Abstract: A new glass system (Bi2O3)50(Fe2O3)10(Li2O)x(K2O)40-x, where x changes in steps of 5 mole fraction between 0 and 40, was selected to study the electrical relaxation and the mixed alkali effect (MAE) phenomena. Measurements of ac conductivity σac, dielectric permittivity ε' and loss factor tan± in the frequency range of 0.12~102 kHz and in the temperature range of 300~650 K were carried out. The temperature dependence of the ac conductivity shows a slow increasing rate at low temperature and high frequency and a rapid increase at high temperature and low frequency. At constant temperature, the ac conductivity is found to be proportional to ωs, where s is the frequency exponent, which is less than 1. Analysis of the conductivity data and the frequency exponent shows that the overlapping large polaron tunnelling (OLPT) model of ions is the most favorable mechanism for the ac conduction in the present glass system. The ac response, the dc conductivity and dielectric relaxation have the same activation energy and they originate from the same basic transport mechanism. The results of the dielectric permittivity show no maximum peak in the temperature and frequency range studied. This absence of maximum peak is an indication of non-ferroelectric behavior of all the studied samples. The MAE has been detected in the ac conductivity, which is the same as the classical MAE in the dc conductivity. The electrical parameters such as dielectric permittivity ε' and real dielectric modulus M' show a typical minimum deviation from linearity by about two orders of magnitude. The loss factor tanδ and the imaginary dielectric modulus M" are insignificantly dependent on composition even at the same transition temperature Tg.

Key words: Dielectric permittivity, Dielectric modulus, Loss factor, Conduction mechanism...