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Structure and electrical properties of lead-iron phosphate glasses

The structure and electrical properties of vitreous and crystalline lead-iron phosphate glasses have been investigated using Raman, Mössbauer, X-ray diffraction and impedance spectroscopies. The Raman spectra for the glasses contained bands characteristic for pyrophosphate groups, whereas the crystallized compositions show bands related to both pyrophosphate and orthophosphate structure. X-ray diffraction patterns showed that Fe3(P2O7)2, FePO4 and Fe7(PO4)6 phases are present in the samples with O/P ratio >3.9. The Mössbauer spectra indicated that with increasing Fe2O3 content in these glasses the concentration of Fe(II) ions increases. The chemical durability of glasses and crystalline compositions was investigated by measuring their weight loss in distilled water at 90oC for up to 32 days. The weight loss of the lead-iron phosphate glasses was up to 100 times less than that for window glass. The electrical properties measured by impedance spectroscopy in the frequency range from 0.01 Hz to 3 MHz and over the temperature range from 303 to 473 K show that the conductivity for these glasses strongly depends upon Fe(II) ion concentration. It was observed that with increasing Fe2O3 content the ratio Fe(II)/Fetot and consequently dc conductivity increases. The dielectric properties such as e˘(w), e˘˘(w) and sac(w) and their variations with frequency and temperature indicate an increase in relaxation intensity with increase in the concentration of Fe2O3. The increase in the dielectric permittivity, e˘(w) with increasing Fe2O3 content is attributed to the increase in the deformation of glass network with increasing bonding defects.

Lead-iron phosphate glasses; electrical conductivity

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