Electrical conductivity and relaxation in MoO3-Fe2O3-P2O5 glasses

The electrical conductivity and dielectric properties of MoO3-Fe2O3-P2O5 glasses have been investigated by impedance spectroscopy in the frequency range from 0.01 Hz to 3 MHz and over the temperature range from 303 to 473 K. With decreasing Fe2O3 content in MoO3-Fe2O3-P2O5 glasses with O/P at 3.5 the dc conductivity, sigma(dc)(omega) decreases by two orders of magnitude, which indicates that the conductivity for these glasses depends on Fe2O3 and is independent of the MoO3 content. Also, the dielectric properties such as epsilon'(omega), epsilon"(omega) and sigma(ac)(omega) and their variation with frequency and temperature indicates a decrease in relaxation intensity with increase in the concentration of MoO3. On the other hand, the dc conductivity for MoO3-Fe2O3-P2O5 glasses with O/P > 3.5 increases with the substitution of MoO3 which has been explained by an increase in the number of non-bridging oxygens and formation of Fe-O-P bonds that are responsible for the formation of small polarons. The increase in the dielectric permittivity, epsilon(omega) with increasing MoO3 content is attributed to the increase in the deformation of the glass network with increasing bonding defects. (C) 2004 Elsevier B.V. All rights reserved.