engleski

Structural and electrical properties of sodium phosphate glasses containing Al2O3 and/or Fe2O3

The relationship between structure and electrical properties for three series of glasses: Na2O- Al2O3-P2O5, (NAP), Na2O-Al2O3-Fe2O3-P2O5, (NAFP), and Na2O-Fe2O3-P2O5, (NFP) has been studied. The structural changes in the NAP, NAFP and NFP glasses have been investigated by Raman and by Raman difference spectroscopy (RDS). The Raman spectra show that the addition of Al2O3 content to sodium phosphate glasses has a different effect on the phosphate network than the addition of Fe2O3. With increasing Fe2O3 content up to 20 mol% the structure changes from chain-like metaphosphate to the pyrophosphate structure. The iron ions play an important role in forming P-O-Fe bonds that strengthen the cross-bonding of shorter phosphate chains. On the other hand, with increasing Al2O3 content up to 20 mol% the sodium metaphosphate is replaced by aluminum metaphosphate where Al(OP)6 units cross-link phosphate chains. The electrical conductivity of these glasses was measured by impedance spectroscopy in the frequency range from 1 Hz to 1 MHz and over the temperature range from 303 to 473 K. The decrease in dc conductivity and in activation energy for glasses in the 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 kJmol-1 for the NAP glasses suggesting ionic conduction. With increasing Fe2O3 content in NAFP and NFP glasses the dc conductivity depends upon the distance between the iron ions and the activation energy of 53.1 kJmol-1 indicates electronic conduction.

phosphate glasses ; Raman spectroscopy ; electrical conductivity

nije evidentirano