Amorphous Si Alloys Research Articles

Solute atom mediated crystallization of amorphous alloys

We propose a new mechanism of crystallization of amorphous alloy which is mediated by additional solute atoms produced by electronic excitation. For a freestanding Pd-19at%Si amorphous alloy film, electron irradiation causes subtle structural change. By contrast, extensive crystallization of Pd-19at%Si amorphous alloy sandwiched by amorphous (a-) SiOx films, i.e., a-SiOx/a-Pd-Si/a-SiOx, occurred by 75 keV and 200 keV electron irradiation. This crystallization was induced by irradiation not only at room temperature but also even at 90 K. It should be emphasized that the crystallization can be realized by 75 keV irradiation at 90 K via the electronic excitation; where both knock-on damage and a possible thermal crystallization can be excluded. A resultant product of the crystallization after electronic excitation (i.e., electron irradiation), hexagonal Pd2Si, differs from that of thermal annealing (orthorhombic Pd3Si). Evidence for decomposition of a-SiOx by electronic excitation contributes essentially to the crystallization of the a-Pd-Si in the composite film has been obtained in this study. Supply of dissociated Si to the a-Pd-Si layer may cause instability of the amorphous phase, which serves as the trigger for the remarkable structural change; i.e., additional solute atom mediated crystallization.

Solidification microstructure manipulation mechanism of hypoeutectic and hypereutectic Al–Si alloys controlled by trace in-situ nano-Fe2B and nano-Fe3Si

In aluminum alloys, the most often utilized cast Al–Si alloy system, the microstructure often needs to be improved by modification and inoculation treatment. This study comprehensively examines the impact of nanocrystals produced by Fe–B–Si amorphous alloys on the solidification behavior and microstructure of hypoeutectic Al–Si7 alloy and hypereutectic Al–Si17 alloy. The nucleation temperature of α-Al is increased and the nucleation of α-Al is easier as well as crystallization platform becomes shorter. For primary Si, the nucleation temperature is decreased and the nucleation is inhibited. The eutectic transformation is promoted and the reaction time is shortened. For α-Al, in situ nano-Fe2B can act as its heterogeneous nucleation sites and promote its nucleation. Meanwhile, the growth of α-Al dendrites is constrained by nearby grains and nanocrystals that do not participate in nucleation, therefore refining the dendrites. Furthermore, nano-Fe2B promotes the eutectic transformation and refines the eutectic microstructure. At the same time, the microstructure of the eutectic groups is refined and the distribution is more dispersed due to the confinement of finer adjacent grains and the hindrance of nanocrystals that do not participate in nucleation.

Influence of Covalent Element B and Si Addition on Magnetocaloric Properties of Gd-Co-Fe-(B,Si) Amorphous Alloys

The effect of covalent element addition on the magnetic and magnetocaloric properties of ferrimagnetic Gd60Co20Fe20 amorphous alloy was studied. Particularly, the co-doping of B and Si promoted the magnetocaloric performance (with a larger magnetic entropy change |ΔSM| at higher working temperature) of the initial Gd60Co20Fe20 amorphous alloy. This is possibly ascribed to the modified magnetic transition behavior. Additionally, the broadened magnetocaloric effect with |ΔSM| of 2.25 J kg−1 K−1 at 222.5 K under a magnetic field change of 0–2 T and high relative cooling power of 396.0 J kg−1 were obtained for (Gd0.6Co0.2Fe0.2)95B2Si3. These properties reveal that the material could be a good candidate as a magnetic refrigerant suitable for active magnetic refrigerators.

Fabrication and optical behavior of AuCuSi amorphous alloy film

Amorphous alloys (AAs) are promising materials due to their unique properties and have been applied in various biomaterial coatings and micro-electro-mechanical systems. However, they have seldom been applied in the optical nano-device. Here, we systematically investigate morphology, microstructure, mechanical and optical properties of an Au–Cu–Si AA and successfully design and fabricate a broadband optical absorber using the Au–Cu–Si AA. Such device achieves an average absorption up to about 95% from 500 to 1500 nm with a thickness less than 300 nm. This is of significance for exploration the feasibility of AAs application in the field of optical nano-devices.

