Amorphous Crystalline Research Articles

A magnetoelectric nanocomposite based on two dimensional Cr2O3 and CoFe2O4

Nanocomposites consisting of 2 dimensional (2D) amorphous Cr2O3-CoFe2O4 and crystalline 2D Cr2O3-CoFe2O4 were prepared and the room temperature magnetoelectric coupling was studied. This study also investigated the effect of crystalline 2D Cr2O3 on the exchange bias induced magnetoelectric coupling in the composites. Evidence for the exchange bias in the composites is obtained from field cooling - zero field cooling (FC-ZFC) measurements. The 2D crystalline Cr2O3 composite exhibits high magnetoelectric coupling coefficient at room temperature when compared to bulk composite for the corresponding Cr2O3. These composites augurs well for applications especially for energy harvesting and spintronics.

In-situ synthesis of mixed-phase carbon material using simple pyrolysis method for high-performance supercapacitor

We report a novel mixed phase carbon material that contains both amorphous as well as crystalline phases for supercapacitor application. The amorphous carbon and crystalline carbon nanotubes are present in this mixed phase material which is prepared using an in-situ process in a simple and cost-effective method. In supercapacitor devices, better performance is achievable when there is good surface accessibility in electrode material and decent ion mobility. Amorphous material provides good surface accessibility whereas crystalline offer better electrons and ions mobility. Hence, the prepared mixed-phase carbon material has advantages for the supercapacitor. The material is tested for supercapacitor application where the electrochemical performances are obtained using Cyclic voltammetry (CV), Galvanostatic charge-discharge (GCD) and Electrochemical impedance spectroscopy (EIS) measurements. The mixed-phase electrode results in a specific capacitance of 37.54 F g−1 at 1 A g−1 and 36.80 F g−1 at 5 mV/s. The storage performance of this material is further increased by integrating it with a few layers of graphene. The prepared composite with a 30 wt. percentage of few-layer graphene gives the better supercapacitive properties and the maximum capacitance achieved by the composite is 282.52 F g−1 at 1 A g−1 and 281.84 F g−1 at 5 mV/s. The fabricated mixed-phase composite (30 wt% of few-layer graphene) offers excellent cyclic stability and 93 % capacitance is retained even after 10,000 cycles at 1 A g−1. These outcomes suggest the mixed-phase composite electrode could be the best choice for high performance supercapacitor applications.

Compositional analysis of oxide-embedded III–V nanostructures

Nanowire growth enables creation of embedded heterostructures, where one material is completely surrounded by another. Through materials-selective post-growth oxidation it is also possible to combine amorphous oxides and crystalline, e.g. III–V materials. Such oxide-embedded structures pose a challenge for compositional characterization through transmission electron microscopy since the materials will overlap in projection. Furthermore, materials electrically isolated by an embedding oxide are more sensitive to electron beam-induced alterations. Methods that can directly isolate the embedded material, preferably at reduced electron doses, will be required in this situation. Here, we analyse the performance of two such techniques—local lattice parameter measurements from high resolution micrographs and bulk plasmon energy measurements from electron energy loss spectra—by applying them to analyse InP-AlInP segments embedded in amorphous aluminium oxide. We demonstrate the complementarity of the two methods, which show an overall excellent agreement. However, in regions with residual strain, which we analyse through molecular dynamics simulations, the two techniques diverge from the true value in opposite directions.

Flexible and tough zirconia-based nanofibrous membranes for thermal insulation

Ceramic nanofibrous materials with both good flexibility and robust mechanical properties are highly desired for harsh environment applications. Herein, we present ZrO2–SiO2 nanofibrous membranes by combining sol-gel and electrospinning methods and introducing amorphous components into crystalline zirconia. The fluffy stacking morphology structure and the mixture of amorphous SiO2 and crystalline ZrO2 contribute to the excellent mechanical properties with high flexibility, large tensile strain, and significantly improved fracture toughness (0.32 MJ m−3), which is rarely reported in ceramic nanofibrous materials at present. Furthermore, the resulting membranes show good fatigue resistance during 500 buckling cycles and maintain 90% of the original stress. Combined with the high-temperature resistance and low thermal conductivity (0.034 W m−1 K−1), the robust mechanical performances facilitate the ceramic nanofibrous membranes a promising candidate for the applications in harsh environments.

