High-frequency power electronic devices require soft magnetic composites (SMCs) with low magnetic loss and high saturation magnetization. In this study, FeSiAl/(Al2O3-Ni) and FeSiAlNi/Al2O3 SMCs were fabricated via sintering FeSiAl/NiO composites at various temperatures. The structural evolution and performance of the resulting SMCs were systematically investigated. At sintering temperatures of 850℃–900℃, a chemical reaction between aluminum (Al) (derived from FeSiAl) and NiO at the FeSiAl/NiO interface, yielded FeSiAl/(Al2O3-Ni) SMCs with a composite coating comprising a uniform Al2O3 layer and a ferromagnetic nickel (Ni) layer. Sintering temperatures exceeding 950℃ accelerated the interdiffusion of Al from the FeSiAl core and that of Ni from the composite coating, facilitated the alloying of FeSiAl and Ni and reduced the homogeneity of the Al2O3 layer, ultimately generating FeSiAlNi/Al2O3 SMCs. The prepared SMCs exhibited low magnetic loss and considerably enhanced saturation magnetization, 8.5%–21.3% greater than that of the raw FeSiAl powder. This work provides a novel strategy for constructing high-quality coatings in SMCs, with the potential to advance the development of high-performance SMCs for high-frequency power electronic applications.

Zintl-phase Mg3(Sb, Bi)2 alloys have garnered significant attention, due to their abundance of constituent elements, non-toxicity, low cost, and intrinsically low thermal conductivity. However, their large-scale application remains limited by the stringent synthesis requirements. In this study, we report a scalable melting–SPS strategy to synthesize Mg3(Sb, Bi)2 alloys with precisely tuning the Bi content. Partial substitution of Sb by Bi effectively modulates carrier concentration and mobility, while the associated mass and strain field fluctuations, together with the softer Mg–Bi bonds, significantly enhance phonon scattering and reduce lattice thermal conductivity. The optimized composition Mg3.5SbBi0.99Te0.01 achieved a peak power factor of 23.56 μW cm−1 K−2 at 373 K, outperforming most reported Mg3(Sb, Bi)2 materials in the near room temperature range. It also delivers a high average ZT of 0.99, comparable to the commercial Bi2Te3-based alloys. Its room-temperature ZT of 0.83 surpasses most previously reported Mg3(Sb, Bi)2 materials. A peak ZT of 1.13 at 423 K further demonstrates this balanced and high performance across 300–773 K, highlighting the strong potential of the scalable fabrication route for practical thermoelectric applications.

This work presents the fabrication of low-loss, high-permeability Fe-Si soft magnetic composites (SMCs) utilizing alumina-coated and subsequently annealed Fe-Si powder. Appropriate annealing preserves a uniform, dense, and continuous alumina insulating layer, enabling optimization of the magnetic properties through powder annealing. The optimal annealing duration for Fe-Si SMCs was identified as 180 min, yielding a minimum core loss of 259.1 mW/cm3 and a peak permeability of 94.85 (measured at 50 mT/100 kHz). The observed reduction in hysteresis loss arises from the combined influence of grain growth and stress relaxation during the annealing process. A uniform insulating layer effectively restricts induced eddy currents to individual powder particles, thereby minimizing eddy current losses. However, prolonged annealing compromises the coating's structural integrity, resulting in a decline in magnetic performance. This work introduces a systematic strategy for enhancing the overall magnetic properties of SMCs by precisely controlling the annealing time of the powders, establishing a distinct correlation between coating evolution and composite performance. These insights provide practical direction for the high-efficiency deployment of soft magnetic composites in high-frequency magnetic applications.

In this study, the flattening of Fe-6.5 wt%Si powders was achieved through ball milling. The effects of different ball milling durations on the aspect ratio of Fe-Si powders, as well as the corresponding structure and magnetic properties of the Fe-Si SMPC, were systematically investigated. The ball milling treatment significantly altered the structure of the Fe-Si powders, leading to a reduction in both the eddy current diameter and the in-plane demagnetization factor. The layered structure formed by the flaky Fe-Si powders demonstrated a remarkable effect in suppressing the eddy current and demagnetization effects. However, excessive ball milling time compromised the structural integrity of the flaky Fe-Si powders, resulting in a degradation of their magnetic properties. The layered Fe-Si SMPC prepared from flaky Fe-Si powders obtained after 24 h of ball milling exhibited excellent magnetic properties, including low magnetic loss (76.12 W/kg at 50 kHz/0.05 T) and significantly enhanced effective permeability (185).

