Argon Annealing Research Articles

Comparative Study of the Physical Properties of Fine-Crystalline Mechanoactivated and Sol–Gel Samples of YBa2Cu3O6.92 High-Temperature Superconductors

A technique based on the sol–gel technology is developed for the synthesis of fine-crystalline YBa2Cu3O6.92 (Tc = 91.5 K) high-temperature superconductors (HTSCs), including the step-by-step annealing of the samples in tablet form at the annealing temperature Tann = 750°C in an argon atmosphere. Having the same microstructure with the average crystallite size $$\left\langle D \right\rangle $$ = 200 nm, the sol–gel samples exhibit different magnetic and thermodynamic properties, depending on the number of anneals in argon. Comparison of the characteristics for sol–gel and mechanoactivated fine-crystalline samples of the same composition made it possible to make an assumption about the implementation of incomplete atomic ordering in sol–gel samples at the first stage of annealing with an increase in the degree of structural ordering during the next two stages. This may be the main reason for the change in the physical characteristics of the HTSC sol–gel samples structured at the nanoscale level, depending on the number of annealings in an argon atmosphere.

Modified coal char materials with high rate performance for battery applications

Global energy consumption has been rising since the early 2000s, and most of the energy supply still comes from burning fossil fuels. Considering the detrimental environmental impacts of fossil fuels, such as CO2 emissions, it is crucial to develop clean energy technologies, such as storage devices that can advance long-term reversible and sustainable energy resources. In this work, we demonstrate the direct use of coal char in anodes tailored for both lithium-ion and sodium-ion batteries. The findings show that acid treatment followed by high-temperature argon annealing results in coal char particles with the desired porous structure, surface properties, and turbostratic nanodomains that deliver high reversible capacity and maintain good electrochemical performance at high rates up to 10C. Long-term cycling stability for 500 cycles can be achieved in cells comprising NMC cathodes at 1C with 73.2% capacity retention. This study sheds light on potential energy storage use cases for coal char outside its traditional utilization.

Hybrid Anodes of Lithium Titanium Oxide and Carbon Onions for Lithium‐Ion and Sodium‐Ion Energy Storage

This study demonstrates the hybridization of Li4Ti5O12 (LTO) with different types of carbon onions synthesized from nanodiamonds. The carbon onions mixed with a Li4Ti5Ox precursor for sol–gel synthesis. These hybrid materials are tested as anodes for both lithium‐ion battery (LIB) and sodium‐ion battery (SIB). Electrochemical characterization for LIB application is carried out using 1 m LiPF6 in a 1:1 (by volume) ethylene carbonate and dimethyl carbonate as the electrolyte. For lithium‐ion intercalation, LTO hybridized with carbon onions from the inert‐gas route achieves an excellent electrochemical performance of 188 mAh g−1 at 10 mA g−1, which maintains 100 mAh g−1 at 1 A g−1 and has a cycling stability of 96% of initial capacity after 400 cycles, thereby outperforming both neat LTO and LTO with onions obtained via vacuum treatment. The performance of the best‐performing hybrid material (LTO with carbon onions from argon annealing) in an SIB is tested, using 1 m NaClO4 in ethylene/dimethyl/fluoroethylene carbonate (19:19:2 by mass) as the electrolyte. A maximum capacity of 102 mAh g−1 for the SIB system is obtained, with a capacity retention of 96% after 500 cycles.

Gradient crystalline coating on a biomedical TiNi alloy prepared by magnetron sputtering and annealing

A gradient crystalline coating was created on a TiNi substrate by magnetron sputtering of a three-layer (Ti–Ni–Ti) nanolaminate with a layer thickness of 60–100 nm and subsequent argon annealing of the sample at 900°С. The coating was synthesized to study the features of its structure formation and phase composition, created by reaction synthesis to improve the corrosion resistance of TiNi implants. TEM, EDS, XRD, and EBSD methods showed that annealing initiated solid-state reaction processes between the nanolaminate layers and the substrate, as a result of which a three-layer amorphous nanolaminate transformed into a gradient two-layer coating bonded with the modified substrate through the diffusion zone. The diffusion growth of the nanolaminate layers during formation of the gradient coating was found to increase 10–20-fold. A comparative assessment of the substrate and coating has shown that oxide and oxycarbonitride layers in the coating effectively improve its biocompatibility.

