Paweł Ławniczak

This paper presents a comprehensive study on the quality and reliability of commercially available medium voltage surge arresters, with particular emphasis on their electrical performance and structural degradation under aging conditions. Samples from four manufacturers were subjected to 8/20 μs aging impulses and accelerated durability tests. Electrical analysis revealed that some products exhibited excessively high residual voltages (U_res) exceeding declared values by an average of 7.5% and high partial discharge (PD) levels. The resistive component of the leakage current (I_LCR) indicated that medium voltage (MV) surge arresters possess higher thermal resistance to aging as compared to the low voltage (LV) ones. Structural analysis performed using powder X-ray diffraction (pXRD) confirmed the presence of ZnO as the primary phase, along with intergranular δ-Bi₂O₃ and Sb₂O₃-based spinel and pyrochlore phases. Study of the powder X-ray diffraction patterns using theWilliamson–Hall method revealed the microstrains exhibiting significant variations in residual lattice strains. This suggests that during varistor ceramic processing distinct sintering protocols have been utilized. Elevated microstrain values (ε_WH) correlated with increased porosity indicated that volatilization ZnO was promoted by high sintering temperatures. Aging processes led to dopants diffusion into grain boundaries and growth of the spinel phase (Zn₇Sb₂O₁₂). Dielectric spectroscopy measurement revealed changes in the real part of varistors’ permittivity (ε) up to 50% under thermal aging. This provides insight into the thermal stability and long-term reliability of medium voltage surge arresters under test.

The spectroscopic, thermal, and electrical properties of polypyrrole ‐co ‐poly(pyrrole‐3‐carboxylic acid) doped with p‐TSA (p‐toluenesulfonate) and AQS (anthraquinone sulfonate) are investigated. The semiconductor‐like electrical characteristics of the systems are demonstrated by the variation in electrical conductivity as a function of temperature. The properties of conductivity and dielectricity are investigated. The investigated copolymers demonstrate 3D conductivity and a constant carrier density near the Fermi energy. Polarons and bipolarons are charge carriers, as indicated by IR and Raman spectra. The number of charge carriers is increased by doping the polypyrrole ‐co ‐poly(pyrrole‐3‐carboxylic acid) copolymer. The molecular structure of the ionized oligomer and the doped ones is analyzed using the density functional theory (DFT) methods. The time‐dependent density functional theory methods are employed to analyze the electron transitions of the copolymers under investigation.

Nanocellulose-based nanocomposites exhibit properties dependent on nanocellulose morphology, affecting thermal, electrical, and molecular characteristics. The study compares imidazole-doped nanocomposites from cellulose nanofibers (CNFs) and nanocrystals (CNCs). Scanning electron microscopy shows CNFs form entangled networks, while CNCs form compact grains, influencing the imidazole’s interaction within the matrix. CNC-based composites have higher electrical conductivity (0.326 S/m at 150 °C) due to weaker imidazole hydrogen bonds and compact structure, facilitating proton transport. In contrast, CNF-based composites, with a disordered structure and stronger hydrogen bonds between imidazole and polymer matrix, exhibit lower conductivity (0.021 S/m at 140 °C) but enhanced thermal stability, degrading above 220 °C. Solid-state nuclear magnetic resonance (NMR) spectroscopy revealed two imidazole species: slowly and rapidly reorienting and exchanging protons. The activation energy for proton exchange and reorientation of imidazole is lower in the CNC-based composite (0.39 eV) than CNF-based (0.44 eV), indicating weaker hydrogen bonds. The CNF matrix is inhomogeneous, and the imidazole molecules bond in different environments. The wider activation energy distribution in CNF composites supports this conclusion. Heteronuclear correlation (¹H-¹⁵N HETCOR NMR) spectroscopy identified imidazole bonding to cellulose OH groups and residual water. Proton transport involves imidazole reorientation and exchange via cellulose OH groups and water, contributing to conductivity.

