Nanocrystalline Character Research Articles

Ductile–brittle indentation fracture transitions in hard coatings

The article has provided a novel way of finding the probability of fracture ( Pf) based on modifications of some established concepts. It has also discussed ductile to brittle as well as brittle to ductile transitions in the same coating/substrate system subject to differences in crystallisation, indenter sharpness, sliding modes and dislocation kinetics. The indentation positioning and nanocrystalline features cause ambiguity in the results and need meticulous analysis. As a result of increased dislocation movement, the crystalline portions toughened in contrast to the amorphous parts, which were more brittle. The Pf, which varies and reaches a maximum of 52% in the amorphous or near-amorphous area, was calculated using the Weibull distribution. Transitions between ductility and brittleness can be seen in sliding indentations. Evidence of adhesive failure, which required better coating component inspection because it happened significantly earlier, was shown. Finite-element modelling was used to analyse the stress and provide information on dislocation motions and the impact of indenter shape on fracture. The outcomes are advantageous for the production of devices based on nano/micro-electro-mechanical systems.

Study of low-dimensional magnetism in zeolitic imidazolate frameworks

Applying the procedure of a rapid synthesis in the aqueous system, nanocrystalline form of ZIF-8 and Cu-ZIF was obtained. The composition of the latter was inferred from the comparison of vibration spectra and lattice specific heats of both compounds which become nearly identical. The nanocrystalline character of both compounds prevented direct comparison of powder XRD patterns and manifested by the appearance of a boson peak in the diamagnetic ZIF-8 specific heat. The low-temperature magnetic contribution in Cu-ZIF specific heat and a Curie-Weiss tail in low-temperature susceptibility may originate from the effect of surface spins while the round maximum observed in the susceptibility at 135 K indicates the presence of strong low-dimensional correlations with the exchange coupling ∼200 K. Corresponding magnetic contribution cannot be observed in the specific heat due to the huge overlap by the high-temperature lattice contribution. Negligible magnetization values at low temperatures correspond to the aforementioned strong antiferromagnetic coupling. Future experimental scenarios are discussed which should provide better understanding of the bulk and surface magnetism in this unique quantum system.

Nanosynthesis and Characterization of Cu1.8Se0.6S0.4 as a Potential Cathode for Magnesium Battery Applications.

Copper selenide (Cu-Se) and copper sulfide (Cu-S) are promising cathodes for magnesium-ion batteries. However, the low electronic conductivity of Cu-Se system results in a poor rate capability and unsatisfactory cycling performance. Mg-ion batteries based on the Cu-S cathode exhibited large kinetic barriers during the recharging process owing to the presence of polysulfide species. This work attempts to circumvent this dilemma by doping Cu1.8Se by sulfur, which replaces the selenium in the CuSe lattice to form Cu1.8Se0.6S0.4 nanocrystalline powder. The presence of sulfur will increase the electronic conductivity, and the presence of selenium will mitigate the effect of polysulfide species that hinder the kinetics of Mg2+. Herein, a Cu1.8Se0.6S0.4 nanocrystalline powder was synthesized by the solid-state reaction, yielding a highly pure and stoichiometric powder. The crystallographic structure of the nanopowder and the conversion-type storage mechanism have been attested via ex situ X-ray diffraction and energy-dispersive X-ray analysis. The nanocrystalline feature of Cu1.8Se0.6S0.4 was demonstrated by high-resolution transmission electron microscopy. An apparent surface morphology change during the charging/discharging process has been visualized by a field emission scanning electron microscope. Diffuse reflectance spectroscopy has discussed the variation of the band gap during charging and discharging. The full Mg/Cu1.8Se0.6S0.4 cells presented an initial discharge capacity of 387.99 mAh g-1 at a current density of 0.02 mA cm-2; moreover, they show moderate diffusion kinetics with ≈ 10-15 cm-2 s-1.

Thermal Conversion of Nanocrystalline Metal Hydroxide Salts to Metal Carbides, Pnictides, Chalcogenides, and Halides.

