Journal of Materials Science最新文献

Gallium-based liquid metal has significant research value in interfacial heat transfer due to high its thermal conductivity. However, its great fluidity frequently causes the risk of leakage and corrosion when in direct contact with heat sinks. In this paper, a high-performance thermal pad with diphase continuous structure reinforced by liquid metal is proposed. Nickel-coated copper particles connected by liquid metal ensure heat-transfer performance, while silicone rubber provides softness and strength. Utilizing the remarkable processability and insulation properties of conventional polymers, they function as a barrier layer to avoid liquid metal from overflowing. The findings indicate that the composite exhibits favorable insulation performance, mechanical characteristics, and a thermal conductivity of up to 12.41 W/(m K). Most notably, the problem of liquid metal overflow has been effectively resolved, rendering it highly applicable in the field of thermal management within the electronics industry.

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This work investigates the effect of the microstructure of the as-quenched precursors prepared at various cooling rates on the soft magnetic characteristics and its sensitivity to the annealing heat rate (HR) of the Fe_83.5Si₃B₁₀P₂Cu_1.5 nanocrystalline alloy. The results of Mössbauer spectra indicate that the cooling rate during the melt spinning process significantly impact the microstructure of as-quenched alloy samples. The decrease in the cooling rate facilitates the formation of an amorphous/nanocrystalline precursor containing more “α-Fe-like” structure and Cu-clusters. Variations of grain size and H_c with heating rate indicate that Fe_83.5Si₃B₁₀P₂Cu_1.5 alloy samples prepared at a low cooling rate are less sensitive to the heating rate during crystallization annealing. The Fe_83.5Si₃B₁₀P₂Cu_1.5 nanocrystalline alloy prepared at low cooling rate can achieve excellent soft magnetic properties with low HR annealing.

High-entropy carbides (HECs), which exhibit a unique combination of properties that render them suitable for a variety of applications, have garnered significant interest. The role of vacancies in HECs, critical to their performance, remains insufficiently explored. This investigation delves into the stability, mechanical characteristics, electronic properties, and thermodynamic features of rock salt-structured (HfTaZrNb)C_1-x (x = 0.0, 0.125, 0.25, 0.375), employing density functional theory and the Debye–Grüneisen model. Our findings confirm the thermodynamic stability of (HfTaZrNb)C_1-x, as indicated by negative formation energies. Increasing vacancy content results in a decrease in lattice constants, modulus, hardness, and minimum thermal conductivity, alongside a reduction in elastic anisotropy and Debye temperature. Conversely, ductility is enhanced. Electronically, the research provides detailed insights into how vacancies influence bonding, elucidating the underlying reasons for variations in mechanical properties. This study deepens our understanding of vacancy impacts at the atomic level in HECs, providing vital data to inform future material design and application strategies.

Three different metal stacks, namely Ti/Au, Ni/Au and Sc/Au, were examined as Ohmic metal contacts to Si-doped, n-type (4.1 × 10¹⁹ cm⁻³), 300-nm thick (Al_0.18Ga_0.82)₂O₃ layers grown by metal-organic chemical vapor deposition. This is a typical composition used for (Al_xGa_1-x)₂O₃ /Ga₂O₃ heterostructure field effect transistors. The effects of postdepositional annealing (300–475 °C) were examined through circular transfer length method (CTLM) measurements to determine both the transfer resistance and specific contact resistivity. The lowest resistances were achieved with Ti/Au, with specific contact resistivity 1.2 × 10^–4 Ω·cm² and transfer resistance 3.82 Ω·mm for as-deposited contacts. Annealing was found to degrade both of these resistances in all cases from the as-deposited values, even though the AGO sheet resistance decreased slightly, from 1191 Ω/□ to 905 Ω/□ after annealing at 475 °C. The temperature dependence of specific contact resistivity is also investigated.

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For energy storage applications, attaining high dielectric permittivity as well as low loss factor is the foremost target. This could be accomplished via filling polymer matrices with inorganic filler which is characterized by relatively high dielectric permittivity. In the present study, polyvinyl butyral (PVB) was used as a matrix material for preparing nanocomposite films filled with different weight fractions (2, 5, 10, and 15%) of barium titanate (BaTiO₃) using the casting approach. The results show that BaTiO₃ (BT) is well incorporated inside the PVB matrix. Although the dielectric permittivity has been decreased from 3.61 to 2.41 at 1 kHz upon filling the PVB matrix with 5 wt. % of BT, the PVB-BT-NPs-5 nanocomposite film shows the lowest loss factor ~ 0.0049, nearly half that for PVB, 0.0092, which implies the increased film ability to keep its stored energy. The PVB-BT-NPs-5 has been irradiated with gamma radiation to investigate its impact on the structure beside its dielectric and thermal properties. The crystallite size of BT has been decreased from 20.64 to 17.77 nm as PVB-BT-NPs-5 nanocomposite film has been irradiated at a dose of 0.5 kGy. The dielectric permittivity has been decreased from 2.41 to 2.37 at 1 kHz, whereas an increase from 0.0049 to 0.0073 in the loss factor is observed. Furthermore, the thermal stability has been decreased due to the deformation induced by gamma rays inside the nanocomposite films. Therefore, these nanocomposite films could be better exploited in energy storage applications in its un-irradiated form.