Our study focuses on molecular rotors with fast‐moving rotators and their potential applications in the development of new amphidynamic crystals. Steroidal molecular rotors with a dipolar fluorine‐substituted phenyl group as the rotator were synthesized and characterized. Three different rotors were investigated with varying numbers of fluorine atoms. A comprehensive analysis was performed using vibrational spectroscopy (Raman, FT‐IR), electronic circular dichroism (ECD), and dielectric response to understand the behavior of the investigated model rotors. The results were supported by theoretical calculations using Density Functional Theory (DFT) methods. The angle‐dependent polarized Raman spectra confirmed the crystallinity of the samples. Nearly frequency and temperature‐independent permittivity suggest low‐frequency librational motion of stators. An in‐depth analysis of ECD spectra revealed high conformational flexibility in solution, resulting in low ECD effects, while in the solid‐state with restricted rotation, significant ECD effects were observed. These findings shed light on the conformational behavior and potential applications of the studied steroidal molecular rotors.

The search for solid electrolytes which have good proton conductivity in anhydrous conditions, thermal and mechanical stability, and are at the same time environmentally friendly and easy to manufacture is a big challenge which we have undertaken. This work presents new solid electrolytes based on cellulose nanocrystals with protic ionic liquid 1-methylimidazolium bis(trifluoromethylsulfonyl) imide (PIL) which have been obtained and whose thermal and conductivity properties and nanoscale organization has been determined. Two membranes were synthesized which differ as to the amount of absorbed PIL. They show excellent thermal stability up to 200 °C. The maximum value of ionic conductivity is about 10⁻² S/m at 200 °C in anhydrous conditions and falls in the range of 10⁻³–10⁻² S/m for temperatures from 150 to 200 °C. The correlation between the transport properties of membranes and their nanostructure has been probed by solid-state nuclear magnetic resonance spectroscopy. The thermal and conductivity properties of the new materials can compete with currently available membranes. Further work on a composite with a similar chemical composition should lead to obtaining a membrane capable of operating in next-generation fuel cells (T > 120 °C).

We present a smart and efficient methodology for the synthesis of a variety of fluorinated silsesquioxanes (SQs) with diverse Si-O-Si core architecture. The protocol is based on an easy-to-handle and selective hydrosilylation reaction. An investigation on the placement of the reactive Si-HC=CH₂ vs. Si-H in the silsesquioxane, as well as silane vs. olefin structure, respectively, on the progress and selectivity of the hydrosilylation process, was studied. Two alternative synthetic pathways for obtaining a variety of fluorine-functionalized silsesquioxanes were developed. As a result, a series of mono- and octa- T₈ SQs, tri- ‘open-cage’ T₇ SQs, in addition to di- and tetrafunctionalized double-decker silsesquioxane (DDSQ) derivatives, were obtained selectively with high yields. All products were characterized by spectroscopic (NMR, FTIR) techniques. Selected samples were subjected to the measurements revealing their dielectric permittivity in a wide range of temperatures (from −100 °C to 100 °C) and electric field frequencies (10⁰–10⁶ Hz).

Nanocrystalline powders of LiCoO₂ were synthesized using a modified solution combustion method, and the effects of the annealing temperature (450–900 °C) on structure and composition were investigated using various methods, including XRD, SEM, EPR, and electrical studies. It was found that, as the process temperature increases, the value of the specific surface area decreases, and, hence, the size of the crystallites increases. XRD analysis showed that phase-pure LiCoO₂ material was maintained without additional phases. EPR studies revealed the presence of two Ni³⁺ complexes resulting from Ni impurities. The electrical properties of the studied LiCoO₂ samples were investigated by using impedance spectroscopy. Comparison of the effect of annealing temperature on electrical conductivity shows a very interesting behavior. As the annealing temperature increases, the DC conductivity value increases, reaching a maximum at a temperature of 500 °C. However, further increase in the annealing temperature causes a steady decrease in the DC conductivity.