Crystallite Domain Research Articles

Assessing the origin of carbonates in a complex soil with a suite of analytical methods

Stable isotope C analysis is the most reliable method used for the distinction and understanding of soil carbonates origin. However, in soils with a complex geological setting the carbonate δ13C signature could lead to incorrect interpretations if used alone. Thus coupling this technique to other methods may be necessary. In this work we evaluated advantages and disadvantages of several methods, some of which are well known while others are still unused, to distinguish among carbonates of different origins in a soil developed on “Valle Versa Chaotic Complex”, a marly geological formation in North-western Italy. For a better evaluation of their potentialities the methods were also applied to simpler situations used as a reference for carbonate of pedogenic and lithogenic origins. Thin sections analysis revealed the presence of three kinds of carbonates in the investigated complex soil: one was pedogenic, while two showed clear lithogenic origin. The lithogenic carbonate that showed a low δ13C (about −9‰) was interpreted as freshwater while isotopic signature increased up to −4‰ with the presence of marls, thus no evidence of pedogenic precipitations could be obtained with isotopic analysis. The mean crystallite domain (L104) was highly variable and related to the amounts of co-precipitated impurities in the carbonates. Thus these methods provided important information about the formation environment. These rarely used techniques permitted to distinguish between pedogenic and lithogenic material in simple systems, but did not adequately support the presence of pedogenic carbonates in the complex soil. Surface areas and porosity evaluated by N2 adsorption are particularly influenced by the processes occurring during calcification such as the development of coatings and pore infillings. The comparison between additive models and measured specific surface area, indeed allowed us to observe the effect of pedogenic carbonate on the physical properties, although it did not permit any quantification. These results indicated that, although all the methods were able to distinguish between pedogenic and lithogenic origins in simple systems, only micromorphology and N2 adsorption techniques allowed for the identification of pedogenic carbonate in a more complex soil system.

Effect of crystal structure on polarization reversal and energy storage of ferroelectric poly(vinylidene fluoride-co-chlorotrifluoroethylene) thin films

A series of ferroelectric poly(vinylidene fluoride-co-chlorotrifluoroethylene) films with different crystallite sizes have been obtained by varying the film processing conditions. The impact of the crystallite size on the dipole switching and the electric energy density has been systematically studied by the electric displacement–electric field hysteresis loop measurements. The films with smaller crystallite sizes display larger polarizability, as evidenced by higher maximum polarization and lower dipole switching field in the charging process. Small crystals also facilitate fast dipole depolarization during the discharging process. Consequently, superior released energy densities have been achieved in the films containing small sizes of the ferroelectric crystallite domains. On the other hand, large crystallite sizes are beneficial for the dielectric breakdown strength and the Weibull distribution of the breakdown field of the films. This study sheds new fundamental light on the optimization of the crystal structures of the ferroelectric polymers for high electric energy storage applications.

A multitechnique approach to assess the effect of ball milling on cellulose.

This paper presents a detailed analysis of effect induced by a dry ball milling process on cellulose structure, morphology and properties. The partial amorphization of cellulose was qualitatively estimated by ATR-FTIR analysis. Through WAXD analysis the crystallinity index and the mean size of the cellulose crystallite domains were calculated, both these parameters showing a progressive decrease as a function of the milling time. In particular, crystallinity index decreased from 0.53 to 0.15 after 60min ball milling, whereas the mean size of the cellulose crystallite domains showed a reduction from the original value of about 4.0nm up to about 3.4nm after 30min. These quantitative results were confirmed by 13C CP-MAS NMR analysis and measurements of the proton spin-lattice relaxation time in the rotating frame (T1ρ1H). Moreover, the increasing of the amount of water absorbed by cellulose samples (from 7.3wt% for untreated cellulose up to 11.6wt% for the cellulose sample ball milled for 60min) and the reduction of the thermal stability were evaluated by TGA. Finally, SEM analysis revealed that the original fibrous structure almost disappeared and was modified to a quasi-circular shape.

