Nanocrystalline Inclusions Research Articles

Crystalline-amorphous-crystalline two-step phase transformation and the resulting supra-nano structure in a metastable iron-based alloy

In this work, we report a crystalline-amorphous-crystalline (CAC) two-step solid-state phase transformation (SSPT) in a 15Cr-2Ni iron-based alloy that results in nanostructures. Microstructurally, the CAC process leads to a localized supra-nano structure having almost equal content of an amorphous matrix and nanocrystalline inclusions less than 6 nm. Dynamically, it is manifested as a glass-transition-like variation of Young's modulus with a sharp surge in internal friction. Through in situ heating and Neutron Scattering experiments, a reduction in the intensities of the austenite diffraction peaks is observed, which is not associated with any intensity increase in other peaks, suggesting the collapse of austenite lattice during heating. The CAC two-step SSPT occurs at temperatures far below the melting point, and the introduction of the dislocations is the indispensable condition giving rise to such a transition. Based on experimental results, we suggest the physical picture of CAC two-step SSPT and a phenomenological model to describe it. Through the analysis, we argue that the CAC two-step SSPT provides a new route to fabricate nanostructured alloys.

Dielectric Relaxation in Nanocrystals: A Scale Effect

The study explores a scale effect inherent to the dielectric relaxation in nanocrystals: the dependence of dielectric relaxation parameters on the size of a nanocrystal. We offer a model of the scale effect for the dielectric relaxation caused by thermally activated motion. In this model, a nanocrystal is considered as a physical infinitesimal volume: a region where a local equilibrium exists. We conclude that the thermally activated motion causes the energy fluctuations in a nanocrystal as a whole. A relation between the intensity of these fluctuations and the size of nanocrystals is derived. According to this relation, the intensity of the fluctuations decreases with the decrease of the nanocrystal sizes. Using the relation, a characteristic of a thermally activated motion–the size of the activation zone–can be determined experimentally. We verify the model using experimental data for the complex dielectric permittivity of the composites (silica gel matrix with undecylenic acid nanocrystalline inclusions of various sizes) in the temperature range from −190 to 50 °C at frequencies 5, 10, 20, and 50 kHz. The results of the experiment agree with the predictions of the model.

Structure and Chemical Composition of Ion-Synthesized Gallium Oxide Nanocrystals in Dielectric Matrices.

The ion-beam synthesis of Ga2O3 nanocrystals in dielectric matrices on silicon is a novel and promising way for creating nanomaterials based on gallium oxide. This research studies the regularities of changes, depending on the synthesis regimes used, in the chemical composition of ion-implanted SiO2/Si and Al2O3/Si samples. It has been shown that the formation of Ga-O chemical bonds occurs even in the absence of thermal annealing. We also found the conditions of ion irradiation and annealing at which the content of oxidized gallium in the stochiometric state of Ga2O3 exceeds 90%. For this structure, the formation of Ga2O3 nanocrystalline inclusions was confirmed by transmission electron microscopy.

Nanostructured ceramic materials synthesized from ZrO2 that can withstand thermal shock when immersed in molten steels

This paper presents a review on the synthesis of nanostructured ceramic materials that can withstand thermal shock when immersed in molten steels and work as solid electrolytes. The authors examine the possibility to obtain heat-resistant dense cera mics from ZrO2 – MgO and ZrO2 – Y2O3 powder systems with a controlled particle structure for the manufacture of solid electrolytes of steel oxidation sensors to be used in contact with corresponding molten steels. The paper describes a method for producing nanostructured ceramics of the ZrO2 – MgO system with enhanced heat resistance from nanocrystalline powders, as well as the properties of sensitive elements. Thus, the paper looks at obtaining zirconium dioxide ceramics that would have a heat-resistant structure due to which it can be used in molten steels. It is shown that due to nanocrystalline inclusions in the ceramic structure the material becomes heat-resistant and conductive when immersed in molten steels at the temperatures of 1,550 to 1,800 oC. The paper also describes the results of a study that looked at the process parameters for the production of sensitive elements with an optimal heatresistant structure. Also presented are the results of field tests conducted for sensitive elements with solid electrolytes of various compositions A ZrO2 + 2.0 wt. % MgO sensitive element made of precipitation synthesized powders proved to have the best performance: i.e. stabilization time; EMF after immersion; variation within the area of stable readings in highly deoxidized steels. The structure of such powder contains a large amount of ellipsoid tetragonal phase precipitates. The researches were conducted using the equipment of the Research sharing center named after D. I. Mendeleev within the framework of the project No. 075-15-2021-688.

