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    Boron-Doped Strontium-Stabilized Bismuth Cobalt Oxide Thermoelectric Nanocrystalline Ceramic Powders Synthesized via Electrospinning
    (SPRINGER, 2014) Kocyigit, Serhat; Aytimur, Arda; Cinar, Emre; Uslu, Ibrahim; Akdemir, Ahmet
    Boron-doped strontium-stabilized bismuth cobalt oxide thermoelectric nanocrystalline ceramic powders were produced by using a polymeric precursor technique. The powders were characterized by using x-ray diffraction (XRD), scanning electron microscopy (SEM), and physical properties measurement system (PPMS) techniques. The XRD results showed that these patterns have a two-phase mixture. The phases are face-centered cubic (fcc) and body-centered cubic (bcc). Values of the crystallite size, dislocation density, and microstrain were calculated by using the Scherrer equation. The lattice parameters were calculated for fcc and bcc phases. The SEM results showed that needle-like grains are formed in boron-undoped composite materials, but the needle-like grains changed to the plate-like grains with the addition of boron. The distribution of the nanofiber diameters was calculated and the average diameter of the boron-doped sample is smaller than the boron-undoped one. PPMS values showed that the electrical resistivity values decreased, but the thermal conductivity values, the Seebeck coefficients, and figure of merit (ZT) increased with increasing temperature for the two samples.
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    Fabrication and characterization of bismuth oxide-holmia nanofibers and nanoceramics
    (ELSEVIER SCIENCE BV, 2013) Aytimur, Arda; Kocyigit, Serhat; Uslu, Ibrahim; Durmusoglu, Senol; Akdemir, Ahmet
    In this article, a novel and simple method to produce both boron doped and undoped holmia stabilized bismuth oxide nanoceramic materials has been put forward. Boron doped and undoped poly ( vinyl alcohol)/bismuth-holmia acetate nanofibers were produced using the electrospinning technique and were calcined at 850 degrees C afterward in order to obtain nanopowder. The characteristics of the nanofibers were investigated with FT-IR, XRD, and SEM. XRD analyses showed that boron undoped holmia stabilized bismuth oxide nanopowders have the face-centered cubic structure (delta-phase), and that the incorporation of boron atoms into the composite prevents the nucleus formation and turns the structure into a more amorphous glassy form. The SEM micrographs of the fibers showed that the addition of boron results in the formation of cross-linked bright-surfaced fibers. The average fiber diameters for electrospun boron doped and undoped PVA/Bi-Ho acetate nanofibers were calculated using the ImageJ software as 102 nm and 171 nm, respectively. (C) 2012 Elsevier B.V. All rights reserved.
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    Synthesis and characterization of boron doped bismuth-calcium-cobalt oxide nanoceramic powders via polymeric precursor technique
    (ELSEVIER SCI LTD, 2013) Aytimur, Arda; Uslu, Ibrahim; Cinar, Emre; Kocyigit, Serhat; Ozcan, Fatih; Akdemir, Ahmet
    In this study, boron doped calcium stabilized bismuth cobalt oxide nanocrystalline ceramic powders were successfully prepared from aqueous boric acid containing calcium bismuth cobalt acetate/poly(vinyl alcohol) hybrid precursor polymer solutions. Then, obtained ceramic powders were characterized via FT-IR. XRD, and SEM techniques. According to X-ray results, fcc and bcc phases coexist in the samples of the nanocrystalline ceramic powders. fcc peaks became sharper and bcc peak decreased with increasing boron content. Structural parameters for face centered cubic structure were calculated using the Scherrer equation. Moreover, dislocation densities and microstrain values were calculated for the nanocrystalline powder samples. (c) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
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    Synthesis and characterization of boron-doped bismuth oxide-erbium oxide fiber derived nanocomposite precursor
    (SAGE PUBLICATIONS LTD, 2014) Aytimur, Arda; Kocyigit, Serhat; Uslu, Ibrahim; Durmusoglu, Senol; Akdemir, Ahmet
    In this study, boron doped and undoped Bi2O3-Er2O3 nanocomposite fibers were produced via electrospinning technique. Obtained fibers were turned into ceramics via calcination process. Obtained nanocomposite fibers and ceramics were characterized by Fourier transform infrared, x-ray diffraction, and scanning electron microscopy techniques. X-ray diffraction results show that boron undoped Bi2O3-Er2O ceramic consisted of face-centered cubic Bi2O3-Er2O phase. However, boron doped Bi2O3-Er2O ceramic consisted of orthorhombic phase. Crystallite sizes of the ceramics were evaluated using Scherrer's equation. Crystallite sizes of boron doped and undoped ceramics were calculated as 50 and 17 nm, respectively. The average fiber diameters for boron doped and undoped poly vinyl alcohol/Bi-Er acetate nanofibers were calculated as 79 nm and 96 nm, respectively. The Brunauer Emmett teller results show that boron undoped and doped Bi2O3-Er2O nanocrystalline powder ceramic structures sintered at 800 degrees C have surface area of 20.44 and 12.93 m(2)/g, respectively.
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    Synthesis and Characterization of PVA/Calix[4]arene Fibers
    (TAYLOR & FRANCIS INC, 2013) Kocyigit, Serhat; Tabakci, Mustafa; Ozaytekin, Ilkay
    In this study, both boron-doped and -undoped poly(vinyl alcohol)/Calix[4]arene fibers were prepared by using an electrospinning technique. Obtained fibers were characterized by FT-IR, DSC, and SEM techniques. The DSC results show that the degradation of the boron-doped fibers started at much higher temperatures. This result indicates the addition of boron increased the thermal stability of the fibers. SEM pictures show that both of the fiber samples are nonbeaded with diameters ranging from 0.5 to 1 mu m. The fiber diameters are not homogeneous and uniformly distributed for boron-undoped samples.
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    Synthesis, Characterization, and Thermoelectric Properties of Electrospun Boron-Doped Barium-Stabilized Bismuth-Cobalt Oxide Nanoceramics
    (SPRINGER, 2014) Cinar, Emre; Kocyigit, Serhat; Aytimur, Arda; Uslu, Ibrahim; Akdemir, Ahmet
    In this study, the boron-doped barium-stabilized bismuth cobalt oxide thermoelectric nanocrystalline ceramic powders were produced by the polymeric precursor technique. The powders were characterized by X-ray diffraction, scanning electron microscopy, and the physical properties measurement system. The X-ray diffraction results showed that these patterns have mixture of two phases as face-centered cubic and body-centered cubic. Values of the crystallite size, the dislocation density, and the microstrain were calculated by the Scherrer equation. According to these values, the crystallite size decreased from 60 to 51 nm with the boron addition in the boron-undoped and boron-doped samples, respectively. The scanning electron microscope results showed that nanograins are rarely seen in the boron-undoped samples, but nanograins turn into needle-like and layered structures with boron addition. The diameters distribution of nanofibers was calculated. The average diameter of the boron-doped sample is smaller than the boron-undoped sample. The physical properties measurement system values showed that the electrical and thermal conductivity, the Seebeck coefficient, and the figure of merit increased with the temperature rise for both samples. The boron-doping effect increased the electrical and thermal conductivity, decreased the Seebeck coefficient, and decreased the figure of merit.