Effects of Thermal Annealing Upon the Nanomorphology of Poly(3‐hexylselenophene)‐PCBM Blends

Grazing incidence X-ray diffraction (GI-XRD) is used to characterize the crystallographic dynamics of low molecular weight (LMW) and high molecular weight (HMW) poly(3-hexylselenophene) (P3HS) films and blend films of P3HS with [6-6-]-phenyl-C(61) -butyric acid methyl ester (PCBM) as a function of 'step-by-step' thermal annealing, from room temperature to 250 °C. The temperature-dependent GIXRD data show how the melting point of P3HS crystallites is decreased by the presence of PCBM. P3HS crystallite domain sizes dramatically increase upon annealing to the P3HS melting temperature. The formation of well-oriented HMW P3HS crystallites with the (100) plane parallel to the substrate (edge-on orientation), when cooled from melt, are observed. We compare the behaviour of P3HS pure and blend films with that of poly(3-hexyl)thiophene (P3HT) pure and PCBM blended films and suggest that the similar temperature dependent behaviour we observe may be a common to polythiophene and related polymers and their blends.

Graphitized carbon on GaAs(100) substrates

We report on the formation of graphitized carbon on GaAs(100) surfaces by molecular beam epitaxy. We grew highly carbon-doped GaAs on AlAs, which was then thermally etched in situ leaving behind carbon atoms on the surface. After thermal etching, Raman spectra revealed characteristic phonon modes for sp2-bonded carbon, consistent with the formation of graphitic crystallites. We estimate that the graphitic crystallites are 1.5–3 nm in size and demonstrate that crystallite domain size can be increased through the use of higher etch temperatures.

Curvature-Coupled Hydration of Semicrystalline Polymer Amphiphiles Yields flexible Worm Micelles but Favors Rigid Vesicles: Polycaprolactone-Based Block Copolymers

Crystallization processes are in general sensitive to detailed conditions, but our present understanding of underlying mechanisms is insufficient. A crystallizable chain within a diblock copolymer assembly is expected to couple curvature to crystallization and thereby impact rigidity as well as preferred morphology, but the effects on dispersed phases have remained unclear. The hydrophobic polymer polycaprolactone (PCL) is semi-crystalline in bulk (T(m) = 60°C) and is shown here to generate flexible worm micelles or rigid vesicles in water from several dozen polyethyleneoxide-based diblocks (PEO-PCL). Despite the fact that `worms' have a mean curvature between that of vesicles and spherical micelles, `worms' are seen only within a narrow, process-dependent wedge of morphological phase space that is deep within the vesicle phase. Fluorescence imaging shows worms are predominantly in one of two states - either entirely flexible with dynamic thermal undulations or fully rigid; only a few worms appear rigid at room temperature (T << T(m)), indicating suppression of crystallization by both curvature and PCL hydration. Worm rigidification, which depends on molecular weight, is also prevented by copolymerization of caprolactone with just 10% racemic lactide that otherwise has little impact on bulk crystallinity. In contrast to worms, vesicles of PEO-PCL are always rigid and typically leaky. Defects between crystallite domains induce dislocation-roughening with focal leakiness although select PEO-PCL - which classical surfactant arguments would predict make worms - yield vesicles that retain encapsulant and appear smooth, suggesting a gel or glassy state. Hydration in dispersion thus tends to selectively soften high curvature microphases.

Crystallization Dynamics of a Single Layer Complex Plasma

We report a series of complex (dusty) plasma experiments, aimed at the study of the detailed time evolution of the recrystallization process following a rapid quench of a two-dimensional dust liquid. The experiments were accompanied by large-scale (million-particle) molecular dynamics simulations, assuming Yukawa-type interparticle interaction. Both experiment and simulation show a ∝t(α) (power-law) dependence of the linear crystallite domain size as measured by the bond-order correlation length, translational correlation length, dislocation (defect) density, and a direct size measurement algorithm. The results show two stages of order formation. On short time scales, individual particle motion dominates; this is a fast process characterized by α=0.93±0.1. At longer time scales, small crystallites undergo collective rearrangement, merging into bigger ones, resulting in a smaller exponent α=0.38±0.06.

