Neutron Diffraction Study of Residual Stress in a Multi-Pass Gas Tungsten Arc Weld [Power Point]
No abstract prepared.
36 MATERIALS SCIENCE↗
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Results for “Neutron diffraction”
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In-situ neutron diffraction study of non-equilibrium phase transformation in advanced high-strength steels
No abstract prepared.
36 MATERIALS SCIENCE↗
Synthesizing pseudo-Kossel lines from neutron transmission data. II. Validation with neutron diffraction data
A new method to recover the orientation matrix of a single crystal with a known unit cell by analyzing synthesized pseudo-Kossel lines from time-of-flight neutron transmission data has been outlined in a companion article [Dessieux et al. (2023). J. Appl. Cryst. 56, https://dx.doi.org/10.1107/S1600576723001346; referred to here as Article I]. In this work, validation of this new technique is presented by employing experimental neutron transmission and diffraction measurements performed on two copper single-crystal specimens. Time-of-flight spectra were recorded during rotation (ω) of the single crystals about a vertical axis perpendicular to the incident neutron beam. The λ–ω maps recorded in transmission are utilized to determine the crystal orientation with respect to the neutron beam, following the procedure presented in Article I. Further, to validate the indexing procedure, the crystal orientations are compared with those obtained via conventional methods using the diffraction data. The resulting pseudo-Kossel lines across the 2D detectors are also observed for the first time.
36 MATERIALS SCIENCE↗
Neutron diffraction discriminates between models for the nanoarchitecture of graphene sheets in glassy carbon
Glassy carbon is a chemically inert, biocompatible, disordered material with the graphene sheet as its basic building block. Structural characterisation techniques have so far been unable to provide definitive distinction between the many proposed models for its structure. Computer based simulation methods have made a step forward by predicting structure from interaction potentials, but the results are sensitive to the choice of the potential. Here we use the white neutron beam of the Spallation Neutron Source at Oak Ridge National Laboratory coupled with the SNAP time-of-flight diffractometer to sample the reciprocal space of glassy carbon and calculate accurate radial distribution functions. From the radial distribution information, we determine graphene sheet dimensions, registration, curvature, and assess defect content to rank the proposed structures in terms of their agreement with experimental data. In this work, we find that the recent models derived from empirical potentials give the best agreement.
36 MATERIALS SCIENCE↗
Effective residual stress prediction validated with neutron diffraction method for metal large-scale additive manufacturing
Not Available
36 MATERIALS SCIENCE↗
Neutron diffraction study on magnetic structures and transitions in Sr 2 Cr 3 As 2 O 2
Sr 2 Cr 3 As 2 O 2 is composed of alternating square-lattice CrO 2 and Cr 2 As 2 stacking layers, where CrO 2 is isostructural to the CuO 2 building-block of cuprate high- T c superconductors and Cr 2 As 2 to Fe 2 As 2 of Fe-based superconductors. Current interest in this material is raised by theoretic prediction of possible superconductivity. In this neutron powder diffraction study, we discovered that magnetic moments of Cr(II) ions in the Cr 2 As 2 sublattice develop a C-type antiferromagnetic structure below 590 K, and the moments of Cr(I) in the CrO 2 sublattice form the La 2 CuO 4 -like antiferromagnetic order below 291 K. The staggered magnetic moment 2.19(4)μ B /Cr(II) in the more itinerant Cr 2 As 2 layer is smaller than 3.10(6)μ B /Cr(I) in the more localized CrO 2 layer. Furthermore, different from previous expectations, a spin-flop transition of the Cr(II) magnetic order observed at 291 K indicates a strong coupling between the CrO 2 and Cr 2 As 2 magnetic subsystems.
74 ATOMIC AND MOLECULAR PHYSICS↗
Oxygen transport pathways in Ruddlesden–Popper structured oxides revealed via in situ neutron diffraction
Ruddlesden-Popper structured oxides, general form A n+1 B n O 3n+1 , consist of n-layers of the perovskite structure stacked in between rock-salt layers, and have potential application in solid oxide electrochemical cells and ion transport membrane reactors. Three materials with constant Co/Fe ratio, LaSrCo 0.5 Fe 0.5 O 4-δ (n = 1), La 0.3 Sr 2.7 CoFeO 7-δ (n = 2), and LaSr 3 Co 1.5 Fe 1.5 O 10-δ (n = 3) were synthesized and studied via in situ neutron powder diffraction between 765 K and 1070 K at a pO 2 of 10 -1 atm. Then, the structures were fit to a tetragonal I4/mmm space group, and were found to have increased total oxygen vacancy concentration in the order La 0.3 Sr 2.7 CoFeO 7-δ > LaSr 3 Co 1.5 Fe 1.5 O 10-δ > LaSrCo 0.5 Fe 0.5 O 4-δ , following the trend predicted for charge compensation upon increasing Sr 2+ /La 3+ ratio. The oxygen vacancies within the material were almost exclusively located within the perovskite layers for all of the crystal structures with only minimal vacancy formation in the rock-salt layer. Finally, analysis of the concentration of these vacancies at each distinct crystallographic site and the anisotropic atomic displacement parameters for the oxygen sites reveals potential preferred oxygen transport pathways through the perovskite layers.
