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    Öğe
    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 Effect of CrFe2O4 Addition on the Ionic Conductivity Properties of Manganese-Substituted LiFeO2 Material
    (Springer, 2024) Gunaydin, Selen; Miyazaki, Hidetoshi; Saran, Sevda; Baveghar, Hadi; Celik, Gultekin; Harfouche, Messaoud; Abdellatief, Mahmoud
    The influence of Mn substitution on the iron lattice sites in LiFeO2 material was investigated with respect to the electronic, crystalline, and electrochemical properties of the material, using the LiFe1-xMnxO2 (x = 0.0, 0.05, and 0.10) series. The electronic structure study was conducted with the acquisition of x-ray absorption fine structure spectroscopy data, while the crystal structure properties of the studied materials were investigated using x-ray diffraction patterns. The data collected for the ionic conductivity properties of the samples by electrochemical impedance spectroscopy under increasing temperature conditions around and above room temperature aided the crystal and electronic structure studies on cathode materials. Furthermore, studies were conducted with the addition of CrFe2O4 material in varying molar concentrations into LiFeO2 material, as CrFe2O4 is known to have thermoelectric properties well above the room temperature of 400 K (127 degrees C). Encouraging results for next-generation battery cathodes were obtained.
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    Öğe
    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.