On the mechanism of field-induced mixed ionic–electronic transport during electro-thermal poling of a bioactive sodium–calcium phosphosilicate glass

We have investigated the charge transport processes during electro-thermal poling of the bioactive glass 46S4 (Na–Ca phosphosilicate glass) by combining poling current measurements, impedance spectroscopy, and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The ToF-SIMS elemental profiles show that the ion depletion region under the anode consists of two layers with similar thickness. The poling current measurements reveal that the poling process takes place on two different time scales. Based on our experimental results, we propose a model of the poling process, in which the Na+ ion depletion is compensated by the transport of electrons and Ca2 + ions.