Browsing by Author "Ulusoy, Seda"

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    Article
    Citation - WoS: 33
    Citation - Scopus: 32
    Characterization of Thin Film Li0.5la0.5ti1-Xalxo3 Electrolyte for All-Solid Li-Ion Batteries
    (Elsevier, 2018-10) Ulusoy, Seda; Gülen, Sena; Aygün, Gülnur; Özyüzer, Lütfi; Özdemir, Mehtap
    Since addition of Al in Li0.5La0.5TiO3 has enhanced ionic conductivity in bulk materials, it is important to apply this material on all solid state thin film batteries. Because some of the good ionic conductors such as Lithium Phosphorus Oxynitride (LiPON) are sensitive to oxygen and moisture and their application is limited, so amorphous Li0.5La0.5Ti1−xAlxO3 (LLTAlO) is a most promising candidate because of its stability. In this study, the crystalline LLTAlO targets were prepared changing the amount of x content by conventional solid state reactions. Using these targets, lithium lanthanum titanium oxide (LLTO) thin film electrolytes were deposited on ITO/SLG substrates by radio frequency magnetron sputtering system in Ar atmosphere. The structural and compositional properties of targets and thin films were characterized by SEM, XRD, Raman spectroscopy and XPS. It was found that all targets are crystalline while the thin films are amorphous. To understand the effect of Al doping on ionic conductivity, electrical measurements were done at room temperature by AC impedance spectroscopy forming ITO/LLTAlO/Al structure like capacitor. Highest ionic conductivity result, 0.96 × 10−6 S·cm−1, is obtained from the nominal thin film composition of Li0.5La0.5Ti1−xAlxO3 (x = 0.05) at room temperature measurements. Heat treatment is also conducted to investigate to understand its effect on ionic conductivity and the structure of the thin films. It is found that ionic conductivity enhances with annealing. Also, temperature dependent ionic conductivity measurements from 298 K to 385 K are taken in order to evaluate activation energy for Li-ion conduction.
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    Master Thesis
    Ionic Conductivity of Li0.5la0.5ti1-Xalxo3 Electrolytelayer for Thin Film Batteries
    (Izmir Institute of Technology, 2016-12) Ulusoy, Seda; Özyüzer, Lütfi; Aral, Gürcan
    In this study, crystalline lithium lanthanum titanium (aluminum) oxide Li0.5La0.5Ti1-xAlxO3 (LLTO) powder targets with different Aluminum (x) content were prepared by conventional solid state reactions as Li0.5La0.5TiO3, Li0.5La0.5Ti0.99Al0.01O3, Li0.5La0.5Ti0.95Al0.05O3, Li0.5La0.5Ti0.90Al0.10O3 and Li0.5La0.5Ti0.85Al0.15O3 compositions. Then, after a couple of calcination processes with regrinding of the prepared stoichiometric powder batch, it is placed into Cu-base plate to be pressed in order to provide a compact, dense and smooth target surface for the thin film deposition. For the thin film fabrication, radio frequency (RF) magnetron sputtering technique is used to sputter the dielectric target. Thin films were deposited on soda-lime glass (SLG) and 256 nm thick indium tin oxide (ITO) layer grown on soda-lime glass (SLG) substrates. For the electrical measurements of LLTO thin film, it was fundamental to have ITO as conducting layer electrode. Targets with various Al (x) compositions were deposited for the investigation of Ti substitution with Al on structural and electrical properties. Besides, crystalline structure of the targets was characterized by X-ray powder diffraction (XRPD) and Raman Spectroscopy analysis while structural, morphological and compositional properties of the thin films were determined by x-ray diffraction (XRD), scanning electron microscope (SEM) and x-ray photoelectron spectroscopy (XPS) respectively. Moreover, in order to understand the effect of Al doping on ionic conductivity, electrical measurements were performed at room temperature by AC impedance spectroscopy forming ITO/LLTO/Al capacitor like structure. Maximum ionic conductivity result is obtained for Li0.5La0.5Ti0.95Al0.05O3 thin film composition. Also, temperature dependent ionic conductivity measurements were performed from 298 K to 373 K to evaluate activation energy for the Li-ion conduction. Keywords: Ionic conductivity, Li0.5La0.5Ti1-xAlxO3, electrolyte, thin film, activation energy, RF magnetron sputtering