Effect of Water on the Changes in Morphology and Proton Conductivity for the Highly Crystalline Hydrocarbon Polymer Electrolyte Membrane for Fuel Cells

The effects of water on the changes in morphology of sulfonated poly(phenylene sulfide) (SPPS) hydrocarbon polymer electrolyte membranes (PEM) with an ion exchange capacity (IEC) of 0-2.0 mequiv/g are investigated using small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM). Wide-angle X-ray scattering (WAXS) was used to characterize the effect of direct sulfonation on the changes in membrane crystalline structure, and it was found that the crystallinity and crystallite domain size decrease and the volume of the amorphous region in the SPPS membranes increases with increasing IEC. The experimental data have been fitted to the Porod law for approaching the analysis of the sharpness of the polymer/water interface, development of the proton channel, or dispersion of water in the hydrated membranes. Porod plots showed positive deviation which revealed that the polymer/water interface in the hydrated SPPS membrane is not smooth but diffused and a well-developed proton channel does not form in the membrane.

Deposition and characterisation of nanocrystalline Mo 2N/BN composite coatings by ECR plasma assisted CVD

In this study, nanocomposite coatings consisting of the nitrides of Molybdenum and boron are deposited on Si using a hybrid ECR-CVD and sputtering of molybdenum using a BF 3–H 2–N 2 reactive gas mixture in He plasma. By controlling the gas ratio, the film composition and crystallinity can be modified. The film structure, chemical and phase composition and mechanical properties are characterised by glancing incidence X-ray diffraction (GI-XRD), Fourier-transform Infrared spectroscopy (FTIR), Time-of-Flight Secondary Ion Mass Spectrometry (tof-SIMS), Scanning and transmission electron microscopy (SEM and HRTEM), and nanoindentation. FTIR measurements indicate that the mass fraction of the BN phase can be varied by changing the gas ratio BF 3/H 2. XRD and SEM observations reveal a decrease in the crystallite size of the γ-Mo 2N phase below 50 nm associated with increasing the BN fraction. XRD line profile analysis indicated an exponential decay in the mean size of coherently diffracting γ-Mo 2N crystallite domains which in turn develop large compressive strains by increasing the film BN fraction. Film hardness ranges from 10 ± 1 to 18.5 ± 0.5 GPa while the reduced elastic modulus decreases monotonously from 220 ± 22 to 94 ± 1 GPa by increasing the BF 3 flow rate from 0 to 1.8 sccm, respectively. However, the ratio of hardness to reduced elastic modulus (H 3/E 2) shows a maximum for films prepared with 0.23 and 0.45 sccm BF 3 suggesting that these nanocomposite films are expected to show improved tribological performance and can therefore be interesting for wear resistance applications.

Growth dynamics of C60 thin films: Effect of molecular structure

The surface morphology and growth behavior of fullerene thin films have been studied by atomic force microscopy and height difference correlation function analysis. In contrast to the large growth exponents (β) previously reported for other organic semiconductor thin-film materials, a relatively small β value of 0.39±0.10 was determined. Simulations of (1+1)-dimensional surface lateral diffusion models indicate that the evolution of deep grain boundaries leads to a rapid increase in β. We suggest that the commonly observed large β values for organic thin films are due to their intrinsically anisotropic molecular structures and hence different stacking directions between crystallite domains.

