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2016 | 129 | 1 | 133-137
Article title

The Electrical Properties of Some Composite Materials Based on Sodium and Tantalum Oxides

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Abstracts
EN
Two samples of Na-Ta oxides were synthesized by the hydrothermal method at reaction temperatures of 160°C (sample A) and 200°C (sample B). For reference, a third sample of pure NaTaO₃ was prepared by the sol-gel method (sample C). Using X-ray diffraction, scanning electron microscopy, UV-vis diffuse reflectance spectra and electric measurements, structural, morphologic, spectroscopic and electric properties of samples were investigated. The structural characterization by X-ray diffraction revealed that samples A and B are mixtures of Na-Ta oxides (including NaTaO₃ and other compounds), whilst sample C is pure NaTaO₃. UV-vis diffuse reflectance spectra allowed evaluation of the band gap energy (E_{g}), resulting in 3.88 eV for sample A, 3.93 eV for sample B and 4.1 eV for sample C. Electrical resistivity measurements, over the temperature range 300-450 K, showed a typical semiconductor behavior of the investigated samples, with the effective activation energy, E_{a} of 0.47 eV (sample A), 0.45 eV (sample B) and 0.82 eV (sample C). Based on the Mott variable range hopping model, the conductivity mechanism in the investigated samples was analyzed. The results shown that the density of states at the Fermi-level, N(E_{F}) is constant in the investigated temperature range and the typical values of N(E_{F}) are 0.713 × 10^{18} eV^{-1} cm^{-3} (sample A), 0.621 × 10^{18} eV^{-1} cm^{-3} (sample B) and 0.855 × 10^{17} eV^{-1} cm^{-3} (sample C). Other parameters of VRH model such as the hopping distance R and the hopping energy W have also been computed and the following values at the room temperature were obtained: R=15.7 nm and W=86 meV (for sample A); R=16.3 nm and W=89 meV (for sample B) and R=26.7 nm and W=147 meV (for sample C).
Keywords
Contributors
author
  • "Politehnica" University, Victoriei No. 2, RO-300006 Timisoara, Romania
author
  • "Politehnica" University, Victoriei No. 2, RO-300006 Timisoara, Romania
  • National Institute for Research and Development in Electrochemistry and Condensed Matter, Plautius Andronescu No. 1, RO-300224 Timisoara, Romania
author
  • National Institute for Research and Development in Electrochemistry and Condensed Matter, Plautius Andronescu No. 1, RO-300224 Timisoara, Romania
author
  • National Institute for Research and Development in Electrochemistry and Condensed Matter, Plautius Andronescu No. 1, RO-300224 Timisoara, Romania
author
  • West University of Timisoara, Faculty of Physics, Bd. V. Parvan no. 4, 300223 Timisoara, Romania
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Document Type
Publication order reference
Identifiers
YADDA identifier
bwmeta1.element.bwnjournal-article-appv129n126kz
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