the x-ray diffraction pattern (XRD) study and also to find out the atomic distances from the source Fe atoms. Due to the smaller ionic radii of B3+ cations than the Fe3+ cations, EXAFS data analysis has revealed that boron atoms did not sit in iron coordination, but formed the LiBO2 crystals and caused minor perturbations around iron atoms by loosening the Fe-O bonds.
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    Electronic and magnetic properties of boron substituted CuFeO2 delafossite oxide
    (Taylor & Francis Ltd, 2024) Ezircan, Ali; Aslan, M. Selim; Miyazaki, Hidetoshi; Akyol, Mustafa; Ozkendir, O. Murat; Ekicibil, Ahmet; Ozturk, Hakan
    Synchrotron x-ray diffraction (SR-XRD) and X-ray absorption fine structure spectroscopy (XAFS) were used to investigate the crystal and electronic properties of boron-substituted CuFeO2 material at room temperature. Without boron substitution, the polycrystalline structures of the trigonal (rhombohedral) Rm' over bar m' CuFeO2 (87.7%) and hexagonal 'P63/mmc' (12.3%), which were also present in each sample but in different proportions, were utilised to identify the base material. XRD patterns revealed that, beyond 10% boron substitution, the metal-oxygen bonds (Fe-O and Cu-O) weakened, resulting in the formation of new tetragonal 'I41/amd' CuFe2O4 crystals. Although the CuFeO2 structure was preserved, it is conceivable that the presence of other crystal structures could lead to the formation of new features. This state arose as a result of CuFe2O4 crystallization and the impact of boron activity on the surrounding oxygen structures. By measuring magnetisation at both swept temperatures (10-300 K) and applied magnetic fields (+/- 30 kOe), the magnetic properties of the samples were investigated. In the 10-300 K temperature range, the polycrystalline samples exhibit a ferromagnetic property without a magnetic phase transition. This suggests that replacing B with Fe in CuFe(1-x)BxO(2 )does not influence the primary magnetic property of CuFeO2. The samples' saturation magnetisation (Ms) values gradually fall as the B substitution content increases with Fe. This is because there's a chance that the non-transition metal B in CuFe1-xBxO(2) will boost antiferromagnetic superexchange Cu-O interactions while lowering the p-d exchange interaction.
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    Electronic structure and electrochemical analysis of the Li2Mn1-xSexO3 materials
    (Elsevier, 2020) Ozkendir, O. Murat; Celik, Gultekin; Ates, Sule; Aktas, Sevda; Gunaydin, Selen; Harfouche, Messaoud; Bondino, Federica
    With the aim of probing the influence of the highly oxidizable selenium in the electrochemically inactive cathode Li2MnO3 material, samples were prepared with selenium substitution in the manganese coordination according to the general formula of Li2Mn1-xSexO3. In Li-ion batteries, oxygen instabilities are one of the major problems confronted that effect the performances of the cathode materials. The crystal and electronic structure properties of the materials were studied with x-ray absorption techniques. Selenium atoms were determined to build Li2SeO4 crystal and due to the oxygen removal during sample preparation mechanisms were determined to cause lower ionic conductivity than the parent Li2MnO3 oxide. The atomic distances in the materials were determined by the fits performed by the commercial code FEFF 8.2. Li2SeO4 crystal was determined as stacked between manganese and lithium atoms and isolated with each other.
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    Electronic Structure Study of Ni-B Alloy Coatings by XAFS Technique
    (Springer, 2021) Ozkendir, O. Murat; Cengiz, Erhan; Karahan, I. Hakki; Klysubun, Wantana
    The crystal and electronic structure properties of Ni-B (nickel-boron) alloy coatings produced by an electrodeposition method have been investigated. The crystal structures of the alloy coatings were determined by x-ray diffraction patterns and supported by extended x-ray absorption fine structure (EXAFS) spectroscopy. The local atomic structure around the Ni atom was obtained from EXAFS studies at the Ni K-edge, and the EXAFS data were fitted with theoretical calculations. With the addition of boron atoms in the nickel environment, NiB composite alloys were formed in the crystals with an orthorhombic Cmcm structure. The analysis revealed a limited effect of boron doping in the electronic structure of the nickel atoms. Boron atoms were determined as sitting between the Ni atoms and causing a disturbance in the crystal structure due to providing inhomogeneous interstitial potential and defects.
