Magnetic Phase Coexistence and Hard-Soft Exchange Coupling in FePt Nanocomposite Magnets

Oxygen-Vacancy-Induced Formation of Pt-Based Intermetallics on MXene with Strong Metal-Support Interactions for Efficient Oxygen Reduction Reaction

The Pt-based alloys can moderate the binding energies of oxygenated species on the catalytic surface, endowing the superior catalytic performance towards oxygen reduction reaction (ORR). Nevertheless, it is still challenging to explore general methods to synthesize structurally ordered intermetallics with uniform distributions. Herein, the strong metal-support interaction is employed to facilitate the interdiffusion of Pt/M atoms by establishing a tunnel of oxygen vacancy on ultrathin Ti3 C2 Tx (MXene) sheets, synthesizing the ordered PtFe, PtCo, PtZn, PdFe, PdZn intermetallics loaded onto Ti3 C2 Tx . Furthermore, the in-situ generation of Ti-O from Ti3 C2 Tx could be bonded with Pt and forming Pt-O-Ti, resulting in charge redistribution through Pt-O-Ti structure. Theoretical calculations demonstrate that the valuable charge redistribution can be observed at the interface and extended even to at the distance of two nanometers from the interface, which can modulate the Pt-Pt distance, optimize Pt-O binding energy and enhance intrinsic activity towards ORR. The strong coupling interaction between PtFe and Ti3 C2 Tx containing the titanium oxide layer endows the high stability of the composites. This work not only presents a general synthesis strategy for intermetallics but also provides a new insight that metal-support interaction is essential for the structural evolution of intermetallics on materials with oxygen vacancies.

Novel Rare Earth (RE)-Free Nanocomposite Magnets Derived from L10-Phase Systems

In the quest for novel rare earth (RE)-free magnetic materials, which also exhibit other additional properties such as good corrosion resistance and potential to operate at higher temperatures, an alloy deriving from the binary FePt system, with Mo and B addition, has been synthesized for the first time, using the out-of-equilibrium method of rapid solidification form the melt. The alloy with the composition Fe₄₉Pt₂₆Mo₂B₂₃ has been subjected to thermal analysis through differential scanning calorimetry in order to detect the structural disorder - order phase transformation as well as to study the crystallization processes. For the stabilization of the formed hard magnetic phase, the sample has been annealed at 600 °C and further structurally and magnetically characterized by means of X-ray diffraction, transmission electron microscopy, ⁵⁷Fe Mössbauer spectrometry as well as magnetometry experiments. It has been proven that after annealing at 600 °C the tetragonal hard magnetic L1₀ phase emerges via crystallization from a disordered cubic precursor and becomes the predominant phase in terms of relative abundance. Moreover, it has been revealed by quantitative analysis via Mössbauer spectroscopy that the annealed sample exhibits a complex phase structure, where the L1₀ hard magnetic phase is accompanied by few other soft magnetic phases, in minority abundance: the cubic A1, orthorhombic Fe₂B and residual intergranular region. The magnetic parameters have been derived from 300 K hysteresis loops. It was shown that, contrary to the as-cast sample which behaves as a typical soft magnet, the annealed sample presents strong coercivity and high remanent magnetization, accompanied by a large saturation magnetization. These findings offers good insight into the potential developing of novel class of RE-free permanent magnets, based on Fe-Pt-Mo-B, where the magnetic performance emerges from the co-existence of hard and soft magnetic phases in controlled and tunable proportions, capable of finding good applicability in fields requiring good catalytic properties and strong corrosion resistance.

Multifunctional Magnetic Nanocomposites: Innovative Processing and Applications

Multifunctional magnetic nanocomposites are among those heterogeneous nanosized systems where at least one phase component is magnetic and can act as an intermediate of either the actuation or the response of the overall system. The main advantage of heterogeneous nanosystems is the possibility of combining and inter-influencing the electronic properties of constituent interfaced nanophases. Consequently, unique physico-chemical properties of the hybrid materials of interest in various applications can be obtained. This Special Issue of Nanomaterials highlights the most advanced processing and characterization tools of some multifunctional magnetic nanocomposites and heterogeneous systems of interest in various applications, from biomedicine to sensoristics and energy-saving materials.

Electric Field Distribution and Dielectric Losses in XLPE Insulation and Semiconductor Screens of High-Voltage Cables

This article presents the electric field distribution E and dielectric losses ΔPdiel. in the insulation system of high-voltage cables. Such a system consists of inner and outer semiconductor screens and XLPE insulation. The aim of this study was to compare the values of E and ΔPdiel. between semiconductor screens and XLPE insulation. The objects of the research were high-voltage cables of 110 kV, 220 kV, 400 kV, and 500 kV. The geometrical dimensions of the cables, especially the radii of individual layers of insulation, as well as the electrical properties of the screens and XLPE, were taken from the literature. Semiconductor screens and XLPE insulation were treated as a system of three concentric cylinders. When determining the electric field distribution, both the electrical permittivity and electrical conductivity, which, in the case of semiconductor screens, play important roles, were taken into account. The obtained results prove that both the electric field distribution E and dielectric losses Pdiel. are significantly larger in XLPE insulation than in semiconductor screens. The intensity E in XLPE insulation is about four orders of magnitude greater than the intensity in semiconductor screens. Dielectric losses ΔPdiel. in XLPE insulation are about eight orders of magnitude greater than the losses occurring in semiconductor screens.

Determination of Dielectric Losses in a Power Transformer

The article presents a method of determining dielectric losses that occur in insulating materials in a power transformer. These losses depend mainly on the electric field stress, pulsation, dielectric loss coefficient, and electrical permittivity of insulating materials. These losses were determined by integrating an expression describing unit losses. The determined dielectric losses were compared with the total losses of the transformer. It turned out that dielectric losses are a fraction of a percent of the total losses. The influence of the electrical permittivity of the insulating liquid and paper insulation on the value of dielectric losses was investigated. This influence was ambiguous, which is characteristic of stratified systems made of materials with different permittivity. An analysis of the influence of the dielectric loss coefficient tan(delta) on the value of dielectric losses in the transformer was carried out. The impact of this coefficient on the amount of dielectric losses turned out to be directly proportional.