Thermal stability, magnetic and magnetocaloric properties of Gd55Co35M10 (M = Si, Zr and Nb) melt-spun ribbons

The thermal stability, magnetic and magnetocaloric properties of Gd55Co35M10 (M = Si, Zr and Nb) melts-pun ribbons were studied. The relatively high reduced glass transition temperature (Tx1/Tm > 0.60) and low melting point (Tm) resulted in excellent glass forming ability (GFA). The Curie temperatures (TC) of melt-spun amorphous ribbons Gd55Co35M10 for M = Si, Zr and Nb were 166, 148 and 173 K, respectively. For a magnetic field change of 2 T, the values of maximum magnetic entropy change (−ΔSM)max for Gd55Co35Si10, Gd55Co35Zr10 and Gd55Co35Nb10 were found to be 2.86, 4.28 and 4.05 J kg−1K−1, while the refrigeration capacity (RC) values were 154, 274 and 174 J kg–1, respectively. The RCFWHM values of amorphous alloys Gd55Co35M10 (M = Si, Zr and Nb) are comparable to or larger than that of LaFe11.6Si1.4 crystalline alloy. Large values of (−ΔSM)max and RC along with good thermal stability make Gd55Co35M10 (M = Si, Zr and Nb) amorphous alloys be potential materials for magnetic cooling operating in a wide temperature range from 150 to 175 K, e.g., as part of a gas liquefaction process.

Implanted neural network potentials: Application to Li-Si alloys

Modeling the behavior of materials composed of elements with different bonding and electronic structure character for large spatial and temporal scales and over a large compositional range is a challenging problem. Cases in point are amorphous alloys of Si, a prototypical covalent material, and Li, a prototypical metal, which are being considered as anodes for high-energy-density batteries. To address this challenge, we develop a methodology based on neural networks that extends the conventional training approach to incorporate pre-trained parts that capture the character of different components, into the overall network; we refer to this model as the ``implanted neural network'' method. We show that this approach works well for the Si-Li amorphous alloys for a wide range of compositions, giving good results for key quantities like the diffusion coefficients. The method is readily generalizable to more complicated situations that involve two or more different elements.

Effects of ozone nanobubles on superior electric storage for anodically oxidized films of Ti-Ni-Si amorphous alloy ribbons

The effects of nanometer-sized bubbles (NBs) of ozone on a superior electric storage capacitor for anodically oxidized films of Ti-15at.% Ni-15at.% Si amorphous alloys were determined in 0.4M H2SO4 solutions with NBs of oxygen and ozone. The Use of ozone NBs accelerates the formation of oxide films at lower than 10V, resulting in uneven surfaces with cavities of 2–10nm in size. The resulting film shows a nearly vertical line in a Nyquist diagram, rapid increases in the imaginary impedance, and a horizontal line near the −90° phase angle in a Bode diagram, demonstrating evidence for use in an electric distributed constant circuit. Further enhancement of the imaginary impedance for the realization of a superior electric storage capacitor is needed.

Formation and structure-property correlation of new bulk Fe–B–Si–Hf metallic glasses

The present work is devoted to designing new Fe–B–Si–Hf multi-component bulk glassy alloys with good soft magnetic and mechanical properties, and also explored the structure-property correlation in the microalloyed Fe–B–Si amorphous alloy with Hf. Based on the cluster-plus-glue-atom model, a series of Fe–B–Si–Hf alloys with cluster formulas [Si–B2Fe8−xHfx]Fe (x=0–0.6) are produced. Our experiments show that a large glass-forming ability along with a critical glass formation size of 2.5mm is reached at [Si–B2Fe7.7Hf0.3]Fe (in at.%: Fe72.5B16.7Si8.3Hf2.5). This glassy alloy shows a high fracture strength ~4000MPa with a plastic strain of 0.5%, a high saturation magnetization ~1.45T and a low coercive force ~1.5A/m. The monotonic variations of the thermal glass stability, microhardness and the magnetic ordering parameters with the concentration of micro-alloying element Hf, the accessibility of calorimetric glass transition and the glass-forming ability of the Fe–B–Si–Hf glassy alloys are explained in terms of the intra- and inter-atomic cluster correlations in the amorphous structures.

About thermostability of biocompatible Ti–Zr–Ta–Si amorphous alloys

About thermostability of biocompatible Ti–Zr–Ta–Si amorphous alloys

Anodic oxidization of Ti–Ni–Si amorphous alloy ribbons and their capacitive and resistive properties

Amorphous titanium oxide film on Ti–Ni–Si amorphous alloy ribbons was prepared by anodic polarization process in ten kinds of electrolyte solutions. Addition of NH4F in (NH4)2SO4 solution accelerates an increase in current, i.e. formation of soluble Ti-fluoride complexes, resulting in the amorphous titanium oxide layers with nanometer-sized pores. Pore size decreases down to 12nm with decreasing of applied voltage from 30 to 5V. However, parallel capacitance Cp, series capacitance Cs, and RCs constant increase with decrease of pore size from 23 to 18nm and then decrease in pore size region from 18 to 12nm by formation of penetrating tunnels in the layer. It needs further enhancement of RCs for realization of superior electric storage capacitor.

