Crystallite Size Distribution Research Articles

Energy-resolved neutron imaging study of a Japanese sword signed by Bishu Osafune Norimitsu.

Our research focuses on elucidating the crystallographic structure of Japanese swords in a nondestructive manner using the neutron imaging instrument RADEN at the Materials and Life Science Experimental Facility of the Japan Proton Accelerator Research Complex(J-PARC). We developed an analysis method combining wavelength-resolved Bragg-edge imaging and wavelength-selective neutron tomography with a new strategy and applied it to an approximately 45-cm blade length Japanese sword signed by Bishu Osafune Norimitsu. Computed tomography was performed, and the three-dimensional analysis captured the characteristic internal structure of Kobuse. Kobuse is the most famous steel-combining structure of Japanese swords, where an outer steel with high-carbon content (Kawagane) covers a core steel with low-carbon content (Shingane). The crystallite size distribution obtained through Bragg-edge analysis could consistently explain the internal structure of two steels observed in neutron tomograms. Our nondestructive imaging revealed deep hardening, forming a wavy pattern more than 5mm from the cutting edge.

Determination of the average crystallite size and the crystallite size distribution: the envelope function approach EnvACS.

A procedure is presented to exactly obtain the apparent average crystallite size (ACS) of powder samples using standard in-house powder diffraction experiments without any restriction originating from the Scherrer equation. Additionally, the crystallite size distribution within the sample can be evaluated. To achieve this, powder diffractograms are background corrected and long-range radial distribution functions G(r) up to 300 nm are calculated from the diffraction data. The envelope function f env of G(r) is approximated by a procedure determining the absolute maxima of G(r) in a certain interval (r range). Fitting of an ACS distribution envelope function to this approximation gives the ACS and its distribution. The method is tested on diffractograms of LaB6 standard reference materials measured with different wavelengths to demonstrate the validity of the approach and to clarify the influence of the wavelength used. The latter results in a general description of the maximum observable average crystallite size, which depends on the instrument and wavelength used. The crystallite site distribution is compared with particle size distributions based on transmission electron microscopy investigations, providing an approximation of the average number of crystallites per particle.

Geological conditions and fluid flow history that lead to the development of large clastic dykes in basins: A case study from Kushiro, Japan

AbstractLarge clastic dykes (the Harutori‐Taro and Harutori‐Jiro dykes) and smaller dykes are exposed in the underground Kushiro Coal Mine (KCM), Japan. This study examines these dykes as a case study to investigate the geological conditions and fluid flow history that lead to the development of large clastic dykes in basins. The composition of the dykes indicates the Beppo and/or Harutori formations as their parent unit. Crystallite size distribution (CSD) analysis reveals Ostwald ripening of the kaolinite in the kaolinitised feldspar from the dykes, suggesting stagnant conditions in the parent unit before the dyke was formed. In contrast, smectite CSDs and the high carbonate content of the dykes suggest that large volumes of fluid flowed through the dykes along the established hydraulic gradient, which was triggered by the breaking of the upper seal. The isotopic and chemical compositions of the calcite and aragonite in the dykes, with moderate siderite and rhodochrosite content, indicate the fluid was a warm (>30°C) mixture of freshwater and saltwater, which was transferred from deeper levels of the parent unit towards the crest of an anticline. Immediately after sand injection, the semi‐closed system of the parent unit near the root of the large dyke was transformed into a major flow channel for overpressurised fluids. Subsequently, a large volume of fluid flowed along the vertical conduit (or dyke) over a long period of time (>1 Myr), which removed fluid from a widespread area (i.e., several hundred square kilometres) of the basin. The results show that thin parent units, poor lateral continuity of the upper seal, and spatially heterogeneous overpressurisation do not preclude the formation of large dykes.