The annealing induced microstructural recovery of flaky Fe powders is critical for determining the magnetic properties and loss behavior of derived layered Fe-based soft magnetic composites. In this work, flaky Fe powders with a high aspect ratio were prepared by ball milling and subsequently annealed at different temperatures to establish the correlation between powder state evolution and composite performance. X-ray diffraction combined with Rietveld refinement revealed pronounced microstructural recovery during annealing, evidenced by increase in crystallite size and the reduction in microstrain from 0.07% in the as-milled powders to 0.015% at 600 ℃. Layered Fe-based soft magnetic composites were then fabricated from the annealed flaky powders to evaluate the effect of powder state regulation on permeability and core loss behavior. The saturation magnetization remained nearly unchanged with increasing annealing temperature, whereas the coercivity decreased markedly, indicating that magnetic softening was mainly governed by defect relaxation and stress release rather than changes in phase constitution. As a result, the effective permeability increased after annealing and reached a maximum value of 75 at 600 ℃, while the total loss decreased from 350 to 140 W/kg at 50 kHz and 50 mT, yielding the best overall magnetic performance. Empirical loss separation further suggested that annealing reduced the hysteresis related contribution while increasing the relative importance of the frequency dependent dynamic contribution. These results demonstrate that powder state regulation induced by annealing provides an effective strategy for optimizing the permeability and loss balance of layered Fe-based soft magnetic composites.

The simultaneous improvement of core loss and saturation magnetization remains a challenge for soft magnetic composites (SMCs) used in high-frequency and high-efficiency power electronic devices. In this work, FeSiAl SMCs with Al2O3-Co composite coating were fabricated via sintering FeSiAl/Co3O4 composite powders, during which interface reactions occurred between FeSiAl and Co3O4. The influence of Co3O4 coating content on the microstructure and properties of the prepared FeSiAl SMCs was systematically studied. The highly intact Al2O3 coating effectively enhanced the insulation between FeSiAl magnetic particles, thus reducing eddy current loss. Meanwhile, the Co coating effectively weakened the magnetic dilution effect induced by the Al2O3 coating, enabling the FeSiAl SMCs to maintain a high saturation magnetization. With increasing Co3O4 coating content, the thickness of the composite coating increased, leading to an elevated resistivity of FeSiAl SMCs and a continuous decrease in core loss. Furthermore, a moderate increase in Co3O4 content below 7.5 wt% was conducive to improving the saturation magnetization. However, when the coating content exceeded 10.0 wt%, insufficient diffusion of Al atoms toward the reaction interface restricted the interface reaction, resulting in the formation of CoO phase in the composite coating and consequently a decline in saturation magnetization. This work provides a novel strategy for the design and preparation of high-quality inorganic coatings in SMCs.

Ni layer and Co layer are the most commonly utilized in commercial Bi2Te3-based thermoelectric device as diffusion barrier layer. However, during the application they still have significant limitations in inhabiting the diffusion of elements. In this study, we found that the Ni layer exhibits a greater tendency to react with Te in Bi2Te3. In contrast, while Co is less prone to react with Bi2Te3, it facilitates interdiffusion with Sn in Sn-based solder at the interface. Therefore, a barrier layer based on p-type Bi2Te3 wafers with electroless plating Co-P (EC) and electroless plating Ni-P (EN) was investigated to avoid the drawbacks of the single barrier layer. CoP/Ni-P barrier layer can be obtained by electroless plating Co and then Ni (ECEN). The Co-P/Ni-P barrier layer demonstrates an excellent diffusion blocking effect, effectively inhibiting the formation of the Ni-Te phase in the EN-plated samples and reducing diffusion between the barrier layer and Sn95Sb5 solder in both EC-plated and EN-plated samples. The intermetallic compounds (IMCs) at the interface of ECEN-plated samples were thinner after annealing compared to those at the interfaces of in the conventional EN-plated and EC-plated samples. The wettability of the ECEN-plated p-type Bi2Te3 surface exceeded that of both the EC-plated and bare surfaces. Ultimately, the bonding strength between p-type Bi2Te3 and the Co-P/Ni-P barrier layer was 10.12 MPa, and the interfacial contact resistance at room temperature was 3.34 mu Omega & sdot;cm2, meeting the requirements for the thermoelectric device fabrication and operation.

