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Results for “lattice parameter determination”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Precision lattice parameter determination from transmission diffraction of thick specimens with irregular cross sections

Accurate determination of lattice parameters from X-ray diffraction requires that the diffraction angles be measured very precisely, and significant errors result if the sample–detector separation differs from that assumed. Transmission diffraction from bones, which have a complex cross section and must be left intact, is a situation where this separation is difficult to measure and it may differ from position to position across the specimen. Here, this article describes a method for eliminating the effect of variable sample cross section. Diffraction patterns for each position on the specimen are collected before and after 180° rotation about an axis normal to the cross section of interest. This places the centroid of the diffracting mass at the center of rotation and provides the absolute lattice parameters from the average apparent lattice parameters at the two rotation angles. Diffraction patterns were collected across the cross section of three specimens: a 3D-printed elliptical cylinder of Hyperelastic Bone (HB), which is composed primarily of synthetic hydroxyapatite (hAp), a 3D-printed HB model of the second metacarpal bone (Mc2), and a modern human Mc2 containing nanocrystalline carbonated apatite (cAp). Rietveld refinement was used to determine precise unit-cell parameters a apparent and c apparent for each pattern of each scan, and these values determined the actual average < a > and < c > for each sample. In conclusion, the results indicate that the 0°/180° rotation method works well enough to uncover variations approaching 1 × 10 -3 Å in cAp unit-cell parameters in intact bones with irregular cross sections.

36 MATERIALS SCIENCE↗
NASA NTRS1996

Transmission Electron Microscope Measures Lattice Parameters

Convergent-beam microdiffraction (CBM) in thermionic-emission transmission electron microscope (TEM) is technique for measuring lattice parameters of nanometer-sized specimens of crystalline materials. Lattice parameters determined by use of CBM accurate to within few parts in thousand. Technique developed especially for use in quantifying lattice parameters, and thus strains, in epitaxial mismatched-crystal-lattice multilayer structures in multiple-quantum-well and other advanced semiconductor electronic devices. Ability to determine strains in indivdual layers contributes to understanding of novel electronic behaviors of devices.

Pike, William T.↗
DOE OSTI2018

The Effect of Silver Ion Occupancy on Hollandite Lattice Structure

The effect of tunnel cations on tunnel size in α-MnO 2 structured (hollandite, cryptomelane) materials has long been of interest, as the tunnel size effects catalytic and transport properties. Previous research on the tunnel size has focused on potassium cryptomelane (K x Mn 8 O 16 ). This paper uses synthetic control of silver content in Ag x Mn 8 O 16 to investigate the effect that tunnel silver occupancy has on the lattice parameters. Materials with silver (x) content between 1.14 and 1.66 were synthesized, synchrotron diffraction and Rietveld Refinement was used to determine lattice parameters. The lattice parameters were found to contract as silver content increases (from 9.774 Å to 9.738 Å), in contrast to previous investigations of other tunnel cations.

36 MATERIALS SCIENCE↗
DOE OSTI2026

High energy X-ray characterization of the microstructure of PuGa alloy samples at macroscopic depths and non-ambient conditions

High energy (95 keV) X-rays were utilized to characterize the microstructure of eight PuGa alloy samples at room temperature and during cooling to ∼10 K. The samples had different Ga content (nominally 0-3.4 at.%), age, and history. A ninth sample, similarly characterized with neutron diffraction, was included to extend the Ga range to 7 at.%. The samples span the range from single phase α (monoclinic) to δ (face-centered cubic) PuGa, as well as a two-phase α′/δ sample. The crystallographic textures, phase fractions, lattice parameters and dislocation densities of each sample were evaluated through distinct analysis techniques. The textures of the samples were modest. In each case, the dislocation densities were relatively high, comparable to cold worked metals and metals exposed to similar radiation dose. At room temperature, the lattice parameters determined in the predominantly single-phase samples were larger than expected based on the nominal Ga concentration. The observed lattice thermal expansions of the single-phase δ samples to 10 K are self-consistent across the samples and consistent with previous measurements reported in the literature. Significantly larger thermal lattice strain is observed in the δ phase of the two-phase material due to mechanical constraint from the α′ phase, which has a three times larger thermal expansion and is much harder than the δ phase. In conclusion, the results demonstrate the unique value of high-energy X-rays for relatively routine microstructural characterization of Pu alloy samples.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Thermodynamic re-modelling of the Cu–Nb–Sn system: Integrating the nausite phase

