scholarly journals Local Structure of Iridate Pyrochlores from Hydrothermal Synthesis

2014 ◽  
Vol 70 (a1) ◽  
pp. C869-C869
Author(s):  
Helen Playford ◽  
Ravi SINGH ◽  
Lieh Jeng Chang ◽  
Kripasindhu Sardar ◽  
Alex Hannon ◽  
...  
Keyword(s):  
Local Structure ◽  
Synthesis Method ◽  
Pyrochlore Structure ◽  
Magnetic Ordering ◽  
Structural Disorder ◽  
Lattice Parameter ◽  
Magnetic Behaviour ◽  
Total Scattering ◽  
X Ray ◽  
Cation Content

Iridate pyrochlores of general formula M2Ir2O7have potential applications in catalysis [1]. They also often exhibit unusual magnetic and electronic properties caused by spin-orbit coupling and geometric frustration [2]. A detailed understanding of structure is necessary to enable these properties to be understood and exploited. Because of the propensity of the pyrochlore structure to accommodate structural disorder, we have chosen to utilise the technique of total scattering to examine the structure of M2Ir2O7(M = Bi, Nd). The sensitivity of our measurements to all the constituent elements is maximised by the combination of both neutron and X-ray total scattering. We find no evidence for magnetic ordering in our samples of Nd2Ir2O7, in contrast to literature reports [3]. By comparing the local structure of our samples with that of one reported to exhibit magnetic ordering, we explore the possibility of a structural origin for the differences in magnetic behaviour. We have found that synthesis method can directly influence the structure of these iridate pyrochlores. Local structural analysis provides evidences of A-site cation deficiency and partial oxidation of Ir(IV) to Ir(V) in samples produced by hydrothermal techniques. Irreversible changes to the lattice parameter upon heating these samples at 400 – 9000C further support the inference that the cation content is somewhat variable. We report the results of reverse Monte Carlo (RMC) refinements using the program RMCProfile, which is capable of simultaneously fitting to X-ray and neutron data, and therefore provides structural models of the greatest possible accuracy. We also report the results of in situ X-ray total scattering measurements which provide local-scale insight into the interesting thermal behaviour and apparent flexible cation content of these materials.

scholarly journals Calculation of total scattering from a crystalline structural model based on experimental optics parameters

2020 ◽  
Vol 53 (3) ◽  
pp. 671-678 ◽  
Author(s):  
Satoshi Hiroi ◽  
Koji Ohara ◽  
Satoru Ohuchi ◽  
Yukihiro Umetani ◽  
Takashi Kozaki ◽  
...  
Keyword(s):  
Amorphous Materials ◽  
Structural Model ◽  
Direct Calculation ◽  
Structural Disorder ◽  
Optical Parameters ◽  
Diffraction Profile ◽  
Total Scattering ◽  
X Ray ◽  
Scattering Measurements ◽  
Total Structure

Total scattering measurements enable understanding of the structural disorder in crystalline materials by Fourier transformation of the total structure factor, S(Q), where Q is the magnitude of the scattering vector. In this work, the direct calculation of total scattering from a crystalline structural model is proposed. To calculate the total scattering intensity, a suitable Q-broadening function for the diffraction profile is needed because the intensity and the width depend on the optical parameters of the diffraction apparatus, such as the X-ray energy resolution and divergence, and the intrinsic parameters. X-ray total scattering measurements for CeO2 powder were performed at beamline BL04B2 of the SPring-8 synchrotron radiation facility in Japan for comparison with the calculated S(Q) under various optical conditions. The evaluated Q-broadening function was comparable to the full width at half-maximum of the Bragg peaks in the experimental total scattering pattern. The proposed calculation method correctly accounts for parameters with Q dependence such as the atomic form factor and resolution function, enables estimation of the total scattering factor, and facilitates determination of the reduced pair distribution function for both crystalline and amorphous materials.

scholarly journals Structural Disorder of Mechanically Activated δ-MgCl2 Studied by Synchrotron X-ray Total Scattering and Vibrational Spectroscopy

