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    Magnesia Stabilized Zirconia Doped With Boron, Ceria and Gadolinia
    (Elsevier Sci Ltd, 2012) Aytimur, A.; Uslu, I.; Koçyiğit, S.; Özcan, F.
    In this study, magnesia stabilized zirconia based nanocrystalline ceramics were produced through a polymer precursor route using gadolinium and boron. The powders were characterized during the various steps by structural and morphological techniques (FT-IR, XRD, and SEM). XRD results proved that a tetragonal phase is predominant for all samples with varying magnesium contents and no monoclinic zirconia solid solution appears. The crystallite sizes of the samples were calculated using Scherrer equation. The smallest crystallite size was obtained for the sample containing Zr/Mg/Ce/Gd/B ratio of 82/0/10/8/0. The lattice parameters were calculated for cubic, tetragonal, hexagonal, and orthorhombic structures. SEM results show all the samples have spherical grains. The average grain diameters were calculated for all the samples. The smallest average grain diameter was obtained for the sample containing Zr/Mg/Ce/Gd/B ratio of 82/0/10/8/0.
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    Synthesis and Characterization of Boron Doped Alumina Stabilized Zirconia Fibers
    (KOREAN FIBER SOC, 2011) Uslu, I.; Tunc, T.; Keskin, S.; Ozturk, M. K.
    Boron doped PVA/Zr-Al acetate nanofibers were prepared by electrospinning using PVA as a precursor. The effect of calcination temperature on morphology and crystal structure was investigated at 250, 500, and 800 degrees C. The study also establishes the effect of boron doping on the morphology of PVA/Zr-Al acetate nanofibers at various calcination temperatures. The measurements showed that the conductivity, pH, viscosity and the surface tension of the hybrid polymer solutions have increased with boron doping. In addition, the fibers were characterized by FTIR, DSC, XPS, XRD and SEM techniques. The addition of boron did not only increase the thermal stability of the fibers, hut also increased the average fiber diameters, which gave stronger fibers. The DSC results indicated that the melting temperature (Tm) of the fibers was increased from 256 to 270 degrees C with the addition of boron. XRD peak patterns showed that after further heat treatment at 800 degrees C, zirconia exists in two phases of tetragonal and monoclinic modifications. Moreover, alumina does not transform into the gamma-Al2O3 and theta-Al2O3 phase at 800 degrees C. The SEM appearance of the fibers showed that the addition of boron resulted in the formation of crosslinked bright surfaced fibers.
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    Synthesis and characterization of erbia and ceria doped calcia stabilized nanocrystalline zirconia based ceramics
    (SPRINGER, 2013) Uslu, I.; Aytimur, A.; Kocyigit, S.; Ozcan, F.; Ozturk, M. K.; Colak, U.
    Er2O3 doped calcia stabilized zirconia based inert matrix fuel containing CeO2 as a surrogate for PuO2 was fabricated for a wide range of concentration using the polymer-to-ceramic conversion technique via metal acetate preceramic hybrid polymer solutions. Samples were characterized by XRD, SEM and AFM techniques. Nanocrystallite size variation in the samples was evaluated using peak broadening values by means of the Scherrer formula. The smallest lattice constant was obtained for the sample containing Zr/Ca/Ce/Er atomic weight ratio of 74/11/10/5. The average grain diameters varied between 64 nm and 129 nm. SEM results show that, the smallest grain size was obtained for the sample containing Zr/Ce/Er atomic weight ratio of 22/2/1. Moreover, surface roughness characteristics of the samples were evaluated by different definitions using intermittent contact mode AFM.
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    Synthesis and Properties of Boron Doped NaxCo2O4 Nanocrystalline Ceramics
    (SPRINGER, 2012) Uslu, I.; Cetin, Saime Sebnem; Aytimur, A.; Yuceyurt, S.; Erdal, M. O.
    Sodium cobalt oxide (NaCo2O4) nanofibers with diameters ranging between 20 and 200 nm were prepared by electrospinning a precursor mixture of PVA/(Na-Co) acetate. This was the first time any such attempt was made. Afterwards, the electrospun nanofibers were subjected to calcination treatment. The characteristics of the fibers were investigated using a Fourier transform infrared spectroscopy, a X-ray diffractometer, and a scanning electron microscopy. The boron doped and undoped NaCo2O4 nanofibers calcined at 850 A degrees C were polycrystalline of the gamma NaxCo2O4 phase having diameters ranging between 20 and 60 nm with grain sizes of 5-10 nm, and the nanofibers calcined at 800 A degrees C were single crystals having linked particles or crystallites with particle sizes ranging between 60 and 200 nm. The results indicated a significant effect of calcination temperature on the crystalline phase and morphology of the nanofibers. It could be seen in the SEM micrograph of the fibers that when boron was added, this resulted in the formation of cross-linked bright-surfaced fibers. The average fiber diameter for boron doped and undoped fiber mats were 204 and 123 nm, respectively. The grain diameters of boron doped and undoped nanocrystalline sintered powders were measured as 140 and 118 nm, respectively.
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    Temperature Dependent Current-Voltage (I-V) Characteristics of Au/N-Si (111) Schottky Barrier Diodes (SBDS) with Polyvinyl Alcohol (Co, Ni-Doped) Interfacial Layer
    (NATL INST OPTOELECTRONICS, 2010) Tunç, T.; Dökme, I.; Altındal, S.; Uslu, I.
    Current-voltage (I-V) characteristics of Au/PVA(Co,Ni-doped)/n-Si (111) SBDs have been investigated in the temperature range of 280-400 K. The zero-bias barrier height (Phi(bo)) and ideality factor (n) determined from the forward bias 1 V characteristics were found strongly depend on temperature. The forward bias semi-logarithmic I-V curves for the different temperatures have an almost common cross-point at a certain bias voltage. While the value of n decreases, the Phi(Bo) increases with increasing temperature. Therefore, we attempted to draw a Phi(bo) vs q/2kT plot to obtain evidence of a Gaussian distribution of the barrier heights, and to calculate the values of mean barrier height and standard deviation at zero bias, respectively.