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 fr om 5.3 to 14.9 mol% Na2O and with a constant Fe/P ratio of 0.67, was invest igated by thermally stimulated polarization current (TSPC), and by depolari zation current (TSDC) techniques. The partial TSDC measurements showed a gr oup of distributed partial peaks, Pi, whose maximum ranged from 186 to 227 K. A group of higher temperature peaks. P-2, was found in a narrower temper ature range from 257 to 264 K, with an additional process. P'(2). at about 240 K. The process PI was caused by a dipolar relaxation showing a compensa tion with the compensation point at T-c = 247 K. The physical meaning of th e 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 rema ining polarization and conductivity. The most likely cause for the electric al relaxation was an interaction between the Na+ ions and the P-O- bonds. I ncreasing the Na+ concentration caused an increase in the TSDC peaks and a slight increase in de conductivity. (C) 2000 Elsevier Science B.V. All righ ts reserved.