Abstract
Conductivity spectra of mixedโalkali ions in iron phosphate glasses have been studied in the frequency range from 400 Hz to 200 kHz, and over a temperature range from 333 K to 493 K. The ac conductivity as a function of temperature was divided into two domains; one where the absolute of ac conductivity is close to the dc conductivity, and one where the absolute magnitude of the ac conductivity is larger than the dc conductivity. The concentration of charge carriers was found to be almost independent of temperature, but was weakly dependent on composition. It seems that the conductivity was essentially determined by the hopping frequency. The activation energy for the hopping frequency is close to that of the dc conductivity and the glasses behave as strong electrolytes. The frequency exponent appears to be independent of temperature, but depends very weakly on composition. The glasses show weak pronounced mixedโalkali effect in the mixed lithium and sodium iron phosphate glasses. The small minimum and maximum in dc conductivity and activation energy, respectively, are further evidence of the low mobility of the lithium and sodium ions in these iron phosphate glasses. We have also presented a scaling of the conductivity spectra, which implies that the relaxation dynamics of charge carriers in the present glasses is weakly dependent on temperature and composition. (ยฉ 2007 WILEYโVCH Verlag GmbH & Co. KGaA, Weinheim)