36 MATERIALS SCIENCE↗
Operando measurement of lattice strain in internal combustion engine components by neutron diffraction
Significance Internal combustion engine components experience extreme thermomechanical cycling during operation, and the continuing need to improve engine efficiency while maintaining or improving reliability drives the development of lightweight materials with improved thermal and mechanical integrity. Understanding the behavior of new materials in dynamic operation requires operando characterization tools, but conventional in situ measurements of material behavior during real engine operation are very limited, and no practical means exist to replicate such extreme dynamics for ex situ study. In this work, we demonstrate that the penetrating power of neutrons can provide noninvasive measurement of lattice strains inside components of a firing engine, enabling the operando study of complex load states and thermal gradients throughout the solid materials.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Reply to “Structural and magnetic behavior of the cubic oxyfluoride SrFeO{sub 2}F studied by neutron diffraction”
In this article we comment on the results published by Thompson et al. (, J. Solid State Chem. 219 (2014) 173–178) on the crystal structure of SrFeO{sub 2}F, who claim the compound to crystallize in the cubic space group Pm-3m. We give a more detailed explanation of the determination of our previously reported structural model with Imma symmetry (Clemens et al., J. Solid State Chem. 206 (2013) 158–169), with addition of variable temperature XRD measurements with high counting time to provide unambiguous evidence for the Imma model being correct for our sample. - Graphical abstract: The crystal structure of SrFeO{sub 2}F is discussed with regards to previous reports. - Highlights: • SrFeO{sub 2}F was synthesized by polymer based fluorination of SrFeO{sub 3}. • Evaluation of the diffraction data shows a pseudocubic cell metric. • Superstructure reflections at low d-spacings indicate deviation from cubic symmetry. • The phase transition temperature from orthorhombic to cubic was determined using variable temperature X-ray diffraction. • Results published by Thompson et al. are critically discussed with respect to those observations.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Resolving the Chemical Formula of Nesquehonite via NMR Crystallography, DFT Computation, and Complementary Neutron Diffraction
Nesquehonite is a magnesium carbonate mineral relevant to carbon sequestration envisioned for carbon capture and storage of CO 2 . Its chemical formula remains controversial today, assigned as either a hydrated magnesium carbonate [MgCO 3 · 3H 2 O], or a hydroxy- hydrated- magnesium bicarbonate [Mg(HCO 3 )OH · 2H 2 O]. Here, the resolution of this controversy is central to understanding this material‘s thermodynamic, phase, and chemical behavior. In an NMR crystallography study, using rotational-echo double-resonance 13 C{ 1 H} (REDOR), 13 C- 1 H distances are determined with precision, and the combination of 13 C static NMR lineshapes and density functional theory (DFT) calculations are used to model different H atomic coordinates. [MgCO 3 · 3H 2 O] is found to be accurate, and evidence from neutron powder diffraction bolsters these assignments. Refined H positions can help understand how H-bonding stabilizes this structure against dehydration to MgCO 3 . More broadly, these results illustrate the power of NMR crystallography as a technique for resolving questions where X-ray diffraction is inconclusive.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Expanding Lorentz and spectrum corrections to large volumes of reciprocal space for single-crystal time-of-flight neutron diffraction. Corrigendum
The author list is amended with the addition of Michal Chodkiewicz, Thomas Weber and Hans-Beat Bürgi. Here, the complete list of authors is Tara Michels-Clark, Andrei Savici, Vickie Lynch, Xiaoping Wang, Michal Chodkiewicz, Thomas Weber, Hans-Beat Bürgi and Christina Hoffmann.