CuO/Cu2O nanoflake/nanowire heterostructure photocathode with enhanced surface area for photoelectrochemical solar energy conversion

Branched heterostructures play an important role in solar energy harvesting through an efficient separation of photogenerated charges as well as enhancement in catalytic reaction sites. Here we report the CuO/Cu2O nanoflake/nanowire heterostructure with the enhanced surface area directly grown on Cu foil through scalable process steps ensuring easy large-scale fabrication. A hydrothermal treatment on Cu2O nanowires, obtained through anodization of Cu foil and argon annealing, leads to a partial conversion of Cu2O into CuO nanoflakes resulting in a heterostructure with a highly enhanced surface area facilitating a higher semiconductor-electrolyte interface. Brief annealing at 250 °C for 5 min on the sample results in a photocurrent density of −1.9 mA/cm2 (at −0.3 V vs. Ag/AgCl under AM1.5G illumination), which is about an order of magnitude higher than the Cu2O nanowires. Further, CuO/Cu2O shell/core heterostructure is fabricated through direct annealing of Cu2O nanowires to understand the effect of highly enhanced surface area over the charge separation due to heterostructure. A comparative study on both heterostructures by photocurrent, electrochemical impedance, and Mott Schottky measurements reveals that although CuO/Cu2O heterojunction helps in charge separation, however, the enhanced surface area obtained through nanoflake morphology has a dominating effect in deciding high photocurrent density.

Investigation of metal elements diffusion in Cr2O3 film and its effects on mechanical properties

Cr2O3 films were deposited on Inconel718 alloy substrate by using an arc ion planting system, and then annealed at 1000 °C in different atmospheres. The diffusion behavior of metallic elements from the substrate in different atmospheres and its effect on mechanical properties of the film were researched. The results show that Ti and Cr elements in the substrate would diffuse to Cr2O3 film surface when the films are annealed in argon, nitrogen and oxygen. A diffusion layer comprised of Cr and TiO2, which could attribute to the residual oxygen in furnace, formed on the surface of the argon-annealed film. In nitrogen atmosphere, Ti and Cr elements were nitrided to form Cr2N and TiN, and then they packed to form a diffusion layer on the film surface. Especially, a mesh-like heave comprised of Cr2O3 and Cr2Ti7O17 formed on the surface of the oxygen-annealed film. However, there is no element diffusion detected in the vacuum-annealed film, while lots of cracks formed on the film surface. Annealing in different atmospheres could improve the adherence strength obviously. The vacuum-annealed film maintains a high hardness, and possesses excellent tribological properties degradation. After argon and nitrogen annealing, the loose diffusion layers result in the hardness decreasing and tribological properties degradation. For the oxygen-annealed film, internal diffusion of oxygen decreases the surface hardness obviously. Moreover, although Cr2Ti7O17 lubricant formed on film surface, the loose surface structure deteriorates the tribological properties.

Strong edge-induced ferromagnetism in sputtered MoS2 film treated by post-annealing

We report edge-induced ferromagnetism in a sputtered molybdenum disulfide (MoS2) film having a long whole-edge length, with the effects of crystallinity improvement including edge reconstruction by sulfur vapor and argon annealing. Strong edge-induced ferromagnetism was observed by annealing, and its saturation magnetization of 13–26 emu/cc was larger than that of a chemical-vapor deposition sample with edge-induced ferromagnetism, as reported previously. Whereas both the annealing steps improved the crystallinity of the sputtered MoS2 film, argon annealing significantly enhanced the ferromagnetism. We conclude that the difference of the ferromagnetism enhancement between the sulfur and argon annealing steps is attributed to the edge reconstruction shape, which depends on the sulfur chemical potential.