Fragile‐to‐Strong Transition in Phase‐Change Material Ge3Sb6Te5

AbstractChalcogenide phase‐change materials combine a remarkable set of properties that makes them promising candidates for future non‐volatile memory applications. Binary data storage exploits the high contrast in electrical and optical properties between the covalent amorphous and metavalent crystalline phase. Here the authors perform an analysis of the liquid phase kinetics of the phase‐change material Ge3Sb6Te5, which is the key to ultrafast switching speeds. By employing four experimental techniques, the viscosity is measured over sixteen orders of magnitude despite its propensity for fast crystallization. These measurements reveal that the liquid undergoes a transition in viscosity–temperature dependence associated with a liquid–liquid phase transition. The system exhibits a shallow viscosity change with temperature near the glass transition which stabilizes the memory cells in the amorphous state and which limits the severity of relaxation processes. Meanwhile, when heated during the writing process, the fragility increases to more than double, causing the viscosity to drop rapidly enabling a nanosecond crystallization speed. This change in viscosity–temperature dependence is highly unusual among glass forming liquids and is reminiscent of the behavior of water. This viscosity transition is also key to the technological success of phase‐change materials for computer memory applications.

Study of novel synthesized Gum-Arabic-Ammonium thiocyanate based polymer electrolyte for testing electrical properties and electrochemical sensing

The novel Gum Arabic-Ammonium Thiocyanate-based solid polymer electrolyte was synthesized using the solvent casting technique, which involved mixing Gum Arabic (GA) with ammonium thiocyanate (NH4SCN) in the presence of water. The different concentrations of NH4SCN admixture with the GA synthesized have been characterized by X-ray Diffraction (XRD), Fourier Transform Infrared (FT-IR), dielectric, and ionic conductivity studies. The structural behavior (amorphous or semi crystalline, vibrational shifts), dielectric constant & dielectric loss behavior, relaxation time, and ionic conductivity response of various NH4SCN concentrations admixture on the GA have shown significant variation and the results are presented in detail. To make the batteries have a better ionic conductivity, the synthesized GA-NH4SCN sample, two cathode materials (MnO2(Cell I) and PbO2 + V2O5(Cell II)), and one anode material (Zn/ZnSO4·7H2O) have been taken for examining the open circuit voltage and discharge characteristics at different resistances as a function of time, and their results were discussed in detail.

Switchable Phase Transition from Crystalline to Amorphous States of Cadmium Sulfate Octahydrate Single Crystals by Shock Waves

Even slight changes occurring in the lattice positions of solid materials enforced by the external forces may give rise to remarkable results in the crystallographic nature. The materials which undergo phase‐change without modifying their overall chemistry are the prominent candidates to be the driving forces for the applications involving phase transitions. In the present context, the authors present and demonstrate the switchable phase transition occurring between crystalline and amorphous nature of cadmium sulfate octahydrate single crystals (3CdSO4·8H2O) impacted by shock waves with which the transition is authenticated via diffraction, vibrational and optical spectroscopic techniques such as powder X‐ray diffractometry, Raman and UV‐Vis spectral analyses. Based on the results attained from diffraction and spectroscopic analyses, it is observed that the switchable phase transition sequence is crystalline–crystalline–amorphous–crystalline–crystalline with respect to the control, one, two, three, and four shock‐wave‐loaded conditions, respectively. Due to the outstanding switching behavior, the title material is strongly suggested for the applications of molecular switching and optical data storage systems.

Plasma-enhanced elemental enrichment of liquid metal interfaces: Towards realization of GaS nanodomains in two-dimensional Ga2O3

Atomic-scale incorporation of elemental impurities into two-dimensional (2D) semiconductors is a significant step towards tailoring novel 2D materials in functional electronics. Here, the elemental functionalization of 2D surface oxide films of gallium-indium (EGaIn) liquid alloy is achieved through plasma-enhanced metal-catalyst-assisted dissociation of H2S on EGaIn surface. The electronic properties of EGaIn/2D Ga2O3 heterointerfaces were considerably altered after surface functionalization. The in-situ material characterizations confirmed the successful dissociation of H2S gas on the surface of EGaIn alloy. Furthermore, material characterizations showed the growth of crystalline domains of GaS inside of Ga2O3 amorphous structure. Consequently, lateral 2D heterointerfaces were developed between amorphous Ga2O3 and crystalline GaS. Comprehensive analysis demonstrated that the combined mechanisms of valence change and electrochemical metallization were engaged in bipolar resistive switching dynamics of functionalized 2D oxide films The considerable increase of high-resistance switching current from 10−15 A to 10−9 A was observed after functionalization of 2D heterointerfaces. The comprehensive studies by conductive atomic force microscopy (c-AFM) demonstrated the surface perturbation of liquid metal interfaces, caused by electrochemical metallization process during resistive switching. The voltage-dependent self-rectifying characteristics and non-Ohmic to Ohmic transition were additionally observed owning to the development of heterointerfaces between the liquid metal and 2D Ga2O3 film.