A general procedure for synthesizing various inorganic compounds in a similar manner is required in the field of material chemistry. The use of solid-state reactive agents with inorganic precursors is a successful approach in this direction. In this study, organic-inorganic hybrid metal hydroxide salts (MHSs) were utilized to synthesize various inorganic compounds by a simple heat treatment method because they can be assumed to be "premixed" inorganic precursors and solid-state reactive agents. Comparative studies revealed that the nanocrystalline characteristics and coordination of the carboxylate of the synthesized MHSs enabled simultaneous dehydration of hydroxides and decomposition of carboxylates and subsequent formation of metals and metal sulfides. Manganese, iron, cobalt, nickel, and zinc sulfides, as well as nickel carbides, pnictides, chalcogenides, and halides were obtained using the same procedure. We believe that using nanocrystalline organic-inorganic hybrid MHSs as both inorganic precursors and organic reactive agents will be a simple and versatile way to prepare a wide variety of inorganic complex compounds.

Synthesis and characterization of pure and Cu-doped WO3 thin films for high performance of toxic gas sensing applications

Oxygen vacancies and the high surface area of nanostructured materials offers stronger gas adsorption active sites for improved gas sensing performance. In the present work, we have deposited WO3-based thin films using a chemical spray pyrolysis technique at a substrate temperature of 400 °C with other optimized preparation parameters. Besides, this study reports the influence of Cu doping at various weight percentages on the structural, morphological, optical and toxic gas sensing properties of WO3 films in detail. The crystalline structure of the material was investigated using the X-ray diffraction technique. Each X-ray diffraction analysis of the films demonstrated a polycrystalline nature, matching the hexagonal phase of WO3 with the (200) plane of preferential orientation of crystal growth. The optical characteristics of the thin film's material were analyzed by UV–Vis absorption spectroscopy. The optical energy bandgap (Eg) of the deposited thin films was estimated using the Tauc relation, and the value was decreased along with the increase in the Cu-doping concentration. The surface roughness of the films has been investigated using atomic force microscopy. The TEM patterns of sprayed Cu-doped WO3 thin films exhibit nanocrystalline features. Detecting toxic gasses is of great importance across the globe due to an alarming enhancement in respiratory, ocular, skin, and lung diseases. Hence, cost-effective and room temperature-operated Cu-doped WO3 thin film sensors to trace low concentrations of toxic gasses have been investigated and systematically reported. It is observed that the sensor response is to be increased with the increase in Cu-doping concentration, particularly the 4 wt.% Cu-doped sensor exhibited a response value of 7.2 and fast response and recovery times in the presence of 50 ppm ammonia vapor.

Mechanochemically Synthesized Chalcogenide Cu3BiS3 Nanocrystals in an Environmentally Friendly Manner for Solar Cell Applications

Ternary wittichenite Cu3BiS3 nanocrystals were prepared mechanochemically using a planetary ball mill from elemental copper, bismuth and sulfur in a stoichiometric ratio in only 5 min. The orthorhombic wittichenite Cu3BiS3 was nanocrystalline with an approximate crystallite size of 38 nm ± 9 nm, as confirmed by Rietveld refinement. The nanocrystalline character of orthorhombic Cu3BiS3 was also proven by transmission electron microscopy. The measured Raman spectrum confirmed the formation of pure wittichenite Cu3BiS3. The morphology characterization demonstrated the homogeneity of the sample. The value of the specific surface area for pure mechanochemically prepared Cu3BiS3 after 5 min was 2.7 m2g−1. The optical properties were investigated using UV–Vis absorption and micro-photoluminescence spectroscopy. From the absorption UV–Vis spectrum, the value of the bandgap energy was determined to be 1.52 eV, which creates an assumption for the use of wittichenite Cu3BiS3 in photovoltaic applications. The optoelectrical properties of the prepared Cu3BiS3 nanocrystals were verified by current–voltage measurements in the dark and under white light illumination. The photocurrent increased by 26% compared to the current in the dark at a voltage of 1 V. The achieved results confirmed a very fast and efficient way of synthesizing a ternary wittichenite Cu3BiS3, which can be used for applications in solar cells.

