Identification of charge carriers and quantification of diffusion coefficients in the energy landscape of S53P4 bioglass.

The ionic conduction of S53P4 glass has been investigated by a combination of electric field assisted ion exchange and thermal electro-poling experiments. The dominant charge carrier being mobile in native S53P4 is identified to be the Na+ ion. By means of alkali proton substitution and alkali deuteron substitution the diffusion coefficient, D(Na+), has been determined. It is found to vary over 2 orders of magnitude due to the distribution of site energies in the potential energy landscape of the glass. The Ca++ ions appear immobile under the conditions of the APS and ADS experiments. However, Ca++ ions become mobile under the conditions of thermal electro-poling. The diffusion coefficient for Ca++ ions, D(Ca++), turns out to be five orders of magnitude smaller than D(Na+) in the bulk.