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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Cleavable quaternary oxychlorides with high magnetic ordering temperatures

Quaternary oxychlorides derived from Ruddlesden–Popper 3d transition metal oxides offer a route to cleavable crystals with bulk antiferromagnetic ordering temperatures reaching at least 550 K. Here, we study the magnetic, optical, and mechanical behavior of Sr 2 FeO 3 Cl, Ca 2 FeO 3 Cl, Ca 3 Fe 2 O 5 Cl 2 , and Sr 3 Fe 2 O 5 Cl 2 . Through optical absorption measurements, we show that these antiferromagnetic semiconductors have optical band gaps of ≈2.1(1) eV. The magnetic ordering symmetries and temperatures were probed by neutron powder diffraction and Mössbauer spectroscopy on polycrystalline samples, demonstrating Néel temperatures (T N ) near room temperature in the single layer Sr 2 FeO 3 Cl (T N ≈ 311 K) and Ca 2 FeO 3 Cl (T N ≈ 360 K), and the double-layer compound Sr 3 Fe 2 O 5 Cl 2 has T N ≈ 545 K. The high-spin moments of Fe 3+ lie within the basal plane and the magnetic structures are compensated within each magnetic layer and characterized by magnetic propagation vectors k = ($\frac{1}{2}$ $\frac{1}{2}$ 0). Magnetization results demonstrate the quasi-2D nature of the magnetism, with a broad maximum in the susceptibility near 2T N for Sr 2 FeO 3 Cl. Scotch tape tests and mechanical exfoliation onto SiO 2 confirm the micaceous nature of these crystals with cleavage down to a single unit cell (two magnetic layers) achieved for Sr 3 Fe 2 O 5 Cl 2 . In conclusion, this paper highlights strong antiferromagnetic interactions, semiconducting band gaps, and cleavability of quaternary Fe-based oxychlorides and motivates future work on crystals and exfoliated flakes of these and related oxyhalide systems.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Lithium cobalt(II) pyrophosphate, Li[subscript 1.86]CoP[subscript 2]O[subscript 7], from synchrotron X-ray powder data

Structure refinement of high-resolution X-ray powder diffraction data of the title compound gave the composition Li{sub 1.865}CoP{sub 2}O{sub 7}, which is also verified by the ICP measurement. Two Co sites exist in the structure: one is a CoO{sub 5} square pyramid and the other is a CoO{sub 6} octahedron. They share edges and are further interconnected through P{sub 2}O{sub 7} groups, forming a three-dimensional framework, which exhibits different kinds of intersecting tunnels containing Li cations and could be of great interest in Li ion battery chemistry. The structure also exhibits cation disorder with 13.5% Co residing at the lithium (Li1) site. Co seems to have an average oxidation state of 2.135, as obtained from the strutural stochiometry that closely supports the magnetic susceptibility findings.

Zhou, Hui↗
DOE OSTI2015

DShaper: An approach for handling missing low-Q data in pair distribution function analysis of nanostructured systems

In this work we discuss the potential problems and currently available solutions in modeling powder-diffraction based pair-distribution function (PDF) data from systems where morphological feature information content includes distances in the nanometer length scale, such as finite nanoparticles, nanoporous networks, and nanoscale precipitates in bulk materials. The implications of an experimental finite minimum Q-value are addressed by simulation, which also demonstrates the advantages of combining PDF data with small angle scattering data (SAS). In addition, we introduce a simple Fortran90 code, DShaper , which may be incorporated into PDF data fitting routines in order to approximate the so-called shape-function for any atomistic model.

36 MATERIALS SCIENCE↗
DOE OSTI2016

A radially accessible tubular in situ X-ray cell for spatially resolved operando scattering and spectroscopic studies of electrochemical energy storage devices

A tubular operando electrochemical cell has been developed to allow spatially resolved X-ray scattering and spectroscopic measurements of individual cell components, or regions thereof, during device operation. These measurements are enabled by the tubular cell geometry, wherein the X-ray-transparent tube walls allow radial access for the incident and scattered/transmitted X-ray beam; by probing different depths within the electrode stack, the transformation of different components or regions can be resolved. The cell is compatible with a variety of synchrotron-based scattering, absorption and imaging methodologies. The reliability of the electrochemical cell and the quality of the resulting X-ray scattering and spectroscopic data are demonstrated for two types of energy storage: the evolution of the distribution of the state of charge of an Li-ion battery electrode during cycling is documented using X-ray powder diffraction, and the redistribution of ions between two porous carbon electrodes in an electrochemical double-layer capacitor is documented using X-ray absorption near-edge spectroscopy.