Production of Nanocomposite Tungsten Carbide Buttons by Mixing with Co and ZrO<sub>2</sub> Nanopowders

The production of nanocomposite tungsten carbide buttons was studied. Using the mechanically induced solid-state mixing technique, the nanopowders were mixed with Cobalt (Co) and Zirconium Oxide (ZrO2). During the consolidation and manufacturing process, the nanocrystalline characteristics of the nanocomposite were improved by replacing Co with ZrO2-2 mol% yttria (YO3), and the average grain size was reduced to 23-49µm. With the advent of fast sintering techniques and the synthesis of nanocomposites from the consolidation of nanocomposite powders, full dense buttons with outstanding properties were produced. These buttons have a very high nano hardness value (24.41GPa) and a low Young's modulus (E) value (332.02 GPa).

Impact of post-annealing temperature on optical and surface properties of tellurium doped ZnO nanocrystalline films

Investigated in this work is the effect of post-annealing temperature on ZnO nanocrystalline thin films doped with 5 at.% tellurium. The spin coating method was used to deposit films on the microscopic glass substrates. XRD, AFM, and UV-spectro-photometry were used to characterize the films structure, surface roughness and optical properties. The XRD spectra showed that the nanocrystalline films are of monocrystalline nature. AFM has confirmed the nanocrystalline character of tellurium-doped ZnO. The transmission of exposed films has been decreased with the increase of annealing temperature. The average transmission of all the films has been revealed to be higher than 80%. The optical band gap varies slightly with post-annealing temperature.

Growth and characterization of α-Ga2O3 on sapphire and nanocrystalline β-Ga2O3 on diamond substrates by halide vapor phase epitaxy

Halide vapor phase epitaxial (HVPE) Ga2O3 films were grown on c-plane sapphire and diamond substrates at temperatures up to 550 °C without the use of a barrier dielectric layer to protect the diamond surface. Corundum phase α-Ga2O3 was grown on the sapphire substrates, whereas the growth on diamond resulted in regions of nanocrystalline β-Ga2O3 (nc-β-Ga2O3) when oxygen was present in the HVPE reactor only during film growth. X-ray diffraction confirmed the growth of α-Ga2O3 on sapphire but failed to detect any β-Ga2O3 reflections from the films grown on diamond. These films were further characterized via Raman spectroscopy, which revealed the β-Ga2O3 phase of these films. Transmission electron microscopy demonstrated the nanocrystalline character of these films. From cathodoluminescence spectra, three emission bands, UVL′, UVL, and BL, were observed for both the α-Ga2O3/sapphire and nc-Ga2O3/diamond, and these bands were centered at approximately 3.7, 3.2, and 2.7 eV.

Structural, dc electrical resistivity and magnetic investigation of Mg, Ni, and Zn substituted Co-Cu nano spinel ferrites

The sol-gel auto-combustion procedure was used to synthesize M (M = Mg, Ni, and Zn) substituted Co0.5Cu0.2M0.3Fe2O4 micro ferrites. X-ray diffraction measurements validated the mono-phase formation and nanocrystalline character of the produced samples. It possesses a monophasic cubic-spinel lattice structure with an average crystallite size ranging from 29.01 to 47.17 nm. The lattice constant determined by XRD analysis falls between 8.374 and 8.474 Å. The morphological characteristics were shown using FESEM analysis, which revealed the almost spherical form of grains with sizes ranging from 40, 50, and 74 nm. The compositional verification was undertaken with the help of the EDS analysis which ensured the presence of elements in desired proportions. IR spectra confirm their spinel spectra with the help of the two absorption bands lying between 1200 and 400 cm−1 resembling their two sites: tetrahedral and octahedral. The magnetic saturation (MS), magnetic moment (M)R, and coercivity (Hc) are found to be the highest for the Ni substituted Co-Cu ferrite system, i.e., MS = 49.5 emu/g. The ratio MR/MS for all ferrites is less than 0.5 indicating their ferromagnetic isotropic nature thereby acting as magnetic semiconductors. The electrical properties were measured using the ‘two probe technique’ with varying temperatures which indicates their semiconducting nature. Ni substituted Co-Cu nanoferrite is preferable for electromagnets and recording purposes the magnetic and electrical behavior of Ni substituted Co-Cu nanoferrite shows its relevance for recording and electromagnetic applications.