Dehydration of goethite during vacuum step-heating and implications for he retentivity characterization

Uncertainty exists over what environmental conditions and mineralogical/chemical properties are required to ensure retention of helium such that (UTh)/He dates record the time of goethite crystallization. We undertook vacuum step heating experiments to determine He diffusion parameters for extrapolation to Earth surface conditions on 10 goethite specimens in which we had created a uniform distribution of 3He. Arrhenius plots of apparent diffusion coefficients on all samples follow the same pattern. At temperatures <200 °C the data define arrays consistent with progressive degassing of increasingly large crystallites. However, above 200 °C the computed diffusivities increase dramatically until about 80% of the helium is extracted, after which they suddenly decline. The sudden increase in diffusivity at 200 °C coincides with the onset of dehydration of the goethite structure, a process which continues throughout the remainder of the step heat. There is a strong correlation between evolved water and 3He amounts. These observations likely reflect previously reported processes of formation, growth, and coalescence of pores as the phase transition to hematite proceeds. While significantly higher dehydration temperatures of ∼270 °C are observed using techniques such as thermogravimetric analysis in air, the long step durations, and vacuum conditions of our experiments destabilize goethite. Orders of magnitude differences in the computed diffusivities among our samples may reflect crystallite-size-distribution control on dehydration kinetics, and the qualitative size distributions we infer from the step heats are consistent with SEM observations of crystallite lengths. Vacuum step-heating experiments in which goethite is decomposing cannot be used to determine He diffusion behavior in nature, but the inferred crystallite size distribution provides some useful indirect evidence. A strong relationship exists between metrics of the crystallite size distribution from step heating results and the degree of He retention in nature inferred from the 4He/3He method. This observation provides evidence supporting the validity of the 4He/3He technique for estimating retention, and further suggests that the dominant control on He retention in nature is the crystallite size distribution. Experiments under hydrothermal conditions in which goethite remains stable may be an alternative approach to address the question of He diffusion behavior in nature.

Accelerated recrystallization of nanocrystalline films as a manifestation of the inner size effect of the diffusion coefficient

The work is devoted to the study of recrystallization occurring during short-term annealing of 100 nm thick polycrystalline films of copper and silver. It is found that in copper films deposited by the method of thermal evaporation onto a substrate at room temperature, a bimodal crystallite size distribution with maxima at 15 and 35 nm is observed. The bimodal distribution in copper films is preserved during annealing, which leads to a shift of both peaks of the crystallite size distribution histograms to the larger sizes region. In contrast to Cu, even in as-deposited Ag films, besides the nanosized fraction, micron-sized crystallites are present. Apparently, these grains are formed due to the phenomenon of self-annealing and weakly evolve during heating owing to grain growth stagnation. The nanosized fraction in as-deposited Ag films is represented by crystallites with the most probable size of 25 nm, which increases to 50 nm as a result of short-term annealing at the temperature of 250 °C. The grain-boundary diffusion coefficient was determined, which is more than 10−18 m2/s for both films of metals. The obtained value indicates a multiple intensification of self-diffusion processes in films, the thickness of which allows us to refer them to macroscopic sample.

Time-Dependent Multi-Particle Model Describing the Hydrogen Absorption of Nanocrystalline Magnesium Powders: A Case Study

Classical kinetic models describing the hydrogen absorption of nanocrystalline metallic hydrides generally do not involve any parameter related to the change in the crystallite size during the hydrogenation at constant temperature. In the present investigation, ball-milled nanocrystalline Mg powders exhibiting lognormal crystallite size distribution have been subjected to hydrogen absorption in a Sievert-type apparatus. Partially absorbed states were achieved by interrupting the hydrogenation cycle at different hydrogen content, i.e., when 15%, 50%, and 90% of Mg powder transformed to MgH2. The evolution of the characteristic size of the nucleating MgH2 phase was determined from X-ray diffraction analysis. Considering the crystallite size distribution of the as-milled powder agglomerate as well as the growth during the isothermal hydrogenation process, a time-dependent multi-particle reaction function ∝CV¯t;R(t) was developed. It was shown unambiguously for this case study that the measured hydrogen absorption curve of the ball-milled Mg powder shows the best correlation with this model when it is compared to classical kinetic functions or the previously developed multi-particle reaction function excluding the change in the average crystallite size during hydrogenation.