batteries↗
DOE OSTI2018

Interactive visualization of multi-data-set Rietveld analyses using Cinema:Debye-Scherrer [nteractive Visualization of Multi-Dataset Rietveld Analyses using Cinema:Debye-Scherrer]

A tool named Cinema:Debye-Scherrer to visualize the results of a series of Rietveld analyses is presented. The multi-axis visualization of the high-dimensional data sets resulting from powder diffraction analyses allows identification of analysis problems, prediction of suitable starting values, identification of gaps in the experimental parameter space and acceleration of scientific insight from the experimental data. The tool is demonstrated with analysis results from 59 U–Nb alloy samples with different compositions, annealing times and annealing temperatures as well as with a high-temperature study of the crystal structure of CsPbBr 3 . A script to extract parameters from a series of Rietveld analyses employing the widely used GSAS Rietveld software is also described. Finally, both software tools are available for download.

36 MATERIALS SCIENCE↗
DOE OSTI2017

ζ-Glycine: insight into the mechanism of a polymorphic phase transition

Glycine is the simplest and most polymorphic amino acid, with five phases having been structurally characterized at atmospheric or high pressure. A sixth form, the elusive ζ phase, was discovered over a decade ago as a short-lived intermediate which formed as the high-pressure ϵ phase transformed to the γ form on decompression. However, its structure has remained unsolved. We now report the structure of the ζ phase, which was trapped at 100 K enabling neutron powder diffraction data to be obtained. The structure was solved using the results of a crystal structure prediction procedure based on fully ab initio energy calculations combined with a genetic algorithm for searching phase space. We show that the fate of ζ-glycine depends on its thermal history: although at room temperature it transforms back to the γ phase, warming the sample from 100 K to room temperature yielded β-glycine, the least stable of the known ambient-pressure polymorphs.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Symmetry-mode analysis for intuitive observation of structure-property relationships in the lead-free antiferroelectric (1-x)AgNbO 3 -xLiTaO 3

Functional materials are of critical importance to electronic and smart devices. A deep understanding of the structure–property relationship is essential for designing new materials. In this work, instead of utilizing conventional atomic coordinates, a symmetry-mode approach is successfully used to conduct structure refinement of the neutron powder diffraction data of (1-x)AgNbO3–xLiTaO3 (0 ≤ x ≤ 0.09) ceramics. This provides rich structural information that not only clarifies the controversial symmetry assigned to pure AgNbO3 but also explains well the detailed structural evolution of (1-x)AgNbO3–xLiTaO3 (0 ≤ x ≤ 0.09) ceramics, and builds a comprehensive and straightforward relationship between structural distortion and electrical properties. It is concluded that there are four relatively large-amplitude major modes that dominate the distorted Pmc21 structure of pure AgNbO3, namely a Λ3 antiferroelectric mode, a T4+ a-a-c0 octahedral tilting mode, an H2 a0a0c+/a0a0c- octahedral tilting mode and a Γ4- ferroelectric mode. The H2 and Λ3 modes become progressively inactive with increasing x and their destabilization is the driving force behind the composition-driven phase transition between the Pmc21 and R3c phases. This structural variation is consistent with the trend observed in the measured temperature-dependent dielectric properties and polarization–electric field (P-E) hysteresis loops. The mode crystallography applied in this study provides a strategy for optimizing related properties by tuning the amplitudes of the corresponding modes in these novel AgNbO3-based (anti)ferroelectric materials.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Pressure-induced structural phase transformation in cobalt(II) dicyanamide

In situ synchrotron powder diffraction has been used to probe the pressure-dependent structural properties of the magnetic molecular framework material Co(dca) 2 [dca = dicyanamide or N(CN) 2 - ]. An orthorhombic ( Pmnn ) to monoclinic ( P 2 1 / n ) transformation to a high-pressure phase, namely γ-Co(dca) 2 , occurs at 1.1 GPa. Structural determination of γ-Co(dca) 2 shows that the rutile-like topology of the pristine material is retained at high pressures, with the lower symmetry allowing a progression of volume-reducing structural distortions. γ-Co(dca) 2 was stable at the maximum pressure measured of 4.2 GPa. Both phases were soft, with bulk moduli ( B 0 ) for α-Co(dca) 2 and γ-Co(dca) 2 of 13.15 (18) and 9.0 (6) GPa, respectively. Modest uniaxial negative linear compressibility ( K ) of the order of -4 TPa -1 was observed over the entire measured pressure range.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