Argon Annealing and Oxygen Purity Affect Structural and Critical Parameters of YBCO Copper Oxide System

We report here the effects of argon annealing on the structural and critical parameters of oxygenated copper oxide system with different oxygen purities (Hp 99.99% and Lp 93%). It is found that the structure of the samples maintains orthorhombic single phase independent of both oxygen purity and annealing. The mean field temperature Tcmf is increased by annealing from 92 to 94 K for Lp sample, but it is decreased from 93 to 90 K for Hp sample. Similar behavior is obtained for crossover temperatures To. Further, the coherence length and interlayer coupling are decreased by annealing for both samples, and their values are higher for Lp samples than those for Hp samples. The excess conductivity analysis reveals two different exponents corresponding to crossover temperature for each plot: The first exponent is obtained in the normal field region at a temperature range of ln e (0 ≥ ln e ≥ − 2), and their values are 1.50, 1.53, 1.62 and 1.47 for both samples, in which the order parameter dimensionality (OPD) is one dimension, while the second exponent is obtained in the mean field region at a temperature range of ln e (− 2 ≥ ln e ≥ − 4), and their values are 0.39, 0.59, 0.56 and 0.41 for both samples, in which the OPD is 3D. Although the critical temperatures are decreased by annealing for both samples, the critical fields and critical currents are increased by annealing for both samples and their values are higher for Hp sample than those for Lp sample. Our results are discussed in terms of oxygen vacancies and concentration of carriers which are produced by annealing and oxygen purity for the considered samples.

Effects of isovalent substitutions and heat treatment on structural and superconducting properties of high-critical temperature superconductors

We have investigated the structural and superconducting properties Y0.5Ln0.5SrBaCu3O6+z of compounds (with Ln = rare earth = Eu, Sm and Nd) by X-ray diffraction with Rietveld refinement, resistivity and AC magnetic susceptibility measurements. Each sample was subject to two types of heat treatment: oxygen annealing [O] and argon annealing followed by oxygen annealing [AO]. For each ionic radius r of Ln, the [AO] treatment increases the orthorhombicity ε, Tc from 82.1 K [O] to 82.47 K [AO] for Y0.5Eu0.5SrBaCu3O6+z, from 80.98 K [O] to 82.02 K [AO] for Y0.5Sm0.5SrBaCu3O6+z and from 78.86 K [O] to 80.54 K [AO] for Y0.5Nd0.5SrBaCu3O6+z and decrease the distance d[Cu(1)-Sr/Ba]. For each r, in the normal state, the [AO] treatment reduced the linear resistivity parameters indicating a diminution of the interaction of carrier charges with phonons. There was a remarkable improvement in the shielding effect S (Amplitude of χ′(T)) in the case of the samples [AO] at all T < Tc and for any applied field Hdc. For each r and heat treatment, S(r) decreases when Hdc and the temperature increase. Remarkable correlations were observed. A combination of several factors such as decrease in d[Cu(1)-(Sr/Ba)]; increase in cationic and chain oxygen ordering; psh and in-phase purity for the [AO] samples may account for the observed data.

Annihilating Pores in the Desired Layer of a Porous Silicon Bilayer with Different Porosities for Layer Transfer

A silicon layer that is tens of micrometers thick on a handle substrate is desired for applications involving power devices, microelectromechanical systems (MEMS), highly efficient silicon solar cells (<50 µm), etc. In general, if the initial silicon layer obtained from the layer transfer process using the etch-stop or ion-cut techniques, which may provide very accurate thickness control, is too thin, then additional epitaxial growth is required to increase the thickness of the silicon layer. However, epitaxial growth under strict predeposition conditions is a time-consuming and expensive process. On the other hand, producing porous silicon via anodization in a hydrofluoric acid solution offers an efficient way to control the dimensions of the generated pores directly on the nano- or macroscale via the current density. When sintering the porous layer via high-temperature argon annealing, the porosity of the porous layer determines whether this porous layer can serve as a device layer or a separation layer. In addition, it is clearly easier to create a transferred layer ten of micrometers thick via anodization than by ion implantation and/or epitaxial deposition.