Understanding the Subsurface Microstructure and Thermal Behavior of Model Oxide Dispersion Strengthened Alloys Through FIB_SEM and TEM

AbstractA potential but an underexplored application of FIB_SEM is its ability to image the subsurface microstructure and capability for an associated chemical analysis. In this article, agglomerated microstructures of two model oxide dispersion strengthened alloy systems, consisting of ZrO2 and Y2O3 dispersions, are evaluated to understand its elevated temperature behaviors. The systems under evaluation are relevant as candidate nuclear structural materials for next-generation fast breeder reactors, and FIB_SEM technique is effectively used along with TEM and EDS for a comprehensive understanding of the material microstructure, and the results are discussed. Distinct microstructures are observed for the two systems with a difference in crystallite size distribution and presence of micron-sized dispersoids in Y2O3. The varied behavior of dispersoids is discussed in terms of its pre-annealing microstructures, and the superiority of ZrO2 over Y2O3 as a dispersoid for ODS alloys is emphasized.

Optimization of Luminescence due to SHI Irradiation on Cr‐Doped BiFeO3 (BFO) Thin Films

AbstractThis study reporting tuning of optical luminescence in Cr‐doped BiFeO3 (BCFO) thin films deposited on glass substrate using spin coater and irradiated with Au+9 (100 MeV) swift heavy ions (SHI) at fluence 1013 ions cm−2. The modification of these thin films has been carried out in its structural and optical properties. An X‐ray diffraction spectra of BCFO thin films confirms rhombohedral perovskite structure with crystallite size distribution of 6–10 nm. Fourier transform infrared (FT‐IR) spectra confirms bonding of Cr in BiFeO3 thin films, however scanning electron microscopy (SEM) images confirm the homogeneous been found to be improved with the band gap tuning in between 2.75 and 2.59 eV via SHI irradiation as per the observations from optical absorption spectra. The purpose of the present study is to synthesize and characterize Cr doped BiFeO3 thin films by a simple spin‐coating method and investigates photovoltaic properties modification due to SHI irradiation for photovoltaic devices.

Impact of ECAP processing on dislocation density and subgrain size in a ti6al4V alloy prepared by direct energy deposition

Ti6Al4V alloy billets were additively manufactured by direct energy deposition and then equal channel angularly pressed (ECAPed) at 700 °C. The originally prepared α′ martensite microstructure was completely converted to an equiaxed fine grain structure during ECAP processing. The α′ martensite decomposed into α + β dual phase structure. The dislocation density in the deposited and ECAPed samples was measured by X-ray profile analysis in samples of two orientations. The dislocation density estimated in the deposition plane was found to be higher than that estimated perpendicularly. This difference is probably a consequence of the internal stresses generated in the samples during the deposition process. A similar anisotropy in dislocation density and crystallite size was found in the ECAPed samples. Lattice constants were measured for the α′ martensite and α phase of the ECAPed alloy. The crystallite size distribution was found to be moderately different for samples cut parallel and perpendicular to the extrusion direction.

Significance of diffraction peak shapes in determining crystallite size distribution: a peak shape analysis procedure for pseudo-Voigt profiles and its application

The width (or breadth) and shape of a diffraction peak are two important characteristics to describe a peak profile. These features are directly associated with the microstructural (size and strain) properties of a material. It is important to separate the contributions of crystallite size and microstrain from the diffraction peak profiles in order to establish their correlation with the physical properties of the sample. While procedures to deconvolve the widths of a diffraction peak profile are extensively documented in the literature, the shape part of the peak profile is usually ignored. In the present work an approach for a quantitative estimation of the peak shape contribution made by crystallite size is discussed to complement the information available via the existing breadth-based methods (BBMs). A relationship between the shape of a diffraction peak profile and the crystallite size distribution for a nanomaterial is presented, which was not hitherto available in the literature. It is shown that the commonly observed difference between crystallite sizes obtained using the Scherrer equation considering two different definitions of peak width,i.e.full width at half-maximum and integral breadth, is also associated with this peak shape parameter. Thus, knowledge of the peak shape has a vital role in microstructural understanding. Therefore, in this work a procedure to isolate the shape part of a diffraction peak profile is described in connection with the existing BBMs used for microstructural analysis. This study further aims to utilize the information on these peak shapes to provide comprehensive details of the effect of crystallite size by considering a log-normal distribution to complement the BBMs. Applications of this approach are shown using several worked examples of practical situations from the literature.

