Electrical conductivity and dielectric properties of Bi2O3–GeO2–PbO–MoO3 glasses

Glasses having compositions 40Bi2O3–20GeO2–(40−x)PbO–xMoO3 (where x = 3, 6, 9, 12 and 15 mol%) were prepared by normal melt quenching technique. The density (d) decreases gradually with the increase of the MoO3 content in such glasses. This may be due to the lower molecular weight MoO3 is substituted by a higher molecular weight PbO. The dc conductivity decreases while the activation energy increases with the increase of the MoO3 content. The dc conductivity in the present glasses is electronic depends strongly upon the average distance, R, between the Mo ions. Analysis of the electrical properties has been made in the light of small polaron hopping model. The parameters obtained from the fits of the experimental data to this model are reasonable and consistent with glass composition. The conduction is attributed to non-adiabatic hopping of small polaron. Dielectric properties (constant ε, loss tan δ, ac conductivity σac, over a range of frequency 0.12–100 kHz and temperature 325–650 K and frequency exponent s) of these glasses have been studied.

Research highlights
► Selecting molybdenum oxide as a transition metal oxide, we have shown a wide glassy range inside the Bi2O3–GeO2–PbO–MoO3 system. Heavy metal oxide-based glasses such as Bi2O3 glasses are very interesting for glass scientists and technologists due to their wide range of technological applications such as optical and optoelectronic devices such as ultrafast switches, infrared windows and optical isolators. Further this system is of interest because MoO3 is conditional glass former and good oxidizing catalysts. In the present work, 40Bi2O3–20GeO2–(40−x)PbO–xMoO3 where x = 3, 6, 9, 12 and 15mol%, have been prepared in order to study the effect of MoO3 on several physical properties such as density and molar volume, the mean spacing (R) between Mo ions, polaron radius (rp), dc electrical conductivity and dielectric properties (dielectric constant ε', loss tan δ and ac conductivity σac over a moderately wide range of frequency and temperature, and also frequency exponent s).
► The conduction of the present glasses was confirmed to be due to primarily non-adiabatic hopping of small polaron between molybdenum ions in the glass network, this corresponded to relatively small polaron coupling constants (γp = 6.95–7.31). The temperature dependence of ac conductivity at high temperatures has been explained using Mott's small polaron hopping model. The conductivity decreased and activation energies increased with increase of MoO3 content at all frequencies. Based on these results, it is concluded that the molybdenum ions, hinders the electronic motion. The frequency dependent conductivity has been explained by correlated barrier hopping model as the frequency exponent, s values due to CBH model agreed with the experimental values of s. The conductivity decreased and activation energies increased with the increase in MoO3 content at all frequencies in the glasses. The ε' and ε" decreased with increase in frequency. This is ascribed to the decrease in electronic contribution and increase in dipolar contribution to the total polarizability. Both ε' and ε" increased with increase in temperature and decreased with increase in MoO3 concentration.