Evaporation-induced self-assembly of C60 on SrTiO3(110) reconstructed surfaces

SrTiO3(110) polar surface was treated with repeated cycles of argon ion sputtering and annealing. Three reconstructions, namely (4 × 1), (2 × 8), and (6 × 8), were identified with subsequent scanning tunneling microscopy measurements. Using the evaporation-induced self-assembly method, C60 molecules deposited onto these reconstruction surfaces demonstrated a quasi-close packing growth mode with substantial differences. Influence factors are revealed from the investigation of these differences, such as the substrate structure and topography as well as the intermolecular and molecular-substrate interactions. Our study emphasizes the feasibility of controllable molecular self-assembly through choosing surface reconstructions.

Annealing induced defects in ZnO nanostructures

ZnO nanostructures that do not exhibit defect-related PL emissions in the as-synthesized form have been exposed to annealing in air and argon environments at 500 °C for 2 h. That resulted in the appearance of some intrinsic defects in ZnO nanostructures. Morphology of the nanorods has also been affected by argon annealing. An intense luminescence peak appears in the PL spectra centred at 502 nm in samples annealed in argon. In contrast, the orange/red emission dominates the PL spectra of oxygen annealed nanostructures.

Surface Reconstructions of SrTiO3(110) Calibrated with STM and LEED

On the SrTiO3(110) surface, a series of reconstructions related to the O‐layer are created via repeated cycles of argon ion sputtering and annealing. These reconstructions, including the (2 × 8), (6 × 8), (1 × 10), and (4 × 4) structures, are studied with scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). Typical structural units in the reconstructed surfaces are identified. Meanwhile, the combined investigations with STM and LEED eliminates the interference that arises from the coexisting multiple structures, and clarifies the otherwise vague understanding of the (1 × 10) and (4 × 4) structures. Such surface reconstructions provide a potential platform for developing molecular ordering and photocatalytic applications.

(Invited) Oxygen Evolution and Reduction on La0.5Sr0.5Co0.8Fe0.2O3- Δ Perovskites with Tunable Structural Features

Oxygen evolution (OER) and oxygen reduction (ORR) reactions are the fundamental processes occurring at the air electrode of metal-air batteries and fuel cells. Presently, large overpotentials are required for these reactions to occur at an appreciable rate. Therefore, development of catalysts capable of reducing the activation losses at the oxygen electrode is highly desirable. Perovskite oxides are one of the most interesting low-cost electrocatalysts for air electrodes, because they can adopt a wide variety of chemical compositions and crystal structures, thereby enabling correlative studies between the electrocatalytic activity and their electronic structure (1, 2). Recently, we reported a possible relation between the cell volume of La0.6Sr0.4Fe0.6Mn0.4O3-δ perovskites and their ORR activity and selectivity (2 e- vs ‘’2+2’’ e- pathway), with lower cell volumes corresponding to higher number of exchanged electrons (3). It was also reported by others that some structural features in the perovskite influence the activity of these mixed oxides for both ORR and OER (4-6). In this presentation, we will discuss our recent studies on the ORR and OER activity of a series of La0.5Sr0.5Co0.8Fe0.2O3- δ electrocatalysts prepared by solution combustion synthesis. The choice of diverse experimental conditions allowed us to tune oxygen deficiency, microstrain and other structural properties. As exemplified in Figure 1, for one of the investigated electrocatalysts, thermal annealing in argon reduces the bond angle between the oxygen atom and the two B-site metal cations, resulting in a higher electrocatalytic activity for both OER and ORR. In addition to structure–electrocatalytic activity correlations, we will complement our comparative studies with analytical scanning electron microscopy and spatially resolved elemental mapping of selected electrode surfaces subjected to accelerated stability tests. Figure 1. Crystal structures of La0.5Sr0.5Co0.8Fe0.2O3- δ prepared from solution combustion using citrate as fuel and thermal annealed in Ar (top right) and in Air (bottom left). Differences in the Co-O-Co bond angle are highlighted. Oxygen evolution (OER, top left) and oxygen reduction (ORR, bottom right) polarization curves recorded in 0.1 M KOH at 5 mVs-1 and 1600 rpm.