Modelling of track formation in nanocrystalline inclusions in Si3N4

A multiscale modeling is applied to investigate structural changes caused by impacts of swift heavy ions in Si3N4 nanoclusters imbedded into amorphous and crystalline silicon nitride matrices. The approach combines the Monte Carlo code TREKIS describing the excitation kinetics of electronic and atomic subsystems and a classical molecular dynamics tracing subsequent relaxation of lattice atoms. Ion impacts in amorphous and crystalline Si3N4 result in formation of a cylindrical amorphous region of a reduced material density, surrounded by a shell with an increased density. The track diameter inside a nanosized inclusion in crystalline or amorphous matrices was found smaller than in surrounding materials, which can be explained by a heat confinement by grain boundaries.

A MnOx–graphitic carbon composite from CO2 for sustainable Li-ion battery anodes

Molten salt CO2 capture and electrochemical transformation (MSCC-ET) has been proposed as a sustainable synthetic method for Mn nanocrystalline inclusions in a graphitic matrix, which paves the way to new methods to produce composite materials.

Unusual dislocation activity in Ge containing Sn particles

We report an unexpectedly high dislocation activity around Sn inclusions in the Ge matrix below the brittle-to-ductile (BDT) transition temperature of Ge as observed using transmission electron microscopy. These dislocations nucleate at the Sn/Ge interface in form of dislocation loops upon solidification of Sn inclusions on cooling. The Sn inclusions solidify ~130 °C below the BDT of Ge. The novel feature is the unusual extent of dislocation loops so far from the inclusions, especially since the mobility of dislocations is limited in Ge below BDT. Considering the velocity of dislocation in Ge below the BDT to be ≈10−11 ms−1, it is normally not enough to increase the loop size from ≈1 nm to more than 300 nm in the short solidification time. We propose that in addition to diffusive type heat propagation, the sudden energy release upon solidification of Sn in Ge matrix can also be carried away by the expanding dislocation loops, thereby enhancing the velocity of dislocations significantly below the BDT. The role of expanding dislocation loops at Sn/Ge interface upon solidification of inclusions is thus fundamentally significant in understanding the rapid dissipation of latent heat from nanocrystalline inclusions embedded in a matrix.

Analysis of elemental distributions and phase separation in rare-earth-doped silica-based fiber preforms and optical fibers

The elemental distribution, phase separation and nanocrystallization process in rare-earth-doped silica-based fiber preforms and optical fibers were studied by using analytical electron microscopy. The particular properties of devitrification processes depending on the fiber core compositions and concentration of rare earth elements was systematically studied in aluminophosphosilicate fibers. It was investigated that the record high (for Modified Chemical Vapour Deposition manufactured samples) concentrations of rare-earth ions (up to 3 at% Yb3+) can be achieved alongside with a reasonably low background optical losses using aluminosilicate glass matrix. Two types of phase separation were revealed in the investigated samples of different composition: the droplet separation and the formation of two interpenetrated glass phases. It was concluded that the second type phase separation can be accompanied by the formation of nanocrystalline inclusions. Possible applications of the obtained glasses in practice for creation of highly-absorbing layers in optical fibers were discussed in the paper.

Epitaxial integration of improper ferroelectric hexagonal YMnO3 thin films in heterostructures

We report on multiple fundamental qualitative improvements in the growth of improper ferroelectric hexagonal YMnO$_3$ (YMO) thin films and heterostructures by pulsed laser deposition (PLD). By a combination of pre-growth substrate annealing and low-energy-fluence PLD, we obtain a two-dimensional growth mode of the YMO films on yttria-stabilized zirconia (YSZ) with ultralow roughness and devoid of misoriented nanocrystalline inclusions. By inserting a sacrificial manganite layer capped with conducting indium-tin oxide between the substrate and the final film, the latter is grown in a fully lattice-relaxed mode and, thus, without any misfit dislocations while maintaining the extraordinary flatness of the films grown directly on pre-annealed YSZ. This provides a template for the fabrication of heterostructures based on hexagonal manganites as promising class of multiferroics with improper room-temperature ferroelectricity and the implementation of these into technologically relevant epitaxial metal|ferroelectric-type multilayers.

Analysis of Structural Features of Periodic Fe/Pd/Gd/Pd Multilayered Systems

The structure of a material promising for magnetic memory elements based on Fe/Pd/Gd/Pd superlattices has been investigated by X-ray analysis and electron microscopy. Microstructural transformations in the superlattices and the influence of microstructure modification on the magnetic properties of the system are determined. It is shown that intense diffusion of Pd atoms to Gd layers occurs in the superlattices under study. The presence of a paramagnetic Pd layer changes the character of exchange interaction between neighboring ferromagnetic layers due to the induced magnetic moment on Pd atoms near the interface because of the interface imperfection. Nanocrystalline inclusions are found in the Pd/Gd/Pd layers, which are suggested to affect the specificity of magnetic ordering in these systems, as confirmed by magnetic measurements.

