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Thermally stimulated current and dc conductivity in Cs2O-Fe2O3-P2O5 and Na2O-Fe2O3-P2O5 glasses

The electrical polarization and conduction mechanisms have been investigated in iron phosphate glasses containing from 0 to 28 mol% Cs2O and 5.3 to 14.9 mol% Na2O. TSDC measurements from 120 to 400 K show two current peaks, P1 attributed to the polarization caused by dipolar defects and P2 due to an interaction between the alkali ions and non-bridging oxygen ions. The dc conductivity and activation energy for the cesium iron phosphate glasses were constant and independent of Cs2O content. With increasing cesium concentration in cesium iron phosphate glasses the slowly moving cesium ions are more tightly bound to the non-bridging oxygen ions causing no measurable contribution to dc conductivity. The conduction in these glasses is electronic, controlled by the electron hopping between iron ions since the ionic conduction is reduced by the low mobility of cesium ions. On the other hand, the increase in sodium concentration in sodium iron phoshate glasses increased the dc conductivity and TSDC peaks. The appearence of two higher temperature processes, P2 and P2`, was attributed to the space charge influenced by the discharge of the traps and conductivity.

phosphate glasses; dc conductivity; Raman spectroscopy

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