Lotus-root-like titanium dioxide photocatalyst with a hierarchical micro-/meso-/macroporous structure

Titanium dioxide agglomerate with a hierarchical micro-/meso-/macroporous structure was synthesized by a very simple method using only titanium alkoxide and water as raw materials. The microscopic morphology of the agglomerate looked like a lotus-root including cylindrical macropores with sizes of 1–10 μm in diameter penetrating into the agglomerate. The agglomerate was composed of TiO2 nanoparticles that form micropores smaller than 1 nm and mesopores smaller than 10 nm. The agglomerate was heat-treated at 300–700oC for 1 h to modify its crystalline phase, crystallite size, and pore size distribution. Anatase-type agglomerates with a micro-/meso-/macroporous structure having specific surface areas of 35–405 m2/g showed high humidity buffering performance and high photocatalytic activity. Both properties are equal to or higher than each of the commercial products. Furthermore, they showed high hydrophilicity with a water contact angle below 20 degrees even before UV light irradiation.

Magneto-structural characterization of different kinds of magnetic nanoparticles

Using well-established measurement techniques like transmission electron microscopy (TEM), dynamic light scattering (DLS), small and wide angle X-ray scattering (SAXS, WAXS), susceptometry, and magnetorelaxometry, the distribution of the physical and magnetic size (magnetic moments) and magnetic anisotropy of a variety of structurally different magnetic nanoparticle samples (MNPs) is analyzed and compared. A term which accounts for the presence of weak magnetic areas (WMAs) within the MNPs was introduced to the widespread analysis model for M(H) data, enabling a consistent interpretation of the data in most of the systems. A comparison of the size distributions as obtained for the physical and the magnetic diameter suggests a multidomain structure for three single core systems under investigation, in all probability evoked by the presence of a wustite phase, as identified by WAXS.Analyzing the relationship d < dm < dc between the average single core diameter d, the effective magnetic (domain) size dm and the cluster diameter dc quantitatively, two qualitatively different magnetic structures in multicore MNP (MCMNP) systems were identified: (i) The magnetic moments of single cores within the MCMNP of fluidMAG tend to build flux closure structures, driven by dipole–dipole interaction. (ii) The magnetic behavior of Resovist® was attributed to the presence of domain sizes of about 12 nm within MCMNP, exceeding the single core diameters of 5 nm. Thereby, WAXS revealed a bimodal crystallite size distribution suggesting a crystallite merging process within the MCMNP. The value of the effective magnetic moment of these MCMNP could be explained within the presented “random moment cluster model” (RMCM).We conclude that the combination of physical and magnetic structure parameters obtained from complementary measurement methods allows a reliable assessment of the magnetic structure of single and multicore MNPs.

Steady state population balance modelling of precipitation processes: Nucleation, growth and size-dependent agglomeration

In this work a numerical methodology to solve the steady state Population Balance Equation (PBE) is developed. Three crystallisation mechanisms are included, namely: nucleation, size-independent growth and size-dependent loose agglomeration. The numerical method is based on the discretisation of the crystal size as distributed variable. In order to describe the loose agglomeration, the numerical methodology solves two PBE: one including the nucleation and growth mechanisms and one accounting for the agglomeration process. From the first PBE, liquid phase composition, supersaturation, developed crystal surface and Crystallite Size Distribution (CSD) are obtained. Similarly, the second PBE leads to the Agglomerate Size Distribution (ASD). The study of the size-dependant agglomeration kernel induces an additional numerical difficulty due to the dependency of both PBE and agglomeration kernel on the particle size. An accelerated fixed point algorithm based on the crossed secant method is adapted to overcome the difficulty and accurately solve the agglomeration PBE. The oxalic precipitation of uranium is simulated using this numerical methodology. First, the experimental results of a reference case are compared with the numerical predictions in terms of particle size distribution, mean size, mass fraction and moments. Then, the operating conditions are varied in order to test the algorithm robustness and performances. In all cases, the crossed secant method ensures the size-dependent agglomeration PBE solution and properly predicts the ASD. The developed numerical methodology predicts the mean particle size under the experimental uncertainty in a reasonable computation time and number of iterations.

