Yazar "Ozkendir, Osman Murat" seçeneğine göre listele

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    An XAFS Study on the Electronic Structure Study of the Boron Substituted CuFeO2
    (Akdeniz Üniversitesi, 2021) Ozkendir, Osman Murat
    CuFeO2 is a well known antiferromagnetic material due to its geometrically frustrated antiferromagnetic (AFM) [TN=11K] character. Besides, delafossite CuFeO2oxide crystal is known to be under the influence of oxygen nonstoichiometry as a result of the change in cation valence bands. In this study, boron atoms were substituted in the Fe coordination and the electronic response on irons valence band is probed. Also, the possible influence of boron substitution on the electrical properties via the photoelectrons’ mean free path is investigated. Due to the high difference in the ionic radii of the host and substituted atoms, different crystal structure formation was expected. However, calculations showed that boron atoms tend to locate in Fe coordination and preferred to be part of the host crystal by bonding with the oxygen atoms. In addition, the presence of the light boron atoms was determined to weaken the scattering intensities which cause a longer mean free path for the photoelectrons which means better conductivity of the material.
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    Comparative Synthesis of Silver Nanoparticles: Evaluation of Chemical Reduction Procedures, AFM and DLS Size Analysis
    (Mdpi, 2023) Chicea, Dan; Nicolae-Maranciuc, Alexandra; Doroshkevich, Aleksandr S.; Chicea, Liana Maria; Ozkendir, Osman Murat
    The size of silver nanoparticles plays a crucial role in their ultimate application in the medical and industrial fields, as their efficacy is enhanced by decreasing dimensions. This study presents two chemical synthesis procedures for obtaining silver particles and compares the results to a commercially available Ag-based product. The first procedure involves laboratory-based chemical reduction using D-glucose (C6H12O6) and NaOH as reducing agents, while the second approach utilizes trisodium citrate dehydrate (C6H5Na3O7 & BULL;2H(2)O, TSC). The Ag nanoparticle suspensions were examined using FT-IR and UV-VIS spectroscopy, which indicated the formation of Ag particles. The dimensional properties were investigated using Atomic Force Microscopy (AFM) and confirmed by Dynamic Light Scattering (DLS). The results showed particle size from microparticles to nanoparticles, with a particle size of approximately 60 nm observed for the laboratory-based TSC synthesis approach.
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    Determination of the atomic coordinations of the substituted light atoms in materials
    (Natl Inst Optoelectronics, 2019) Ozkendir, Osman Murat
    Light atoms' substitution into a heavy atom coordination in materials can be a difficult process for analysis. Light atoms, which have close ionic radii with the target atom, may sit at the heavy atom's coordination. In such a case, scientist may not differ the signals from the heavy and light atom to differentiate the exact atomic coordinations of the substituted atom. As an example study, boron substitution into the chromium coordinations is studied. In the samples with boron substitution more than 10%, they became polycrystalline material where boron and chromium tended to own their own crystal structures. However, in the samples with lower substitution amounts, for x=0.05 and 0.10, boron atoms seem to sit in the Cr coordinations without any trace from boron atoms. The boron signals in the XRD patterns has not been detected, and accordingly some hypothesis put forwarded, such as; boron sat in the Cr coordinations or cause defects/impurities that can not be detected in patterns due to low amount of the light atoms. Studies were carried on a series of Li-ion battery cathode materials with the general formula LiCr1-xBxO2. The analysis were performed by the x-ray absorption fine structure (XAFS) technique. As a result of the study, 10% boron substitution was determined as a treshold to protect the LiCrO2 crystal structure.
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    Evaluating electronic and structural properties of Au and Cu substituted AgCl electrode for application in surface electromyography
    (Elsevier Sci Ltd, 2021) Alcan, Veysel; Ozkendir, Osman Murat
    The material content of electrodes is very much important for improving the signal quality of surface electromyography (sEMG) in various environments, in particular, long-term monitoring. The electronic and structural properties of silver/silver chloride (Ag/AgCl), a popular biopotential electrode for sEMG recording, were studied under different conditions by X-ray absorption fine structure (XAFS) spectroscopy calculations. The effects of substitution of good-conducting elements (Cu and Au) on Ag coordination were tested at different temperatures as well as possible defect conditions. In the Au-substituted AgCl material, an extension of the Ag K-edge spectra was detected due to the rich quantum symmetry of Au valence level. Hence, it was determined that Au atoms bond with Cl atoms stronger than Ag atoms. Additionally, it was determined that Au atoms also changed the ionic properties of Ag atoms by losing Ag-Cl bonds.