Light-assisted ozone gas-sensing performance of SnO2 nanoparticles: Experimental and theoretical insights

We report herein an investigation on the ozone gas-sensing performance at room temperature of SnO2 nanoparticles assisted by a light-emitting diode. X-ray diffraction and high-resolution transmission electron microscopy analyses indicated the nanocrystalline characteristics of the SnO2 particles after heat treatment. Besides, optical measurements pointed out that the nanoparticles presented an optical gap of approximately 3.8 eV with a broad photoluminescence emission at around 625 nm, which was linked to the presence of oxygen vacancies, suggested by XPS analysis. With regard to the light-assisted gas-sensing measurements, electrical analysis revealed a clear dependence of the ozone sensing performance on the wavelength of the source of illumination chosen, with the highest ozone response being reached upon excitation in the ultraviolet region. Theoretical calculations showed that the (110) surface could increase the stability of photogenerated carriers and contribute to enhancing the gas-sensing features under ultraviolet excitation due to the presence of [SnO6] and [SnO5] clusters, which are capable of inducing an electron-hole dissociation and a reliable chemical environment for O3 interaction.

Structural, morphological, and DC-electrical examination of Ni1-xCdxFe2O4 nanoparticles fabricated via Sol-gel auto-combustion

Using the sol–gel process, the authors hope to shed insight on the structural, morphological, and DC-electrical properties of Ni1-xCdxFe2O4 nanoparticles. Using a high-quality ceramic crucible in the programmed furnace, the sintering temperature was regulated at 550 °C for 4 h. The existence of Bragg's reflections, which belong to the cubic spinel structure with the Fd 3 m-O h7 space group, confirmed the phase purity and nanocrystalline character of Ni1-xCdxFe2O4 nanoparticles when XRD patterns were examined closely. Using Debye-formula, Scherrer's crystallite size (t) was calculated and determined to be 23.311 nm. The intrinsic and extrinsic vibrations of Ni1-xCdxFe2O4 nanoparticles were observed by IR; v2 = 561.29 cm−1 and v1 = 420.48 cm−1. The metal ion dispersion degree and roughness distribution at the surface of Ni1-xCdxFe2O4 nanoparticles were discovered using AFM. The semiconducting nature of Ni1-xCdxFe2O4 nanoparticles was further shown by the DC-resistivity as a function of temperature. Comprehensive intra-atomic and molecular restrictions affecting the range of applications for Ni1-xCdxFe2O4 nanoparticles have been investigated in this study.

The Influence of Annealing Temperature on the Structure and Magnetic Properties of Nanocrystalline BiFeO3 Prepared by Sol\u2013Gel Method

In this work, BiFeO3 powders were synthesized by a sol–gel method. The influence of annealing temperature on the structure and magnetic properties of the samples has been discussed. X-ray diffraction studies showed that the purest phase was formed in the temperature range of 400 °C to 550 °C and the samples annealed at a temperature below 550 °C were of nanocrystalline character. Mössbauer spectroscopy and magnetization measurements were used as complementary methods to investigate the magnetic state of the samples. In particular, the appearance of weak ferromagnetic properties, significant growth of magnetization, and spin-glass-like behavior were observed along with the drop of average grain size. Mössbauer spectra were fitted by the model assuming cycloidal modulation of spins arrangement and properties of the spin cycloid were determined and analyzed. Most importantly, it was proved that the spin cycloid does not disappear even in the case of the samples with a particle size well below the cycloid modulation period λ = 62 nm. Furthermore, the cycloid becomes more anharmonic as the grain size decreases. The possible origination of weak ferromagnetism of the nanocrystalline samples has also been discussed.

Optical and microstructural characterization of nanocrystalline Cu doped ZnO diluted magnetic semiconductor thin film for optoelectronic applications