Investigation of electrodeposited copper layer with island twinning structure on Zr substrate

ABSTRACT In this study, the surface properties of copper layers on a zirconium substrate were investigated. The copper deposits with thicknesses of 25, 50, and 100 μm were formed using the electroplating method. The evaluations of coating thickness, surface morphology, crystallite size, and grain distribution were performed by using the relevant analytical equipment. The results showed that by increasing the thickness of the copper layer, a more uniform cauliflower morphology was obtained. Also, by increasing the thickness of the copper deposit, the crystallite size was decreased from 70 to 20 nanometers and the strain energy was decreased from 2.9 × 10−3 J to 6.5 × 10−3 J. The copper layer with a thickness of 100 μm was the most wear resistance compared to other coatings. The highest hardness value, uniform morphology, and more twin islands in different areas were the main reasons for improving the wear resistance of the copper layer with a thickness of 100 μm.

Dielectric properties and crystallite size distribution of modified lead-free sodium-bismuth titanate ceramics

Influence of (K0.5Bi0.5)TiO3 (KBT) dopants on crystal and microstructure, ferroelectric and dielectric properties of ceramic composition from morphotropic phase boundary in the system (1–x–y)(Na0.5Bi0.5)TiO3 – xBaTiO3 – y (K0.5Bi0.5)TiO3 (x = 0.06, y = 0–0.15) additionally modified by ZnO additives was studied using a complex of methods. Changes from 42.8 nm to 62.6 nm of the volume-weighted crystallite size distribution function G(L) corresponding to coherent scattering regions were observed. The microstructure and the second harmonic generation data indicated a change in the relative content of polar nanoregions in tetragonal nonpolar matrix. Decrease in temperatures of phase transitions T m and T d was observed with KBT concentration increasing.

In Ukrainian

The study of the microstructure of nanocrystalline substances by the method of powder diffractometry based on the physical broadening of diffraction lines involves the use of diffraction data of standard polycrystalline samples, preferably, one nature with the test samples with the size of crystallites exceeding 100 nm. In the absence of such standards, researchers resort to the existing dependence of the width of diffraction peaks on the angle of diffraction for the standard sample or the construction of theoretical instrumental profiles due to the collimation parameters of x -rays used. In this paper a comparative study of the microstructure of nanocrystalline titanium oxide (anatase), tin oxide iron oxide (magnetite), synthesized in various ways, using several methods of analysis of powder diffractograms, was carried out. To evaluate the average crystallite sizes of the studied oxides, the Sherer equation with a graphical method of determining the width of instrumental profile and the influence of dublet radiation was chosen. Methods of profile analysis of diffraction spectra, such as a method of whole profile modeling of powder diffractograms (WPPM) and the chord method, were used to construct crystallite size distribution functions and determine the average size of crystallites of the oxides. Modeling of instrumental diffraction profiles of titanium, tin and iron oxides was performed using X -rays collimation parameters determinated using a polycrystalline silicon as standard and pseudo -Voigt function, which best describes the form of diffraction peak. The crystallite size distribution functions were constructed by means of WPPM and chords methods based on the instrumental profiles. It has been found that the values of average size of the crystallites, obtained by the methods of Sherer, WPPM and chords, differ within the one order of magnitude for each oxide. Thus, for titanium oxide this value is within 12-18 nm, for tin oxide within 7-10 nm, the iron oxide of iron within 9-12 nm. Analysis of size crystallite distribution functions and average sizes of the crystallites of the studied oxides showed the advisability of using different methods of studying microstructure to clarify the true type of the size crystallites distribution and establish its connection with the conditions and the synthesis method.

Effect of substrate and annealing temperature on the physical properties of the thin films of SnSe2-SnSe alloy

Thin films of SnSe2-SnSe alloy were deposited at substrate temperatures 300 and 473 K by thermal evaporation. The 473 K as-deposited layers were re-grown on annealing from 523 to 623 K. The films show mixed phases of hexagonal SnSe2 and orthorhombic SnSe and display corresponding vibrational modes. The unit cell parameters and axes strain of the layers vary and show crystallite size distributions with changes in annealing temperature (Ta). Moreover, the film smoothness increases at elevated temperatures. The films as-deposited at 300 K exhibit direct bandgaps (Eg) of 1.15 and 1.52 eV. Further, the Eg values of 473 K layers vary from 1.47 to 1.56 eV with a change in temperature from 523 to 623 K and show an absorption coefficient (α) ≥ 5 × 104 cm−1. In addition, the refractive index (n) decreases, and optical mobility (μopt) increases with an increase in Ta. The above optical response indicates the films to be optically active and suitable in photonic devices in the visible and NIR portion of the EM spectrum. The PL emission peaks were observed at 805.1 and 1064.22 nm, which confirmed the presence of direct bandgaps of the SnSe2 and SnSe phases.

