engleski

Influence of Crystallization on Electrical Conductivity of Zinc Iron Phosphate Glasses

Crystallization of the 10ZnO-30Fe2O3-60P2O5 glass was analyzed by impedance spectroscopy (IS), X-ray diffractometry (XRD), differential thermal analysis (DTA) and scanning electron microscopy (SEM). The electrical conductivity was measured for as-quenched glass and after thermal treatment up to 650 C at various crystallization times. The presence of crystalline Fe3(P2O7)2 and Zn2P2O7 grains formed after thermal treatment at temperatures close to the first crystallization temperature at 600 C, decreases the electrical conductivity as compared with the as-quenched glass. The decrease in electrical conductivity is explained by a reduction in concentration of Fe(II) and weakening in interaction between Fe sites in glass matrix. Further thermal treatment at higher temperature, 650 C, leads to formation of ferric orthophosphate, FePO4 along with pronounced growth of Fe3(P2O7)2 crystals. The conductivity enhancement for glasses crystallized at 1 and 5 hours is related to the conduction at the interfaces between the crystallites and glassy phase. For glasses heat treated for 12 hours the microcrystallites are formed causing a drop in electrical conductivity due to the blocking of the conduction pathways for the electron hopping between Fe sites at the crystal/glass matrix interfaces. Main influence on the total conductivity of these glasses is attributed to the formation of larger crystalline grains and disappearance of glassy matrix. On the other hand, the bulk conductivity within crystalline grains strongly depends on the orientation of the formed crystallites.

Crystallization; Electrical conductivity; Zinc iron phosphate glasses

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