Currently available Cu–Nb–Sn phase diagrams lack the recently discovered nausite phase (Cu,Nb)Sn 2 , which is an important intermediate in the course of thermal processing of superconducting Nb 3 Sn wires. Processing decisively determines the resulting microstructure of Nb 3 Sn and, thus, its superconducting properties. Lack of suitable and complete phase diagrams, however, obstructs rational design of such thermal processing procedures. To close this gap and to obtain valid knowledge of homogeneity and stability range of nausite, various Cu–Nb–Sn samples, which are heat-treated between 300 °C and 500 °C, are investigated. By means of energy-dispersive X-ray spectroscopy (EDX), a temperature-dependent homogeneity range of nausite is observed, which covers average mole fractions of Cu between 0.09 and 0.15. This is correlated with a change in the mean atomic volume and can be seen in the lattice parameters determined by X-ray diffraction (XRD). Additionally performed first-principles calculations on different CuSn 2 and NbSn 2 model structures confirm this trend. Furthermore, the peritectic decomposition of nausite to NbSn 2 and liquid at 586 °C is determined by means of in situ XRD and differential scanning calorimetry (DSC). By using the CALPHAD (CALculation of PHase Diagrams) approach, all these findings are used to extend a previous thermodynamic description of the Cu–Nb–Sn system by including the nausite as an additional phase. Finally, with this noteworthy integration, the updated modelling of the Cu–Nb–Sn system can be used for optimizing the multistage heat-treatment steps during processing superconducting Nb 3 Sn wires.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Surface speciation and interactions between adsorbed chloride and water on cerium dioxide

Abstract: Ceria particles with different specific surface areas were contaminated with chloride and water, then heat treated at 500 and 900 °C, to investigate the sorption behaviour onto the metal oxide. The association of chloride with the particles was investigated using electron microscopy and energy dispersive x-ray analysis. Results from xray photoelectron spectroscopy, x-ray absorption spectroscopy (XAS) and infrared spectroscopy show that the amount of chloride and water adsorbed on the particles increases with surface area. These species are mostly removed upon heat treatment, from 6.3 to 0.8 at% Cl- on high specific surface area, and 1.4 to 0.4 at% on low specific surface area particles. Lattice parameters determined by x-ray diffraction reveal that chloride is not incorporated into the bulk ceria structure, but crystal size does increase upon contamination. Sintering of contaminated high specific surface area particles occurs with heat treatment at 900 °C, until they resemble low specific surface area particles synthesised at this temperature. The Ce L-edge XAS of ceria particles shows that chloride is not present in the first co-ordination sphere around Ce(IV) ions, so is not directly bonded to Ce as a chloride in the bulk structure.

Sutherland-Harper, Sophie↗
DOE OSTI2016

Investigations of cations distributions and morphology of cobalt ferrite magnetic nanoparticles

Cobalt ferrite nanoparticles were synthesized by co-precipitation method and structural properties was investigated by X-ray diffraction (XRD) at room temperature. X-ray diffraction data was used to determine lattice parameter, X-ray density, distributions of cations among tetrahedral and octahedral sites, site radii, ionic radii and bond length of inverse spinel cobalt ferrite. XRD analysis revealed crystallinity and high intense peak correspond to cubic inverse spinel structure with average crystalline size measured by X-ray line profile fitting was found to be 13nm for most intense peak (311). The surface morphology and microstructural feature was investigated by TEM analysis which revealed that particle size varying from 12-22 nm with selected electron diffraction pattern (SAED).

