Nanocomposites and nanomaterials

Impedance spectroscopy of nanocomposite opal-NaBi(MoO4)2:Gd3+
1Khalil J. Hamam, 1Bilal Abu Sal, 2Moiseyenko V.N., 2Ohiienko O.V., 2Derhachov M.P.
1 Applied Physics Department Faculty of Science, Tafila Technical University P.O. Box 40, Al-Eis 66141, Tafila – Jordan
2 Physics, Electronics and Computer Systems Department, Oles Honchar Dnipro National University. Prospect Gagarina, 72, Dnipro-49010, Ukraine. 
E-mail: vnmois@ukr.net 

Single crystals of NaBi(MoO4)2 doped with rare-earth metal ion are promising materials for solid lasers and require comprehensive study. The crystals are disordered in the distribution of Na+ and Bi3+ ions in two nonequivalent type positions, while gadolinium ions Gd3+ occupy the position of bismuth [1]. 
In this work, we studied the conductive properties of opal-NaBi(MoO4)2:Gd3+ nanocomposite by impedance spectroscopy. Samples were prepared by compressing the powder of nanocomposite at room temperature into round tablets. Both faces of the tablets were silvered. The real and imaginary components of the complex impedance as well as the phase shift were measured in the frequency range from 1Hz to 1MHz and temperature range from 290 K to 390 K using Solartron-1260 Impedance/Gain Phase Analyzer. The applied voltage signal had an amplitude of 0.2 V with an accuracy of 0.1%. Samples were heated then cooled in one cycle. Impedance hodographs (Nyquist plots) for nanocomposite were undeformed semicircles. The semicircle centers were below the abscissa, which indicates a deviation from the ideal Debye behavior, and is characteristic of ionic conductors. It was found that the bulk conductivity can be described by the Arrhenius equation with activation energy Ea = 0.17 eV. The type of conductivity mechanism in the nanocomposite was determined from the frequency dependence of the conductivity described as σ(ω) = σ(0) + A ωn, where n is decreasing from 0.99 to 0.77 as the temperature increases. This confirms the hopping mechanism of conductivity in the nanocomposite. The results obtained suggest that the conductivity in the nanocomposite is mainly ionic and is due to the migration, which includes alternating jumps of oxygen ions (O2–) and Na+ cations.

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