A series of Zn 1-x Cu x O nanocrystalline films were deposited on a silica substrate using e-beam evaporation technology. The physical properties of the deposited film were closely examined using x-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDXS), atomic force microscopy (AFM), and spectroscopic ellipsometry (SE). The deposited film's structure revealed the formation of a hexagonal wurtzite structure, with no extra phases found. According to AFM analysis, the deposited Zn 1-x Cu x O (x = 0.0, 0.04, 0.08, 0.12, 0.16, and 0.2) film has nanocrystalline characteristics. The present findings show that increasing Cu content up to x ≤ 0.2 reduces the direct optical energy gap E g from 3.286 eV (x = 0) to 2.934 eV (x = 0.2), which can be attributed to the sp-d exchange coupling. The refractive index dispersion extracted from SE analysis for Cu-doped ZnO thin films increased as the Cu dopant increased. In addition, the refractive index dispersion of the deposited film was studied using a single oscillator model proposed by Wemple-DiDomenico (WDD). It was found that the oscillator energy E o decreases as the Cu concentration increases, while the dispersion energy E d increases. As a result of the improvement in the optical energy band gap and the tunability of the values of the dispersive oscillator parameters E o , E d , n 0 , ε 0 , M -1 , and M -3 with increasing Cu doping levels, Cu doped ZnO films are a good candidate for optoelectronic device applications. • E-beam techniques is used to deposit a series of thin film of Cu doped ZnO. • The deposited film's structure show the formation of a hexagonal wurtzite structure. • SE technique is used to obtained the direct energy gap and found that E g is reduced from 3.286eV to 2.934eV with Cu concentration increases from 0 up to 0.2. • The SE analysis reveal that refractive index dispersion of Cu-doped ZnO thin films has increased as the Cu dopant has increased.

Mechanochemistry as an Alternative Method of Green Synthesis of Silver Nanoparticles with Antibacterial Activity: A Comparative Study.

This study shows mechanochemical synthesis as an alternative method to the traditional green synthesis of silver nanoparticles in a comparative manner by comparing the products obtained using both methodologies and different characterization methods. As a silver precursor, the most commonly used silver nitrate was applied and the easily accessible lavender (Lavandula angustofolia L.) plant was used as a reducing agent. Both syntheses were performed using 7 different lavender:AgNO3 mass ratios. The synthesis time was limited to 8 and 15 min in the case of green and mechanochemical synthesis, respectively, although a significant amount of unreacted silver nitrate was detected in both crude reaction mixtures at low lavender:AgNO3 ratios. This finding is of particular interest mainly for green synthesis, as the potential presence of silver nitrate in the produced nanosuspension is often overlooked. Unreacted AgNO3 has been removed from the mechanochemically synthesized samples by washing. The nanocrystalline character of the products has been confirmed by both X-ray diffraction (Rietveld refinement) and transmission electron microscopy. The latter has shown bimodal size distribution with larger particles in tens of nanometers and the smaller ones below 10 nm in size. In the case of green synthesis, the used lavender:AgNO3 ratio was found to have a decisive role on the crystallite size. Silver chloride has been detected as a side-product, mainly at high lavender:AgNO3 ratios. Both products have shown a strong antibacterial activity, being higher in the case of green synthesis, but this can be ascribed to the presence of unreacted AgNO3. Thus, one-step mechanochemical synthesis (without the need to prepare extract and performing the synthesis as separate steps) can be applied as a sustainable alternative to the traditional green synthesis of Ag nanoparticles using plants.

An advancement in the synthesis of unique soft magnetic CoCuFeNiZn high entropy alloy thin films

Discovery of advanced soft-magnetic high entropy alloy (HEA) thin films are highly pursued to obtain unidentified functional materials. The figure of merit in current nanocrystalline HEA thin films relies in integration of a simple single-step electrochemical approach with a complex HEA system containing multiple elements with dissimilar crystal structures and large variation of melting points. A new family of Cobalt–Copper–Iron–Nickel–Zinc (Co–Cu–Fe–Ni–Zn) HEA thin films are prepared through pulse electrodeposition in aqueous medium, hosts nanocrystalline features in the range of ~ 5–20 nm having FCC and BCC dual phases. The fabricated Co–Cu–Fe–Ni–Zn HEA thin films exhibited high saturation magnetization value of ~ 82 emu/g, relatively low coercivity value of 19.5 Oe and remanent magnetization of 1.17%. Irrespective of the alloying of diamagnetic Zn and Cu with ferromagnetic Fe, Co, Ni elements, the HEA thin film has resulted in relatively high saturation magnetization which can provide useful insights for its potential unexplored applications.

Optical metallography and DTA/TGA Analysis of Shape memory alloy: Cu74Zn22 Al4(Wt.%)

Phase changing materials play very important role in design of actuators and sensors in many equipment. Allow of copper, Zinc and Aluminium exhibits shape memory features. In presented experimental investigation, Cu74Zn22 Al4(Wt.%) was prepared by mechanical alloying using high energy ball milling process. By mechanical alloying, nano-crystalline features were developed. Powder was converted into pellets and sintered and forged for optical metallography characterization. DTA/TGA analysis was performed to exhibits shape memory features. When shape memory material changes its phase, energy in form of heat either released or absorbed. Optical metallographs indicates that sintered and forged samples exhibits different features.

