engleski

Impedance spectroscopy studies of iron phosphate glasses doped with PbO

Impedance spectroscopy is a popular analytical tool in materials research and development because its results may be correlated with many complex materials variables: from mass transport, rates of chemical reactions, corrosion, and dielectric properties, to defects, microstructure, and compositional influences on the conductance of solids. The relation between structure and electrical properties for glass system (43.3-x)PbO-(13.7+x)Fe2O3-43P2O5 (0 x 30) have been investigated by Raman and impedance spectroscopy. Impedance spectra were interpreted by means of equivalent circuit modelling, using complex non-linear least square (CNLLSQ) procedure. The Raman spectra of the (43.3-x)PbO-(13.7+x)Fe2O3-43P2O5 (0 x 30) glasses show predominantly pyrophosphate structure and high tendency for crystallization with increasing Fe2O3 content  33.7 mol%. The changes in the glass network and glass stability against crystallization are followed by characteristic features of impedance spectra. The impedance spectra of glass samples indicate single conduction mechanism attributed to electron hopping from Fe(II) to Fe(III) ions. Consequently, electronic conductivity increases with increasing Fe2O3 content and Fe(II)/Fetot ratio in glasses. On the other hand, in crystallized compositions, electrical properties are strongly affected by microstructure. The impedance spectra contain features related to microstructure: interior of the grains (crystalline phase) and grain boundaries (glassy phase). Equivalent circuit modelling is used to separate grains from grain boundaries contribution to the electrical conductivity. With increasing Fe2O3 content in crystallized samples, electrical conductivity associated with grains increases to a constant value, whereas, for a grain boundaries decreases. This is related to enhanced tendency for crystallization, which diminishes the glassy phase in compositions with high Fe2O3 content.

iron phosphate glasses; impedance spectroscopy

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