Amino acid synergetic effect on structure, morphology and surface properties of biomimetic apatite nanocrystals

Alanine, arginine and aspartic acid have been used as co-reagents during the synthesis of a biomimetic calcium-deficient hydroxyapatite (CDHA) for the synergistic coupling of synthesis and functionalization. The surface and bulk characterizations are consistent with a binding model in which the amino acid is preferentially bound to the CDHA nanocrystal surface by its lateral chain group. The ζ-potential measurements show that the amino acid-functionalized CDHA surface charge shifts towards neutral compared to CDHA synthesized in the absence of amino acids. Amino acids bound to the crystal induce crystal growth inhibition predominantly at the Ca-rich surfaces during the initial stages of crystallization. Moreover, high-resolution transmission electron microscopy measurements suggest a model for needle-shaped CDHA nanocrystals formation in the presence of either arginine or aspartic acid based on the oriented aggregation of primary crystallite domains specifically along the c-axis direction and the self-assembly of preformed nanoparticles. The results have significant importance for the control of the shape, morphology and aggregation of the CDHA nanocrystals, while the observed surface modifications are of marked importance for the nature, stability and reactivity of the functionalized surfaces produced.

Thermal Properties and Crystallization Behaviors of Polylactide and Its Enantiomeric Blends

AbstractThermal properties and crystallization behaviors of polylactide and its enantiomeric blends are investigated. DSC results demonstrate that only homopolymer crystallite is observed in PDLA and PLLA single polymers. A relatively stronger crystal structure, stereocomplex, can be achieved by mixing the two PLAs in a 1:1 ratio. For non‐equimolar blends, both types of crystallites are formed at lower temperature than that of the single polymer counterparts. The degree of reduction in crystallization temperature is dependent on the degree of deviation of blend content from the equimolar value and the mobility of the polymer chain. The composition of the two crystallite domains is also dependent on the blend content, where the stereocomplex content is maximized in a 1:1 blend, and decreases upon varying the mixing ratio from equimolar value. Infrared spectroscopy is employed to follow the crystallization mechanisms of the non‐equimolar blend. Results indicate a domination of stereocomplex formation band characteristics, despite evidences suggesting an existent of homopolymer crystallite formation, probably due to the involvement of CH··OC hydrogen bonding, which leads to larger change in dipole moment responsible for infrared transitions.

Characteristics of vanadium-substituted mesoporous silica with wormhole framework structure: effects of vanadium content

Vanadium-substituted wormhole framework structure (V-WMS) mesoporous silicas (V-WMS) with various Si/V ratios in the range of 15 and 200 were prepared at ambient temperature by neutral surfactant templating pathway. The materials were synthesized by using dodecylamine as a template and tetraethylorthosilicate as a silicon source. They were characterized by energy dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (XRD), N2 adsorption–desorption, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared absorption spectroscopy (FT-IR) and ultraviolet-visible absorption spectroscopy. V-WMS samples shown characters of larger framework wall thickness, small crystallite domain sizes, and complementary textural mesoporosities in comparison with M41S materials. These mesoporous V-WMS samples exhibited irregularly shaped mesoscale fundamental particles which aggregated into larger particles. They also demonstrated better thermal stability than MCM-41. An absorption band of FT-IR at ca. 960 cm−1 was assigned to the vibration of Si–O–V linkages. These samples also showed one strong UV–visible absorbance with overlapping maxima at about 255 nm. The results show that vanadium was incorporated into the structure of wormhole mesoporous silica (WMS). However, for V-WMS with high vanadium content (Si/V < 25), a broad shoulder in XRD pattern was observed at about 3–4°, suggesting the presence of impurity phase of vanadium species in the sample. The efforts in preparing V-WMS specimens by neutral-template synthesis route had led to new mesoporous silica molecular sieves with catalytically active vanadium centers.

On the Microstructure of HPT Processed Cu under Variation of Deformation Parameters

The evolution of strength characteristics and the microstructure of copper subjected to high pressure torsion (HPT) are studied under variation of strain and hydrostatic pressure. Measurements of Multiple X-ray Bragg Profile Analysis (MXPA) yield microstructural parameters like dislocation density and arrangement, as well as crystallite (domain) size and distribution, and long-range internal stresses. TEM investigations are carried out to analyse the structural elements and to compare them with the results of MXPA. The strength behaviour is studied by microhardness measurements. The investigations are performed within wide ranges of resolved shear strains 􀁊 = 1 to 400 and of applied pressures p = 0.8 to 8 GPa. The onset of the deformation stages IV and V is strongly affected by the hydrostatic pressure i.e. shifted to higher values of stress and strain with increasing pressure. The experimental results indicate the occurrence of recovery effects, which seem to be of static as well as of dynamic nature, and to be responsible for extended ductility in SPD materials.

