Mössbauer and small polaron hopping conduction studies of alkali borogermanate glasses containing iron
Mössbauer, DTA and dc conductivity of glasses in system Na2B4O7 - GeO2 - Fe2O3 prepared by press quenching was studied at temperatures between 323 and 573 K. ‘Tg-Δ rule’ i.e. a linear relationship between the glass transition temperature (Tg) and Mössbauer quadrupole splitting (Δ) is applied to the glass samples. A slope of the straight line obtained from the plot of Tg vs Δ (i.e. 798°C/ mm s−1)−1 for the glass samples implies that the Fe3+ atoms substitute tetrahedral GeO4 atoms and play a role of network former. A linear decrease of Δ proves that the symmetry of distorted FeO4 tetrahedra was linearly increased with Fe2O3 content. The dc conductivity was found to be decrease as the Fe2O3 content was increased while the activation energy increases with decreasing Fe2O3 content. From the conductivity temperature relation, it was found that small polaron hopping model was applicable at temperature above 350K ; the electrical conduction at T > 350K was due to nonadiabatic small polaron hopping of electrons between iron ions.
KeywordsGlass Transition Temperature Isomer Shift Glass Sample Quadrupole Splitting Fe2O3 Content
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