The structure of nano-twinned rhombohedral YCuO 2.66 solved by electron crystallography

In the search for frustrated spin interactions, a YCuO 2.66 phase has been synthesized by a treatment under oxygen pressure of YCuO 2.5 . X-ray powder diffraction and electron diffraction studies have been conducted. Electron diffraction shows that the sample is twinned on a 10 nm scale. Precession electron diffraction data obtained from a twinned crystal was treated in order to obtain intensities corresponding to only one of the orientations of the twins. From this data a structure solution was obtained where, as in YCuO 2.5 , the Cu atoms form triangular planes. The Cu atoms are linked in two dimensions by oxygen atoms in the present structure whereas in YCuO 2.5 they are only linked in one-dimensional chains.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Using a machine learning approach to determine the space group of a structure from the atomic pair distribution function

Here a method is presented for predicting the space group of a structure given a calculated or measured atomic pair distribution function (PDF) from that structure. The method utilizes machine learning models trained on more than 100 000 PDFs calculated from structures in the 45 most heavily represented space groups. In particular, a convolutional neural network (CNN) model is presented which yields a promising result in that it correctly identifies the space group among the top-6 estimates 91.9% of the time. The CNN model also successfully identifies space groups for 12 out of 15 experimental PDFs. Interesting aspects of the failed estimates are discussed, which indicate that the CNN is failing in similar ways as conventional indexing algorithms applied to conventional powder diffraction data. This preliminary success of the CNN model shows the possibility of model-independent assessment of PDF data on a wide class of materials.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2023

Lorentz factor for time-of-flight neutron Bragg and total scattering

We report the three fundamental origins of the Lorentz factor for neutron time-of-flight powder diffraction are revisited. A detailed derivation of the Lorentz factor is presented in the context of diffuse scattering modelling in reciprocal space when perfect periodicity is assumed, and the total scattering pattern is constructed in its discrete form – the factor in this case becomes 1/Q 2 (or d 2 ). Discussion is also presented with respect to practical data reduction where a vanadium measurement is usually taken as the normalization factor (to account for various factors such as detector efficiency), and it is shown that the existence of the Lorentz factor is independent of such a normalization process.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Trisodium citrate, Na 3 (C 6 H 5 O 7 )

The crystal structure of anhydrous trisodium citrate, Na 3 (C 6 H 5 O 7 ), has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional theory (DFT). There are two independent five-coordinate Na + and one six-coordinate Na + cations in the asymmetric unit. The [NaO 5 ] and [NaO 6 ] polyhedra share edges and corners to form a three-dimensional framework. There are channels parallel to the a and b axes in which the remainder of the citrate anions reside. The only hydrogen bonds are an intramolecular one between the hydroxy group and one of the terminal carboxylate O atoms and an intermolecular one between a methylene group and the hydroxyl O atom.

Rammohan, Alagappa↗
DOE OSTI2019

Syntheses, crystal structures, and comparisons of rare-earth oxyapatites Ca2RE8(SiO4)6O2 (RE = La, Nd, Sm, Eu, Yb) and NaLa9(SiO4)6O2

Six different rare-earth oxyapatites including Ca2RE8(SiO4)6O2 (RE = La, Nd, Sm, Eu, Yb) and NaLa9(SiO4)6O2 were synthesized using solution-based processes followed by heat treatments. The crystal structures of the synthesized oxyapatites were solved from X-ray powder diffraction (XRD) and electron probe microanalysis (EPMA). All the oxyapatites were isostructural with the hexagonal space group P63/m and showed similar unit cell parameters. The isolated [SiO4]4- tetrahedra in each crystal are linked by the cations at 4f and 6h sites occupied by RE3+ and Ca2+ in Ca2RE8(SiO4)6O2 or La3+ and Na+ in NaLa9(SiO4)6O2. The lattice parameters, cell volumes, and densities of the synthesized oxyapatites fit well to the trendlines calculated from literature values. The compositions of crystals were verified with EPMA measurements.

oxyapatite↗
DOE OSTI2021

Structural, vibrational, thermal, and magnetic properties of mullite-type NdMnTiO 5 ceramic

