Investigation of bioglass–electrode interfaces after thermal poling

Abstract

Electrical and electrochemical processes in a bioactive soda-lime phosphosilicate glass and in a bioabsorbable soda-lime phosphate glass during thermal poling were studied by means of thermally stimulated polarization and depolarization current measurements (TSPC and TSDC), ac impedance spectroscopy, and SEM/EDX analyses. The thermal poling was done by sputtering thin Pt electrode films onto the faces of the glass samples and by applying voltages up to 750 V to the electrodes at temperatures up to 513 K. The poling leads to the formation of interfacial layers under the electrodes which are responsible for two depolarization current peaks. The Na + depletion layer under the anode causes an additional semicircle in a Nyquist plot of the ac impedance. The SEM/EDX profiles suggest that redox and transport processes of Na + ions are responsible for the formation of the interfacial layers, while the Ca 2+ ions are immobile under the poling conditions. From the EDX profile of the Na + depletion under the anode, we calculate a hypothetical voltage drop in the depletion layer under the assumption that there is no charge compensation. Since the calculated voltage drop is much larger than the poling voltage, we conclude that the negative charge density due to Na + depletion must be compensated, at least to a large extent, by the presence of other charge carriers, most likely protons.

Depletion Layer Formation in Alkali Silicate Glasses by Electro-Thermal Poling

“…It represented the formation of an alkali ion depletion layer at the anode, which heavily influenced the electrical behavior of the bioactive glass. 6,10 The impedance of the depletion layer continued to increase throughout poling for both the 46S4 and present glasses. Within the first 5 minutes of poling, a low frequency capacitance plateau was observed to form in Fig.…”

“…The largest peak corresponded to Na + transport while the remaining peaks were attributed to the annihilation of anode and cathode layers formed during poling between the glass and electrodes. 10 TSDC measurements on 2L8NS, 5L5NS and LS revealed a single major peak for each glass. Activation energies associated with these peaks could only be calculated for the mixed alkali glasses, viz.…”

“…6 where the sample was previously poled with V p = 25 V. An investigation of TSDC for 46S4 bioglass was reported by Mariappan and Roling. 10 Their data show three current density peaks with increasing sample temperature. The largest peak corresponded to Na + transport while the remaining peaks were attributed to the annihilation of anode and cathode layers formed during poling between the glass and electrodes.…”

“…A thin layer depleted of alkali ions has been reported to form consistently during electro-thermal poling of glasses. 1,10 However, bulk electrical conductivity and charge compensation via anion migration or cation injection from the anode remain in question. 3,[15][16][17] The extent of electro-thermal poling has been shown to be dependent on both ionic and electronic conductivities.…”

Programmable Persistent Interfacial Metallic State Induced by Frozen Ions in Inorganic–Glass Solid Electrolyte

“…Here, we report the programmable persistent interfacial metallic state realized by producing persistent EDL through the thermal poling process, in which the sample is cooled down under the applied voltage. [ 23 ] …”