查看更多>>摘要：Fe-based nanocrystalline alloys with unique dual-nano-phase structure and superior magnetic softness have aroused tremendous interest, yet they generally suffer from the harsh annealing process due to the poor thermal stability. In this study, a high-entropy strategy was proposed to enhance the soft-magnetic property and nanostructure stability of Fe-based nanocrystalline alloys by adding P and C elements in the FeCuSiBPC alloy system. This alloying approach by complicating the composition will greatly increase the mixing entropy, which significantly increase the frequency factor for the formation of α-Fe grains and activation energy for the formation of compounds, which on one hand enhance the competition and soft-impingement effects due to the increased number density of a-Fe grains, and on the other hand hinder the precipitation of compounds in the intergranular amorphous interphase due to the improved crystallization resistance. These both contribute to a thermodynamically and kinetically stable dual-nano-phase structure with fine a-Fe grains embedded in amorphous matrix. Following this strategy of nanostructure stabilization by tuning the compositional complexity, FeCuSiBPC alloy with enlarged processing window and enhanced soft-magnetic properties were successfully obtained. This high-entropy strategy can be applied in a verity of alloy systems to develop high performance nanocrystalline alloys with excellent thermal stability suitable for large-scale industrial processing.
查看更多>>摘要：Prussian White (PW) layers were deposited on Au/Cr/Si substrates by electrodeposition and characterized by different techniques. Scanning electron microscopy (SEM) images and Raman mapping reveal a uniform and homogeneous deposit while scanning transmission electron microscopy (STEM) images disclose the grain boundary pattern and the thickness of 300 nm of the PW layer. Resistive switching (RS) effect with an ON/OFF ratio of about 10~2 was observed. The RS mechanism was investigated from the log-log current-voltage plots. Ionic conduction was observed with an activation energy of 0.4 eV that could be associated with potassium ions as possible charge carriers at the grain boundaries. The endurance characteristics were investigated and a stable abnormal RS was observed for consecutive 500 cycles. Moreover, the retention was also evaluated and the high resistive state (HRS) and low resistive state (LRS) were stable up to 1000 s.
查看更多>>摘要：The current work involves the synthesis of Mn_xCo_(0.5-x)Zn_(0.5)Fe_2O_4 (x = 0.0, 0.1, 0.2, 0.3, and 0.4) by adopting sol-gel auto combustion technique. For all the samples, the single-phase spinel structure with cubic symmetry was assured by the XRD studies. The crystallite size lies in the nanoscale range of 35.4-43.6 nm as estimated by utilizing Debye-Scherrer formula. FTIR spectroscopy affirms the formation of spinel structure due to the appearance of characteristic vibrational bands near 400 and 600 cm"1 which corresponds to the octahedral and tetrahedral sites respectively. FESEM micrographs reveal the presence of non-uniform grain growth which was agglomerated, inhomogenous in size and shape, and having porous morphology. VSM study exhibits soft ferromagnetic nature due to the low coercivity value. There is a decrement in the saturation magnetization with increasing Mn~(2+) concentration which is due to the decrease in the crystallite size and non-magnetic nature of the Mn~(2+).
查看更多>>摘要：Complex boron substructures lead to diversity properties for transition metal borides (TMBs), that provides them many application possibilities in numerous fields. To clarify the actual effect of boron substructures on mechanical, magnetic and electrical properties, we prepared polycrystalline β-FeB samples with zigzag boron chains by high pressure and high temperature. β-FeB exhibits high saturation magnetization (79.54 emu/g), good antioxidant capacity (> 800 K), high hardness (15.62 GPa) and low resistivity (3.4 × 10~(-6) Ω m); thus, it is a promising magnetic material for extreme environmental applications. Subsequently, we performed first-principle calculations combined with X-ray photoelectron spectroscopy analysis and found that the free electrons transferred from Fe atoms stabilize the zigzag boron chains. Spin selection occurs during electron transfer and bonding, with majority spin state electrons as the main participants. The zigzag boron chain substructure provides excellent mechanical properties, at the expense of electrical and magnetic properties. Therefore, we speculate that the spin-selective electrons transfer between the metal and boron substructure can effectively modulate the electrical, mechanical, and magnetic properties of TMBs. This study introduces an effective route for the design, preparation, and applications of high-hardness multifunctional TMBs.
