Diffraction Line-broadening Analysis Research Articles

Kinetics and energetics of room-temperature microstructure in nanocrystalline Cu films: The grain-size dependent intragrain strain energy

The fast kinetics of the low-temperature microstructure evolution in nanocrystalline metals requires an additional driving force from the excess intragrain energy in addition to the driving forces from the grain boundary energy, surface or interface energy, and thermal strain energy. If the excess volume of the grain boundary induces lattice distortions in grain interiors, the intragrain energy is the elastic-strain energy and can be determined from a grain-size-dependent strain model. Considering the available intragrain strain energy, we use transmission electron microscopy, x-ray diffraction line-broadening analysis, and theoretical models to investigate the kinetics and energetics of room-temperature nanostructure relaxation and abnormal grain growth in electroplated nanocrystalline Cu films devoid of thermal strains and high-density dislocations. The experimental data of grain sizes and microstrains are consistent with the theoretical size-dependent strain model. The limited nanostructure relaxation of Cu occurs with the grain boundary width reduction and intragrain strain release, which cannot alter the structural anisotropy and intrinsic high-energy state of nanograins. Based on quantitative descriptions of the variations in grain size, microstrain, and transformed fraction during abnormal grain growth, the possible driving forces and grain boundary mobility were systematically evaluated. The results indicate that the size-dependent intragrain strain energy provides a crucial driving force for rapid nanograin growth and texture transition, whereas the low nanograin boundary mobility in Cu films is probably correlated with the strained-lattice migration and faceted-boundary migration.

Residual stress and diffraction line-broadening analysis of Al2O3/Y-TZP ceramic composites by neutron diffraction measurement

Time-of-flight neutron diffraction and Rietveld analysis have been used to investigate the residual stresses, crystallite structure and microstructural features in Al2O3/Y-TZP ceramic composites fabricated by two different green processing techniques (a novel tape casting and conventional slip casting) and with different zirconia content (5 and 40vol.% Y-TZP). The change in lattice parameters, individual peak shifts and peak-broadening were analyzed, in order to calculate the uniform residual stress field (mean phase stresses and peak-specific stresses) and the non-uniform microstrains. Peak-specific residual stresses were calculated for different hkl reflections both for the Al2O3 matrix and the Y-TZP particulates. The sign and the magnitude of the peak-specific residual stress are highly dependent on the individual hkl reflection studied and on the volume fraction of zirconia. Peak broadening was observed in the Y-TZP reflections, due to non-uniform microstrains. Both the mean phase stress field and the non-uniform microstrains were mainly influenced by the Y-TZP content in the studied Al2O3/Y-TZP composites, irrespective of the measured direction and the fabrication process.

Microstructure of sol–gel derived Mn-doped gahnite: Correlation of TEM and XRD investigations

Powder ZnAl2O4 (gahnite) samples doped with 0, 4.3, 7.6 and 11.7at% Mn (in relation to Zn) were prepared by a sol–gel technique followed by thermal treatment. The effect of manganese doping on microstructure of the samples has been investigated by transmission electron microscopy and X-ray diffraction. Diffraction patterns showed that all samples were cubic with a spinel structure, space group Fd3¯m. Diffraction lines were broadened indicating nanocrystalline samples. Transmission electron microscopy investigations confirmed that the samples were nanocrystalline. Particles (grains) in the samples, as observed by transmission electron microscopy, were evenly shaped and grain size distribution could be fitted to a lognormal function. Grain sizes determined by TEM analysis and crystallite sizes obtained from diffraction line-broadening analysis were similar. Both decreased with increasing manganese doping level. Increase in doping level from 0 to 11.7at% Mn caused the change in grain size from 25.0(7)nm to 14.2(3)nm and the change in crystallite size from 24.1(1)nm to 18.0(1)nm. Doping Mn2+ cations acted as defects in the gahnite structure that increased lattice strain from 0.07(1)% for undoped sample to 0.21% for sample doped with 11.7at% Mn, and disturbed the crystallites to grow.