Phase Control of Nanocrystalline Inclusions in Bioprecipitated Titania with a Panel of Mutant Silica-Binding Proteins.

The biomimetic route to inorganic synthesis presents an opportunity to produce complex materials with superior properties under ambient conditions and from nontoxic precursors. While there has been significant progress in using solid-binding peptides (SBPs), proteins, and organisms to produce a variety of inorganic and hybrid structures, it has been more challenging to understand the interplay of solution conditions and solid-binding peptide (SBP) sequence, structure, and self-association on synthetic outcomes. Here, we show that fusing the Car9 silica-binding peptide-but not the silaffin-derived R5 peptide-to superfolder green fluorescent protein (sfGFP) enhances the ability of micromolar concentrations of protein to induce rapid titania (TiO2) precipitation from acidified solutions of tetrakis(di-lactato)-oxo-titanate (TiBALDH). TiO2 is produced stoichiometrically and although predominantly amorphous, contains nanosized anatase and monoclinic TiO2(B) inclusions. Remarkably, the phase of these nanocrystallites can be tuned from about 80% TiO2(B) to about 65% anatase by using Car9 mutants impaired in their ability to drive the formation of higher-order sfGFP-Car9 oligomers. Our results suggest that the presentation of multiple basic side chains in an extended plane formed by SBP self-association is critical to template the formation of monoclinic crystallites and underscore the subtle influence that single or dual substitutions in dodecameric SBPs can exert on the yield and crystallinity of biomineralized inorganics.

Phase Transformations in Nd–Fe–B-Based Alloys under High Pressure Torsion at Different Temperatures

In this work, we studied the behavior of the Nd–Dy–Fe–Co–Cu–B alloy for permanent magnets under high pressure torsion (HPT). In the initial state of the studied alloy, it mainly contained the crystalline phase τ1 (Nd, Dy)2(Fe, Co, Cu) 14B. After HPT at room temperature (THPT = 30°C), a mixture of an amorphous phase with nanocrystalline inclusions of the τ1 phase is observed in the alloy. In the equilibrium phase diagram, this state is equivalent to a mixture of the τ1 phase with the melt at the temperature Teff= ∼1100°C. The thus determined Teff value is called the effective temperature. When the THPT temperature of the HPT treatment increases to 300 and 400°C, the amorphous phase disappears, and the Fe2B and γ-Fe phases appear instead. In the equilibrium phase diagram, this state is equivalent to a mixture of phases τ1+ Fe2B + γ-Fe, which is observed in the temperature range from ∼950 to ∼1050°C. We explain this phenomenon by the fact that with an increase in the HPT temperature THPT, the rate of formation of defects during deformation remains constant, but the rate of their thermal relaxation (annihilation) increases. This is equivalent to decrease in the effective temperature Teff in the equilibrium phase diagram. The previously predicted decrease in Teff with an increase in THPT is observed for the first time.

Formation of Si nanocrystals in LP CVD semi-insulating polycrystalline silicon films

Influence of oxygen on silicon nanocrystals formation peculiarities and size in semi-insulating polycrystalline silicon thin films has been demonstrated by the means of local atomic surrounding sensitive electronic structure experimental studies. Low-pressure chemical deposition from the gas phase at a relatively low temperature leads to formation of semi-insulating polycrystalline silicon film containing nanocrystals with the grain size of 20–40 nm. At the same time, films oxygen doping result in formation of silicon nanocrystals arrays with the mean particle size less than 10 nm. Possibility of size-controlled Si nanocrystals formation followed by electronic structure reconstruction of amorphous films with nanocrystalline inclusions is discussed and can be found prospective for a range of possible applications.

Role of the electronically-active amorphous state in low-temperature processed In2O3 thin-film transistors.

Metal oxide (MO) thin-film transistors (TFTs) are expected to enable low-cost flexible and printed electronics, given their excellent charge transport, low processing temperatures and solution processability. However, achieving adequate mobility when processed scalably at low temperatures compatible with plastic electronics is a challenge. Here, we explore process-structure-transport relationships in blade-coated indium oxide (In2O3) TFTs via both sol-gel and combustion chemistries. We find that the sol-gel chemistry enables n-type TFTs when annealed at 200 °C to 225 °C with noticeable electron mobility ((3.4 ± 1.3) cm2V-1s-1) yet minimal In2O3 crystallinity and surprisingly low levels of the metal-oxygen-metal (M-O-M) lattice content (≈46 %). Increased annealing temperatures result in the appearance of nanocrystalline domains and an increase in M-O-M content to ≈70 %, without any further increase in mobility. An actetylacetone combustion-assisted ink lowers the external thermal budget required for In2O3 crystallization but bypasses the electronically-active amorphous state and underperforms the sol-gel ink at low temperatures. Grain boundary formation and nanocrystalline inclusions in these films due to rapid combustion-assisted crystallization are suggested to be the likely origin behind the significantly compromised charge transport at low-temperatures. Overall, this study emphasizes the need to understand the complex interplay between local order (nanocrystallinity) and connectivity (grain boundary, amorphous phases) when optimizing low-temperature processed MO thin films.