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    Investigating a Pb-free n-i-p perovskite solar cell with BFCO absorber using SCAPS-1D
    (Elsevier GmbH, 2024) Mahammedi, Nassim Ahmed; Benameur, Afif; Gueffaf, Hamza; Merabet, Boualem; Ozkendir, Osman Murat; Sato, Shin-Ichiro
    In recent years, perovskite solar cells (PSCs) have gained significant attention as highly efficient photovoltaic (PV) devices. Despite achieving record levels of power conversion efficiency (PCE), the commercialization of Pb-based PSCs has been hindered by factors such as lead toxicity and stability. As a potential alternative, Pb-free Bi-based all-inorganic PSCs show promising efficiency. In this study, we utilized the Solar Cell Capacitance Simulator (SCAPS-1D) to optimize a Bi2FeCrO6-based (BFCO) PSC and analyzed the impact of absorber thickness, doping concentration, and external parameters on its PV performance. We have found that an optimized n-i-p architecture with an absorber thickness of 150 nm yielded a maximum PCE of 7% at ambient temperature (with open-circuit voltage, short-circuit current density, and fill factor of 1.12 V, 12 mA/cm2, and 53.7%, respectively). Furthermore, we found that decreasing the defects density Nt of the BFCO layer below 1013 cm−3 could increase the PCE to above 10%. Our findings also revealed that the temperature had a negative effect on the solar cell, and the optimum conditions were at ambient 300 K. These results are encouraging for advancing Pb-free PSCs and enhancing their design and integration into tandem SCs. © 2024 The Authors
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    Investigation of the Effects of Varying Temperature Conditions on the Electronic Levels of LiNi2Sn Material: An Ab-Initio Study
    (2023) Ozkendir, Osman Murat
    In this study, the electronic and crystal structures of the LiNi2Sn material—reported to have a stable crystal structure but not yet thoroughly studied—were examined at various temperatures, and traces of the thermoelectric property were looked for in light of the results. A test research was carried out with a fresh perspective on the thermoelectric property traces on the electrical and crystal structures in order to promote the studies of thermoelectric materials, and the results were provided with complete analysis. Theoretical investigations using X-ray absorption fine structure (XAFS) spectroscopic calculations were made into the electronic structural characteristics of the LiNi2Sn material. Calculations were made with XAFS code FEFF 8.20 under increasing temperature conditions of 300 K, 323 K, 373 K, and 423 K. Findings from the study included the quantity and potency of the atoms' outer shell electrons, which are where the photoelectrons are directed. The results of the study are compatible with the literature data.
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    Local Structure of Heusler-Type Fe2V1-XTaXAl Thermoelectric Materials Studied by X-Ray Absorption Fine-Structure Spectroscopy
    (Wiley-V C H Verlag Gmbh, 2022) Takahashi, Kouki; Miyazaki, Hidetoshi; Kimura, Koji; Ozkendir, Osman Murat; Nishino, Yoichi; Hayashi, Kouichi
    The local structure around doping Ta atoms in Fe2V1-xTaxAl alloys is investigated using X-ray absorption fine-structure (XAFS) and synchrotron radiation X-ray diffraction (SR-XRD) measurements to elucidate the origin of the reduction in their thermal conductivity. XAFS and SR-XRD results show that with the substitution of Ta atoms at the V site, local strain exists around the doped Ta atoms. The reduction in the thermal conductivity due to Ta doping in the Fe2V1-xTaxAl alloys is attributed to the increase in the average atomic mass substituted with the heavy element Ta as well as the existence of the local strain.
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    Machine learning based prediction of lattice thermal conductivity for half-Heusler compounds using atomic information
    (Nature Portfolio, 2021) Miyazaki, Hidetoshi; Tamura, Tomoyuki; Mikami, Masashi; Watanabe, Kosuke; Ide, Naoki; Ozkendir, Osman Murat; Nishino, Yoichi
    Half-Heusler compound has drawn attention in a variety of fields as a candidate material for thermoelectric energy conversion and spintronics technology. When the half-Heusler compound is incorporated into the device, the control of high lattice thermal conductivity owing to high crystal symmetry is a challenge for the thermal manager of the device. The calculation for the prediction of lattice thermal conductivity is an important physical parameter for controlling the thermal management of the device. We examined whether lattice thermal conductivity prediction by machine learning was possible on the basis of only the atomic information of constituent elements for thermal conductivity calculated by the density functional theory in various half-Heusler compounds. Consequently, we constructed a machine learning model, which can predict the lattice thermal conductivity with high accuracy from the information of only atomic radius and atomic mass of each site in the half-Heusler type crystal structure. Applying our results, the lattice thermal conductivity for an unknown half-Heusler compound can be immediately predicted. In the future, low-cost and short-time development of new functional materials can be realized, leading to breakthroughs in the search of novel functional materials.