Tuning the Microstructure of γ-Ba4Nb2O9 Polymorph Prepared from Single-Molecular Precursor

Although γ-Ba4Nb2O9 was considered to be metastable at room temperature (RT) and, therefore, prepared only by quenching from high temperatures, a new procedure for preparation of pure γ-Ba4Nb2O9 from a single-molecular precursor, the oxalate-based complex {Ba2(H2O)5[NbO(C2O4)3]HC2O4}·H2O, is described. This study focuses on controlling the phase composition and the crystallite domain lengths by altering preparation conditions, namely, (i) the time for which samples were held at the given temperature and (ii) the cooling rate. The high-temperature γ-Ba4Nb2O9 polymorph has been successfully retained and stabilized at RT; the desired crystallite size in the nanoscale regime, ranging from ∼5 to 20 nm, can easily be tuned. The crystallite domain length and lattice strain were calculated from X-ray diffraction line-broadening analysis performed during Rietveld structure refinement.

Coherency Strain and Dislocations in Copper-Rich-Precipitate Embrittled A710 Ferritic Steels

The irradiation embrittlement of reactor pressure vessel steels was studied on surrogate samples of A710 ferritic steels, which is rich in copper. Dislocations and coherency strain caused by the copper-rich precipitates, as a function of aging time, were studied by small-angle neutron scattering, diffraction line-broadening analysis, transmission electron microscopy, and Eshelby inclusion method. Aging has induced copper-rich precipitate nucleation and growth, thus impeding the dislocation motion and hardening the steels. The precipitates are coherent with the matrix up to about 3.5 nm in radius, when they become semi coherent with the ferritic matrix, thus relaxing strains/stresses and softening it. There is good agreement between all experimental techniques used and the Eshelby inclusion model.

Effects of polyelectrolytic peptides on the quality of mineral crystals grown in vitro

Charged amino acids such as arginine, lysine, glutamic acid, and aspartic acid are abundant in noncollagenous proteins that regulate mineralization. Synthetic peptide forms of these amino acids have been shown to affect crystal growth in precipitation of mineral crystals in solution. However, little is known about the effects of these peptides on the viability and phenotype of bone marrow stromal cells (BMSCs) or on the in vitro mineralization process. Bone marrow was harvested from neonatal rat femora and cultured under conditions to induce mineralized nodule formation. Mineralized bone nodules were grown while supplementing the cultures with one of five polyelectrolytes: polystyrene sulfonate (PSS), poly-L: -glutamic acid (PLG), poly-L: -lysine (PLL), poly-L: -aspartic acid (PLA), and sodium citrate (SC), as well as a nontreated control group. The viability and the rate of collagen synthesis under the effect of these agents were characterized by cell-counting and dye-binding assays, respectively. Raman microspectroscopy was conducted on mineralized bone nodules to determine the effect of the polyelectrolytes on the mineralization, type-B carbonation, and crystallinity of the mineral phase. Morphology of resulting mineral crystals was investigated using X-ray diffraction line-broadening analysis (XRD). PSS had toxic effects on cells whereas the remaining agents were biocompatible, as the cell viability was either greater (PLG) or not different from controls. The total collagen production by day 21 was 27% and 42% lower than controls for PLL and PSS, respectively. Culture wells stained positively for alkaline phosphatase in the presence of polyelectrolytes, indicating that osteogenic differentiation was not impacted negatively. Raman microspectroscopy revealed that the type-B carbonation of the crystal lattice increased when treated with PLG, PLL, or PSS. Crystallinity of PLL and PSS was smaller than that of control. The mineral/matrix ratios of nodules did not change with polyelectrolyte treatment, with the exception of the PSS-treated group, which was less mineralized. XRD analysis of bone nodules indicated that PLA-treated samples were significantly longer than controls along the 002 direction. Overall, the results suggest that the polypeptides consisting of charged amino acids are biocompatible and that they have the potential to affect crystal quality and morphology in vitro in the presence of cells. However, the mechanisms by which these effects come into play remain to be investigated.