Catalysts ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1089
Author(s):  
Toru Wada ◽  
Ashutosh Thakur ◽  
Patchanee Chammingkwan ◽  
Minoru Terano ◽  
Toshiaki Taniike ◽  
...  
Keyword(s):  
Early Stage ◽  
Mechanical Energy ◽  
Structural Disorder ◽  
Reliable Determination ◽  
Total Scattering ◽  
X Ray ◽  
Powerful Approach ◽  
Ft Ir ◽  
Grinding Time

A combination of synchrotron X-ray total scattering and molecular simulation is a powerful approach for reliable determination of the structure of δ-MgCl2 as an indispensable component of heterogeneous Ziegler–Natta catalysts. Here, the same approach is applied to mechanically activated MgCl2. Four types of mechanically activated MgCl2 samples are prepared using ball-milling in the absence and presence of different donors. The development of structural disorder along the grinding time is compared. It was found that the presence of donors accelerates the formation of δ-MgCl2 in an early stage of grinding, while elongated grinding eventually results in δ-MgCl2 with similar extents of structural disorder in the absence and presence of different donors. The FT-IR investigation consistently verified the morphological similarity between the firmly ground samples. Thus, the structure of δ-MgCl2 is likely governed by mechanical energy when sufficiently ground.

scholarly journals In situ oxidation kinetics of magnetite nanoparticles by total scattering

2014 ◽  
Vol 70 (a1) ◽  
pp. C736-C736
Author(s):  
Antonio Cervellino ◽  
Ruggero Frison ◽  
Antonella Guagliardi ◽  
Giuseppe Cernuto ◽  
Norberto Masciocchi ◽  
...  
Keyword(s):  
Materials Science ◽  
Particle Diameter ◽  
Indirect Evidence ◽  
Lattice Parameter ◽  
Oxidation States ◽  
Ex Situ ◽  
Total Scattering ◽  
X Ray ◽  
Specific Subset

Iron oxide nanoparticles (NPs) show different structures as a function of oxidation state. In particular, magnetite (Fe3O4) NPs are easily oxidized in air at moderate temperatures, eventually yielding maghemite (Fe2O3). Oxidation proceeds via the creation of iron vacancies. While the vacancies may be created with a random distribution throughout the octahedral Fe sites, they eventually order over a specific subset of these sites, lowering the symmetry from F-centered (magnetite) to P-centered (cubic maghemite). By ex situ X-ray Total Scattering studies of magnetite-maghemite NPs in different oxidation states[1] we have recently studied, by the DFA method[2], the correlation between particle diameter, stoichiometry and lattice parameter in polydisperse NP samples unraveling also the size dependence of lattice parameter and composition. Moreover, we have shown indirect evidence of the formation of a polycrystalline surface layer of maghemite on a magnetite core in the intermediate oxidation states. Motivated by the excellent ex-situ results, we have also performed in-situ studies where magnetite NPs were oxidised in air at moderate temperatures (50-200 C). We present here an in-situ study performed at the X04SA-Materials Science beamline of the Swiss Light Source synchrotron[3]. Total Scattering X-ray diffraction patterns were collected every few minutes, while the oxidation was completed within several hours. The mechanism of NPs oxidation - whereas a surface oxidised layer is formed by outwards diffusion of Fe, then the vacancies so created order themselves giving rise to the maghemite-magnetite phase transition, will be examined in great detail. We will discuss, on robust statistical basis, the calculation of kinetic and diffusion constants, the temperature effect on the lattice constant and on the thickness of the surface oxidised layer; the different possible structural models for the cubic-maghemite NPs. We thank for support Fondazione Cariplo (2009-0289).

Local Structure of Ba1–xSrxTiO3and BaTi1–yZryO3Nanocrystals Probed by X-ray Absorption and X-ray Total Scattering

ACS Nano ◽  
2013 ◽  
Vol 7 (12) ◽  
pp. 11435-11444 ◽  
Author(s):  
Federico A. Rabuffetti ◽  
Richard L. Brutchey
Keyword(s):  
Local Structure ◽  
Total Scattering ◽  
X Ray ◽  
X Ray Absorption

scholarly journals A combined fit of total scattering and extended X-ray absorption fine structure data for local-structure determination in crystalline materials

