Ionic conductivity and dielectric properties of vanadium pentoxide xerogels

Abstract

The electrical transport properties of cation-exchanged M_xV₂O₅·yH₂O (M = Al, Li, Zn, Ni, Na, Ag, H₃O, K, Ba and Cs) xerogels have been studied in a broad frequency range 1 KHz–10 GHz between 190 and 300 K. In the low-frequency domain (1–100 kHz), the ionic conductivity has been obtained by the a.c. admittance method with respect to the nature of the exchanged cations. A correlation between the conductivity activation energy and the ionic radii has been evidenced. Dielectric absorption measurements have been investigated from 1 MHz to 10 GHz (radio and microwave frequencies). The dielectric spectra exhibit dielectric relaxations corresponding to cation local hopping and water molecule reorientations. The influence of cationic species on the water mobility is discussed. Some explanations of these mechanisms with respect to the experimental results are proposed.