Microstructure evaluations of carbon nanotube/diamond/silicon carbide nanostructuredcomposites by size–strain line-broadening analysis methods

Efforts have been made to manufacture novel composite materials with improved propertiesby incorporating multi-wall carbon nanotubes (MWNTs) into metal or brittle ceramic.Here we prepared dense MWNT/diamond/silicon carbide (SiC) composites underhigh-pressure and high-temperature (HPHT) conditions by anchoring MWNTs into adiamond/SiC matrix. The measured mechanical properties indicate that the compositeshave both superior hardness and enhanced fracture toughness. Moreover, we haveundertaken an x-ray diffraction line-broadening analysis to elucidate how themicrostructures including domain sizes and micro-strains depend on the externally appliedtemperature and how the microstructures correlate to the macroproperties of theas-fabricated composites.

Microstructural characterization of amorphous and nanocrystalline boron nitride prepared by high-energy ball milling

Microstructural parameters like crystallite size, lattice strain, stacking faults and dislocation density were evaluated from the X-ray diffraction data of boron nitride (BN) powder milled in a high-energy vibrational ball mill for different length of time (2–120 h), using different model based approaches like Scherrer analysis, integral breadth method, Williamson–Hall technique and modified Rietveld technique. From diffraction line-broadening analysis of the successive patterns of BN with varying milling time, it was observed that overall line broadening was an operative cause for crystallite size reduction at lower milling time (∼5 h), whereas lattice strains were the prominent cause of line broadening at higher milling times (>19 h). For intermediate milling time (7–19 h), both crystallite size and lattice strain influence the profile broadening although their relative contribution vary with milling time. Microstructural information showed that after long time milling (>19 h) BN becomes mixture of nanocrystalline and amorphous BN. The accumulations of defects cause this crystalline to amorphous transition. It has been found that twin fault ( β′) and deformation fault ( α) significantly contributed to BN powder as synthesized by a high-energy ball-milling technique. Present study consider only three ball-milled (0, 2 and 3 h) BN powder for faults calculation because fault effected reflections (1 0 1, 1 0 2, 1 0 3) disappear with milling time (>3 h). The morphology and particle size of the BN powders before and after ball milling were also observed in a field emission scanning electron microscope (FESEM).

Studies of oxide-based thin-layered heterostructures by X-ray scattering methods

Some X-ray scattering methods (X-ray reflectometry and Diffractometry) dedicated to the study of thin-layered heterostructures are presented with a particular focus, for practical purposes, on the description of fast, accurate and robust techniques. The use of X-ray scattering metrology as a routinely working non-destructive testing method, particularly by using procedures simplifying the data-evaluation, is emphasized. The model-independent Fourier-inversion method applied to a reflectivity curve allows a fast determination of the individual layer thicknesses. We demonstrate the capability of this method by reporting X-ray reflectometry study on multilayered oxide structures, even when the number of the layers constitutive of the stack is not known a-priori. Fast Fourier transform-based procedure has also been employed successfully on high resolution X-ray diffraction profiles. A study of the reliability of the integral-breadth methods in diffraction line-broadening analysis applied to thin layers, in order to determine coherent domain sizes, is also reported. Examples from studies of oxides-based thin-layers heterostructures will illustrate these methods. In particular, X-ray scattering studies performed on high- k HfO 2 and SrZrO 3 thin-layers, a (GaAs/AlOx) waveguide, and a ZnO thin-layer are reported.

X-ray Diffraction Line Broadening on Vibrating Dry-Milled Two Crows Sepiolite

AbstractA reference sample of sepiolite and products of its comminution by vibrating dry-milling have been studied using X-ray diffraction (XRD) line-broadening analysis, complementary field emission scanning electron microscopy (FESEM) images and surface area measurements. The apparent crystallite sizes determined via XRD are in agreement with observations on FESEM images. The sepiolite aggregates consist of lath-shaped agglutinations of prisms and pinacoids elongated along [001], each lath including several crystallites in that direction. The surface area magnitudes are in the range of previous experimental measurements of other sepiolites. The results obtained show the effectiveness of vibro-milling as the procedure to use for the comminution of sepiolite.