Nanoscale X-Ray Diffraction of Silk Fibers

This report focuses on current possibilities and perspectives of scanning X-ray nanodiffraction for probing nanoscale heterogeneities in silk fibers such as nanofibrillar skin-core morphologies, nanocrystalline inclusions and fine fibers down to submicron diameters.

Yb3+-activated optical fibers with a core fabricated by sintering powders with vibration mixing of the melt

Using sintering of powders in combination with vibration mixing of the melt, glasses for cores of preforms of optical fibers of the composition SiO2-Al2O3-P2O5-Yb2O3 with a rather high (up to 0.5 at. %) ytterbium content were fabricated. Lasing on ytterbium ions was obtained in light guides with a core of these glasses. To increase the lasing efficiency, further optimization of the process parameters is required to reduce optical losses. It is shown that one of the causes of optical losses is the inhomogeneity of the glass microstructure at the nanoscale level and the formation of nanocrystalline inclusions, which are SiO2, YbP3O9, and YbPO4.

Photo-induced enhancement of the dark conductivity in nanocrystalline germanium/amorphous silicon composite thin films

A light-induced increase in the dark conductivity is observed in composite thin films consisting of hydrogenated amorphous silicon (a-Si:H) containing nanocrystalline germanium (nc-Ge) inclusions, synthesized by co-deposition in a dual-chamber plasma enhanced chemical vapor deposition system. Unlike the Staebler-Wronski effect or persistent photoconductivity observed in amorphous semiconductors, this photo-induced excess conductivity is observed even in composite nc-Ge/a-Si:H films with a minimal photosensitivity. The decay of the excess conductivity follows a single-exponential time dependence, with a temperature independent time constant. We propose that spatial separation of photo-excited charge carriers by the compositional morphology present in the film, with tunneling of photo-excited holes into the germanium nanocrystalline inclusions, is involved in the creation and removal of this effect.

Microstructure, composition, and luminescent properties of bismuth-doped porous glass and optical fiber preforms

The microstructure of porous glass has been studied by using electron microscopy and X-ray microanalysis. Porous glass has an average pore size of about 4 nm in its interior, while larger pores and channels, up to 40 nm in size, exist in a surface layer, which is about 200 nm in thickness. Transparent consolidated samples with a bismuth concentration in the range ≤ 0.01–0.8 at. % were prepared by impregnation of porous glass with an aqueous solution of bismuth nitrate followed by thermal treatment. The addition of aluminum nitrates to the soaking solution results in the reduction of the bismuth content in the samples. The composition inhomogeneity of the porous glass and nanocrystalline inclusions were investigated on the nanolevel by means of transmission electron microscopy. The luminescence spectra of the samples were typical for aluminosilicate host glasses. The luminescence bands had the same shape in the entire bismuth concentration range from ≤0.01 to 0.8 at.%. The band intensities depend on the bismuth concentration and reach their maxima at 0.1–0.5 at.%.

Efficient hydrogen and deuterium permeation reduction in Al2O3 coatings with enhanced radiation tolerance and corrosion resistance

One of the major bottlenecks in the development of the breeding blanket of the DEMO fusion reactor is the suppression of tritium permeation through structural steels as well as their protection against dissolution-corrosion by interaction with high temperature heavy liquid metals. Reduction of tritium permeation and corrosion of structural steels are crucial issues in order to enhance reactor safety and avoid operational implications. As a solution to these two daunting challenges, we developed multifunctional alumina coatings capable to tackle, at the same time, tritium permeation and Pb–Li corrosion. The coatings are deposited by pulsed laser deposition and are essentially amorphous, with nanocrystalline inclusions. By optimizing the deposition process, we provide experimental evidence that PLD-grown alumina yields a permeation reduction factor for hydrogen and deuterium well above 104, even after electron irradiation, and a suitable protection against corrosion by the Pb–16Li eutectic. Given these results, the multifunctional, PLD-grown alumina coatings stand out as a viable solution to some of the long-lasting issues related to fusion technologies.

Development of the technology of manufacturing connecting elements in cascade photodetectors

In this paper, we report on the initial studies of cascade photodetectors. The heterostructures used in this work are based on InP. InP is the most suitable material for converting the solar spectrum in the range from 0.95 to 1.2 μm. It is proposed to use nanocrystalline inclusions as a connecting element. For this, nanocrystals GaP are best suitable. Because this material (GaP) does not create an absorption of the incident radiation.