Interpretation of electrical polarization and depolarization mechanisms of bioactive glasses in relation to ionic migration

Electrical polarization and depolarization processes of the 45S5 type bioactive glass (BG) was studied by a thermally stimulated depolarization current (TSDC) and an complex impedance measurements. The depolarization processes were found to consist of three processes, which were observed as three peaks, P1, P2 and P3, in the TSDC spectra. P1 and P2, observed at lower than the glass transition temperature, were attributed to the sodium ionic migration from the interstitial positions after polarization procedure coordinated among neighboring silicate and phosphate to stabler positions. This migration process is presumed to relate to a shift in the ionic conductivity elucidated by the ac method. P3 observed at higher temperature for the BG polarized at more than 500°C for long period was ascribed to the ionic migration activated by a local deformation. The depolarization of BG consisted of three processes that depended on the neighboring coordinations of traveling sodium ions during polarization.