Moisture effects on AC dielectric strength and partial discharge inception voltage in natural monoesters

It is essential to analyse the dielectric performance in a humid environment of insulating liquids of plant origin, considered as alternatives to mineral oil (MO) which is not environmentally friendly. This paper focuses on the effects of different moisture levels on the dielectric strength and partial discharge initiation voltage of two natural monoesters, based on castor oil (CO) and palm kernel oil (PKO), and MO. The different samples were moistened with a glycerol solution, then sealed and stored for 12 days to allow further diffusion of moisture into the samples. Dielectric strength was statistically evaluated from IEC 60156. Partial discharge inception voltage (PDIV) experiment was performed in conformity with a modified IEC 61294 purpose at ambient temperature. Based on the experimental observations, the moisture has different behavior on dielectric strength and PDIV of insulating oils. Monoesters have a better withstand to water contamination than MOs in power transformers.

Boosted dielectric performance of organic‐inorganic nanocomposites based on BaTiO3 via 2D TiO2 templates

Organic-inorganic hybrid dielectrics composed of nanoscale ceramic fillers in polymer matrices have attracted considerable attention because they can overcome the inherent limitations such as the low dielectric constant, high dielectric loss, and low film density associated with mechanically flexible pristine polymer materials. Barium titanate (BaTiO3), a representative perovskite-based material with a high permittivity, is suitable for applications as nanofillers in nanocomposite dielectrics. X-ray diffraction combined with Raman analysis suggest that a two-step hydrothermal synthesis, which uses synthesized TiO2 nanosheets as a template, is an effective method for the synthesis of pure BaTiO3 nanoparticles compared with other methods. Ultrasonic treatment is employed to disperse BaTiO3 nanoparticles with different concentrations in polyvinyl alcohol (PVA) polymer, and the dielectric performance of the nanocomposite films has been examined. In this study, 20 wt% BaTiO3-PVA nanocomposite dielectric showed superior capacitance and dielectric constant performance, i.e., five times higher than that of the pristine PVA.

Micro-structural, magnetic and dielectric performance of rare earth ion (Sm3+) doped MgCd ferrites

The combined effects of Sm3+ substitution together with the addition of 3 wt% Bi2O3 endowed the MgCd ferrites with excellent magnetic permeability and dielectric permittivity. Various concentrations of Sm3+ (x=0.00, 0.03, 0.06, 0.09, 0.12, and 0.15) were employed to modify the permeability (μ') and permittivity (ε') of the MgCd ferrites. XRD, SEM, VSM and vector network analysis techniques were used to characterize the samples. The measurement results reveal that the ferrites processed a saturation magnetization of up to 36.8 emu/g and coercivity of up to 29.2 Oe via the conventional solid-state reaction method. The surface morphology SEM confirms that with increasing Sm3+ concentration, the grain shape changes from a polygon to a circle. Moreover, the outstanding dielectric performance of dielectric permittivity can achieve 23. The excellent properties obtained in Sm3+-substituted Mg ferrites suggest that they could be promising candidates for modern high-frequency antenna substrates or multilayer devices.

Preparation of Polyimide Films with Ultra-Low Dielectric Constant by Phase Inversion

Due to the high value of its dielectric constant, polyimide does not meet the requirements of the development of integrated circuits and high-frequency printed circuits. The development of novel low dielectric constant polyimide materials for the preparation of flexible copper clad laminates is of theoretical and practical significance in the application of polyimide for 5G communications. In this work, different fluorinated graphene/polyamic acids (FG/PAA) were used as the precursor, and the porous polyimide film was successfully prepared by phase inversion. The dielectric constant of the porous polyimide film is relatively low, being less than 1.7. When the content of fluorinated graphene is 0.5 wt%, the overall dielectric performance of the porous film is the best, with a dielectric constant of 1.56 (10 kHz) and a characteristic breakdown field strength of 56.39 kV/mm. In addition, the mechanical properties of the film are relatively poor, with tensile strengths of 13.87 MPa (0.2 wt%), 13.61 MPa (0.5 wt%), and 6.25 MPa (1.0 wt%), respectively. Therefore, further improving the breakdown resistance and mechanical properties of the porous film is essential for the application of porous ultra-low dielectric polyimide materials.

Enhanced Ferroelectric, Dielectric Properties of Fe-Doped PMN-PT Thin Films

Fe-doped 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-PT) thin films were grown in Pt/Ti/SiO2/Si substrate by a chemical solution deposition method. Effects of the annealing temperature and doping concentration on the crystallinity, microstructure, ferroelectric and dielectric properties of thin film were investigated. High (111) preferred orientation and density columnar structure were achieved in the 2% Fe-doped PMN-PT thin film annealed at 650 °C. The preferred orientation was transferred to a random orientation as the doping concentration increased. A 2% Fe-doped PMN-PT thin film showed the effectively reduced leakage current density, which was due to the fact that the oxygen vacancies were effectively restricted and a transition of Ti4+ to Ti3+ was prevented. The optimal ferroelectric properties of 2% Fe-doped PMN-PT thin film annealed at 650 °C were identified with slim polarization-applied field loops, high saturation polarization (Ps = 78.8 µC/cm2), remanent polarization (Pr = 23.1 µC/cm2) and low coercive voltage (Ec = 100 kV/cm). Moreover, the 2% Fe-doped PMN-PT thin film annealed at 650 °C showed an excellent dielectric performance with a high dielectric constant (εr ~1300 at 1 kHz).