engleski

Studies of lead-iron phosphate glasses by Raman, Mossbauer and Impedance Spectroscopy

The effect of Fe2O3 content on conductivity and glass stability against crystallization in the glass system PbO-Fe2O3-P2O5 has been investigated using Raman, XRD, Mössbauer and impedance spectroscopy. Glasses of the molar composition (43.3-x)PbO-(13.7+x)Fe2O3-43P2O5, (0ŁxŁ30), were prepared by quenching melts in air. With increasing Fe2O3 content and O/P ratio there is corresponding reduction in the length of phosphate units and an increase in the Fe(II) ion concentration which causes a higher tendency for crystallization. Raman spectra of the glasses show that the interaction between Fe sites, which is essential for electronic hopping, strongly depends on the cross-linking of the glass network. The electronic conduction of these glasses depends not only on the Fe(II)/Fetot ratio, but also on easy pathways for electron hopping in a non-disrupted pyrophosphate network. The Raman spectra of crystallized compositions indicate a much lower degree of cross-linking since more non-bridging oxygen atoms are present in the network. Despite the significant increase in the Fe2O3 content and Fe(II) ion concentration, there is a considerable weakening in the interactions between Fe sites in crystalline compositions. The impedance spectra reveal a decrease in conductivity that is caused by poorly defined conduction pathways, which result from the disruption and inhomogeneity of the crystalline phases that are formed during melting.

Phosphate glasses; electrical conductivity; impedance spectra

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