engleski

Dielectric Properties of Zinc-Iron Phosphate Glasses

Dielectric properties of zinc-iron phosphate glasses with the general composition (40-x)ZnO-xFe2O3-60P2O5 (mol%) have been measured by impedance spectroscopy in the frequency range from 0.01 Hz to 4 MHz and over the temperature range from 303 to 473 K. The dielectric parameters, dielectric kpermitivitty, tan delta and ac conductivity are found to increase with increasing Fe2O3 and Fe(II)/Fetot. The dielectric permittivity for these glasses is independent of the ZnO content and arises mainly from the polaron hopping between Fe(II) and Fe(III) ions suggesting an electronic conduction. At low frequency the dispersion was investigated in terms of dielectric loss. The thermal activated relaxation mechanism dominates the observed relaxation behavior. The relaxation observed on the M´´ or Z´´ functions is correlated to both localized and long-range conduction. The overlapping of the M´´ or Z´´ peaks suggests the same activation energy and existence of a single carrier that are related to the same relaxation processes. The structure and valance state of iron in these glasses have been determined using Mossbauer and Raman spectroscopy. Both Fe(II) and Fe(III) ions present in octahedral coordination act as dipoles, and the increase of the iron concentration contribute to the dielectric permittivity increase. The Raman spectra show that with increasing Fe2O3 content there is corresponding reduction of in number of Q2 phosphate units and an increase in non-bridging oxygens as more Q1 phosphate units are formed in the glass network.

Dielectric properties; iron phosphate glases; impedance spectroscopy

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