Dislocations and crystallite size distribution of cadmium oxide thin films synthesized by spray pyrolysis technique

Cadmium oxide (CdO) thin films have been successfully deposited on amorphous glass substrates by spray pyrolysis technique at a temperature, 573 °K using aqueous solution of cadmium nitrate 4-Hydrate powder with a concentration of 0.1 M. The X-ray diffraction (XRD) studies have revealed that the films exhibit cubic crystal structure. The modified Williamson–Hall and Warren–Averbach methods are used successfully for analyzing the XRD line profile for determining the crystallite size, dislocation densities and crystallite size distribution in CdO thin films. The crystallite size (D) and integral breadths (d) (D = 44.139 nm and d = 32.237 nm) are obtained by the modified Williamson Hall, while the area-weighted average grain sizes and volume-weighted obtained of modified Warren–Averbach method are xvol=46,06nm andxarea=29,7nm, respectively. The size parameter (Lo), dislocation density (ρ), effective outer cut-off radii (Re) and dislocation arrangement parameter (μ) gotten of Warren–Averbach are 35.53 nm, 2.0 × 1015 m−2, 7 nm and 0.31 nm, respectively. The particle size distribution (x) derived of XRD and estimated of size parameter is the size distribution function f(x) of log-normal.

Hysteresis in Heat Capacity of MWCNTs Caused by Interface Behavior.

The paper is concerned with the study of structural disorder as well as the emergence and causes of heat capacity hysteresis in multiwall carbon nanotubes. The investigation methods are X-ray diffraction analysis, Raman spectroscopy, transmission electron microscopy, and calorimetric tests: thermogravimetric analysis, differential scanning calorimetry, and the thermal relaxation method for heat capacity hysteresis. Multiwall carbon nanotubes are shown to be composed of one or several types of zigzag–armchair domains. The domain structure of nanotube samples is responsible for the generation of uniaxial elastic microstrains and viscoelastic bending strains at domain interfaces. The thermomechanical behavior of interfaces is the chief cause of temperature hysteresis of heat capacity. The number of hystereses corresponds to the number of domain types in the structure, and values of hysteresis are determined by the crystallite size, thermal conductivity, and normal temperature distribution of strain. The found mechanism of heat capacity hysteresis can be helpful in preventing jumps in thermal properties and managing thermal memory in multiwall carbon nanotubes.

Rate Capability of LiFePO4 Cathodes and the Shape Engineering of Their Anisotropic Crystallites

For cuboid and ellipsoid crystallites of LiFePO4 powders, by X-ray diffraction (XRD) and microscopic (TEM) studies, it is possible to determine the anisotropic parameters of the crystallite size distribution functions. These parameters were used to describe the cathode rate capability within the model of averaging the diffusion coefficient D over the length of the crystallite columns along the [010] direction. A LiFePO4 powder was chosen for testing the developed model, consisting of big cuboid and small ellipsoid crystallites (close to them). When analyzing the parts of big and small rate capabilities, the fitting values D = 2.1 and 0.3 nm2/s were obtained for cuboids and ellipsoids, respectively. When analyzing the results of cyclic voltammetry using the Randles-Sevcik equation and the total area of projections of electrode crystallites on their (010) plane, slightly different values were obtained, D = 0.9 ± 0.15 and 0.5 ± 0.15 nm2/s, respectively. We believe that these inconsistencies can be considered quite acceptable, since both methods of determining D have obvious sources of error. However, the developed method has a clearly lower systematic error due to the ability to actually take into account the shape and statistics of crystallites, and it is also useful for improving the accuracy of the Randles-Sevcik equation. It has also been demonstrated that the shape engineering of crystallites, among other tasks, can increase the cathode capacity by 15% by increasing their size correlation coefficients.