This work investigates the influence of minute additions of cobalt (Co) on the hydrogen absorption characteristics, phase composition, binding energy, and adsorption energy of the Zr₇₀V_24.6Fe_5.4−xCo_x (wt%) (x = 0 ~ 2.0) alloys. The research revealed that the Zr₇₀V_24.6Fe_4.4Co_1.0 alloy exhibits the peak hydrogen absorption capacity. In comparison with the Zr₇₀V_24.6Fe_5.4 (wt%) alloy, the hydrogen absorption properties increase from 80196.34 Pa cm³ g⁻¹ (x = 0) to 133364.79 Pa cm³ g⁻¹ (x = 1.0 wt%), representing a 66.30% improvement in performance. The enhancements in performance can be attributed to: an increase in lattice volume due to the addition of Co, which promotes the diffusion of hydrogen atoms within the lattice; a phase transition of the AB₂ phase from Zr(V_0.75Fe_0.25)₂ to Zr(V_0.91Co_0.09)₂, and a significant decrease in the binding energy of Zr from 182.99 eV (x = 0) to 182.30 eV (x = 1.0 wt%), V in the alloy from 530.91 eV (x = 0) to 530.35 eV (x = 1.0 wt%), thereby enhancing the alloy’s reactivity; according to the density functional theory calculations, the weighted adsorption energy of the alloy for H₂ is increased from 35.11 to 38.14 eV. These research findings offer valuable guidance for the development of getters, and besides, expected to help promote further application of getters in high-tech fields such as military and medical.

To investigate the effect of Co(OH)₂ on the performance of the special capacitor, graphene was holed (HG) using microwave and KMnO₄ and electrostatically sprayed with CNT to prepare a laminated structure bamboo woodceramics matrix (C/HG@BE). Then, Co(OH)₂ was electrodeposited on the matrix to form a supercapacitor electrode (C/HG@BE-Co-x). The results showed that the Mn nanoparticles generated by KMnO₄ under the action of microwave were partially embedded in the graphene sheet mesh and formed holes in the graphene sheet after removal. The matrix had a clear laminated structure and good electrical conductivity. The electrical resistivity was approximately 0.163 Ω cm at 1000 ℃ sintering temperature and remained low after the electrode was modified Co(OH)₂. Meanwhile, the Co(OH)₂ was uniformly deposited on the surface and within pores of the wall of the matrix and anchored by PPy to reduce fall. The electrode of C/HG@BE-Co-₁₅₀₀ modified with Co(OH)₂ exhibited a good pseudocapacitance effect. At the current density of 0.1 A/g, the specific capacitance was approximately 255.12 F/g, and the retention of specific capacitance was maintained at 83.75% after 10000 cycles. When the energy density was 40.78 Wh/kg, the power density was 480 W/kg, indicating excellent electrochemical performance, which contributed of the synergistic action of electronic double layer capacitor and pseudocapacitance.

In wide-bandgap semiconductor power device packaging, die bonding refers to attaching the die to substrate. Thereby, the process temperature of Ag sintering for the die bonding should be low to prevent damage to fragile dies. Herein, an organic-free strategy using Ag nanostructures derived from the thermal decomposition of metal–organic decomposition (MOD) was proposed to achieve low-temperature bonding. Significant effects on bonding performance were determined by the thermal decomposition temperature, which in turn determined the organic content and sintering degree of Ag nanostructures. At a low thermal decomposition temperature of 160 °C, incomplete decomposition resulted in high organic content in the Ag nanostructures, causing large pores inside the Ag joints owing to the generation of gaseous products. Owing to the Ag particles with naked surfaces and wide size distribution, the Ag nanostructure obtained at 180 °C showed an excellent bonding performance, resulting in a high shear strength of 31.1 MPa at a low bonding temperature of 160 °C. As the thermal decomposition temperature was 200 °C, sintering among Ag particles increased the particle size, resulting in a reduction of surface energy and driving force for sintering. We think that uncovering this underlying mechanism responsible for the bonding performance will promote the application of Ag MOD in the die bonding of WBG power devices.

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