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    Probing local distortion around structural defects in half-Heusler thermoelectric NiZrSn alloy
    (Nature Portfolio, 2020) Miyazaki, Hidetoshi; Ozkendir, Osman Murat; Gunaydin, Selen; Watanabe, Kosuke; Soda, Kazuo; Nishino, Yoichi
    The half-Heusler NiZrSn (NZS) alloy is particularly interesting owing to its excellent thermoelectric properties, mechanical strength, and oxidation resistance. However, the experimentally investigated thermal conductivity of half-Heusler NZS alloys shows discrepancies when compared to the theoretical predictions. This study investigates the crystal structure around atomic defects by comparing experimental and theoretical X-ray absorption fine structure (XAFS) spectra of the crystal structure of a half-Heusler NZS alloy. The results of both Zr and Ni K-edge XAFS spectra verified the existence of atomic defects at the vacancy sites distorting the C1(b)-type crystal structure. We concluded that the distortion of the atoms around the interstitial Ni disorder could be the probable reason for the observed lower thermal conductivity values compared to that predicted theoretically in half-Heusler alloys. Our study makes a significant contribution to the literature because the detailed investigation of the lattice distortion around atomic defects will pave the way to further reduce the thermal conductivity by controlling this distortion.
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    Structure and ionic conductivity of NASICON-type LATP solid electrolyte synthesized by the solid-state method
    (Elsevier Sci Ltd, 2024) Oksuzoglu, Fatih; Ates, Sule; Ozkendir, Osman Murat; Celik, Gultekin; Eker, Yasin Ramazan; Baveghar, Hadi
    The area of commercial battery innovation to replace safer batteries in widely used secondary batteries offers promising research into solid-state electrolytes (SSEs). Compared to lithium-ion electrolytes, solid-state electrolytes are inherently safer because they replace solvents with non-flammable materials. One of the promising materials for electrolytes today is based on inorganic materials, especially ceramics. Ceramics with superior mechanical, chemical and electrochemical stability and stability against high temperatures are of great interest. NASICON structured Li1.3 Al0.3 Ti1.7 (PO4)3 (LATP) is the most studied type of solid electrolyte due to its stability against air and humidity and high ionic conductivity. In this study, LATP samples were synthesized by solid-state synthesis method. The structural, morphological and charge transport properties (ionic conductivities) of the synthesized samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Since the modifications applied during the sample preparation process can change the crystal structure and size of the target material, in this study, in order to minimize the formation of impurity phases and to achieve high ionic conductivity it was applied the different synthesis steps (temperature, time, grinding speed, etc.) from the literature. While the ionic conductivity value obtained is among the best values obtained by LATP synthesis methods in the literature, it is the best ionic conductivity value (1.3 x 10-3 S cm-1) obtained by the solid state synthesis method.
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    Study of the local structure and electrical properties of gallium substituted LLZO electrolyte materials
    (Elsevier Science Sa, 2019) Aktas, Sevda; Ozkendir, Osman Murat; Eker, Yasin Ramazan; Ates, Sule; Atav, Ulfet; Celik, Gultekin; Klysubun, Wantana
    The solid-state lithium batteries are more stable than the batteries with liquid electrolyte, however their performance are also worse especially due to the low ionic conduction of their electrolyte. Garnet-type Li7La3Zr2O12 is a promising solid-state electrolyte candidate for lithium batteries. In this work the influence of gallium substitution on the electrical, crystal and electronic structure properties in the Li7La3Zr2O12 material were studied. Li7-3xGaxLa3Zr2O12 solid electrolytes were synthesized by solid state reaction method and characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), AC impedance spectroscopy and X-ray absorption spectroscopy (XAS) techniques. XRD and XAS analyses showed that the x = 0.05 sample is formed in the tetragonal phase with a space group of I4(1)/ acd:2 and the rest are formed in the cubic phase with a space group of I-43d due to strong coupling between outer shell electrons of the oxygen (O) and gallium (Ga) atoms. Electrochemical impedance spectroscopy (EIS) studies indicated that the tetragonal phase has the highest ionic conductivity, 3.04 x 10(-6) S cm(-1), among all other cubic phases. (C) 2019 Published by Elsevier B.V.
