The dielectric and electrical behavior of a sodium silicate glass (soda-lime-silica; SLS) and a sodium borosilicate glass (D263T) are systematically and comprehensively characterized by a combination of ac and dc techniques at various temperatures and electric fields. This study reveals that Na+ migration primarily influences the dielectric loss, energy efficiency, and leakage current in these glasses, with a less detrimental effect in D263T due to its higher activation energy for ionic conduction. Moreover, this study identifies an additional relaxation mechanism contributing to the leakage current in D263T which was not observed in SLS. The origin of this mechanism has not been extensively explored, and it is believed to arise from a more limited migration of Na+ ions associated with the short migration and accumulation of a second and less mobile ion near the anode.

Ionic conductivity in silicate glasses is a major issue in the energy sector due to its detrimental effect on electric energy generation and storage and has received increasing attention over the past years. In this study, surface modification of soda-lime-silica (SLS) float glass via acid-leaching treatment (pH 1) was implemented to understand the impact on ionic transport. The acid-leaching treatment created a sodium-depleted "silica-like" structure in the near-surface region with depths of 110 +/- 20 nm for the air-side and 93 +/- 2 nm for the tin-side of the SLS glass. Using the thermally stimulated depolarization current technique, two thermally activated relaxation peaks were found to be associated with different ion migration mechanisms. The first peak (P1) with activation energy of similar to 0.85 eV was attributed to dc conduction of Na+ ions through the glass bulk. A second overlapping peak (P2) at a higher temperature was found to be related to a more limited Na+ ion migration through the acid-leached structure, due to H+ conduction, or a coupled contribution of both mechanisms.

Low-alkali boroaluminosilicate glasses have attracted increasing attention in high-temperature dielectric applications due to their excellent dielectric, mechanical, and thermal properties. While the breakdown strength could be enhanced by reducing alkali concentration, we demonstrate an effective approach to improve the breakdown reliability of these low-alkali glasses by selectively coating a thin layer of polymers on anodes. It is shown that the dielectric breakdown of the glasses is dominantly determined by the magnified electric field in the depletion layer; that employment of a thin polymer coating on the anode side substantially mitigates the local field enhancement and improves the high-field reliability of the glass-polymer laminate. Cathode side polymer coating improves the laminate performance as well.

Parylene C coating is used to mitigate local electric field intensification in high-alkali BAS (Schott D263T) glass and low-alkali BAS glass (Schott AF32) with the aim of improving the dielectric breakdown characteristics. The breakdown events in these glasses were analyzed using a two-parameter Weibull probability distribution. Our findings demonstrate that the parylene C coating effectively mitigates the intensified electric field and reduced the risk of surface damage from thermal shock. Consequently, the weakest breakdown events are shifted to higher breakdown voltages and longer times, leading to a significant increase in the Weibull modulus. For anode-coated D263T glass, the Weibull modulus increases from 19.90 to 45.88 (a 130.55% enhancement), while for anode-coated AF32 glass, the increase is from 3.82 to 28.53 (a 646.86% enhancement), compared to uncoated glass. Although cathode-coated glass also demonstrates an improvement in the Weibull modulus, the enhancement is not as substantial as that observed in the anode-coated glass. Furthermore, we employ a finite element analysis model to simulate our experimental observations, aiming to enhance our understanding of the impact of polymer coatings on the dielectric breakdown of glasses with spatial and compositional fluctuations.

Ionic conduction in silicate glasses is mainly influenced by the nature, concentration, and mobility of the network-modifying (NWM) cations. The electrical conduction in SLS is dominated by the ionic migration of sodium moving from the anode to the cathode. An activation energy for this conduction process was calculated to be 0.82eV and in good agreement with values previously reported. The conduction process associated to the leakage current and relaxation peak in TSDC for HPFS is attributed to conduction between nonbridging oxygen hole centers (NBOHC). It is suggested that ≡Si-OH = ≡Si-O- + H0 under thermo-electric poling, promoting hole or proton injection from the anode and responsible for the 1.5eV relaxation peak. No previous TSDC data have been found to corroborate this mechanism. The higher activation energy and lower current intensity for the coated HPFS might be attributed to a lower concentration of NBOHC after heat treatment (Si-OH + OH-Si = SiO-Si + H2O). This could explain the TSDC signal around room temperature for the coated HPFS. Another possible explanation could be a redox reaction at the anode region dominating the current response.