查看更多>>摘要：The crystal structure, pressure composition isotherms, and electrochemical properties of Zr_(0.2)Ti_(0.2)Ni_(0.2+x)Cr_(0.2)Mn_(0.2) (x = 0, 0.025, 0.05, 0.075, and 0.1) high-entropy alloys (HEAs) were investigated. The crystal structures of all the HEAs consisted of two phases: a primary phase with a C14-type (Zr_(0.5)Ti_(0.5))Mn_2 hexagonal structure and a secondary phase with a B2-type Ti_(0.6)Zr_(0.4)Ni cubic structure. Rietveld analysis revealed that the secondary phase increased with an increase in the x value. The hydrogen storage capacity of the HEAs was lower than that of the alloy with x = 0 because of an increase in the B2-type Ti_(0.6)Zr_(0.4)Ni phase, whereas the change in enthalpy of hydride formation (|ΔH|) decreased with increasing x, leading to the instability of hydrides. The alkaline treatment was performed by immersing HEA powders or electrode in a 6 M KOH aqueous solution at 378 K for 2 h. The Zr_(0.2)Ti_(0.2)Ni_(0.2)Cr_(0.2)Mn_(0.2) alloy surface changed to a porous and rough structure, and a ZrO_2 passive thin layer on their surface, which is replaced by NiO or Ni(OH)_2 after the alkaline treatment. The charge-discharge tests conducted using the HEA negative electrodes for Ni-MH batteries depict that the discharge capacity increased with an increase in x, and the highest discharge capacity was 368 mAh g~(-1) at x = 0.075 after the alkaline treatment. On increasing the x value, the high-rate dischargeability and cycle performance were also enhanced.
查看更多>>摘要：The fabrication of 2:17-type Sm-Co-Fe-Cu-Zr magnets that have served as the strongest high-temperature permanent magnets for nearly half a century requires a strict processing control to form full cellular na-nostructure. Considering that slow cooling after solution-treatment may enable a more homogeneous temperature field inside the chamber and more slight magnetic properties difference among the magnets in mass production than rapid cooling, here we performed a comparative study on a model magnet Sm_(25)Co_(46.9)Fe_(19.5)Cu_(5.6)Zr_(3.0) (wt%) to investigate how the post-solutionizing cooling rate affects the micro-structure and magnetic properties. In comparison with the rapid cooling condition, slow cooling produces coarser cellular nanostructure and lower defects density at the solution-treated state. Such initial micro-structural difference leads to slower 1:5 H growth kinetics and slower defects dissociation kinetics during the subsequent aging process, characterized by the smaller fraction of 1:5 H cell boundary phase and the higher density of remanent defects in the slowly-cooled final magnets. Since the 1:5 H phase plays a dominant role on the coercivity and the remanent defects are harmful to hard magnetic properties, further work reveals that longer aging time can promote the formation of 1:5 H phase and to reduce the harmful defects for achieving better magnetic performance in the slowly-cooled magnets. These findings may be helpful for achieving uniform magnetic performance in mass production of 2:17-type Sm-Co-Fe-Cu-Zr magnets.
查看更多>>摘要：In Al alloys, many experiments have shown the effectiveness of Al_3X precipitates in promoting the primary grain nucleation such as Al_3Ti, Al_3Er and Al_3Sc, preventing the α-Al grain recrystallization such as Al_3Cr and Al_3Zr, and strengthening the matrix such as Al_3Li and Al_3Ni. Almost all of those experiments have been measuring the stable structures, and none of them have been focusing on the intrinsic properties of Al_3X and their stabilities as a function of crystal structure and lattice constants due to the experimental limitations. In this study, the first-principle calculation is used to predict the metastablity of different Al_3X structures including L1_2, DO_(22), DO_(23), DO_(19), DO_(18), DO_(24), R3m and P6_3/mmc. The varitions of lattice constant have been achieved by changing external pressure from 0 to 50 GPa. It was found that the L1_2 structure not only had a smaller lattice mismatch with α-Al, but also had a higher symmetry than the other structures, and the stability of the L1_2 structure was enhanced when external pressure was applied, and some other structures may undergo a transition to the L1_2 structure, while the elastic modulus of the L1_2 structure was improved. In addition, the elastic modulus of the Al_3X precipitation phases of different structures was found to increase with decreasing distance between atomic pairs, and the distance between Al-X and X-X pairs had a much greater effect on the elastic modulus than the Al-Al pairs.