Structural and microstructural characteristics of B-doped PbTe semiconductor

The main task of this paper was accurate determination of structural and microstructural parameters of B-doped PbTe semiconductor (“p” type). Four samples (undoped PbTe, and three doped with initial B contents: 1 %, 3 % and 8 %) were synthesized using the Bridgman method and analysed using X-ray powder diffraction (XRD) technique. Structural features were obtained using the Rietveld method and microstructural by diffraction-line broadening methods. Microstructural measurements contain both crystallite domain sizes and microstrain calculations obtained by the Warren-Averbach and the simplified integral-breadth methods.

Characteristics of Gallium-Substituted Hexagonal Mesoporous Silica: Effects of Gallium Content

Gallium-substituted hexagonal mesoporous silicas (Ga-HMS) with various Si/Ga ratios in the range of 15 and 200 were prepared at ambient temperature by neutral surfanctant templating pathway. The materials were synthesized by using dodecylamine as a template and tetraethylorthosilicate as a silicon source. They were characterized by energy dispersive X-ray spectroscopy, powder X-ray diffraction (XRD), N2 adsorption-desorption, thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared absorption spectroscopy and ultraviolet-visible absorption spectroscopy. Ga-HMS samples had high surface areas and uniform mesoporous channels, which are similar to MCM-41. However, they differed from MCM-41 in presenting only a single peak in XRD patterns. They also possessed other characters of larger framework wall thickness, small crystallite domain sizes, and complementary textural mesoporosities in comparison with M41S materials. Ga-HMS materials had micropores and the hysteresis loops were obvious. These small crystallite size and complementary textural mesoporosity provided better access of the framework-confined mesopores. These mesoporous Ga-HMS samples exhibited irregularly shaped mesoscale fundamental particles which aggregated into larger particles. They also demonstrated better thermal stability than MCM-41. The textural pore volumes of Ga-HMS specimens could be up to 20 times as large as the framework volumes. The surfactant could be removed completely by calcination at 650∘C. An absorption band of FT-IR at ca. 960 cm–1 was assigned to the vibration of Si–O–Ga linkages. These samples also showed an absorbance band at 255 nm and 250 nm in UV-vis spectra. The results show that gallium was incorporated into the structure of HMS. The efforts in preparing Ga-HMS specimens by neutral-template synthesis route had led to new mesoporous silica molecular sieves with catalytically active gallium centers.

X-ray diffraction studies of the decomposition and microstructural characterization of cold-worked powders of Cu–15Ni–Sn alloys by Rietveld analysis

The present work concerns study of the precipitation sequence due to aging below the critical aging temperature of cold-worked powder samples of industrially important Cu–Ni–Sn alloys with compositions, Cu–15 wt.% Ni–(5, 8, 13) wt.% Sn. The analysis adopts a recently developed JAVA based software Materials Analysis Using Diffraction (MAUD), based on Rietveld’s whole X-ray pattern fitting methodology. The evoluted phases have been characterized microstructurally in terms of different defect parameters, namely, stacking, twin and compound fault probabilities, crystallite (domain) sizes, microstrains (root mean square, rms strains), dislocation densities, preferred orientation parameters, etc. The analysis also includes quantitative estimation of phase abundances of the precipitating phases. The decomposition due to aging with varying Sn composition and aging period has been critically studied and the percentage of volume fraction of the evoluted phases has been evaluated and compared. The results depict, for the three different alloy compositions, three distinct different types of precipitation sequence comprising α, γ and δ phases with continuously varying volume fractions with aging time. The size-strain-shape analysis adopting the Popa model reveals almost isotropic values of both the crystallite sizes and rms strains in all [ h k l ] directions for the evoluted phases. The values of all the above defect parameters have been evaluated and compared for elucidating a better structure–property relationship.

