X-ray powder diffraction investigation of new oxynitride precursors: rare earth oxide compounds of fluorite- and sheelite-type structures in the Yb-(Zr,W)-O system

2007 ◽  
Vol 22 (4) ◽  
pp. 344-351 ◽  
Author(s):  
Pascal Maillard ◽  
Patricia Bénard-Rocherullé ◽  
Thierry Roisnel ◽  
Franck Tessier
Keyword(s):  
Rietveld Method ◽  
Cubic Phase ◽  
Second Phase ◽  
Line Broadening ◽  
X Ray Diffraction ◽  
Solid State Method ◽  
Space Group ◽  
X Ray ◽  
Profile Matching ◽  
T Phase

Nanocrystallized oxide precursors of colored (oxy)nitrides related to the system Yb-(Zr-W)-O have been successfully prepared using a chimie douce process—the amorphous citrate route. The process involves first a formation of fine and homogeneous powdered solids obtained by calcination at 600 °C, a temperature much lower than that of the conventional solid-state method. At this stage, the X-ray diffraction patterns exhibit large line broadening effects. Finally, two well-crystallized and pure quaternary oxides have been readily obtained by heating and under annealing conditions at 850 and 900 °C for 12 h. For one of the patterns, all the X-ray diffraction lines can be easily indexed to a cubic phase with the fluorite structure conforming to the Fm3m space group [Yb2Zr1.21W0.41O6.65◻1.35 called C-phase: a=5.1864(2) Å]. The second phase adopts the sheelite-type structure [Yb2ZrWO8 called T-phase: space group I41/a, a=5.1584(5), and c=10.8246(6) Å]. By taking into account the present compositions determined by EDS measurements, Rietveld structure refinements produce final RB factors of 0.015 and 0.044, and Rwp factors of 0.069 and 0.089, respectively. In order to characterize the microstructure of the materials (crystallite size and lattice distortion) at the nanometer scale, a study based on diffraction line broadening analysis applying the whole pattern refinement method was also undertaken with confidence. The results show smooth angular variations of the values of FWHMs, indicating that the microstructural properties are isotropic for the cubic and tetragonal oxides. More precisely, the results indicate that whatever the profile fitting approach used (“profile matching” procedure and Rietveld method), the reliability factors Rwp are systematically better with a combined size strain than with zero strain considerations. The strain magnitudes observed for the C-phase-850 °C as well as for the T-phase-900 °C should be viewed as realistic strain.

Crystal structure and powder X-ray diffraction data for new Tb3CuAl3Ge2 compound

2015 ◽  
Vol 30 (1) ◽  
pp. 63-66 ◽  
Author(s):  
Chao Zeng ◽  
Guoqiang Lin ◽  
Weijing Zeng ◽  
Wei He
Keyword(s):  
Crystal Structure ◽  
Rietveld Refinement ◽  
Diffraction Data ◽  
Rietveld Method ◽  
Unit Cell ◽  
Type Structure ◽  
X Ray Diffraction ◽  
Quaternary Compound ◽  
Space Group ◽  
X Ray

The crystal structure of new Tb3CuAl3Ge2 quaternary compound was studied by the Rietveld method from powder X-ray diffraction (XRD) data. The Tb3CuAl3Ge2 compound crystallized in the hexagonal Y3NiAl3Ge2-type structure with space group P-62m (no. 189) and lattice parameters a = 7.0041(2) Å, c = 4.1775(1) Å, V = 177.48 Å3. There is only one formula in each unit cell, Z = 1, and the density of Tb3CuAl3Ge2 is ρx = 7.1696 g cm−3. The reliability factors characterizing the Rietveld refinement results are Rp = 6.43%, Rwp = 8.65%, RB = 4.81%, and RF = 4.09%, respectively. The powder XRD data of Tb3CuAl3Ge2 were presented and the reliability of indexation is F30 = 120.9(0.0073, 34).