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS2002

Effect of the Chemical State of the Surface on the Relaxation of the Surface Shell Atoms in SiC and GaN Nanocrystals

The effect of the chemical state of the surface of nanoparticles on the relaxation in the near-surface layer was examined using the concept of the apparent lattice parameter (alp) determined for different diffraction vectors Q. The apparent lattice parameter is a lattice parameter determined either from an individual Bragg reflection, or from a selected region of the diffraction pattern. At low diffraction vectors the Bragg peak positions are affected mainly by the structure of the near-surface layer, while at high Q-values only the interior of the nano-grain contributes to the diffraction pattern. Following the measurements on raw (as prepared) powders we investigated powders cleaned by annealing at 400C under vacuum, and the same powders wetted with water. Theoretical alp-Q plots showed that the structure of the surface layer depends on the sample treatment. Semi-quantitative analysis based on the comparison of the experimental and theoretical alp-Q plots was performed. Theoretical alp-Q relations were obtained from the diffraction patterns calculated for models of nanocrystals with a strained surface layer using the Debye functions.

Palosz, B.↗
NASA NTRS2003

The Traps of using Conventional Methodology of Evaluation of Powder Diffractograms for Determination of the Lattice Parameters of Nanocrystals

Inherent errors introduced by the algorithm of standard procedures of evaluation of powder diffractograms when applied for nanopowders are shown. The implications of the errors are discussed in connection with some results reported in the literature. Alternate methodology of evaluation of powder diffractograms of nanocrystals is presented.

Curreri, Peter A.↗
DOE OSTI2016

X-Ray diffraction on large single crystals using a powder diffractometer

Information on the lattice parameter of single crystals with known crystallographic structure allows for estimations of sample quality and composition. In many cases it is sufficient to determine one lattice parameter or the lattice spacing along a certain, high- symmetry direction, e.g. in order to determine the composition in a substitution series by taking advantage of Vegard’s rule. Here we present a guide to accurate measurements of single crystals with dimensions ranging from 200 μm up to several millimeter using a standard powder diffractometer in Bragg-Brentano geometry. The correction of the error introduced by the sample height and the optimization of the alignment are discussed in detail. Finally, in particular for single crystals with a plate-like habit, the described procedure allows for measurement of the lattice spacings normal to the plates with high accuracy on a timescale of minutes.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Shear strength of a refractory high entropy alloy MoNbTaVW under high pressure

Radial X-ray diffraction (R-XRD) was performed in situ using a Panoramic Diamond Anvil Cell on the refractory high entropy alloy MoNbTaVW. The lattice parameters were determined through a Le Bail fit using a body centered cubic (BCC) lattice of symmetry $Im$$\overline{3}$$m$ (international space group number 229). Upper and lower bounds to the shear strength were determined up to 80 GPa nonhydrostatically using copper as a pressure standard. The equation of state was derived at the magic angle ψ = 54.7° and yielded a bulk modulus of K 0 = 220.8 ± 1.65 GPa. The experimental lattice parameters and bulk modulus match closely with corresponding density functional theory (DFT) calculations. The BCC phase remains stable up to the highest pressure of 80 GPa studied and is shown to be elastically anisotropic. The shear strength was found to saturate around 70 GPa with a value of τ = 1.75 GPa, and the shear moduli are presented in different limits of iso-strain and iso-stress.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Growth and microtopographic study of CuInSe{sub 2} single crystals

The CuInSe{sub 2} single crystals were grown by chemical vapour transport (CVT) technique using iodine as transporting agent. The elemental composition of the as-grown CuInSe{sub 2} single crystals was determined by energy dispersive analysis of X-ray (EDAX). The unit cell crystal structure and lattice parameters were determined by X-ray diffraction (XRD) technique. The surface microtopographic study of the as-grown CuInSe{sub 2} single crystals surfaces were done to study the defects, growth mechanism, etc. of the CVT grown crystals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