Formation of Bright White Plasma Electrolytic Oxidation Films with a Uniform Maze-Like Structure by Anodizing Aluminum in Ammonium Tetraborate Solutions

Bright white plasma electrolytic oxidation (PEO) films with uniform maze-like structures were obtained by anodizing Al in an ammonium tetraborate solution. High-purity Al plates were galvanostatically anodized in 0.3–2.4 M ammonium tetraborate solutions at 303–343 K and 10–100 Am−2. A PEO film consisting of an outer porous layer consisting of amorphous alumina and crystalline alumina with α-and γ-phases and an inner amorphous barrier alumina layer was obtained on the Al surface. An extremely uneven PEO film with various pore sizes and many cracks was formed in a 0.3 M ammonium tetraborate solution, whereas a relatively uniform porous PEO film with similar pore sizes was obtained in 0.9–2.4 M solutions. This difference in the PEO film morphology was due to the plasma generation behavior while anodizing. The lightness of the PEO film increased with increasing anodizing time and PEO film thickness; thus, a bright white PEO film measuring 87.5 in lightness (L*) was formed on the Al surface. The water wettability of the PEO film exhibited weak hydrophilicity. Moreover, a superhydrophobic PEO film with a contact angle of 154° was easily fabricated by self-assembled monolayer modification. Similar bright white PEO coatings were successfully fabricated on various industrial alloys.

Vanadium recovery from spent iron sorbent used for the treatment of mining-influenced water

Vanadium was recovered successfully from spent iron sorbent (ferric oxyhydroxide, CFH-12) using a two-step process including alkaline leaching and precipitation with CaCl2. The spent CFH-12 was collected from a field study in which a filter system was used to remove vanadium from mining-influenced water (referred to as MIW-treated CFH-12). Fresh CFH-12 was treated with synthetic vanadium solution (SVS-treated CFH-12) to compare the recovery process with the field study. First, a full factorial design was performed to optimize the precipitation process using synthetic leaching solution. The optimal conditions were found to be two times the theoretical dosage of CaCl2, a precipitation temperature of 60°C, and a precipitation pH of 12.7. Vanadium desorption from the spent sorbents was conducted using 1 M NaOH, a contact time of 30 minutes and a CFH-12 solid-to-liquid ratio of 0.15 kg/L. The results revealed that vanadium could be efficiently precipitated from the leaching solution of MIW-treated CFH-12 and SVS-treated CFH-12. A higher dosage of CaCl2 was required to recover vanadium from MIW-treated CFH-12 due to the complexity of the leaching solution, which resulted in a lower vanadium content in the product. XRD analysis showed that the product recovered from SVS-treated CFH-12 mainly contained Ca5(VO4)3OH and a small amount of CaCO3. TEM images revealed that the calcium vanadate hydroxide particles were round in shape, about 0.2–0.4 µm in size and formed aggregates. The product recovered from MIW-treated CFH-12 contained amorphous calcium vanadate and crystalline Ca(OH)2. XPS analysis confirmed that vanadium existed as V5+ in all of the recovered products.

Rational nanopositioning of homogeneous amorphous phase on crystalline tungsten oxide for boosting solar water oxidation

Surface defect engineering of metal oxide is a promising approach for efficient photoelectrochemical (PEC) water splitting. However, the role of an amorphous overlayer with disordered crystallinity is debated, as it can induce crucial charge traps and undesired charge recombination. Herein, we demonstrate a rationally designed nanopositioning of a homogenous amorphous phase on the surface of crystalline metal oxide via a facile surface defect engineering to strongly enhance photoelectrochemical (PEC) water oxidation. The nanopositioning of the localized amorphous phase generates crystalline–amorphous (CA) homogeneous boundaries on the crystalline metal oxide. The amorphous phase provides the increased active adsorption sites, while the exposed crystalline phase promotes the charge transport. The results of analysis conducted on the rationally designed model case of crystalline–amorphous tungsten oxide (CA-WO3) photoanode confirm a 2.5-fold higher photocurrent density (3.34 mA cm−2) at 1.23 V versus reversible hydrogen electrode under 1 sun illumination compared with the bare crystalline WO3 (1.35 mA cm−2). With the rationally designed surface defects, we achieve the high-efficiency charge separation and catalytic kinetics. This work provides guidance for the rational design of surface defects on crystalline metal oxides for boosting the PEC water splitting.