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    Study on crystallographic and electronic structure of micrometre-scale ZnO and ZnO:B rods via X-ray absorption fine-structure spectroscopy
    (Int Union Crystallography, 2021) Erat, Selma; Ozkendir, Osman Murat; Yildirimcan, Saadet; Gunaydin, Selen; Harfouche, Messaoud; Demir, Bunyamin; Braun, Artur
    X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) spectra were recorded to investigate the electronic structure and local crystal structure of ZnO and ZnO:B powders produced via hydrothermal synthesis. ZnO and ZnO:B grow as micrometre-scale rods with hexagonal shape, as confirmed by scanning electron microscopy micrographs. The number of broken ZnO:B rods increases with increasing B concentration, as observed in the images, due to B atoms locating in between the Zn and O atoms which weakens and/or breaks the Zn-O bonds. However, no disorder within the crystallographic structure of ZnO upon B doping is observed from X-ray diffraction results, which were supported by EXAFS results. To determine the atomic locations of boron atoms in the crystal structure and their influence on the zinc atoms, EXAFS data were fitted with calculated spectra using the crystal structure parameters obtained from the crystallographic analysis of the samples. EXAFS data fitting and complementary k-weight analysis revealed the positions of the B atoms - their positions were determined to be in between the Zn and O atoms.
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    The effect of Ti to the crystal structure of Li7-3xMxLa3Zr1.8Ti0.2O12 (M= Ga, In) garnet-type solid electrolytes as a second dopant
    (Sage Publications Inc, 2022) Saran, Sevda; Eker, Yasin Ramazan; Ates, Sule; Celik, Gultekin; Baveghar, Hadi; Ozkendir, Osman Murat; Atav, Ulfet
    Garnet-type solid-state electrolytes are promising candidates for solid-state lithium batteries, nevertheless their ionic conductivity is still not enough for commercial applications. On the other hand, doping still is the common way to improve the ionic conductivities of these solid electrolytes. In this study, mono and dual-doped garnet-type solid electrolytes were synthesised by substituting indium (In), gallium (Ga), indium-titanium (In-Ti) and gallium-titanium (Ga-Ti) to the Li7La3Zr2O12 structure by a solid-state reaction method. The contribution of substitutions to the formation of crystal phases was investigated by X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). On the other hand, morphological analyses were done by scanning electron microscope (SEM) and the ionic conductivities of the solid electrolytes were determined by electrochemical impedance spectroscopy (EIS). The study showed that while Li7-3xInxLa3Zr2O12 (for x = 0.05, 0.10, 0.15, 0.20) and Li7-3xGaxLa3Zr2O12 (for x = 0.05) samples were formed in tetragonal phase with a space group of I41/acd:2, dual substituted Li7-3xInxLa3Zr1.8Ti0.2O12 and Li7-3xGaxLa3Zr1.8Ti0.2O12 solid electrolytes for all x values were formed in cubic phase with a space group of I-43d. The highest conductivity is reached for Li6.85Ga0.05La3Zr1.8Ti0.2O12. The radial distribution function studies showed that when more In and Ga atoms take place in the sites of Li atoms, more O atoms take place in the vicinity of both substituted In and Ga atoms within the Li7La3Zr1.8Ti0.2O12 (LLZTO) crystal framework which can eventuate in a change in the conduction mechanism.
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    The effect of two different substituted atoms in lithium positions on the structure of garnet-type solid electrolytes
    (Tubitak Scientific & Technological Research Council Turkey, 2021) Saran, Sevda; Ozkendir, Osman Murat; Atav, Ulfet
    Li7La3Zr2O12 (LLZO), lithium lanthanum zirconate is a promising garnet-type solid electrolyte that is being intensively studied for solid-state lithium batteries. The properties of LLZO such as compatibility with the lithium electrode, stability, and ionic conductivity make them to be used in all solid-state batteries. Moreover, lithium ion concentration and distribution, doping different cations, chemical composition, and interaction between different dopants have remarkable effects on the ionic conduction of LLZO material. Herein, we investigate the solid electrolyte, Li-6.4(Ga(1-y)In(y))(0.2)La3Zr2O12 (y = 0.05, 0.10, 0.15, 0.20), by probing the influence of indium substitution to gallium sites at the same lithium concentration on the structure and the lithium ion conduction. A conventional solid state route, ball milling was used to synthesize the materials. Crystal structure, morphology, ionic conduction, and local electronic structure were analysed by X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and X-ray absorption fine structure (XAFS) techniques, respectively. The results revealed that the existence of indium effected the conduction adversely, although made no significant changes on the local structure.
