Structural Characterization of Ceria–zirconia Powder Catalysts Prepared by High-energy Mechanical Milling: A Neutron Diffraction Study

Neutron diffraction measurements were carried out on samples of CeO2–ZrO2 powder catalysts prepared by high-energy mechanical milling. The formation of solid solution was evidenced across the entire composition range examined. Quantitative phase evaluation by the Rietveld method indicated formation of tetragonal structure for low CeO2 content, whereas cubic solid solutions were the stable form at high CeO2 loading. In addition, a pseudocubic or tetragonal t″ cell with axial ratio of unity and with internal deformation of the oxygen sublattice was observed at intermediate composition (50 mol% CeO2). Thermal annealing up to 1000 °C showed expansion of the unit cell parameters; an increase in the degree of tetragonality at the expense of cubic and monoclinic phase was observed for composition CexZr1−xO2 (x < 0.5).

Download Full-text

Neutron Diffraction Study on Ce-Doped Nickel Ferrite Nanoparticles

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.855.22 ◽

2020 ◽

Vol 855 ◽

pp. 22-27

Author(s):

Engkir Sukirman ◽

Yunasfi ◽

Andon Insani ◽

Wisnu Ari Adi

Keyword(s):

Neutron Diffraction ◽

Mole Fraction ◽

Rietveld Method ◽

Magnetic Moments ◽

Site Occupancy ◽

Neutron Diffraction Pattern ◽

High Energy ◽

Neutron Diffraction Study ◽

Cubic Symmetry ◽

A Site

The NiCexFe2-xO4 polycrystalline spinel compound with composition x = 0.005, 0.010, 0.015, and 0.02 was synthesized by the solid reaction method using the high energy milling (HEM) apparatus. Measurement of the neutron diffraction patterns is carried out at room temperature using a high resolution powder neutron diffractometer (HRPD), wavelength λ = 1.8213 Å. The measured neutron diffraction data were analyzed by the Rietveld method utilizing the FullProf analysis code. The results of the neutron diffraction pattern refinement revealed that the sample has a cubic symmetry, the Fd-3m space group, mixed inverse spinel structure, A-site occupied by cation Fe3+, Ni2+, dan Ce3+. Whereas the B-site is only occupied by Fe3+ and Ni2+. The mole fraction of Fe3+ at the B-site is greater than the Fe3+ mole fraction at the A-site, whereas the mole fraction of Ni2+ at the B-site is smaller than the mole fraction of Ni2+ at the B-site. As a result of Ce3+ doping, oxygen position parameters increase, magnetic moments on B-site, and the net magnetic moments decrease. Ni2+ concentrations at the A-site and the B-site were not affected by the amount of Ce3+ substitutions. Without substitution and after Ce3+ substitution, the O-site occupancy factor is still oxygen deficient.

Download Full-text

Structural, electrical characterization and oxygen-diffusion paths in LaSrGa1-xMgxO4-δ (x=0.0-0.2) layered perovskites: an impedance spectroscopy and neutron diffraction study

New Journal of Chemistry ◽

10.1039/d1nj01662h ◽

2021 ◽

Author(s):

Carlos Marino ◽

Juan Basbus ◽

Ana L. Larralde ◽

Jose Antonio Alonso ◽

Maria Teresa Fernandez-Diaz ◽

...

Keyword(s):

Impedance Spectroscopy ◽

Neutron Diffraction ◽

Structural Characterization ◽

Oxygen Diffusion ◽

Electrical Characterization ◽

Neutron Diffraction Study ◽

Oxygen Ions ◽

Diffusion Paths ◽

Layered Perovskites

This work presents the results of the structural characterization of LaSrGa1-xMgxO4-δ oxides with x=0.0-0.2 (LSGM'); these oxides with layered K2NiF4-type structure are potential electrolytes of oxygen ions with applications in...