Hollow nanospheres comprising amorphous NiMoS4 and crystalline NiS2 for all-solid-state supercapacitors

Phase engineering offers a promising strategy to tailor the physiochemical properties to further improve their electrochemical performance toward energy storage. However, it remains a challenge to fabricate well-defined amorphous/crystalline hetero-phase metal sulfides with high-density heterointerfaces. Herein, the synthesis of hetero-phase combination of amorphous NiMoS4 and crystalline NiS2 that possesses hollow nanosphere structure decorated by nanosheets (named as H-NiMoS4/NiS2) is reported. Benefiting from the construction of the hollow nanosphere coated by nanosheets, amorphous/crystalline hetero-phase junction, and strong Ni-S hybridization, H-NiMoS4/NiS2 electrode exhibits high specific capacity, outstanding rate capability and excellent cycling stability. Moreover, an all-solid-state supercapacitor was assembled with H-NiMoS4/NiS2 as cathode and needle coke oxide (NCO) as anode, which can achieve remarkably high energy density of 38.6 Wh kg−1 at a power density of 958.6 W kg−1 and outstanding capacity retention of 83.7% after 20,000 cycling. The preparation of novel H-NiMoS4/NiS2 nanomaterial with a hetero-phase of amorphous and crystalline provides a new solution for improving the structural stability and capacitor storage performance as electrodes for supercapacitors.

Scalable production of single 2D van der Waals layers through atomic layer deposition: bilayer silica on metal foils and films

The self-limiting nature of atomic layer deposition (ALD) makes it an appealing option for growing single layers of two-dimensional van der Waals (2D-VDW) materials. In this paper it is demonstrated that a single layer of a 2D-VDW form of SiO2 can be grown by ALD on Au and Pd polycrystalline foils and epitaxial films. The silica was deposited by two cycles of bis(diethylamino) silane and oxygen plasma exposure at 525 K. Initial deposition produced a three-dimensionally disordered silica layer; however, subsequent annealing above 950 K drove a structural rearrangement resulting in 2D-VDW. The annealing could be performed at ambient pressure. Surface spectra recorded after annealing indicated that the two ALD cycles yielded close to the silica coverage obtained for 2D-VDW silica prepared by precision SiO deposition in ultra-high vacuum (UHV). Analysis of ALD-grown 2D-VDW silica on a Pd(111) film revealed the co-existence of amorphous and incommensurate crystalline 2D phases. In contrast, ALD growth on Au(111) films produced predominantly the amorphous phase while SiO deposition in UHV led to only the crystalline phase, suggesting that the choice of Si source can enable phase control.

First-Principles Determination of Intergranular Atomic Arrangements and Magnetic Properties in Rare-Earth Permanent Magnets

Development of high-performance permanent magnets relies on both the main-phase compound with superior intrinsic magnetic properties and the microstructure effect for the prevention of magnetization reversal. In this article, the microstructure effect is discussed by focusing on the interface between the main phase and an intergranular phase and on the intergranular phase itself. First, surfaces of main-phase grains are considered, where a general trend in the surface termination and its origin are discussed. Next, microstructure interfaces in SmFe12-based magnets are discussed, where magnetic decoupling between SmFe12 grains is found for the SmCu subphase. Finally, general insights into finite-temperature magnetism are discussed with emphasis on the feedback effect from magnetism-dependent phonons on magnetism, which is followed by explanations on atomic arrangements and magnetism of intergranular phases in Nd-Fe-B magnets. Both amorphous and candidate crystalline structures of Nd-Fe alloys are considered. The addition of Cu and Ga to Nd-Fe alloys is demonstrated to be effective in decreasing the Curie temperature of the intergranular phase.