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    The Impact of Boron Compounds on the Structure and Ionic Conductivity of LATP Solid Electrolytes
    (Mdpi, 2024) Oksuzoglu, Fatih; Ates, Sule; Ozkendir, Osman Murat; Celik, Gueltekin; Eker, Yasin Ramazan; Baveghar, Hadi; Basyooni-M. Kabatas, Mohamed A.
    The increasing demand for safe and high-energy-density battery systems has led to intense research into solid electrolytes for rechargeable batteries. One of these solid electrolytes is the NASICON-type Li1+xAlxTi2-x(PO4)3 (LATP) material. In this study, different boron compounds (10% B2O3 doped, 10% H3BO3 doped, and 5% B2O3 + 5% H3BO3 doped) were doped at total 10 wt.% into the Ti4+ sites of an LATP solid electrolyte to investigate the structural properties and ionic conductivity of solid electrolytes using the solid-state synthesis method. Characterization of the synthesized samples was conducted using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS). The XRD patterns of the boron-doped LATP (LABTP) samples show that the samples have a rhombohedral phase with space group R3c together and low amounts of impurity phases. While all the LABTP samples exhibited similar ionic conductivity values of around 10-4 S cm-1, the LABTP2 sample doped with 10 wt.% H3BO3 demonstrated the highest ionic conductivity. These findings suggest that varying B3+ ion doping strategies in LATP can significantly advance the development of solid electrolytes for all-solid-state lithium-ion batteries.
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    Turkey's energy transition from fossil-based to renewable up to 2030: milestones, challenges and opportunities
    (Springer, 2021) Erat, Selma; Telli, Azime; Ozkendir, Osman Murat; Demir, Bunyamin
    The energy demand of Turkey has been increasing along with increasing life standards and population and growing economy particularly since the 1980s. Most of the oil and natural gas have been imported by Turkey due to insufficient domestic reserves. Nowadays, the population of Turkey is about 83 million. The Turkish economy grew by 3% in the last 30 years and became the 18th largest economy in the world and the 6th one in Europe. Turkey aims to use energy resources efficiently, effectively and eco-friendly. Concerning climate change, Turkey signed the Paris Agreement and pledged a 21% reduction in greenhouse gas emission by the year 2030. While the energy world is in an inevitable transition to green energy, Turkey, which has a huge potential to achieve 100% energy transition in renewable energy, is still the 17th largest country in the utilization of renewable energy. Although Turkey has already reached the 2023 targets concerning the utilization of renewable energy, there is a long path to reach the target of reducing greenhouse gas emissions. The 2030 targets of Turkey are to increase the installed solar capacity up to 38,000 MW, wind capacity up to 25,000 MW and geothermal capacity up to 4000 MW. Turkey officially announced that the utilization of renewable energy will be 32%. However, taking into account the potential and success in 2023 targets, it was seen that 2030 targets should be revised and increased from 32% to at least 50%. This study presents the milestones, challenges and opportunities of Turkey on the way of the energy transition toward renewable up to 2030. The energy goals of Turkey which are to use domestic energy resources efficiently and effectively were discussed and presented in detail. The aim of Turkey is to reduce the energy import dependency (76%). The installed energy capacities, energy consumption and projections, energy security and energy policies of Turkey were also presented. [GRAPHICS] .
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    XAFS study on the boron substituted LiGaO2 semiconductor material
    (Elsevier, 2020) Gundogmus, Hakan; Gunaydin, Selen; Klysubun, Wantana; Ozkendir, Osman Murat
    An XAFS study was performed on the electronic and crystal structure properties of LiGa1-xBxO2 (LGO) material in where boron atoms were substituted at the gallium sites. Studies were carried out by the X-ray powder diffraction (XRD) patterns and supported by the Extended-XAFS data. The analysis on the substituted materials revealed interesting mechanisms at the boron sites that preserved the crystal symmetry in the entire bulk. It was determined that, boron atoms do not lie in the Ga sites due to inequivalent ionic radii and formed a crystal LiB3O5, which has the same crystal geometry and space group of the parent LGO. With the presence of the boron atoms on the vicinity of the gallium atoms, tiny shifts on the main edge spectra resulted from the change in the oxidation of the gallium atoms.