Comparative Study of Nanostructured CuSe Semiconductor Synthesized in a Planetary and Vibratory Mill.

Copper(II) selenide, CuSe was prepared from Cu and Se powders in a stoichiometric ratio by a rapid, and convenient one-step mechanochemical synthesis, after 5 and 10 min of milling in a planetary, and an industrial vibratory, mill. The kinetics of the synthesis, and the structural, morphological, optical, and electrical properties of CuSe products prepared in the two types of mill were studied. Their crystal structure, physical properties, and morphology were characterized by X-ray diffraction, specific surface area measurements, particle size distribution, scanning, and transmission electron microscopy. The products crystallized in a hexagonal crystal structure. However, a small amount of orthorhombic phase was also identified. The scanning electron microscopy revealed that both products consist of agglomerated particles of irregular shape, forming clusters with a size ~50 μm. Transmission electron microscopy proved the nanocrystalline character of the CuSe particles. The optical properties were studied using UV–Vis and photoluminescence spectroscopy. The determined band gap energies of 1.6 and 1.8 eV for the planetary- and vibratory-milled product, respectively, were blue-shifted relative to the bulk CuSe. CuSe prepared in the vibratory mill had lower resistivity and higher conductivity, which corresponds to its larger crystallite size in comparison with CuSe prepared in the planetary mill.

Tailoring thermal development of gamma alumina sorbents material using combustion synthesis: the effect of amino acids (G, A, N) and equivalence ratio

Using a combustion synthesis, the range of achievable textures is broader than using conventional synthesis methods and can be controlled more successfully. As a tool allowing the achievement and control of desired textures, here we bring about wet chemistry synthesis using aluminium nitrate nonahydrate (ANN) precursor systematically combined with different fuels (amino acids). The amino acids; glycine (G), alanine (A) and asparagine (N) have been specifically selected in order to show the role of gradual increase in their: (1) molar mass, (2) enthalpy of combustion, (3) amine groups content and (4) ratio to ANN. Detailed (micro) structural and thermal characterisations confirm that the nanocrystalline character and thermomechanical stability were not diminished in the course of this synthesis. The conditions leading to development of different morphologies from gels to powders were found to be heavily under the influence of fuel/oxygen ratio, i.e. of the smouldering versus flaming mechanism of the combustion. Higher content of nitrates (predominately from amino-rich amino acids) strongly promoted auto-combustion behaviour. As-derived alumina precursors have been thermally treated at various temperatures (quenched and soaked), to monitor γ- and α-alumina crystallisation, with respect to the development of morphology. Different texture types have been observed, such as porous wormhole, porous and porous expanded flakes. Higher fuel levels promote specific surface increase. This combustion synthesis allows facile tailoring of nanocrystalline γ-alumina with different morphological features, whereas samples having optimal parameters were suitable for catalyst support application on behalf of rapid sorption performance.

Kinetics of densification/phase transformation and transport properties of Mg-Sn cubic/trigonal composites

The Mg-Sn materials are interesting because of useful semiconducting properties and particularly because of their earth abundant, environmentally friendly constituent elements. The cubic Mg2Sn phase appears in the equilibrium phase diagram and has been extensively studied, while the transport properties of the trigonal phase—that does not appear in the phase diagram—have not been reported. We produced dense composites composed of cubic (stable) and trigonal (metastable) phases using a combination of high energy ball milling and current activated pressure assisted densification (CAPAD). We present a kinetic study of the densification and cubic to trigonal phase transformation. In addition, we present transport property measurements of cubic/trigonal composites. We determine densification rates and observe distinct densification regimes, attributed to the cubic-to-tetragonal phase transformation as well as porosity removal. Transport property measurements reveal that altering the amount of metastable phase in the composites changes both the electrical and thermal properties. The electrical conductivity significantly increases with increasing trigonal phase fraction. The thermal conductivities are similar for all compositions, which is likely due to the nanocrystalline character of the composites.