engleski

Mixed electronic-ionic conductivity in lead iron phosphate glasses doped with sodium oxide

Iron phosphate glasses behave as typical semiconductors, exhibiting electronic conduction by electron hopping from Fe(II) to Fe(III) ions. On the other hand, electrical conductivity of alkali containing iron phosphate glasses consists of both, electronic and ionic conduction. The ionic conduction should be proportional to the concentration and mobility of alkali ions, whereas, the electronic conduction follows the electron hopping theory. The aim of the study was to investigate electrical properties of the glasses of quaternary system Na2O-PbO-Fe2O3-P2O5 exhibiting, in general, mixed ionic-electronic conduction with predominance of ionic or electronic component depending on composition. Glasses were examined by impedance spectroscopy in the wide frequency and temperature range (0.01 Hz - 3 MHz, 303 - 473 K). The impedance spectra were analyzed numerically by means of electrical equivalent circuit modeling, using complex non-linear least square procedure. It was found that conductivity for glasses containing &pound ; ; 15 mol% Na2O is predominantly electronic and is controlled by electron hopping between iron ions. In these glasses the sodium ions have such low mobility, caused by ion-polaron interaction, that they make no detectable contribution to the total conductivity. For glasses with Na2O content  15 mol%, the conductivity increases significantly indicating ionic conductivity. Special attention was paid to a relationship between the type of conductivity (electronic and/or ionic) and the shape of impedance spectra. It was found that characteristic features of impedance spectra follow the changes of the nature of the electrical conduction.

iron phosphate glasses; ionic conductivity; electronic conductivity

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