99 GENERAL AND MISCELLANEOUS↗
Response to reply on “Structural and magnetic behavior of the cubic oxyfluoride SrFeO{sub 2}F studied by neutron diffraction”
Clemens et al. reported on the results published by us (Thompson et al. J. Solid State Chem. 219 (2014) 173–178) on the crystal structure of SrFeO{sub 2}F, which they suggest to actually crystallize in the orthorhombic space group Imma rather than the cubic Pm-3m structure at lower temperatures (Clemens et al. J. Solid State Chem. (2015), (http://dx.doi.org/10.1016/j.jssc.2015.02.022)). In this report, we provide evidence to support their claim that at lower temperatures (<523 K) the structure is evidently Imma. Furthermore, we will highlight the significance of our previous report and comment on the proposed explanations of the magnetic behavior of SrFeO{sub 2}F reported by both groups.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Expanding Lorentz and spectrum corrections to large volumes of reciprocal space for single-crystal time-of-flight neutron diffraction
Evidence is mounting that potentially exploitable properties of technologically and chemically interesting crystalline materials are often attributable to local structure effects, which can be observed as modulated diffuse scattering (mDS) next to Bragg diffraction (BD). BD forms a regular sparse grid of intense discrete points in reciprocal space. Traditionally, the intensity of each Bragg peak is extracted by integration of each individual reflection first, followed by application of the required corrections. In contrast, mDS is weak and covers expansive volumes of reciprocal space close to, or between, Bragg reflections. For a representative measurement of the diffuse scattering, multiple sample orientations are generally required, where many points in reciprocal space are measured multiple times and the resulting data are combined. The common post-integration data reduction method is not optimal with regard to counting statistics. A general and inclusive data processing method is needed. In this contribution, a comprehensive data analysis approach is introduced to correct and merge the full volume of scattering data in a single step, while correctly accounting for the statistical weight of the individual measurements. Development of this new approach required the exploration of a data treatment and correction protocol that includes the entire collected reciprocal space volume, using neutron time-of-flight or wavelength-resolved data collected at TOPAZ at the Spallation Neutron Source at Oak Ridge National Laboratory.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
X-ray and neutron diffraction study of the defect crystal structure of the as-grown nonstoichiometric phase Y{sub 0.715}Ca{sub 0.285}F{sub 2.715}
This work begins a series of papers aimed at studying the defect structure of nonstoichiometric phases R{sub 1-y}Ca{sub y}F{sub 3-y} with a tysonite-type (LaF{sub 3}) structure. In the single-crystal structure of Y{sub 0.715}Ca{sub 0.285}F{sub 2.715} with a tysonite-type small unit cell (sp. gr. P6{sub 3}/mmc, a = 3.9095(2) A, c = 6.9829(2) A; Z = 2; R{sub w} = 2.16%), the displacements of Y{sup 3+} cations and F{sup 2-} anions from 6{sub 3} symmetry axes were observed for the first time. The X-ray diffraction pattern shows weak satellites insufficient for structural calculations. The LaF{sub 3} structure type is stabilized up and down on the temperature scale due to anion vacancies and the symmetrizing effect of Ca{sup 2+} cations lying on 6{sub 3} symmetry axes. At 120 Degree-Sign C the fluoride-ion conductivity in the nonstoichiometric phase Y{sub 0.715}Ca{sub 0.285}F{sub 2.715} is five orders of magnitude higher than that in the stoichiometric phase {beta}-YF{sub 3}. The transition to a superionic state is caused by a deviation from stoichiometry and is not associated with reconstructive phase transformation.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Shifting and tilting towards enhanced piezoelectricity in high-temperature ceramics: an average structure study of (1 − x )BiFe 2/8 Ti 3/8 Mg 3/8 O 3 – x PbTiO 3 through X-ray and neutron diffraction
A comprehensive report is provided of the average structure of a high Curie temperature ferroelectric ceramic, (1 − x)BiFe 2/8 Ti 3/8 Mg 3/8 O 3 –xPbTiO 3 (BFTM–xPT) when x = 0.25–0.375 at room temperature. Both neutron and synchrotron X-ray powder diffraction data were collected and combined Rietveld refinements were completed. These data revealed that, of the compositions studied, BFTM–xPT crystallizes as mixed phase material. At x = 0.25–0.275, the average structure of each phase is best described by space groups R3c and Cc. At 0.30 ≥ x ≥ 0.35, a morphotropic phase boundary is present and is best modelled by space groups P4mm and Cc, where space group Cc is the dominant phase. As the concentration of PbTiO 3 increases, the amount of octahedral tilting decreases and x = 0.375 exhibits a loss of octahedral tilting and crystallizes in space groups P4mm and Cm. In conclusion, an updated phase diagram at room temperature of this novel system is given and structural intricacies responsible for its piezoelectric properties are revealed.
high Curie temperature↗
Understanding Structure–Activity Relationships in Sr 1– x Y x CoO 3–δ through in Situ Neutron Diffraction and Electrochemical Measurements
In this study, we report a systematic study on temperature-dependent local structural evolution, oxygen stoichiometry, and electrochemical properties of an oxygen-deficient perovskite Sr 0.7 Y 0.3 CoO 3–δ (SYC30) for oxygen electrocatalysis. The obtained results are then closely compared with its analogue Sr 0.9 Y 0.1 CoO 3–δ (SYC10) of different crystal structures to establish structure–activity relationships. The comparison shows that both SYC30 and SYC10 consist of alternate layers of oxygen-deficient Co1-polyhedra and oxygen-saturated Co2-octahedra with Co1-polyhedra being responsible for V o •• migration. It is also found that the distribution and concentration of oxygen vacancies within the Co1-layer are, respectively, less symmetrical and lower in SYC30 than those in SYC10, making the former unfavorable for oxygen transport. A molecular orbital energy analysis reveals that the energy gap between Fermi level and O 2p level in the active Co1-polyhedra is larger in SYC30 than that in SYC10, further suggesting that SYC10 is a better oxide-ion conductor and thus a better electrocatalyst for oxygen reduction reaction, which is unambiguously confirmed by the subsequent electrochemical measurements.
36 MATERIALS SCIENCE↗