Al–Si アモルファス合金の照射耐性と析出促進過程の計算機実験

Al–Si アモルファス合金の照射耐性と析出促進過程の計算機実験

Fine-Grained Si Alloy Prepared By Melt Spinning and Its Electrochemical Performance for Li Ion Battery Anode

Silicon is candidate as an anode material for high energy Li ion batteries. Among Si materials, Si alloys attract great interests from a viewpoint of high durability and high coulombic efficiency. We found that sputter-deposited some of amorphous Si alloys (ex. Si-Sn-Ti ternary alloy) showed high electrochemical performance from the combinatorial study. In the present study, we synthesized amorphous Si alloys by using a Melt Spinning process and investigated the potential toward volume production as well as the electrochemical performance.To obtain amorphous Si alloys, the ease of mixing between Si and added metals or the chemical mixing enthalpy is an important factor. In the case of Si-Sn-Ti alloy, the mixing enthalpy decreases by increasing Ti/(Ti+Sn) ratio and it is expected for easier preparation of the amorphous alloys at higher Ti/(Ti+Sn) ratios (Fig. 1). The SEM/EPMA elemental mapping of several Si-Sn-Ti alloy indicated that the Si atoms in Ti rich composition alloy (Si/Sn/Ti=60/10/30 wt%) is more uniformly and finely dispersed than Sn rich composition alloy (Fig. 2). The electrochemical performance will be reported in the presentation. This work was partially supported by the project “Research and Development of Lithium ion Battery Application / Research and Development of High Capacity Si-based Alloy Anode” of the New Energy and Industrial Technology (NEDO).

Designing a toxic-element-free Ti-based amorphous alloy with remarkable supercooled liquid region for biomedical application

A series of toxic-element-free Ti–Zr–Ta–Si amorphous alloy ribbons have been successfully prepared by melt-spinning. The differential scanning carlorimetry (DSC), X-ray diffraction analysis, bending test and microhardness test are conducted for studying the thermal and mechanical properties. The results show that the Ti42Zr40Ta3Si15 metallic glass ribbon present excellent ductile behavior by the bending testing, without any fracture cracking after bending over 180 degree. In addition, this amorphous alloy possesses a very high glass transition and crystallization temperature of 799 and 898 K, respectively, as well as a very wide supercooled liquid region of 99 K. This amorphous alloy exhibits promising thermal stability during isothermal annealing at the middle temperature of its supercooled region, with more than 3000 s incubation time for isothermal annealing at 823 K (550 °C). This amorphous alloy also shows much lower value of corrosion current density (2.27 × 10−9 A/m2) than the 304 stainless steel in the 0.3 mass% sodium cloride solutions. This Ti42Zr40Ta3Si15 alloy is believed to be a promising based alloy for fabricating the bulk metallic glass foam by the spacer technique in the application of biomedical implants.

Invited Presentation: Research on Nano-Si/C Nanocomposites as Anode for Li-Ion Batteries

Nanosized silicon has been paid much attention as high capacity anode materials for Li-ion batteries since our first report in 1999. The main challenge for Si anode is the large volume variation during lithium insertion and extraction, which shows a linear dependence on the capacity. Several problems are caused consequently: 1) the total specific capacity of anode has to be limited due to fairly strict restriction on volume variation of batteries during operating, especially for tablet devices. Thus, the advantages of the high theoretical capacity and the volumetric energy density are not as significant as expected. 2) The solid electrolyte interphase (SEI) on the surface of silicon is not as stable as graphite and could be very thick, which consume lithium from cathode and nonaqueous electrolyte irreversibly, leading to low columbic efficiency, capacity fading, increase of internal resistance and gas release. 3) Nanosized silicon particles tend to agglomerate or merge into big pieces and follow further cracking, leading to the formation of the SEI on freshed surface and the loss of electronic contact for active particles. In order to solve above problems, great efforts have been paid and many strategies have been considered. Among them, SiOx, amorphous Si alloy and nano-Si/C composite are more promising for practical application in view of the electrochemical performances and cost. In this report, we will summarize our investigation on the formation of very thick solid electrolyte interphase (SEI) on naked silicon anode at low rate, direct 3Dvisualization of multiple layer structured SEI. The optimization on additive, binder and microstructure for controlling interfacial properties and maintaining the structure stability of nano-Si/C composite anodes will be reported. Acknowledgment: Financial support from CAS project (KJCX2-YW-W26), "Strategic Priority Research Program" of the Chinese Academy of Sciences,Grant No. XDA09010102 and National project 973 (2012CB932900) are appreciated.

