Activation energies (Ea) for ionic conduction in low-alkali boroaluminosilicate glasses due to alkaline-earth (Ba, Ca) and alkali (Na) ion transport have been estimated using thermally stimulated depolarization current (TSDC) and AC impedance spectroscopy techniques. The TSDC plot showed distinct relaxation peaks which shifted to higher temperatures with increasing ramp rates, and the dielectric dispersion plot showed individual low frequency relaxation peaks indicating space charge polarization due to transport of cations with different Ea (0.93, 1.83, and 3.5 eV for Na, Ba, and Ca, respectively). The higher value of Ea for Ca transport is attributed to mixed alkaline earth effect.
The dielectric breakdown statistics of alkali‐free glass was determined for various thicknesses with electrodes having controlled morphology and continuity. The characteristic electrical breakdown field strength increased from 400 to 1100 MV/m as the glass substrate thickness decreased from 58 to 5 μm, respectively. Surface roughness RMS values of as‐drawn and etched glass substrates were in the 0.9–1.8 nm range, which is small in comparison to the glass substrate thickness. The glass etching, itself did not have significant effect on the dielectric breakdown strength. The dielectric breakdown strength was also independent of the sputtered‐deposited electrode composition (Au, Pt); however, electrode thickness played an important role in controlling the breakdown process. The Au electrode morphology transitioned from a continuous sheet for thicker electrodes to discrete nano‐scale islands for very thin electrodes (<2 nm thick). The thin electrode morphology provides a unique opportunity to explore the intrinsic properties and high dielectric breakdown strength regime (1100 MV/m) in glasses with Weibull modulus values approaching 100.
Electrical conduction in silica-based glasses under a low electric field is dominated by high mobility ions such as sodium, and there is a transition from ionic transport to electronic transport as the electric field exceeds 108 V/m at low temperatures. Electrical conduction under a high electric field was investigated in thin low-alkali boroaluminosilicate glass samples, showing nonlinear conduction with the current density scaling approximately with E1/2, where E is the electric field. In addition, thermally stimulated depolarization current (TSDC) characterization was carried out on room-temperature electrically poled glass samples, and an anomalous discharging current flowing in the same direction as the charging current was observed. High electric field conduction and TSDC results led to the conclusion that Poole-Frenkel based electronic transport occurs in the mobile-cation-depleted region adjacent to the anode, and accounts for the observed anomalous current.
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