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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 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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    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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    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.