scholarly journals On the crystal structure of the ordered vacancy compound Cu3In5Te9

2019 ◽  
Vol 65 (4 Jul-Aug) ◽  
pp. 360 ◽  
Author(s):  
G. E. Delgado ◽  
C. Rincón ◽  
G. Marroquin
Keyword(s):  
Crystal Structure ◽  
Diffraction Data ◽  
Rietveld Method ◽  
Structural Models ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
Unit Cell Parameters ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters

The crystal structure of the ordered vacancy compound (OVC) Cu3In5Te9 was analyzed using powder X-ray diffraction data. Several structural models were derived from the structure of the Cu-poor Cu-In-Se compound b-Cu0.39In1.2Se2 by permuting the cations in the available site positions. The refinement of the best model by the Rietveld method in the tetragonal space group P2c (Nº 112), with unit cell parameters a = 6.1852(2) Å, c = 12.3633(9) Å, V = 472.98(4) Å3, led to Rp = 7.1 %, Rwp = 8.5 %, Rexp = 6.4 %, S = 1.3 for 162 independent reflections. This model has the following Wyckoff site atomic distribution: Cu1 in 2e (0,0,0); In1 in 2f (½,½,0), In2 in 2d (0,½,¼); Cu2-In3 in 2b (½,0,¼); in 2a (0,0,¼); Te in 8n (x,y,z).

scholarly journals X-Ray Powder Diffraction Studies of Mechanically Milled Cobalt

2012 ◽  
Vol 626 ◽  
pp. 913-917
Author(s):  
W.S. Yeo ◽  
Z. Nur Amirah ◽  
H.S.C. Metselaar ◽  
T.H. Ong
Keyword(s):  
Grain Size ◽  
Phase Transformation ◽  
Surface Energy ◽  
Phase Formation ◽  
Rietveld Method ◽  
High Energy ◽  
Cubic Phase ◽  
X Ray Diffraction ◽  
Structure Defects ◽  
X Ray

The allotropic phase transformation of cobalt powder prepared by high-energy ball milling was investigated as a function of milling time. Measurement of crystallite size and micro-strain in the powder systems milled for different times were conducted by X-ray diffractometry. The X-ray diffraction (XRD) peaks were analyzed using the Pearson VII profile function in conjunction with Rietveld method. X-ray diffraction line broadening revealed that allotropic transformation between face-centred-cubic phase (fcc) and hexagonal close-packed phase (hcp) in cobalt is grain size dependent and also on the accumulation of structure defects. The results showed that the phase formation of cobalt depends on the mill intensity that influences of both the grain size and the accumulation of structure defects. However, this theory alone is not adequate to explain the effects in this work. It was found that the total surface energy (Ω) theory satisfactorily explains the phase transformation behavior of cobalt. The smaller value of surface energy (Ω) of the fcc crystal than the hcp phase when size decreases may alter the qualitative aspects of the phase formation.

scholarly journals Reinvestigation of the crystal structure of Ca2Ce8(SiO4)6O2 apatite by Rietveld refinement

2018 ◽  
Vol 74 (7) ◽  
pp. 955-959 ◽  
Author(s):  
Nicolas Massoni ◽  
Ronan Hegron ◽  
Lionel Campayo
Keyword(s):  
Crystal Structure ◽  
Cell Volume ◽  
Rietveld Refinement ◽  
Diffraction Data ◽  
Rietveld Method ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Apatite Type

Ca2 Ln 8(SiO4)6O2 apatites with Ln = La, Ce, Pr, Nd, Sm, Eu, Gd and Tb crystallize in space group P63/m. The crystal structure of apatite-type Ca2Ce8(SiO4)6O2 [dicalcium octacerium hexakis(silicate) dioxide], which has been synthesized by calcination, was refined from powder X-ray diffraction data using the Rietveld method. A database survey shows that contrary to the previously published Ca2Ce8(SiO4)6O2 structure [Skakle et al. (2000). Powder Diffr. 15, 234–238], the cell volume of the structure reported here is consistent with those of other Ln apatites.

