Enhanced thermoelectric properties of Mg2Si0.58Sn0.42 compounds by Bi doping

N-type Mg₂Si_0.58Sn_0.42 − xBi_x (0 ≤ x ≤ 0.015) compounds were prepared by melting the element metals in sealed tantalum tubes followed by hot pressing. The XRD results indicate that all samples are composites containing both major magnesium silicide solution phase and minor magnesium stannide solution phase. The Hall measurements show that the carrier concentrations and electrical conductivities increase with the increase of Bi doping amount. It was found that the intrinsic excitation shifts to high temperature due to Bi doping, which leads to the increase of the peak-temperatures of the Seebeck coefficient. The maximum dimensionless figure of merit is 0.65 at 700 K for the sample x = 0.015.     

纳米晶NiSi2/Ti5Si3复合涂层耐磨耐蚀性能研究

采用双阴极等离子溅射技术在TC4合金表面制备了纳米晶NiSi2/Ti5Si3复合涂层。利用XRD、SEM和TEM研究了复合涂层的微观组织特征,利用纳米压入和声发射划痕仪考察了复合涂层的硬度、弹性模量以及涂层与基体的结合力。结果表明：纳米晶NiSi2/Ti5Si3复合涂层由外层厚度为7 μm的NiSi2沉积层和其下3 μm厚的Ti5Si3扩散层组成,沉积层的平均晶粒尺寸约为40 nm,而扩散层的平均晶粒尺寸约为70 nm,且存在大量的栅栏状孪晶。纳米晶NiSi2/Ti5Si3复合涂层硬度呈梯度分布,与基体具有较高的结合强度,其结合力为49 N。纳米晶NiSi2/Ti5Si3复合涂层的比磨损率较TC4合金降低一个数量级以上,且对载荷和温度不具敏感性。与TC4合金相比,纳米晶NiSi2/Ti5Si3复合涂层的腐蚀电流密度降低了两个数量级,且具有更大的容抗弧值     

Oxidation behavior at 300–1000 °C of a (Mo,W)Si2-based composite containing boride

The oxidation behavior of a (Mo,W)Si₂ composite with boride addition was examined at 300–1000 °C for 24 h in dry O₂. The oxidation kinetics was studied using a thermobalance, and the oxide scales were analyzed using a combination of electron microscopy (SEM/EDX, FIB, BIB) and XRD. Accelerated oxidation was found to occur between 500 °C and 675 °C, with a peak mass gain at 625 °C. The rapid oxidation is attributed to the vaporization of molybdenum oxide that leaves a porous and poorly protective silica layer behind. At higher temperature (700–1000 °C) a protective scale forms, consisting of a dense SiO₂/B₂O₃ glass.     

Is there a future for semiconducting silicides? (invited)

Silicon is commercially by far the most important semiconductor, however, because silicon has an indirect band gap it would initially appear to be unsuitable for optoelectronic applications. A major research challenge is, therefore, to achieve high intensity light emission from silicon and to engineer active and passive optical structures within it. This paper examines the potential of semiconducting silicides (principally, βFeSi₂ and Ru₂Si₃) for silicon-based optoelectronic applications. It traces the history of the subject from the first photoluminescence spectrum from βFeSi₂ to a working LED which uses βFeSi₂ precipitates as a route for fast radiative recombination. Recent results on semiconducting Ru₂Si₃ are also reported, which show, for the first time, that this material can be fabricated by high dose ion implantation. They also reveal a direct band gap of 0.91 eV. The future for semiconducting silicides is examined and, although there are still barriers to overcome — the future looks bright.     

金属硅化物及其复合材料的研究进展

从金属硅化物的物理及力学性能出发指出了影响其应用的最大障碍是室温脆性,分析了金属硅化物的强韧化手段和机理,认为复合化是目前有效的强韧化方法,最后列举了金属硅化物常用的几种制备技术及其各自的优势和缺点,并且以MoSi_2为例综述了金属硅化物的应用现状.     

