Condutividade iônica e eletrônica em vidros 0,50[xAg2O(1-x)V2O5].0,50P2O5
Abstract
Mixed conductive glassy materials have in their composition, in addition
to a glass former, a metallic element in two oxidation states and ions with high
mobility, generally alkaline or Ag+ ions. These materials can be used in solid
state batteries. However, from a scientific point of view, there are still some
issues to be solved, such as the mechanism that best explains the behavior of
electric conduction in these materials, and why there is a marked drop in
conductivity as a function of composition, for equimolar compositions between
the modifier that introduces the ionic conduction, and the transition metal oxide
that introduces the electronic conduction. Therefore, to advance the frontier of
knowledge about the conduction mechanisms present in mixed conductive
glasses, the ternary system of the glass family 0.50[xAg2O(1-x)V2O5].0.50P2O5,
(0 ≤ x ≤ 1) was chosen. Each vitreous composition was synthesized and
characterized by X-ray diffraction, differential scanning calorimetry, Helium
pycnometry, and impedance spectroscopy. The impedance spectroscopy
measurements of the composition x=0.6 revealed a semicircle with a
deformation at low frequency. This semicircle cannot be adjusted by a single
RC circuit. The analysis of the pre-exponential factor and the activation
energies of the glasses shows lower values for the glasses rich in vanadium,
that is, in the "electronic" region, when compared to the pre-exponential factor
of the glasses of the region richest in silver, or in the "ionic" region. This
behavior is in accordance with the theoretical expressions for each of the
conductivity mechanisms. In an attempt to quantify the ionic and electronic
contributions, the electromotive force method (F.E.M) was applied. This method
was selected because, theoretically, it allows a precise quantification of the
electronic and ionic conductivities. However, the experimental results showed
that the generated electrochemical cell did not correspond to the expected one,
therefore it was not possible to quantify the ionic and electronic contributions to
the total electrical conductivity.