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    Effect of concentration of Sm2O3 and Yb2O3 and synthesizing temperature on electrical and crystal structure of (Bi2O3)(1-x-y)(Sm2O3)(x)(Yb2O3)(y) electrolytes fabricated for IT-SOFCs
    (ELSEVIER SCIENCE BV, 2016) Kayali, Refik; Ozen, Murivet Kasikci; Bezir, Nalan Cicek; Evcin, Atilla
    For intermediate temperature solid oxide fuel cells (IT-SOFCs), (Bi2O3)(1-x-y)(Sm2O3)(x)(Yb2O3)(y) ternary systems (x=0.01 and y = 0.11), (x=0.05 andy= 0.07), (x=0.07 and y=0.05), and (x=0.11 and y=0.01) as electrolytes have been fabricated at different temperatures (700, 750, and 800 degrees C) by solid state ceramic technique (SST). The characterization of the samples has been performed by X-ray powder diffractometer (XRD), scanning electron microscopy (SEM), four point-probe method (FPPM), X-ray energy diffraction spectroscopy (EDX), and differential thermal analysis (DTA). XRD measurements have shown that only the samples (Bi2O3)(1-x-y)(Sm2O3)(x)(Yb2O3)(y) (x=0.01, y=0.11 synthesized at 700, 750, and 800 degrees C) and (x=0.05, y=0.07 synthesized at 800 degrees C) have stable fluorite type face centered cubic (FCC) delta-phase. SEM images have shown the morphology of the stable samples. The conductivity and the operation temperature region of the samples have been determined from Arrhenius curves obtained from the FPPM measurements data and they vary from 1.83 to 9.95 x 10(-1) S cm(-1). Moreover, activation energy of the samples have been calculated by means of Arrhenius curves of the samples and relationships between them and the conductivity of the samples have been investigated in detail. The results obtained from XRD and FPPM measurements were confirmed by the DTA measurements. (C) 2016 Elsevier B.V. All rights reserved.
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    Investigation of structural, electronic and optical properties of pure and Ag-doped TiO2 nanofibers fabricated by electrospinning
    (WILEY-V C H VERLAG GMBH, 2016) Bezir, Nolan Cicek; Evcin, Atilla; Kayali, Refik; Ozen, Murivet Kasikci; Oktay, Ayse
    Pure and 1, 2, and 3 wt% Ag doped TiO2 nanofibers were prepared by electrospinning method at different applied voltages and heights at a constant flow rate of 2 mL/h. Characterization of the prepared samples was performed by x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microcopy (AFM),four point probe method (FPPM), the differential scanning calorimetry/the thermal gravimetric analysis (DSC/TGA), ultraviolet/visible spectrometry (UV/VIS), and energy dispersive X-ray spectrometer (EDX). It was found that the thermally untreated pure TiO2 nanofibers and thermally treated (at 500 degrees C) samples have the crystalline phase of anatase (A), and mixed anatase and rutile (A+R) phases, respectively. It was also observed that the content of the silver does not affect the crystal structure, but plays strengthening role in the rutile structure. SEM micrographs showed that all fabricated nanofiber samples have uniform morphologies, and AFM measurements indicated that the nanofibers were formed in three-dimensional coils. The band gap values of the nanofiber samples obtained from UV/VIS measurements revealed that band gap values of the nanofiber samples decrease while the diameter of the nanofiber increases.