Effect of Cu Addition on Soft Magnetic Properties of Fe–Zr–Si Amorphous Alloy

Effect of Cu Addition on Soft Magnetic Properties of Fe–Zr–Si Amorphous Alloy

Effect of germanium on the microstructure and the magnetic properties of Fe–B–Si amorphous alloys

In this work, we present a systematic study on the crystallization kinetics and the magnetic properties of melt-spun Fe80B10Si10−xGex (x=0.0−10.0) amorphous alloys. The activation energy for crystallization, determined by differential scanning calorimetry, displayed a strong dependence on the Ge content, reflecting a deleterious effect on the alloys' thermal stability and their glass forming ability with increasing Ge concentration. On the other hand, the alloys exhibited excellent soft magnetic properties, i.e., high saturation magnetization values (around 1.60T), alongside Curie temperatures of up to 600K. Complementary, for increasing Ge substitution, the ferromagnetic resonance spectra showed a microstructural evolution comprising at least two different magnetic phases corresponding to a majority amorphous matrix and to Fe(Si, Ge) nanocrystallites for x≥7.5.

Ab initio molecular dynamics simulation of lithiation-induced phase-transition of crystalline silicon

We have studied the lithiation-induced amorphization of crystalline silicon by using first-principles calculations. Ab initio simulations show that crystalline silicon amorphizes at a ratio of 0.3 Li atoms per Si atom. Upon amorphization, the tetrahedral Si network suddenly collapses and the average number of Si atoms around Li significantly decreases from 4.6 to 2.6. We suggest the presence of ring structures, made of pure Si atoms and composite Li–Si atoms, as representative local structures of Li–Si amorphous alloy.

Low temperature catalyst enhanced etch process with high etch rate selectivity for amorphous silicon based alloys over single-crystalline silicon based alloys

We present a catalyst enhanced etch process with high etch rates for amorphous Si based alloys (e.g. α-Si, α-Si:C, α-Si:P, α-SiCP) and low etch rates for crystalline Si (e.g. c-Si, c-Si:C, c-Si:P, c-SiCP) with etch rate ratios up to ~200. The addition of a suitable surface catalyst such as Ge (e.g. from GeH4) during HCl based etch processes increases both, the etch rate of amorphous Si alloys and the etch rate selectivity against c-Si alloys. The Ge source dynamically forms a SiGe surface layer during the etch process. Ge penetrates fast into α-Si through diffusion, forming an α-SiGe film with high [Ge] concentration. Ge diffusion into c-Si however is very limited; a rather slow surface-sub-surface exchange reaction (segregation) causes a penetration depth of only one monolayer. Repeated cycles of a selective chemical vapor etch process following a non-selective deposition process enable effective selective epitaxial growth.

Periodically Laser Patterned FeBSi Amorphous Ribbons: Phase Evolution and Mechanical Behavior

AbstractThe properties of amorphous alloys are significantly influenced by structural relaxation and partial/full crystallization induced by thermal annealing of the alloy. In this paper, the phase evolution and mechanical behavior of laser‐patterned FeBSi amorphous alloys are reported. The laser patterning was employed to cause localized thermal effects on the surface of amorphous ribbons. The laser irradiation with a lower fluence (12 J · cm−2) caused significant embrittlement of the alloy due to the structural relaxation. The partial crystallization of an amorphous alloy into α‐Fe(Si) was also observed with laser irradiation using higher laser fluences (15 and 17 J · cm−2). The embrittlement effect due to laser‐irradiation‐induced crystallization was more severe than that due to structural relaxation.

Hydrogen sensing ability of Pd-based amorphous alloys

Pd-based amorphous alloys have been investigated as materials for hydrogen sensor. We prepared thin films of Pd–Cu–Si alloys that are typical Pd-based amorphous alloys by RF magnetron sputtering method. And we examined their H 2 response by measuring the change of electric resistance of thin films exposed in N 2 and H 2 under various conditions. The thin films of Pd–Cu–Si amorphous alloys showed H 2 responses in wide H 2 concentration range from 1% to 100%. They showed negative correlation between the H 2 response and temperature. The 90% response time was under 1 s at 323 K and 373 K, and it is fast enough for the hydrogen sensor of fuel cell vehicles. We also examined the effect of O 2, H 2O and some impurity gases (CO, CH 4 and CO 2) on the H 2 response. We found that O 2 and H 2O do not affect the H 2 response of the alloys, but the impurity gases delayed the H 2 response time of the alloys at 323 K. However, this effect was reduced by raising the experiment temperature from 323 K to 373 K. These results indicate that the Pd–Cu–Si amorphous alloys have excellent H 2 sensing ability.