Effect of nanocrystallization on the electrical conductivity enhancement and Mössbauer hyperfine parameters of iron based glasses

Abstract

Selected glasses of Fe2O3–PbO2–Bi2O3 system have been transformed into nanomaterials by annealing at temperature close to crystallization temperature (Tc) for 1 h. The effects of the annealing of the present samples on its structural and electrical properties were studied by Mössbauer spectroscopy, transmission electron micrograph (TEM), differential scanning calorimeter (DSC) and dc conductivity (σ). Mössbauer spectroscopy was used in order to determine the states of iron and its hyperfine structure. The effect of nanocrystalization on the Mössbauer hyperfine parameters did not exhibit significant modifications in present glasses. However, in case of glass ceramic nanocrystals show a distinct decrease in the quadrupole splitting (Δ) is observed, reflecting an evident decrease in the distortion of structural units like FeO4 units. In general, the Mössbauer parameters of the nano-crystalline phase exhibit tendency to increase with PbO2 content. TEM of as-quenched glasses confirm the homogeneous and essentially featureless morphology. TEM of the corresponding glass ceramic nanocrystals indicates nanocrystals embedded in the glassy matrix with average particle size of about 32 nm. The crystallization temperature (Tc) was observed to decrease with PbO2 content. The glass ceramic nanocrystals obtained by annealing at Tc exhibit improvement of electrical conductivity up to four orders of magnitude than the starting glasses. This considerable improvement of electrical conductivity after nanocrystallization is attributed to formation of defective, well-conducting phases “easy conduction paths” along the glass–crystallites interfaces.