A study of polarization mechanisms in sodium iron phosphate glasses by partial thermally stimulated depolarization current

The electrical polarization of sodium iron phosphate glasses, containing from 5.3 to 14.9 mol% Na2O and with a constant Fe/P ratio of 0.67, was investigated by thermally stimulated polarization current (TSPC), and by depolarization current (TSDC) techniques. The partial TSDC measurements showed a group of distributed partial peaks, P1, whose maximum ranged from 186 to 227 K. A group of higher temperature peaks, P2, was found in a narrower temperature range from 257 to 264 K, with an additional process, P2′, at about 240 K. The process P1 was caused by a dipolar relaxation showing a compensation with the compensation point at Tc=247 K. The physical meaning of the compensation point could not be related to analogous phenomena in organic polymers. The higher temperature peaks represent space charge relaxations greatly affected by the increase in Na2O content and influenced by the remaining polarization and conductivity. The most likely cause for the electrical relaxation was an interaction between the Na+ ions and the P–O− bonds. Increasing the Na+ concentration caused an increase in the TSDC peaks and a slight increase in dc conductivity.