ZIF-67 with Argon annealing treatment for visible light responsive degradation of organic dyes in a wide pH range

Abstract Zeolite imidazolate frameworks (ZIFs) are a novel kind of zeolite materials with regular porous network structures, belonging to mental-organic frameworks (MOFs). Thanks to their high porosity and large specific surface area, ZIFs could have potential applications in the field of photocatalysis. In this paper, visible light responsive photocatalyst of ZIF-67 was synthesized by a one-step hydrothermal method under a mild condition. We explored three organic dyes in aqueous solutions were degraded under visible light irradiation. And corresponding photocatalytic performances of ZIF-67 with controllable synthetic conditions were evaluated systematically. It was found that ZIF-67(9 h) had the highest degradation efficiency. Besides, the ZIF-67(9 h) were heated in Ar can maintain their crystal structure and microporous form, but exposed more sites to improve photocatalytic activity with partial bond breakage. More than 75% methyl orange (MO), 85% methyl blue (MB) and 54% Rhodamine B (RhB) can be degraded with a 0.5 g L−1 ZIF-67(9 h)(Ar) under visible light irradiation. Moreover, the ZIF-67(9 h)(Ar) demonstrates a strong pH changing tolerance in both acid and alkaline aqueous solutions, the degradations can be well performed in a wide pH range from 3.0 to 11.0.

Robust carbon nanotube composite fibers: Strong resistivities to protonation, oxidation, and ultrasonication

Carbon nanotube (CNT) fibers have great potential in the field of high performance fibers. However, poor inter-tube coupling between bundles resulting in low structural and mechanical stability under strong acid, ultrasonication and high-temperature oxidation limited the practical applications of CNT fibers in extreme environment. Here we report the preparation of robust carbon nanotube/carbon (CNT/C) composite fibers with highly aligned and dense structure utilizing an ultrafast Joule heating tension-annealing approach. CNT fibers prepared by floating catalytic chemical vapor deposition were infiltrated by polyacrylonitrile (PAN) solution, followed by programable tension annealing in argon for 10 s. Such a short process carbonized infiltrated PAN, resulting in the formation of CNT/C fibers within which CNTs were bonded by pyrolytic carbon. Due to the carbon-bonded structure, the composite fibers exhibited improved resistivity against structure damages when exposed to strong acid, ultrasonication, and high-temperature oxidation. Comparing with the pristine CNT fibers, such composite fibers showed 320% improvement in breaking load, 354% increase in strength (2.3 GPa) and 667% increase in modulus (60 GPa), respectively. Moreover, such composite fibers have low densities (1.48 g/cm3) and excellent flexibility and toughness. These combined features could broaden the application of the CNT/C composite fibers in many areas.

Gram scale synthesis of monoclinic VO2 microcrystals by hydrothermal and argon annealing treatment

We report gram scale synthesis of 100% phase fraction of VO2 (M) monoclinic in powder form with reversible phase transition by combining hydrothermal method and Ar annealing at high temperature. Optimization of single phase VO2 (M) growth and its phase transition characteristics have been analysed systematically by varying growth parameters such as time, synthesis temperature and post growth annealing conditions. Argon annealing of hydrothermally grown VO2 powders at 800 °C found to play key role in obtaining VO2 (M) phase in gram scale with characteristic phase transition temperature of 68 °C. In-situ TEM has been performed to investigate the microstructure and phase change across the annealing temperature. Detailed characterizations have been carried out to correlate the phases, microstructure and transition temperature of VO2 with respect to growth parameters.