Structures and phase transitions of B-Ta2O5 and Z-Ta2O5: two high-pressure forms of Ta2O5

2000 ◽  
Vol 56 (4) ◽  
pp. 659-665 ◽  
Author(s):  
I. P. Zibrov ◽  
V. P. Filonenko ◽  
M. Sundberg ◽  
P.-E. Werner
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Pressure ◽  
Rietveld Method ◽  
High Pressure Chamber ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Transmission Electron ◽  
Heat Treated

A sample of Ta2O5, ditantalum pentaoxide, heat-treated in a `toroid'-type high-pressure chamber at P = 8 GPa and T = 1470 K, was studied by X-ray powder diffraction and high-resolution transmission electron microscopy (HRTEM). Two high-pressure modifications of Ta2O5, isostructural with B-Nb2O5 and Z-Nb2O5, were identified from the X-ray powder pattern. Both structures were refined by the Rietveld method from the X-ray diffraction data: B-Ta2O5, a = 12.7853 (4), b = 4.8537 (1), c = 5.5276 (2) Å, β = 104.264 (2)°, V = 332.45 Å3, Z = 4, space group C2/c; Z-Ta2O5, a = 5.2252 (1), b = 4.6991 (1), c = 5.8534 (1) Å, β = 108.200 (2)°, V = 136.53 Å3, Z = 2, space group C2. The Z-Ta2O5 modification is new. The Ta atoms are six-coordinated in B-Ta2O5 and seven-coordinated in Z-Ta2O5. The two structures are closely related, which makes an intergrowth and a transformation between them possible. An idealized model of the intergrowth structure has been given. The HRTEM study showed defect-rich B-Ta2O5 crystals, which could be interpreted as an intergrowth between the B-Ta2O5 and Z-Ta2O5 phases.

scholarly journals LCP crystallization and X-ray diffraction analysis of VcmN, a MATE transporter fromVibrio cholerae

2016 ◽  
Vol 72 (7) ◽  
pp. 552-557 ◽  
Author(s):  
Tsukasa Kusakizako ◽  
Yoshiki Tanaka ◽  
Christopher J. Hipolito ◽  
Teruo Kuroda ◽  
Ryuichiro Ishitani ◽  
...  
Keyword(s):  
Single Crystal ◽  
Diffraction Data ◽  
Unit Cell ◽  
Cubic Phase ◽  
X Ray Diffraction ◽  
Unit Cell Parameters ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters ◽  
Mate Transporter

Multidrug and toxic compound extrusion (MATE) transporters, one of the multidrug exporter families, efflux xenobiotics towards the extracellular side of the membrane. Since MATE transporters expressed in bacterial pathogens contribute to multidrug resistance, they are important therapeutic targets. Here, a MATE-transporter homologue fromVibrio cholerae, VcmN, was overexpressed inEscherichia coli, purified and crystallized in lipidic cubic phase (LCP). X-ray diffraction data were collected to 2.5 Å resolution from a single crystal obtained in a sandwich plate. The crystal belonged to space groupP212121, with unit-cell parametersa= 52.3,b= 93.7,c= 100.2 Å. As a result of further LCP crystallization trials, crystals of larger size were obtained using sitting-drop plates. X-ray diffraction data were collected to 2.2 Å resolution from a single crystal obtained in a sitting-drop plate. The crystal belonged to space groupP212121, with unit-cell parametersa= 61.9,b= 91.8,c= 100.9 Å. The present work provides valuable insights into the atomic resolution structure determination of membrane transporters.

scholarly journals Crystal Chemistry of Six Grossular Garnet Samples from Different Well-Known Localities

Minerals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 767
Author(s):  
Sytle M. Antao
Keyword(s):  
Ionic Radius ◽  
Rietveld Method ◽  
Cubic Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cubic Phases ◽  
Backscattered Electron ◽  
Grossular Garnet ◽  
Elemental Maps ◽  
Monochromatic Synchrotron