In this study, a layered Fe soft magnetic composites (Fe SMCs) with phosphate insulating layer have been fabricated by phosphoric acid passivation combined with subsequent cold pressing. The microstructure and formation mechanism of phosphate insulating layer on the surface of flaky Fe particles have been revealed. The effect of phosphoric acid concentration on the magnetic properties of layered Fe SMCs was also investigated systematically. The flaky Fe particles could be well insulated by the uniform insulating layer, and its thickness increases with increasing the phosphoric acid concentration from 0 g/mL to 0.02 g/mL. However, further increasing the phosphoric acid concentration to 0.03 g/mL and 0.04 g/mL would result in the discontinuous and uneven phosphate insulating layer. Correspondingly, the frequency stability of permeability, as well as the peak quality factor for the Fe SMCs gradually improve with increasing the phosphoric acid concentration, while total core loss first decreases and then increases. The Fe SMCs with the phosphoric acid concentration of 0.02 g/mL display excellent structural and magnetic properties. For instance, their effective magnetic permeability is stable at 60, and the core loss is lower (206 W/kg at 50 kHz and 0.05 T). The results show that the layered Fe SMCs with phosphate insulating layer have a good application prospect in high frequency electromagnetic conversion equipment.

We prepared Fe soft magnetic composites (SMCs) with lamellar structure by using the flaky Iron powder, and studied the effects of types of iron powder on the microstructure and properties of Fe SMCs. The results show that the atomized iron powder and the reduced iron powder are deformed into flaky structure after ball milling, and these flaky iron powder have greater magnetic susceptibility and eddy current diameter perpendicular to the magnetic flux direction. In addition, compared with flaky gas atomized iron powder, the flaky reduced iron powder has large aspect ratio and lower coercivity. Therefore, the Fe SMCs with flaky reduced iron powder exhibit relatively high permeability (82) and low eddy current loss (0.033 W/kg at 50 kHz, 0.05 T), which shows the potential possibility of application at high frequency.

Achieving low magnetic loss and high permeability remains a challenge for Fe–Si soft magnetic composites (SMCs). In this work, anisotropic Fe–Si/BN SMCs were prepared with the flaky Fe–Si/BN powders. Effects of BN content on the structure and electromagnetic properties of the Fe–Si/BN SMCs were studied. When the BN content increased, the surfaces of the flaky Fe–Si powders were gradually completely covered by BN nanosheets, a uniform BN coating formed and thickened. Owing to the low demagnetization factor of the flaky Fe–Si powders in the in-plane direction, demagnetization effect was effectively reduced. In addition, dynamic loss was significantly reduced by the increased BN content due to the good insulation of the BN coating. When the BN content was 6 wt

Fe-Si/BN soft magnetic composites (SMCs) with layered structure were prepared with flaky Fe-Si/BN powders through low-speed ball milling, molding, and annealing. Effect of annealing temperature on the microstructure and magnetic properties of the layered Fe-Si/BN SMCs was studied. The results showed that structure of the Fe-Si/BN SMCs exhibited good thermal stability. When the annealing temperature increased from 500 to 800 °C, the density of the Fe-Si/BN SMCs gradually increased, leading to gradually decreased resistivity and increased dynamic loss. In addition, the increase in annealing temperature is beneficial for eliminating residual stresses within the Fe-Si/BN SMCs, resulting in decreased hysteresis loss and significantly improved effective permeability. Nevertheless, excessively high annealing temperature at 900 °C caused sintering and bonding between the flaky Fe-Si powders, which deteriorated the magnetic properties. The layered Fe-Si/BN SMCs annealed at 800 °C exhibited good magnetic properties, such as low magnetic loss (82.7 W/kg at 50 kHz and 0.05 T) and remarkably high effective permeability (143 at 100 kHz).

The development of high-performance soft magnetic composites (SMCs) is crucial for next-generation power electronics, particularly for applications requiring low core losses and high permeability at elevated frequencies. In this study, we introduce a novel 2D/2D heterostructure SMC by integrating flaky Fe powders with exfoliated hexagonal boron nitride (h-BN) nanosheets. This SMCs exhibit enhanced electromagnetic properties, with a layered structure that significantly suppresses eddy current losses while maintaining superior magnetic performance. A controlled ball milling process forms a uniform h-BN insulating layer, which not only improves the electrical resistivity but also enhances the frequency stability of the material. Density functional theory (DFT) calculations predict the thermodynamic feasibility of FeB formation at the Fe/h-BN interface, which is experimentally validated through X-ray photoelectron spectroscopy (XPS), supporting the theoretical findings. Magnetic and electrical characterization reveals that an optimal h-BN content of 7.5 wt% leads to an 84.7 % reduction in core losses compared to uncoated Fe SMCs, while preserving high permeability and a superior quality factor at high frequencies. These results highlight the potential of 2D/2D heterostructures in soft magnetic composites for energy-efficient applications in next-generation power electronics and electromagnetic devices.

