Abstract
Microwave techniques were applied to the study of dielectric properties of phosphate glasses on the basis of contributions from permanent and induced dipolar polarization of local structural units interacting with the electrical component of the electromagnetic radiation. The dielectric constant of the selected glass system (100 − x)(50P 2O 5·25Li 2O·25Na 2O)· xFe 2O 3, where 0 ≤ x ≤ 21 is in mol%, was measured using a microwave setup assembled to measure the phase shift of the standing wave pattern produced by the insertion of the sample. It is shown that the Fe 2+ ions contribute effectively to the dielectric constant, as expected from the interactions of the dipoles of the local charge compensation pairs with the microwave radiation. However, there is the possibility of occurrence of some ions Fe 3+, in general, at low iron content, which reinforces the glass structure and, therefore, decreases the dielectric constant. There is a gradual conversion from Fe 3+ to Fe 2+ as the iron ions increases. This is possibly the reason of the anomaly in the dielectric constant values observed in the results. These assumptions can be checked by results of electronic paramagnetic resonance (EPR) and optical absorption (OA). The dielectric constant of the glasses studied in this work was found to increase with the temperature in the range of 25–330 °C.
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