Electrical conductivity in mixed-alkali iron phosphate glasses

The electrical conductivity of mixed-alkali, sodium and potassium, iron phosphate glasses has been studied in the frequency range from 0.1 Hz to 10 kHz and over a temperature range from 303 to 423 K. The dc conductivity of the alkali-free iron phosphate glasses was 5–10 times higher than that of the single- or mixed-alkali iron phosphate glasses containing a total of 20 mol% alkali. The dc conductivity for the mixed-alkali, sodium and potassium, iron phosphate glasses is independent of the Na/K ratio and there is no evidence of any mixed-alkali effect. The sodium and potassium ions have such a low mobility in both single- and mixed-alkali iron phosphate glasses that they make no detectable contribution to the total conductivity that is electronic in origin. The Raman spectra for all the glasses are identical which indicates that the structure of the single- or mixed-alkali glasses are the same.