Designing magnetic insulation coatings remains a challenge for high-performance soft magnetic composites (SMCs). In this study, the layered Fe SMCs with magnetic insulating layer were fabricated through ball milling, and pressing processes. The impacts of NiZnFe2O4 content on the structure and electromagnetic properties of the Fe SMCs were investigated. The results showed that a uniform NiZnFe2O4 insulating layer was formed on the surface of flaky iron powder during the ball milling process, and the layer thickness increased with the NiZnFe2O4 content. As the NiZnFe2O4 content increased from 0 wt% to 12.5 wt%, the saturation magnetization of the Fe/NiZnFe2O4 composite particles decreased linearly, indicating precise control over the insulating layer. Concurrently, the frequency stability of the magnetic permeability of the Fe SMCs was progressively augmented. Owing to the low demagnetization factor of the flaky Fe powders in the in-plane direction, demagnetization effect was effectively reduced in the layered Fe SMCs, and they exhibited a high permeability. The magnetic loss increased initially and then decreased with increasing NiZnFe2O4 content, while excessive nanoparticle agglomeration led to increased hysteresis and excess losses. The Fe SMCs with 5.0 wt% NiZnFe2O4 content demonstrated superior performance with high saturation magnetization (193 emu/g), good frequency stability of permeability, and low magnetic loss (590 W/kg at 0.05 T/50 kHz). This study provides new insights into the design of magnetic insulation layers for soft magnetic composites and lays the foundation for the development of high-frequency magnetic materials.

Simultaneous optimization of core loss and saturation magnetization in soft magnetic composites (SMCs) is crucial for the development of high frequency and high power in power electronic devices. In this work, FeSiAl/ (Al2O3-Co) and FeSiAlCo/Al2O3 SMCs were prepared by sintering FeSiAl/Co3O4 composite powders at different temperatures. The corresponding structural evolution mechanism and magnetic properties of the prepared SMCs were studied systematically. When the sintering temperature was below 950 degrees C, a chemical reaction at the FeSiAl/Co3O4 interface occurred and led to the formation of Al2O3-Co composite coating. The Al2O3 coating, as an isolation band, can effectively hinder the interdiffusion between Co coating and FeSiAl magnetic powder. When the sintering temperature increased to above 1000 degrees C, the interdiffusion began to occur and was accelerated by the high temperature and chemical potential educed by concentration gradient, finally resulting in the formation of FeSiAlCo alloy. The prepares SMCs exhibited a low core loss due to the high integrity of Al2O3 coating. Its saturation magnetization and permeability significantly increased with the sintering temperature due to the generation of Co coating with ferromagnetism. This work provides a new strategy for the construction of ceramic oxide coating with high integrity and elemental doping of magnetic powder in SMCs, which is expected to be applied to the preparation of high-performance SMCs.

Lamellar Fe based soft magnetic composites (SMCs) were fabricated using flaky iron powders obtained by ball milling. The magnetic properties of Fe based SMCs were optimized by regulating the width-thickness ratio of the iron powders, which was achieved by varying the ball milling time. During the ball milling process, the iron powder was subject to the squeezing and shearing forces exerted by the steel ball, thereby transforming into a lamellar morphology. The thickness of the lamellar iron powder gradually decreases with the ball milling time increases. And the width-to-thickness ratio of iron powder is significantly increased, which reduces the two-dimensional demagnetization factor of iron powder in magnetization direction and the effective eddy current diameter in the lamellar direction. Consequently, the magnetic permeability of iron powder core is significantly improved, and the eddy current loss is decreased, while the saturation magnetization exhibits slightly decline. When the ball milling time reaches 12 h, the lamellar Fe SMCs exhibit superior comprehensive performance, characterized by high saturation magnetization (215.48 emu/g), good magnetic permeability (78) and very low eddy current loss (0.745 kW/m3).