2009 ◽  
Vol 42 (5) ◽  
pp. 867-877 ◽  
Author(s):  
V. Krayzman ◽  
I. Levin ◽  
J. C. Woicik ◽  
Th. Proffen ◽  
T. A. Vanderah ◽  
...  
Keyword(s):  
Fine Structure ◽  
Multiple Scattering ◽  
Structure Determination ◽  
Local Structure ◽  
Group Symmetry ◽  
Total Scattering ◽  
Exafs Data ◽  
X Ray ◽  
Absorption Fine ◽  
X Ray Absorption

Reverse Monte Carlo (RMC) refinements of local structure using a simultaneous fit of X-ray/neutron total scattering and extended X-ray absorption fine structure (EXAFS) data were developed to incorporate an explicit treatment of both single- and multiple-scattering contributions to EXAFS. The refinement algorithm, implemented as an extension to the public domain computer softwareRMCProfile, enables accurate modeling of EXAFS over distances encompassing several coordination shells around the absorbing species. The approach was first tested on Ni, which exhibits extensive multiple scattering in EXAFS, and then applied to perovskite-like SrAl1/2Nb1/2O3. This compound crystallizes with a cubic double-perovskite structure but presents a challenge for local-structure determination using a total pair-distribution function (PDF) alone because of overlapping peaks of the constituent partial PDFs (e.g.Al—O and Nb—O or Sr—O and O—O). The results obtained here suggest that the combined use of the total scattering and EXAFS data provides sufficient constraints for RMC refinements to recover fine details of local structure in complex perovskites. Among other results, it was found that the probability density distribution for Sr in SrAl1/2Nb1/2O3adoptsTdpoint-group symmetry for the Sr sites, determined by the ordered arrangement of Al and Nb, as opposed to a spherical distribution commonly assumed in traditional Rietveld refinements.

Insight into the local structure of barium indate oxide-ion conductors: An X-ray total scattering study

2012 ◽  
Vol 41 (1) ◽  
pp. 50-53 ◽  
Author(s):  
Alessandro Mancini ◽  
J. Felix Shin ◽  
Alodia Orera ◽  
Peter R. Slater ◽  
Cristina Tealdi ◽  
...  
Keyword(s):  
Local Structure ◽  
Total Scattering ◽  
X Ray ◽  
Scattering Study ◽  
Oxide Ion Conductors ◽  
Oxide Ion ◽  
Insight Into ◽  
Ion Conductors

Local Structure of Si-Al-Ca-Na-O Glasses from Coupled Neutron and X-ray Total Scattering Data

2012 ◽  
Vol 116 (43) ◽  
pp. 13114-13123 ◽  
Author(s):  
Andrea Bernasconi ◽  
Monica Dapiaggi ◽  
Alessandro Pavese ◽  
Daniel T. Bowron ◽  
Silvia Imberti
Keyword(s):  
Local Structure ◽  
Scattering Data ◽  
Total Scattering ◽  
X Ray

Raman Spectroscopy and Structural Disorder in Gd2(ZrxTi1−x)2O7

1988 ◽  
Vol 135 ◽  
Author(s):  
M. Oueslati ◽  
M. Balkanski ◽  
P.K. Moon ◽  
H.L. Tuller
Keyword(s):  
Solid Solution ◽  
Pyrochlore Structure ◽  
Structural Disorder ◽  
X Ray Diffraction ◽  
X Ray ◽  
Oxygen Ion ◽  
Frequency Independent ◽  
Frenkel Defects ◽  
End Members ◽  
Peak Widths

AbstractRaman measurements on the Gd2(ZrxTi1−x)2O7, solid solution show increasing peak widths as the composition is varied from Gd2Ti2O7, to Gd2Zr2,O7. The increase in peak width is interpreted as reflecting an increase in structural disorder with increasing x in this pyrochlore structure material. Structural disorder occurs readily in such oxides by the formation of cation anti-site defects and anion frenkel defects. We have previously observed that this leads to a marked increase in oxygen ion conduction with increasing x. Preliminary results also indicate that certain peaks in the Raman spectra are characteristic of the end members of the solid solution and may occur at the same frequency independent of composition. The Raman results are discussed in relation to earlier x-ray diffraction and ionic conductivity data obtained in this group.

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