engleski

Effect of crystallization on the electrical properties of iron phosphate glasses

Electronically conducting glasses of the composition 43Fe2O3-57P2O5 glass, melted at different temperatures, were analyzed by X-ray diffractometry (XRD), differential thermal analysis (DTA) and scanning electron microscopy (SEM). The main crystalline phases formed during thermal treatments are ferrous-ferric pyrophosphate, Fe3(P2O7)2, and ferric orthophosphate, FePO4. The effects of the annealing of iron phosphate glasses on their electrical conductivity were studied by impedance spectroscopy. The electrical conductivity was measured for as-quenched glass and after thermal treatment up to 800 °C. The presence of crystalline Fe3(P2O7)2 grains formed after thermal treatment at temperatures close to the first crystallization temperature, TC1, 724 °C, leads to formation of ferric orthophosphate, FePO4 along with pronnounced growth of Fe3(P2O7)2 crystals. Electrical conductivity of this glass-ceramics is lower than before their thermal treatment. The decrease in electrical conductivity is exlained by considerable weakening in the interaction between Fe sites in crystalline glasses, caused by poorly defined conduction pathways. This is a result of the presence of larger crystalline grains and disappearance of glassy matrix in fully crystallized sample. For the glasses melted at higher temperatures, the electrical conductivity increases with increasing Fe(II) ion content. The formation of crystalline Fe3(P2O7)2 at crystallization temperature increases the electrical conductivity. Therefore, the most conductive pathways is the polaron motion through interfaces between crystalline grains.

Iron phosphate glasses; Electrical properties; Crystallization

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