Oxygen Vacancies Allow Tuning the Work Function of Vanadium Dioxide

AbstractThe evolution of electron valence bands, core levels, and work function of vanadium dioxide (VO2) thin films upon argon ion sputtering and annealing, as commonly done to obtain atomically clean surfaces, with and without low‐pressure oxygen atmosphere during annealing is investigated by ultraviolet and X‐ray photoemission spectroscopy. Both sputtering and annealing in vacuum introduce lower oxidation state V species, leading to an increased intensity of V 3d derived bands close to the Fermi level. Such oxygen deficient surfaces exhibit low work function values as low as 4.40 eV. Annealing the sample under low‐pressure oxygen atmosphere (few times 10−4 mbar partial O2 pressure) results in stoichiometric VO2 surfaces with a high work function of up to 6.70 eV. Moreover, the work function of the VO2 can be continuously tuned between the high and low limits by adjusting the atomic ratio of oxygen and vanadium at the surface. Appropriately adjusted VO2 can thus be employed as moderate electron as well as superior hole injecting electrode material in electronic and optoelectronic devices.

ФАЗОВЫE ПРЕВРАЩЕНИЯ ПОРОШКОВОГО СПЛАВА Co66Cr28Mo6 ПРИ СЕЛЕКТИВНОМ ЛАЗЕРНОМ ПЛАВЛЕНИИ И ВЫСОКОТЕМПЕРАТУРНЫХ ОТЖИГАХ

В работе исследованы фазовый состав и его изменения при температурных отжигах порошкового сплава Co66Cr28Mo6 и зубной коронки, полученной из того же порошка с помощью 3D- печати методом селективного лазерного плавления.&#x0D; Рентгенодифракционные исследования исходного порошка Co66Cr28Mo6 и неотожженной коронки показали, что лазерная печать полностью переводит двухфазный порошок (90 % ГЦК +10 % ГПУ) в однофазный твердый раствор ГЦК на основе высокотемпературной гранецентрированной кубической модификации b-Со с заметным увеличением межплоскостных расстояний по сравнению с b-Со.&#x0D; &#x0D; Работа выполнена при поддержке Минобрнауки России в рамках государственного задания ВУЗам в сфере научной деятельности на 2017-2019 годы. Проекты № 3.6263.2017/ВУ и № 16.8158.2017/8.9.&#x0D;

Chromogenic MoO3 thin films: thermo-, photo-, and electrochromic response to working pressure variation in rf reactive magnetron sputtering

The thermochromic, photochromic, and electrochromic properties of molybdenum trioxide (MoO3) thin films were studied. MoO3 thin films were deposited by rf reactive magnetron sputtering and the influence of deposition parameters, i.e. O2/Ar gas ratio and working pressure, on the chromogenic properties was investigated. Thermochromism was induced by annealing the samples in either air or argon in the range 23–300 °C for 2 h. We found that the highest response was obtained for samples grown at 5.3 × 10−1 Pa, although films annealed in air showed a maximum coloration around 250 °C that became bleached above this temperature. As for the annealing in argon, the thermochromic effect increased even at 300 °C. By exposing samples to UV irradiation in air, photochromism could be induced for different intervals ranging from 0 to 3 h. The highest photochromic response was obtained for samples deposited at 1.3 Pa. Cyclic voltammetry for 20 cycles in a 1 M LiClO4 in propylene carbonate solution, inside a glovebox filled with argon, was used to evaluate the electrochromic response. Samples that showed optimum electrochromic response were deposited at 1.6 Pa. These results are explained in terms of the optical, structural, surface chemical composition, and vibrational modes.