Electrical properties of sodium phosphate glasses containing Al2O3 and/or Fe2O3. Part II

The electrical properties for three series of glasses: xNa2O–(40−x)Al2O3–60P2O5, (20⩽x⩽35), (NAP); 20Na2O–xAl2O3–(20−x)Fe2O3–60P2O5, (5⩽x⩽15), (NAFP), and xNa2O–(40−x)Fe2O3–60P2O5, (20⩽x⩽35), (NFP) glasses were measured by impedance spectroscopy in the frequency range from 1 Hz to 1 MHz and over the temperature range from 303 to 473 K. It was shown (in Part I) that the addition of Fe2O3 has significant effects on the structure of these glasses and Fe ions play a different structural role in phosphate network than that of Al ions. Such effects reflect changes in the origin of electrical conduction. With increasing Fe2O3 content in NAFP and NFP glasses the dc conductivity depends upon distance between iron ions and the activation energy of 53.1 kJ mol−1 indicates electronic conduction. On the other hand, the decrease in dc conductivity and activation energy for glasses in NAP series is attributed to the decrease in Na2O content from 35 to 20 mol%. The activation energy varies from 80.1 to 72.4 kJ mol−1 for NAP glasses suggesting ionic conduction. The impedance analysis for these glasses shows that the changes in the electrical conduction mechanisms coincide with the changes in the structure.