Abstract
Ionic conductivity is a property of rapidly increasing interest. Various models attempting to explain ionic conductivity of glass systems have shown limited agreement with experimental results; however, none have been comprehensive. By using molecular dynamics simulations, the diffusion of ion species through a network can be directly observed, providing insights into the mechanisms and their relation to ionic conductivity models. In this report, a method of utilizing molecular dynamics simulations is proposed for the study of the ionic mobility of Na, Li, and K ions in binary silicate glasses. Values found for glasses with x = 0.1, x = 0.2, and x = 0.3 alkali content are between 10-5 and 10-4 cm2·s-1·V-1 and did not change significantly with composition or temperature. This is in agreement with the interstitial pair and weak-electrolyte models used to explain ionic conductivity in glasses.
Highlights
In non-crystalline alkali silicate materials, alkalis are the most mobiles species; self-diffusion of alkali ions is generally understood as an exchange of cationic pairs between sites (Kahnt, 1991)
Certain glass compositions have been studied in literature due to their remarkably high ionic conductivity when compared to crystals (Minami et al, 1977), phosphates doped with silver (Rodrigues et al, 2011), and lithium (Robert et al, 1981)
The results presented here which show a constant mobility with respect to temperature and composition, suggest that a change in the number of effective charge carriers is what causes the increase in ionic conductivity in these alkali silicate glasses
Summary
In non-crystalline alkali silicate materials, alkalis are the most mobiles species; self-diffusion of alkali ions is generally understood as an exchange of cationic pairs between sites (Kahnt, 1991). Since alkali ions are loosely associated and not strongly confined (when compared with the mostly rigid glass network), they can more jump between sites (Greaves et al, 1991). Certain glass compositions have been studied in literature due to their remarkably high ionic conductivity when compared to crystals (Minami et al, 1977), phosphates doped with silver (Rodrigues et al, 2011), and lithium (Robert et al, 1981). The electric conductivity, σ , can be defined as σ = Zeμn, Increasing the conductivity of phosphate glasses by adding various modifiers has been of interest due to their already promising conductivity values (Martin and Angell, 1986; Martin, 1991).
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