Mechanical and physical properties of high-velocity oxy-fuel-sprayed iron aluminide coatings

Tensile tests and thermal-expansion measurements were performed on free-standing, high-velocity oxy-fuel (HVOF)-sprayed Fe3Al coatings produced at spray-particle velocities of 390, 560, and 620 m/s. To examine the relationship between properties and spray conditions, the microstructures of the coatings were characterized in terms of the fractions of unmelted particles, porosity, and oxide inclusions, as well as the dislocation density assessed by X-ray diffraction (XRD) line-broadening analysis. Residual coating stresses were determined as a function of coating thickness using curvature measurements. The tensile behavior was entirely brittle at room temperature; fracture strengths increased with spray-particle velocity; and the increase in fracture-strength results from decreasing fractions of microstructural defects and better interparticle bonding. The mean thermal-expansion coefficients for the coatings were lower than those for an equivalent wrought material; the differences were attributed to a 7 to 15 vol pct fraction of oxide inclusions.

Determination of dislocation densities in HCP metals from X-ray diffraction line-broadening analysis

X-Ray diffraction (XRD) line-broadening analysis has been performed on highly textured Zr-2.5Nb specimens which had been deformed in tensile tests to produce well-controlled dislocation structures. An iterative deconvolution method has been applied to extract the broadening function for the material, using as standards, a Zr single crystal and a 0 pct deformed specimen. In both cases, for specific tensile tests, a significant contribution to the basal line braodening was observed, which was clearly not directly related to the dislocation structure generated by the deformation, i.e., so-called c-component dislocations having a component of their Burgers vectors perpendicular to the basal plane. Calculations showed that the extent of basal line broadening cannot be attributed to the secondary effect of strain from a-type dislocations, i.e., dislocations with Burgers vectors parallel with the basal plane. It is concluded that most of the line broadening observed was the result of intergranular strain distributions. These distributions are most prominent for grains oriented with their c-axes perpendicular to the tensile-deformation axis and resulted in basal-plane line broadening even when there were few, if any, c-component dislocations present.

Determination of dislocation densities in HCP metals from X-ray diffraction line-broadening analysis

Determination of dislocation densities in HCP metals from X-ray diffraction line-broadening analysis

Simultaneous Synthesis and Consolidation of Nanostructured MoSi2

A new process combining electric field activation and the imposition of pressure from mechanically activated powder mixtures is demonstrated as a means to simultaneously synthesize and densify nano-MoSi2 in one step. Nanophase reactants (Mo + 2Si) produced by mechanical activation are reacted by field activation with the simultaneous application of a uniaxial pressure. Mo + 2Si powders were comilled in a specially designed planetary mill to obtain nanometric reactants but to avoid formation of any product phases. These were then subjected to high alternating currents (1600 A) and pressures of 106 MPa. Under these conditions, a reaction is initiated and completed within a short period of time (3–6 min). The relative density of the product ranged from 82 to 93%. The crystallite size of the MoSi2 compound was determined by x-ray diffraction line-broadening analysis using the Langford method. The size ranged from 58 to 75 nm.

Anionic effects on the size and shape of apatite crystals grown from physiological solutions.

Comparatively little is known of the role tissue fluid electrolytes have in establishing the size and shape of apatite crystals deposited in skeletal tissues. In vitro accretion experiments using synthetic apatite seed crystals comparable in size to bone apatite were performed to assess the extent to which these crystalline features may be affected by direct electrolyte/mineral interactions. A constant composition method was used to maintain the accretion reactions under physiological-like solution conditions (1.33 mmol/liter Ca(2+), 1.0 mmol/liter total inorganic phosphate, (0 or 26) mmol/liter carbonate, 270 mmol/kg osmolality, pH 7.4, 37 degrees C). When the mass of the new accretions equaled the initial seed mass, the solids were harvested and the net change in crystal size resulting from the new accretions was assessed by X-ray diffraction line-broadening analysis. All the electrolytes examined in this study inhibited the accretion rate. The order of effectiveness was phosvitin > polyaspartate approximately polyglutamate > 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) > bovine serum albumin (BSA) > citrate. Citrate and BSA also reduced the mean crystal size of the harvested solids compared with those harvested in the absence of added electrolyte, a finding that suggests that citrate and BSA suppressed growth of the seed crystals in favor of the proliferation of new smaller crystals. In contrast, a net increase in size following accretion compared with controls suggests that the other more strongly inhibiting electrolytes stimulated growth of the primary seed crystals and/or of the secondary crystals. These size changes, however, were anisotropic, with the anions effecting primarily increases in crystal width/thickness rather than in length. The effects were also more pronounced in the presence of carbonate. Our findings suggest that the strength of the interaction with the crystal surface may be relatively more important than molecular size or conformational complexity in establishing the effect that electrolytes have on apatite growth and proliferation. The results also suggest that adsorbed electrolytes may be a significant factor in controlling the size of apatite crystals in skeletal tissues by inducing proliferation of new crystals and/or affecting crystal shape by selectively modifying growth of the lateral dimensions.