Mullite-type $R$Mn 2 O 5 ($R$ = Y, rare-earth element) ceramics are of ongoing research attention because of their interesting crystal-chemical and magnetic properties. We report nuclear and magnetic structures of NdMnTiO 5 together with its spectroscopic, thermogravimetric, and magnetic properties. The polycrystalline sample is prepared by solid-state synthesis and characterized from neutron and X-ray powder diffraction data Rietveld refinements. NdMnTiO 5 crystallizes in the orthorhombic space group $Pbam$ with metric parameter $a$ = 755.20(1) pm, $b$ = 869.91(1) pm, $c$ = 582.42(1) pm, and $V$ = 382.62(1) 10 6 pm 3 . The Mn 3+ and Ti 4+ cations are observed to be located in the octahedral and pyramidal sites, respectively. The vibrational features in these polyhedral sites are characterized by Raman and Fourier transform infrared spectroscopes. The higher decomposition temperature of NdMnTiO 5 , compared to other $R$Mn 2 O 5 phases, is explained in terms of the higher bond strength of Ti-O bonds than those of Mn-O bonds. Temperature-dependent DC magnetic susceptibility suggests a paramagnetic to antiferromagnetic phase transition at 43(1) K. Inverse susceptibility in the paramagnetic region above 120 K follows the Curie-Weiss law, resulting in a magnetic moment of 6.33(1) μ B per formula unit. Neutron diffraction data collected at 7.5 K reveal that the magnetic moments of Nd 3+ and Mn 3+ in NdMnTiO 5 are incommensurately ordered with a propagation vector $k$ = (0, 0.238, 0.117).

36 MATERIALS SCIENCE↗
DOE OSTI2020

Design of higher valency in covalent organic frameworks

The valency (connectivity) of building units in covalent organic frameworks (COFs) has been primarily 3 and 4, corresponding to triangles and squares or tetrahedrons, respectively. We report a strategy for making COFs with valency 8 (cubes) and “infinity” (rods). The linker 1,4-boronophenylphosphonic acid—designed to have boron and phosphorus as an isoelectronic combination of carbon-group elements—was condensed into a porous, polycubane structure (BP-COF- 1 ) formulated as (–B 4 P 4 O 12 –)(–C 6 H 4 –) 4 . It was characterized by x-ray powder diffraction techniques, which revealed cubes linked with phenyls. The isoreticular forms (BP-COF- 2 to 5 ) were similarly prepared and characterized. Large single crystals of a constitutionally isomeric COF (BP-COF- 6 ), composed of rod units, were also synthesized using the same strategy, thus propelling COF chemistry into a new valency regime.

Gropp, Cornelius↗
DOE OSTI2017

pH-Dependent Single-Step Rapid Synthesis of CuO Nanoparticles and Their Optical Behavior

This paper reports the pH-dependent growth of copper oxide (CuO) nanoparticles by wet chemical precipitation method using pH value of the samples as the only variable parameter. The phase purity, morphology, optical behavior, and elemental analysis of synthesized nanoparticles are shown to be critically dependent on the pH of the samples. Scanning electron microscope (SEM) results shows that a higher pH results well-defined CuO nanoflakes. X-ray powder diffraction (XRD) results disclosed that the growth of pure CuO with monoclinic structure at higher pH 8, whereas mixed phase was formed at lower pH 7. The average crystallite size of samples prepared at pH 8 to 10 was varying from 23.36 to 25.78 nm. The infrared spectroscopy showed that the O–H stretching peaks become narrow with an increase in the pH value. Optical results revealed the existence of the sharp absorption edges with precise excitonic features and photoluminescence bands both located at visible and near infrared spectral region attributed to the excellent optical behavior and narrow size distribution of particles. The additional near infrared band in photoluminescence spectrum located at 860 nm is attributed the defect-related luminescence. The growth mechanism of CuO nanostructures was discussed in the light of our findings.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Structure and thermal behavior of a nickel complex based on a V-shaped bis(4-(1H-imidazol-1-yl)phenyl)amine ligand

A new coordination polymer ([Ni(BIPA)(bpdc)(H{sub 2}O){sub 2}]){sub n} has been prepared based on a new V-shaped bis(4-(1H-imidazol-1-yl)phenyl)amine (BIPA) ligand. Complex was characterized by elemental analysis, IR spectra, X-ray powder diffraction, thermal analysis and single crystal X-ray analysis. Complex exhibits a 1D → 3D structure. Hydrogen bonds play an important role in the formation of supramolecular network structure. Thermal analysis indicates that complex exhibits a high thermal stability.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