First-Principles Study of the Structure and Magnetic Properties of Fe{sub 8}Rh{sub 8–} {sub x}Z{sub x} (Z = Mn, Pt, Co; x = 1, 2, 3) Alloys

The results of first-principles studies of the structure and magnetic properties of Fe–Rh–Z alloys conducted using the VASP package are reported. The magnetic moments and lattice parameters are determined, and the possibility of existence of stable tetragonal distortions in Fe–Rh–Z alloys with various magnetic configurations set by the level of doping with Mn, Pt, and Co is examined. It is demonstrated that the equilibrium lattice parameter and the type of magnetic ordering change with the concentration of the third element.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Synthesis and Characterization of Sol–Gel Auto Combustion-Derived Ce/Zr-Substituted Strontium Hexaferrite Nanoparticles

In this work, Ce/Zr-substituted strontium hexaferrite (SrFe{sub 12}O{sub 19}) nanoparticles have been synthesized by the sol–gel auto combustion method and the synthesized samples were annealed at 900 {sup ∘}C for 3 h. The powder XRD pattern revealed that all the diffraction peaks match the hexagonal phase of strontium hexaferrite and the lattice parameters are determined. The VSM study revealed that the values of saturation magnetization, coercivity and remanent magnetization are decreased for the Ce/Zr-substituted strontium hexaferrite sample. Thermal analysis reveals the formation of a hexagonal phase above 670 {sup ∘}C. The specific vibration band of hexagonal ferrite was observed in the range 400–600 cm{sup −1}. The FE-SEM image shows that the particles are spherical shaped and particle size varied from 37 to 44 nm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Assessment of diagenesis in archaeological human second metacarpal bones using the intensity of the small angle X-ray scattering D -period peak

Bone consists mainly of carbonated apatite (cAp) nanoplatelets embedded in a matrix of collagen fibrils. Earlier, high-energy small angle X-ray scattering (SAXS) studies of archaeological adult human second metacarpal bones (mc2) found collagen D-period peaks with high-intensity I D in specimens in which microcomputed tomography (microCT) showed little diagenesis and I D ~ 0 for specimens where microCT revealed severe diagenesis (Park et al. 2022 Int. J. Osteoarchaeol. 32, 170–181 (doi:10.1002/oa.3053); Stock et al. 2022 Int. J. Osteoarchaeol. 32, 120–131 (doi:10.1002/oa.3049)). Here, the present paper uses SAXS at beamline 1-ID, Advanced Photon Source, Argonne National Laboratory and other techniques to study a set of 10 mc2 from an early Medieval cemetery at Greding, Germany. We hypothesized that non-invasive measurement of I D would provide an accurate and rapid (approx. 6 min/specimen) assessment of diagenesis in archaeological mc2. Results of Raman spectroscopy, laboratory microCT and backscattered electron, reflected light and polarized transmitted light microscopies confirmed the SAXS determinations, but lattice parameter values from X-ray diffraction were uncorrelated with I D value. Age-at-death estimates placed the 10 mc2 in three age categories (young adult, middle adult, old adult): lattice parameters from X-ray diffraction were uncorrelated with age at death. Cross-sectional bone area fraction from microCT dropped noticeably for the older age cohort.

Raman spectroscopy↗
DOE OSTI2018

Formation of superlattice structure in irradiated materials: a phase field study

The formation and self-organization of fission gas bubbles under irradiation is a unique phenomenon, which affects the swelling behavior and mechanical stability of nuclear materials. We develop a phase field model to investigate the formation mechanism of fission gas bubbles, and associated material properties under different irradiation condition. The thermodynamic and kinetic origin of superlattice formation is systematically analyzed. In particular, the symmetry of the superlattice is dictated by the anisotropic diffusion of interstitial atoms, while the lattice parameter is determined by the instability of vacancy and gas concentration waves. The spatial distribution of gas bubbles strongly depends on the nucleation, growth and coarsening process, which leads to the formation of self-organized superlattice. This study provides a new insight into designing target experiments to tailor desired microstructure under irradiation.

36 MATERIALS SCIENCE↗