Download Full-text

Microstructure characterization of multifunctional As4S4/Fe3O4 nanocomposites prepared by high-energy mechanical milling

Materials Characterization ◽

10.1016/j.matchar.2017.08.028 ◽

2017 ◽

Vol 132 ◽

pp. 303-311 ◽

Cited By ~ 11

Author(s):

O. Shpotyuk ◽

Z. Bujňáková ◽

M.J. Sayagués ◽

P. Baláž ◽

A. Ingram ◽

...

Keyword(s):

Mechanical Milling ◽

High Energy ◽

Microstructure Characterization

Download Full-text

Neutron Diffraction Study of 1,2,3-Trichlorobenzene-d3

Zeitschrift für Naturforschung A ◽

10.1515/zna-1994-4-513 ◽

1994 ◽

Vol 49 (4-5) ◽

pp. 599-610

Author(s):

Dirk Groke ◽

Gernot Heger ◽

Bernd Peter Schweiss ◽

Alarich Weiss

Keyword(s):

Neutron Diffraction ◽

Diffraction Study ◽

Structural Changes ◽

Molecular Geometry ◽

Neutron Diffraction Study ◽

Strong Variation ◽

Compound A ◽

Cell Parameters ◽

Difference Fourier ◽

Temperature Factors

In order to explain the observed 35Cl-NQR anomaly of the title compound, a neutron diffraction study on single crystals was carried out at 295 K and 158 K. No significant structural changes concerning phase transitions or molecular disorder between the two experiments were observed. The space group is P21/c = C2h5 with 8 molecules per unit cell. The asymmetric unit contains 2 molecules. The cell parameters were determined to a = 1264(4) pm, b = 825(2) pm, c = 1503(3) pm, ß = 14.3(3)° at 295 K and a = 1243(2)pm, b = 815(1) pm, c = 1494(2) pm, ß = 114.3(1)° at 158 K. The molecules show rigid-body behaviour. No significant changes of the molecular geometry were observed. A strong variation of the temperature factors as function of the temperature was detected. An anharmonicity of the librational potential of the molecules was found by evaluation of the thermal parameters as function of temperature. For verifying the existence of dynamic processes which lead to a bleaching out of the 35Cl-NQR lines difference, Fourier syntheses were calculated. A reorientation or an order-disorder process as suggested by 35Cl-NQR spectroscopy above 230 K could not be confirmed within the error of the experiments. The degree of deuteration of the samples was determined by refinement of the occupation factors of the deuterium sites.

Download Full-text

Characterization of Ni-CNTs Nanocomposites Produced by Mechanical Alloying

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.829.515 ◽

2013 ◽

Vol 829 ◽

pp. 515-519 ◽

Cited By ~ 4

Author(s):

Shaghayegh Gharegozloo ◽

Hossein Abdizadeh ◽

Abolghasem Ataie

Keyword(s):

Mechanical Milling ◽

Milling Time ◽

High Energy ◽

X Ray Diffraction ◽

Metal Matrix Nanocomposites ◽

X Ray ◽

Milling Method ◽

Particle Refinement ◽

Matrix Nanocomposites

The interest in using CNTs as the reinforcement of metal matrix nanocomposites has been growing considerably due to their enhanced properties. In the present work, nickel was reinforced by carbon nanotubes (CNTs) via high energy mechanical milling method. The effects of various amounts of CNTs (5%, 10%, 20% and 30%) and different milling times (1, 5, 10 and 15 hours) were investigated. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM) analysis were used for evaluation of phase composition, morphology and magnetic properties of the samples, respectively. The results showed a homogeneous dispersion of CNTs into the nickel matrix phase by mechanical milling. It was observed that the increase in the milling time, for a particular amount of CNTs, caused a decrease of mean crystallite size from 56 nm to 35 nm. The increase of CNTs amount also resulted in the powder particle refinement. VSM analysis showed that with the increase of CNTs from 0% to 30%, the magnetization of the samples decreases from 52.36 to 30.74 emu/g, and the coercivity of the nanocomposites increases from 61.45 to 114 Oe.