Effect of Sintering Temperature on Hardness of Bioactive Glass/Cordierite

In this study, a composite of bioactive glass and cordierite (BG/cordierite) was proposed to increase the strength of bioactive glass (BG). Both BG and cordierite were separately synthesized with the method of glass melting and used to fabricate BG/cordierite with sintering temperature in the range from 600 to 1000 °C. The BG/cordierite were characterized using X-ray diffraction (XRD), density, bulk density, porosity and hardness test. The XRD pattern shows amorphous phase and crystalline phase such as combeite, wollastonite and larnite appeared after sintering. The highest hardness value show by BG/cordierite with sintering temperature 950 °C (BG/C950) with 251 Hv.

Impact of atomic layer deposited TiO2 on the photocatalytic efficiency of TiO2/w-VA-CNT nanocomposite materials

Titanium oxide (TiO2) has been widely investigated as a photocatalytic material, and the fact that its performance depends on its crystalline structure motivates further research on the relationship between preparation methods and material properties. In this work, TiO2 thin films were grown on non-functionalized wave-like patterned vertically aligned carbon nanotubes (w-VA-CNTs) via the atomic layer deposition (ALD) technique. Grazing incidence X-ray diffraction (GIXRD) analysis revealed that the structure of the TiO2/VA-CNT nanocomposites varied from amorphous to a crystalline phase with increasing deposition temperature, suggesting a “critical deposition temperature” for the anatase crystalline phase formation. On the other hand, scanning transmission electron microscopy (STEM) studies revealed that the non-functionalized carbon nanotubes were conformally and homogeneously coated with TiO2, forming a nanocomposite while preserving the morphology of the nanotubes. X-ray photoelectron spectroscopy (XPS) provided information about the surface chemistry and stoichiometry of TiO2. The photodegradation experiments under ultraviolet (UV) light on a model pollutant (Rhodamine B, RhB) revealed that the nanocomposite comprised of anatase crystalline TiO2 grown at 200 °C (11.2 nm thickness) presented the highest degradation efficiency viz 55% with an illumination time of 240 min. Furthermore, its recyclability was also demonstrated for multiple cycles, showing good recovery and potential for practical applications.

One-step integration of amorphous RuBx and crystalline Ru nanoparticles into B/N-doped porous carbon polyhedra for robust electrocatalytic activity towards the HER in both acidic and basic media

Amorphous RuBx and crystalline Ru nanoparticles integrated into B/N-doped porous carbon polyhedra via a facile one-step thermal-reduction exhibited remarkable HER electrocatalytic performances in both alkaline and acidic media.

Analysis of the approximation to saturation magnetization and dynamics of demagnetization of PrDyCoFeB amorphous spin glass

An analysis of the field and time dependencies of the magnetization of PrDyFeCoB amorphous crystalline microwires is presented. It is found that the magnetization curve near the saturation field has a smoother approximation to saturation than in a ferromagnet, according to theoretical predictions for the spin-glass state of the alloy in the amorphous state within the framework of the random magnetic anisotropy model. Deviations of the dynamics of relaxation of the magnetization of microwires from the logarithmic time dependence and the disappearance of this difference when observing magnetic relaxation in a magnetic field are found. This indicates the typical dynamics of the magnetization reversal of a spin glass in a zero field and the ferromagnetic character of demagnetization in a nonzero field. The results indicate the presence in the PrDyFeCoB microwires of an exotic magnetic state of the material with stochastic local magnetic anisotropy. Keywords: spin glass, ferrimagnet, rare earth alloys, random magnetic anisotropy.

Особенности синтеза карбида кремния методом холодной имплантации атомов отдачи углерода

The Auger electron spectroscopy method confirmed a high concentration of carbon atoms (~ 85 at. % ), introduced into silicon by cold implantation of recoil atoms. Carbon atoms are concentrated in a thin (~ 5 nm) near-surface region of silicon. Annealing of such a structure did not reveal a noticeable diffusion of carbon, which does not allow obtaining a layer of SiC with a thickness of more than a few nm. The solution to this problem was carried out by the use of radiation-stimulated diffusion. This made it possible to control the distribution profiles of carbon atoms in a wide range. Annealing at 1150 oC allowed to obtain layers of amorphous crystalline SiC with a thickness of 50-150 nm. Higher annealing temperatures are required to obtain a single-crystal SiC film.

Oxygen-Vacancies and Dense Crystalline–Amorphous Interfacial Sites Synergistically for Enhanced Capacitance Were Prepared Via Dealloying Synchronous Heterophase Synthetic Strategy

Oxygen-Vacancies and Dense Crystalline–Amorphous Interfacial Sites Synergistically for Enhanced Capacitance Were Prepared Via Dealloying Synchronous Heterophase Synthetic Strategy