查看更多>>摘要：Colloids consisting of the CoCrCuFeNi high-entropy alloy nanoparticles in ionic liquid with the l-butyl-3-methylimidazolium ([BMIM]~+) cation and the tetrafluorborate ([BF4]~-) anion were obtained by the DC magnetron sputtering of high-entropy alloy target in vacuum, onto the surface of [BMIM.BF4] ionic liquid. The method of the nanoparticle colloid preparation is based on negligibly small vapour pressure of the ionic liquid, which allows its application in vacuum. The high-entropy alloy nanoparticle colloids were studied by HRTEM microscopy and SQUID magnetometry. Results of the structural and magnetic analyses show that the colloids contain ultra-small single-crystalline nanoparticles of an uneven shape and typical size of (2-3) nm. The nanoparticles have relatively narrow size distribution which is typical for this preparation method. The high-entropy alloy nanocolloids show complex magnetic properties that are a function of temperature, applied magnetic field and mass content of the nanoparticles in the colloids. The obtained results imply significant magnetic interactions between the ionic liquid and the high-entropy alloy nanoparticles.
查看更多>>摘要：Four new Bi(III) phosphates, K_6Bi_(13)(PO_4)_(15), K_5Bi(P_2O_7)_2, and A_5Bi_5(PO_4)_4(P_2O_7)_2 (A= K, Rb) with the different condensed P-0 groups have been successfully synthesized via the solid-state reactions. The single crystals X-ray diffractions show that they crystallize in the different space groups (K_6Bi_(13)(PO_4)_(15): C2; K_5Bi(P_2O_7)_2: P1; K_5Bi_5(PO_4)_4(P_2O_7)_2 and Rb_5Bi_5(PO_4)_4(P_2O_7)_2: P2_1/c). The structure of K_6Bi_(13)(PO_4)_(15) can be described as a three-dimensional (3D) network composed of the Bi-0 polyhedra and PO_4 tetrahedra with K atoms filling in the space to balance the residual charges. K_5Bi(P_2O_7)_2 features 2D [BiP_4O_(14)]_∞, layers built by the BiO_6 oc-tahedra and P_2O_7 dimers and the adjacent [BiP_4O_(14)]_∞ layers are bridged by the K atoms. A_5Bi_5(PO_4)_4(P_2O_7)_2 (A = K, Rb) contain two different condensed P-0 groups, PO_4 tetrahedra and P_2O_7 dimers, which are connected by Bi-0 polyhedra to construct the complicated 3D framework with K/Rb atoms located in the tunnels. Note that, the compounds that simultaneously contain two different types of P-0 groups are still rare in phosphates. Detailed structural comparisons of Bi~(3+)-containing phosphates indicate that the Bi/P ratios have a significant effect on the condensed degrees of PO_4 groups. Furthermore, TG-DSC, IR, UV-Vis-NIR diffuse reflectance spectra and SHG test for title compounds have also been reported.
查看更多>>摘要：The recent development of electronic devices and control over their electro-magnetic and thermoelectric characteristics via electron spin has attracted a significant attention. Herein, we have addressed magnetic and thermoelectric calculations of K_2MZ_6 (M = Os, Ir, and Z = CI, Br) by quantum simulations. By comparing energies in antiferromagnetic, and ferromagnetic states, it turns out that lower energy corresponds to ferromagnetic (FM) states. Further, to confirm structural stability of FM state, tolerance factor was utilized. The Curie temperature has been reported by Heisenberg classical model. Moreover, the band structures (BS) and density of states (DOS) were analyzed to categorize half metallic (HM) ferromagnetism. To deeply understand the governing Half metallic ferromagnetism, the partial DOSs was tackled by p-d hybridization, exchange energies, and double-exchange model. The system is 100% spin polarized which is assured by integer magnetic moment.
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Elsevier