Download Full-text

A neutron diffraction study of xylitol: derivation of mean square internal vibrations for H atoms from a rigid-body description

Acta Crystallographica Section B Structural Science ◽

10.1107/s010876810301557x ◽

2003 ◽

Vol 59 (5) ◽

pp. 653-663 ◽

Cited By ~ 21

Author(s):

Anders Østergaard Madsen ◽

Sax Mason ◽

Sine Larsen

Keyword(s):

Neutron Diffraction ◽

Rigid Body ◽

Diffraction Study ◽

Mean Square Displacement ◽

Neutron Diffraction Study ◽

Mean Square ◽

Anisotropic Displacement Parameters ◽

Good Agreement ◽

Internal Vibrations

A neutron diffraction study of xylitol (C5O5H12) is presented. The nuclear anisotropic displacement parameters have been analysed showing that the carbon–oxygen skeleton conforms to a rigid-body (TLS) description. Applying this TLS model to the xylitol H atoms allows characterization of the internal molecular displacements of the H nuclei, assuming that the observed H nuclear mean-square displacements are a sum of the internal displacements and rigid-body displacements. These internal molecular displacements are very similar for chemically equivalent H atoms and in good agreement with the values obtained by other methods. In all cases the smallest eigenvector of the residual mean-square displacement tensor is almost parallel to the X—H bond. The use of ab initio calculations to obtain the internal vibrations in xylitol is discouraging. Another 12 structures extracted from the literature which have been investigated by neutron diffraction were subjected to a similar analysis. The results for the nine compounds investigated at low temperature conform to the results from xylitol and provide estimates of the internal vibrations of H atoms in a range of chemical environments.

Download Full-text

Alternative materials for radiovoltaics

10.32469/10355/67527 ◽

2017 ◽

Author(s):

◽

Bradley R. Nullmeyer

Keyword(s):

Monte Carlo ◽

Neutron Diffraction ◽

Diffraction Study ◽

Pair Correlation ◽

High Energy ◽

Neutron Diffraction Study ◽

Beta Radiation ◽

Reverse Monte Carlo ◽

Tritium Production ◽

Alternative Materials

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] This work explores alternative materials for the improvement of radiovoltaic devices. First, lithium fluoride is explored as an effective material for generating and retaining tritium radionuclides for use in radiovoltaics. This development aims to solve a decades-old problem of inadequate tritium hosts, which have been consistently limited in their ability to retain the radioisotope and effectively deliver energy to transducing semiconductors. This new method of tritium production and retention offers new possibilities for use of what has been deemed the safest radioisotope, and offers a simple, rapid production process, which can greatly reduce cumbersome isotope loading processes associated with existing methods of fabrication for devices reliant on tritium or other radioisotopes. The primary focus of this work is the exploration of molten selenium-sulfur as a radiation-resistant semiconductor for radiovoltaic devices. Radiovoltaics have thus far been unable to utilize high energy alpha and beta radiation due to rapid performance degradation imposed by radiation damage. This work includes the exhibition of long-term power output from an alphavoltaic device fueled by 210Po. The 57+ day lifetime of this device is in great contrast to reports of conventional semiconductors, which have consistently exhibited short lifetimes. Moreover, this report details a neutron diffraction study of irradiated Se-S material, which indicates strong radiation-resistance in the liquid phase. With liquid selenium established as a promising material for radiovoltaics, this work also presents a neutron diffraction study on the material's atomic structure, which has been the subject of dispute in published literature. The neutron diffraction study is accompanied by Reverse Monte Carlo analysis, resulting in reliable conclusions regarding the overall structure near the melting point. The analysis of Reverse Monte Carlo models in comparison to experimental data identifies in the pair correlation function a key indicator of 3-fold coordinated defects which disrupt the liquid selenium structure under extreme conditions.

Download Full-text