Ternary alloying of Mo_5Si_3 with Zr, Ti, Co and V

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Corrosion behaviour of amorphous Ni–Si thin films on AISI 304L stainless steel

Abstract

Nanoscale Ni – Si thin films are widely used in commercial microelectronic devices because of their promising electrical properties as well as their chemical stability. However, their application in corrosive environment has not been frequently addressed in the literature. In this study, amorphous Ni_0.66Si_0.33, Ni_0.40Si_0.60, and Ni_0.20Si_0.80 thin films are prepared on AISI 304L stainless steel by means of ion-beam sputter (IBS) deposition and their corrosion behaviour is studied using potentiodynamic polarisation measurements. The electrochemical measurements were conducted in 0.05M HCl solution at room temperature. By means of optical interferometer, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), the surface morphology and chemical composition of the thin films were examined before and after the electrochemical measurement. The evaluated results showed that the Ni–Si thin films may exhibit improved corrosion resistance over the 304L substrate provided that Si content is high enough to facilitate the formation of a Si-rich passive film.     

Transition-Metal-Catalyzed 1,2-Carboboration of Alkenes: Strategies,Mechanisms, and Stereocontrol

During the past decade, many research groups have described catalytic methods for 1,2-carboboration, allowing access to structurally complex organoboronates from alkenes. Various transition metals, especially copper, palladium, and nickel, have been widely used in these reactions. This review summarizes advances in this field, with a special focus on the catalytic cycles involved in different metal-catalyzed carboboration reactions, as well as the regio- and stereochemical consequences of the underlying mechanisms. 1,2-Carboboration of other unsaturated systems, such as alkynes and allenes, is outside of the scope of this review.     

Synthesis of hybrid metal oxides with high degradation efficiency via a self-propagating process of metallic glasses

Establishing hetero-junctions are widely regarded as an efficient strategy in the area of photocatalysis. In this work, the series of hybrid CuO/ZrO₂/Y₂O₃ compounds were synthesized by self-propagating combustion of Cu₆₀Zr_40-xY_x (x = 0, 5, 10, 15) metallic glasses. The combustion process is self-sustaining and can be efficiently regulated with the ratio of Zr/Y. The synthesized products are irregularly shaped and uniformly dispersed with a particle size of approximately 100 nm–5 μm. The presence of Y₂O₃ in the hybrid oxides stabilizes the ZrO₂ phase and narrows the bandgap energy of as-synthesized powders. For the photocatalytic ability in degrading Methylene Blue (MB), it was demonstrated that the optimal addition of yttrium in the precursor is approximately 10 at% to the formation of best photocatalysts in the current work. Our findings not only provide the new approach to synthesize highly photocatalytic hybrid metal oxides, but also extend the functional applications of amorphous alloys.     

Exploration on the origin of enhanced piezoelectric properties in transition-metal ion doped KNN based lead-free ceramics

In this work, we studied effects of Ni₂O₃ and Co₂O₃ doping on crystal structures, microstructures, orthorhombic and tetragonal phase transition temperature (T_o-t), and electrical properties of [Li_0.06(Na_0.57K_0.43)_0.94][Ta_0.05(Sb_0.06Nb_0.94)_0.95]O₃ (LNKTSN) lead-free ceramics. The experimental results showed that the Ni₂O₃ addition with appropriate amount could shift the T_o-t downwards to the room temperature, and thus obviously increasing the room-temperature piezoelectric coefficient (d₃₃), dielectric coefficient (ε_r) and electromechanical coupling coefficient (k_p) of the LNKTSN ceramics. These were consistent with previous experimental results obtained in Fe₂O₃ doped LNKTSN ceramics. On the contrary, Co³⁺ doping shifted continuously the T_o-t upward and deteriorated obviously piezoelectric properties of LNKTSN ceramics. Fe, Co and Ni had similar ion radii and were expected to result in the same (donor or acceptor) doping effects on electrical properties of LNKTSN ceramics. The different doping effects between Co³⁺ (deterioration) and Ni³⁺ or Fe³⁺ (improvement) on the electrical properties of LNKTSN ceramics suggested that the coexistence of orthorhombic and tetragonal phases at room temperature due to downward shift of T_o-t, rather than ion doping (donor or acceptor doping) effects was the main cause for enhanced room-temperature piezoelectric properties. This conclusion can be extended to all KNN-based materials in general, thus offering principle guide for future development of new lead-free materials with good piezoelectric properties.