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    Electronic structure study of Sn-substituted Li2MnO3 cathode material
    (Elsevier, 2020) Ozkendir, O. Murat
    Li2MnO3, a well known Li-ion battery cathode material, is used against instabilities of other cathode materials despite of its weak performance. To this aim, Sn4+-substitution of Mn could enrich the electronic properties providing during the molecular interactions of valence electrons. Within this work, electronic structure features of Sn-substituted Li2MnO3 material (Li2Mn1-xSnxO3) have been studied by the X-ray absorption fine structure (XAFS) spectroscopy calculations regarding variant x values of 0.00, 0.10, and 0.20. Higher electronegativity of the substituted Sn atom versus the host Mn atom could govern the electronic interactions via the hybridized bonds built between Sn and O atoms. The obtained results indicated that the Sn-substitution could yield better cathode properties for the Li-ion battery devices.
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    Temperature Dependency of Sodium Ionic Activity in β-NaFeO2 Material
    (Springer, 2023) Ozkendir, O. Murat; Saran, Sevda
    An investigation of temperature-dependent ionic activity of a representative sodium oxide material was carried out in the current research work due to the known importance of heat challenges in the battery development process. To assess the heat effects on the ionic conductivity capabilities, the electrochemical, electronic, and crystal structure properties of beta-NaFeO2 and beta-NaFeO2:Bi2Te3 composite materials were examined. The ionic conductivity of samples was slightly decreased by increasing the temperature, especially above 50-70 degrees C. In contrast, better results were achieved for the beta-NaFeO2:Bi2Te3 composite material than the parent beta-NaFeO2 material as an indicator of the impacts of thermoelectric properties. At comparable temperatures, x-ray absorption (XAS) and x-ray absorption fine structure (XAFS) spectroscopic data were collected and processed to demonstrate the physical background influence of the increase in temperature on the atoms of the materials. It was found that the sodium atoms were the greatest contributors to the ionic conductivity loss at an increasing temperature among the materials. By separating from the spinel structure Fe-O ligand, sodium atoms increased the ionic capacitance by raising the temperature with a worse ionic conductivity. However, studies on the beta-NaFeO2:Bi2Te3 composite material revealed a better ionic conductivity change than the beta-NaFeO2 material with increasing temperature. This achievement was very clearly highlighted, particularly at the best working temperatures of Bi2Te3 material with a mechanism of absorbing waste heat and emitting free electrons. Additionally, the inactivity of beta-NaFeO2 material could be determined by the instability of Na sites, which worsens with the increase in heat.
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    The relationship between ionic activities and temperature in Li2Na2MnO4 material
    (Natl Inst Optoelectronics, 2023) Ozkendir, O. Murat
    In order to investigate the structural behaviours of Na4MnO4 and lithium substituted Na4MnO4 materials (Li2Na2MnO4) under conditions of increasing temperature, and to determine whether or not they possess the necessary characteristics to be a candidate for battery cathode, these materials' electronic and crystal structure properties were studied at temperatures of 300 K, 323 K, 343 K, 373 K, and 423 K. Studies on the electronic structure have shown that lithium substituted compounds and their parent materials both exhibit a stable electronic structure at high temperatures. The alkali metals (Na and Li) and also Mn are strongly linked to the oxygen atoms in the crystal, as evidenced by the durability of the crystal structure. Although the examined materials lacked the necessary qualities to serve as a battery cathode, the high electronic data loss with rising temperatures suggested that they may have good thermoelectric capabilities at room temperature with an unaffected, stable crystal structure. The outcomes of study are very compatible with the research reported in the literature.