engleski

Electrical Relaxation in Phosphate Glasses

Investigation of the electrical relaxation mechanisms in phosphate glasses where transition metal oxide such as iron oxide is the network former and network modifier is presented. The relaxation processes in iron phosphate glasses exhibiting electronic and mixed electronic-ionic conduction is discussed in terms of experimental results. Phosphate glasses containing iron are electronically conducting glasses where the polaronic conduction is due to the electron hopping from low to high iron valence state. Special attention is given to the concentration of the charge carriers, ions and polarons, their interaction, magnitude of ionic an electronic conductivity as a consequence of the structural disorder in iron phosphate glasses doped with other metal ions. Transport and dynamic processes in iron phosphate glasses, where a second transition metal oxide such as MoO3, Cr2O3, Bi2O3 is added has been discussed. The identification of structural defects caused by ion/polaron migration, the analysis of dipolar states, the dielectric relaxations and distribution of relaxation times in iron phosphate glasses containing various alkali ions was performed on the basis of the impedance spectroscopy. In iron phosphate glasses at certain content of alkali ion the electrical conductivity and activation energy for dc conductivity is not influenced by alkali ions. It is shown that in iron phosphate glasses the complex impedance plot usually consist of one semicircle indication single mechanisms of conductivity. However, it is interesting to note that the polaronic conductors display a behavior similar to ionic conductors because of their similar dependence on frequency and temperature. The changes in electrical conductivity from parent phosphate glass to fully crystallized glass (glass-ceramics) by impedance spectroscopy are analyzed. Since the method allows the separation of the electrical phenomena with various relaxation time constants e.g. electrode and bulk properties there is a correlation between the shape of the IS spectra and the nature of electrical transport. Changes in the characteristic features of IS follows the changes in glass and crystallized glass network. Using IS, the contribution of glass matrix, crystallized grains and grains boundary to the total electrical conductivity for lead-iron phosphate glasses is analyzed. It was shown that decrease in conductivity is caused by discontinuities in the conduction pathways as a result of the disruption and in homogeneity of crystalline network where two or more crystalline phases are formed.

Electrical Properties; Phosphate Glass

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