Study of electrical properties of MoO3–Fe2O3–P2O5 and SrO–Fe2O3–P2O5 glasses by impedance spectroscopy. II

The electrical and dielectric properties for three series of MoO3–Fe2O3–P2O5 and one series of SrO–Fe2O3–P2O5 glasses were measured by impedance spectroscopy in the frequency range from 0.01 Hz to 3 MHz and over the temperature range from 303 to 473 K. It was shown in Part I that the MoO3 is incorporated into phosphate network and the structure/properties are strongly influenced by the overall O/P ratio. The Fe2O3 content and Fe(II)/Fetot ratio in these glasses have significant effects on the electrical conductivity and dielectric permittivity. With decreasing Fe2O3 content in MoO3–Fe2O3–P2O5 glasses with O/P at 3.5 the dc conductivity, σdc(ω) decreases for 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 ε′(ω), ε″(ω) and σac(ω) 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 formation of small polarons. The increase in the dielectric permittivity, ε′(ω) with increasing MoO3 content is attributed to the increase in the deformation of glass network with increasing bonding defects. For SrO–Fe2O3–P2O5 glasses the conductivity and dielectric permittivity remained constant with increasing SrO.