FeSiAl/(Al2O3-Ni) 2 O 3-Ni) soft magnetic composites (SMCs) were prepared by sintering FeSiAl/NiO composite powders, and the formation mechanism of the Al2O3-Ni 2 O 3-Ni composite coating and performance of the FeSiAl SMCs with different NiO coating content were studied. During sintering, high temperature promoted a reaction between Al and NiO at the FeSiAl/NiO interface, resulting in the in-situ formation of a composite coating comprising Al2O3 2 O 3 coating with high integrity and ferromagnetic Ni coating. The interdiffusion of Al and O 2- toward the interface ensured the continuation of the reaction and growth of the composite coating. The composite coating thickened with the increasing NiO coating content, thus showing reduced real part of permeability. Saturation magnetization considerably increased until the NiO coating content exceeded 12.5 wt% owing to residual NiO. Excessive NiO coating content led to the generation of a large amount of Ni, which was not conducive to the integrity of the Al2O3 2 O 3 coating and increased magnetic loss. The FeSiAl SMCs with 5.0 wt% NiO coating content exhibited exceptional performance with high saturation magnetization (135.3 emu/g), good frequency stability of permeability, and low magnetic loss (63.7 W/kg at 0.05 T/20 kHz). (c) 2024 The Society of Powder Technology Japan. Published by Elsevier BV and The Society of Powder Technology Japan. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Bismuth telluride-based thermoelectric devices are the only thermoelectric devices that are currently used in large-scale commercial applications. In actual production, nitric acid roughening solution corrodes them and generates a black substance on the surface that is difficult to remove. The exact composition of the black film is not known, which makes its removal even more difficult. In this study, it was observed by x-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM) that the black substance may be formed by the reaction of Sb 2 Te 3 in p -type bismuth telluride with nitric acid. Valence analysis by x-ray photoelectron spectrometry (XPS) showed the presence of Te in the black substance in the valence states of Te 4+ and Te 6+ , and Sb in the valence state of Sb 3+ . Fourier transform infrared spectrometry (FTIR) results showed the existence of four chemical bonds, including ν Te-O , ν Sb-O , ν Te-O-Te , and ν Te-O-Te , while ν N=O and δ N=O were also detected at 1361 cm −1 and 1039 cm −1 , respectively, indicating the presence of NO3 − in the black substance. Synthesizing the experimental phenomena and literature data, the composition of the black substance was presumed to be x TeO 2 -Sb 2 O 3 -HNO 3 (2 < x < 3), and the corresponding reaction chemical equation was given. This study provides an important reference for further optimization of the production process.

The design of magnetic insulation coating structure has always been a challenge for high-performance soft magnetic composites (SMCs). In this work, we prepared Fe-Si SMCs with silicate/nano-Fe composite coating successfully by in-situ oxidation method combined with spark plasma sintering (SPS). The formation mechanism of the composite coating and its effect on the electro-magnetic properties of Fe-Si SMCs were investigated. The results showed that a uniform Fe2O3 coating can be obtained by reactions between Fe and H2O/O2 during in-situ oxidation process, and became thicker with the increased oxidation time. After sintering, the oxide coating was transformed into a composite coating composed of Fe2SiO4 with excellent insulation and nano-Fe with high ferromagnetism, which resulted from the interfacial reaction between Fe2O3 coating and Fe-Si core. The increased oxidation time led to the gradually thicker composite coating, and resulted in a linear decrease in saturation magnetization, indicating good controllability of the coating. However, excessive oxidation time led to the increased eddy current loss as well as the core loss due to the weakened resistivity. Thus, the Fe-Si SMCs exhibited high saturation magnetic induction (1.66T) and very low core loss (643.9 kW/m3 at 0.1 T/50 kHz) especially when the oxidation time was 1 h.

以微米级Cu粉为基体相,纳米Al2O3颗粒为绝缘相,采用机械球磨和放电等离子烧结工艺相结合的方法制备Al2O3/Cu复合材料,研究Al2O3含量对复合材料微观结构、电阻率和热导率的影响.结果表明,Al2O3/Cu复合材料为核-壳结构,随Al2O3含量增加,Al2O3包覆层对Cu基体的包覆效果逐渐提升;当w(Al2O3)为5％ 时,Al2O3/Cu复合材料的热导率较高,为85.92 W/(m·K),但电阻率偏低,仅为12.6 m?·cm.当w(Al2O3)增加至15％ 时,虽然Al2O3/Cu复合材料的密度降至6.69 g/cm3,孔隙率较高,但电阻率显著提高至2.09×108 m?·cm,约为Cu电阻率的1011倍,且热导率为7.6 W/(m·K),明显高于传统金属基板的热导率.