Synthesis and characterization of amino acid-functionalized hydroxyapatite nanorods

Synthesis of aqueous colloids of amino acid-functionalized hydroxyapatite (HAP; Ca10(PO4)6(OH)2) nanoparticles with rod-like morphology and uniform size was achieved by hydrothermal crystallization at 80 °C and pH 9 in highly supersaturated solutions with a Ca2+∶amino acid molar ratio of 1∶2. Stable suspensions of positively charged nanorods, less than 80 nm in length and ca. 5 nm in width, were obtained in the presence of glycine, alanine, serine, lysine and arginine, and together with FTIR spectroscopy data this was consistent with a general model in which the α-carboxylate of the amino acid was preferentially bound to the crystal surfaces. Variations in the size and shape of the nanoparticles with amino acid used were consistent with differences in the strength of binding at the HAP surfaces. In comparison, stable colloids could not be prepared with aspartic acid due to a relatively low surface charge; instead, the precipitate consisted of highly elongated nanorods, ca. 150 × 3.5 nm in dimension. XRD textural analysis suggested a model for nanorod formation based on the oriented aggregation and fusion of primary crystallite domains specifically along the c axis direction. Colloids consisting of HAP/alanine or HAP/arginine nanoparticles were cross-linked in situ by thermal, hydrothermal or chemical polymerisation of surface-attached and unbound amino acids to produce aggregated nanostructures with variable degrees of long-range order.

Microstructural characterization of the evoluted phases of ball-milled α-Fe 2O 3 powder in air and oxygen atmosphere by Rietveld analysis

Transformation reaction induced due to ball-milling of iron oxide, α-Fe 2O 3 in both air and oxygen atmospheres under closed milling condition has been studied for detailed characterization of the microstructure of all the evoluted phases on milling up to 10 h. The methodology adopted for characterization involves Rietveld’s whole X-ray profile fitting technique adopting the most recently developed software, material analysis using diffraction (MAUD), which incorporates Popa model for crystallite (domain) size and microstrain (root mean square, r.m.s. strain). The analysis also considers lattice defect related features of the microstructure, viz. stacking, twin, compound fault density and dislocation density parameters. The study also undertakes quantitative estimation of volume fractions of the phases evoluted (Fe 3O 4: Fd-3m:1 and FeO: Fm-3m). The results reveal transformation of α-Fe 2O 3 to Fe 3O 4 and finally to FeO occurs in both air and oxygen atmospheres, and the reaction speed is slower in oxygen environment. The reaction is controlled by oxygen partial pressure, which decreases on continued milling. A critical oxygen partial pressure is reached at 3–4 h of milling, when Fe 3O 4 phase attains maximum saturation with nano-order (7–8 nm) crystallite sizes, reduced r.m.s. strain and high dislocation density (∼10 12 cm −2). Prolonged milling (7–10 h) results in further reduction of oxygen partial pressure, resulting in complete transformation of α-Fe 2O 3 and Fe 3O 4 to FeO, having nano-order (6–7 nm) crystallite sizes, high r.m.s. strain (∼10 −2) and high dislocation density values (∼10 12 cm −2) in both the environments, except that the transformation reaction is slowed down in oxygen.

STM and Raman spectroscopic study of graphite irradiated by heavy ions

Highly oriented pyrolytic graphite was irradiated with swift heavy ions (Ne, Cr, Fe, Ni, Zn, Xe and U) of fluences between 10 11 and 10 14 ions/cm 2 in energy range MeV–GeV. The combination of scanning tunneling microscopy (STM) and Raman spectroscopy studies shows that large numbers of tracks protrude from the surface. The disordered crystal lattice is leading to a Raman-active D mode. Quantitative analysis of the peak intensity indicates that the size of the crystallite domain is larger than the mean distance between in-plane tracks observed by STM.