Reliability of the Simplified Integral-Breadth Methods in Diffraction Line-Broadening Analysis

A comparison between different simplified integral-breadth methods, often used in the Rietveld-refinement programs to calculate coherent domain size and lattice strain, is carried out. It is shown that systematic differences exist for both domain size and strain, when they simultaneously broaden diffraction lines. Among different approximations, the values of domain size exceptionally scatter and sometimes are completely false (negative or not real). A comparison to the alternative Fourier method shows that all the simplified integral-breadth methods overestimate domain size, but especially the Cauchy–Cauchy approximation. The root-mean-square strain and the upper limit of strain are related in the general case of the Voigt strain-broadened line profile. It is shown that they should not differ much as the profile changes between the Gauss and Cauchy extremes. The pure-Gauss size-broadened profile is incompatible with the definitions of surface-weighted domain size and column-length distribution function.

Transparency Effects of a Standard Specimen in Diffraction Line-Broadening Analysis

Transparency Effects of a Standard Specimen in Diffraction Line-Broadening Analysis

Determination of Dislocation Densities in Hexagonal Close-Packed Metals using X-Ray Diffraction and Transmission Electron Microscopy

AbstractX-ray diffraction (XRD) line-broadening analysis has been used to determine dislocation densities in zirconium alloys with hexagonal closepacked (hep) crystal structures and a complex distribution of dislocations reflecting the plastic, anisotropy of the material. The validity of the technique has been assessed by comparison with direct measurements of dislocation densities in deformed polycrystalline and neutron-irradiated single crystal material using transmission electron microscopy (TEM). The results show that-there is good agreement between the XRD and TEM for measurements on the deformed material whereas there is a large discrepancy for measurements on the irradiated single crystal; the XRD measurements significantly underestimating the TEM observations.

X-Ray diffraction characterization of iridium dioxide electrocatalysts

An X-ray diffraction (XRD) line-broadening analysis of coatings of pyrolytic iridium dioxide supported on amorphous silica microbeads is reported. The influence of the temperature of pyrolysis and of the annealing treatments on the average crystallite sizes of the IrO2 and Ir phases have been studied in detail. The values obtained for IrO2 are lower than those obtained from an analgous RuO2 system. However, the analysis suggests that in both cases the crystalline phase grows within an amorphous microcrystalline environment where impurities are mostly segregated in the amorphous phase and then released to the atmosphere. The lattice parameters are also calculated. Compared with the reference values, slightly greater values are obtained both for IrO2 and for Ir.

Controlled microstructural properties of zinc oxide powder formed by the thermal decomposition of zinc hydroxynitrate

A detailed analysis of the microstructural properties, i.e., microdistortion, size and shape of crystallite, of zinc oxide produced by thermal decomposition of zinc hydroxynitrate Zn 3(OH) 4(NO 3) 2 is presented. The physico-chemical parameters of the reaction, such as the heating rate, mean decomposition rate, sample mass and residual pressure, are important in determining the microstructure of the ZnO produced. Under the experimental conditions used, the shape of the crystallites is cylindrical on average. By modifying the parameters it is possible to modulate the crystallite sizes and also their anisotropic form factor over a limited range. The influence of the residual pressure is prominent in the formation of reticular microdistortions. Strain-free ZnO, of interest in diffraction line-broadening analysis, can be prepared only in small quantities under vacuum, the upper limit for the precursor mass being about 25 mg.