Electrical conduction in silica-based capacitors under a combined effect of intermediate electric field and temperature (2.5 – 10 kV/mm, 50-300°C) is dominated by localized motion of high mobility ions such as sodium. Thermally stimulated polarization and depolarization current (TSPC/TSDC) characterization was carried out on poled fused silica and AF32 glass samples. Two relaxation mechanisms were found during the depolarization step and an anomalous response for the second TSDC peak was observed. Absorption current measurements were performed on the glass samples and a time-dependent response was observed when subjected to different electro-thermal conditions. It was found that at low temperature (T = 175 °C) and short times, the current follows a linear behavior (I α V) while at high temperature (T = 250 °C), the current follows V 0.5 . TSPC/TSDC and absorption current measurements results led to the conclusion that (1) Poole-Frenkel dominates conduction at high temperatures and at longer times and that (2) ionic blockage and/or H + /H3O + injection are responsible for the observed anomalous current response.

Metal - Insulator - Metal (MIM) and Metal - Insulator- Semiconductor (MIS) capacitors were fabricated by spin coating poly (methyl methacrylate) (PMMA) as the insulating material. Here, we consider the effect of dissimilar contact electrodes systems (Cu/Pt and Cu/n-Si) on the dielectric and electrical response. From the frequency- and temperature- dependent dielectric measurements, it was found that Cu/PMMA/n-Si interface has an additional contribution that affects the dielectric properties. Activation energies obtained from the ohmic conduction in forward bias showed a higher value in activation energy for Cu/PMMA/n-Si compared to that for Cu/PMMA/Pt, demonstrating the possible contribution of interfacial regions. Further experiments under reverse bias were carried out to study the importance of polarization in the electrical response.

Charge transport in the temperature range 80 K < T < 300 K was studied in a composite of carbon spheres (CS), prepared via hydrothermal carbonization of sucrose, and the conducting polymer polyaniline (PANi). PANi was synthesized via the oxidative polymerization of aniline with ammonium peroxydisulfate (APS) in acidic media. The CS/PANi composite was prepared by coating the spheres with a thin polyaniline (PANi) film doped with hydrochloric acid (HCl) in situ during the polymerization process. Temperature dependent conductivity measurements show that three dimensional variable range hopping of electrons between polymeric chains in PANi-filled gaps between CS is the predominant transport mechanism through CS/PANi composites. The high conductivity of the CS/PANi composite makes the material attractive for the fabrication of devices and sensors.

A set of uniform carbon microspheres (CS) whose diameters have the order of $ 0.125 \mu m$ to $10 \mu m $ was prepared from aqueous sucrose solution by means of hydrothermal carbonization of sugar molecules. A pressed pellet was composed by mixing CSs with polyethylene oxide (PEO). Electrical characterization of the pellet was carried out showing Ohmic current-voltage characteristics and temperature-dependent conductivity in the range $ 80K < T < 300K.$ The conductivity reached a maximum value of $ 0.245 S/cm $ at $ 258K. $ The dependence of conductivity on temperature was theoretically analyzed to determine predominating mechanisms of electron transport. It was shown that thermally-induced electron tunneling between adjacent spheres may take on an important part in the electron transport through the CS/PEO composites.

We discuss recent work on graphene-based reconfigurable terahertz metamaterials. In particular two approaches towards constructing reconfigurable metamaterials are analyzed and compared, namely: (i) graphene only plasmonic structures, and (ii) graphene-metal hybrid metamaterials. Whereas in the first type of structures graphene has two simultaneous roles: (a) as a plasmonic medium, therefore defining the terahertz structural response of the metamaterial, and (b) as a reconfigurable medium, thus inducing changes in the metamaterial terahertz response, in the second type of structures the terahertz response is set primarily by the metallic pattern and graphene has just the role of constituting a reconfigurable medium. It is observed that whereas relaxation time is the most important parameter affecting the quality of the terahertz response in plasmonic metamaterials, for the analyzed graphene-metal hybrid metamaterial geometries, the conductivity swing in graphene is the main parameter affecting the terahertz response of the device.

Carbon spheres with diameters in the range 125 nm–10 μm were produced via hydrothermal carbonization of sucrose. Annealing at 800 °C under a flow of dry N2 gas increased the carbon content, reduced the sphere diameter making their shape more uniform, increased the crystallinity within the spheres and rendered them conducting. The band gap of the carbon spheres was found to be 2.82 eV and the conductivity was 0.15 S/cm at room temperature. A Schottky diode using these spheres was fabricated and electrically characterized. The ratio of the ON to the OFF current at ±1 V was ~20 and the turn-on voltage was ~0.6 V. Using the standard thermionic emission model of a Schottky junction, the diode ideality parameter was calculated to be ~2.4 and the barrier height was 0.52 eV. A simple circuit was designed to test the diode as a half wave rectifier with an input 100 Hz, 5 V peak-to-peak signal. The rectified output with an efficiency of 5.7 was tapped across a 22 kΩ load resistor. This is the first study demonstrating a real application using conducting carbon spheres fabricated via an easy, rapid, cheap, and green technique.