Two isotropic grossular (ideally Ca3Al2Si3O12) samples from (1) Canada and (2) Tanzania, three optically anisotropic grossular samples (3, 4, 5) from Mexico, and one (6) anisotropic sample from Italy were studied. The crystal structure of the six samples was refined in the cubic space group Ia3¯d, using monochromatic synchrotron high-resolution powder X-ray diffraction (HRPXRD) data and the Rietveld method. The compositions of the samples were obtained from electron microprobe analyses (EPMA). The HRPXRD traces show a single cubic phase for two isotropic samples, whereas the four anisotropic samples contain two different cubic phases that were also resolved using X-ray elemental line scans, backscattered electron (BSE) images, and elemental maps. Structural mismatch from two cubic phases intergrown in the birefringent samples gives rise to strain-induced optical anisotropy. Considering the garnet general formula, [8]X3[6]Y2[4]Z3[4]O12, the results of this study show that with increasing unit-cell parameter, the Y-O distance increases linearly and rather steeply, the average <X-O> distance increases just slightly in response to substitution mainly on the Y site, while the Z-O distance remains nearly constant. The X and Z sites in grossular contain Ca and Si atoms, respectively; both sites show insignificant substitutions by other atoms, which is supported by a constant Z-O distance and only a slight increase in the average <X-O> distance. The main cation exchange is realized in the Y site, where Fe3+ (ionic radius = 0.645 Å) replaces Al3+ (ionic radius = 0.545 Å), so the Y-O distance increases the most.

Temperature- and moisture-dependent powder X-ray diffraction studies of kanemite (NaSi2O4(OH)·3H2O)

2015 ◽  
Vol 79 (1) ◽  
pp. 103-120 ◽  
Author(s):  
Daniela Schmidmair ◽  
Volker Kahlenberg ◽  
Daniel M. Többens ◽  
Herwig Schottenberger ◽  
Jochem De Wit ◽  
...  
Keyword(s):  
Rietveld Method ◽  
Single Layer ◽  
Significant Loss ◽  
Monoclinic Space Group ◽  
Ambient Conditions ◽  
X Ray Diffraction ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
X Ray ◽  
Ambient Temperatures

AbstractThe high-temperature- and moisture-dependent behaviour of synthetic kanemite (NaSi2O4(OH)·3H2O orSKS-10) has been studied byin situpowder X-ray diffraction. Heating experiments in the range between ambient temperatures and 250°C confirm earlier investigations that the dehydration of kanemite occurs in two steps. According to our results the two different reactions start at ∼30 and 75°C. The dehydration products have the following compositions: NaSi2O4(OH)·H2O (monohydrate) and NaSi2O4(OH), respectively. The crystal structures of both phases have been solved at ambient conditionsab initiofrom laboratory powder diffraction data using samples that have been carefully dehydrated at 60 and 150°C, respectively, and refined subsequently by the Rietveld method. Basic crystallographic data are as follows: NaSi2O4(OH)·H2O: orthorhombic, space groupPna21,a= 7.2019(1),b= 15.3252(2),c= 4.8869(1) Å,V= 539.37(1) Å3,Z= 4; NaSi2O4(OH): monoclinic, space groupP21,a= 6.3873(1),b= 4.8876(1),c= 7.1936(1) Å, β = 93.36(1)°,V= 224.19(1) Å3,Z= 2. Both compounds belong to the group of single-layer silicates based on Si2O4(OH) sheets. The sodium cations are located between the tetrahedral sheets and are surrounded by oxygen atoms from silicate anions and/or water molecules. Depending on the dehydration step the coordination numbers of the alkali ions vary between six (kanemite) and five (NaSi2O4(OH)). Kanemite and its two dehydration products show structural similarities which are discussed in detail. Moisture-dependent diffraction studies at ambient temperatures indicate that kanemite is stable between 10% and at least 90% relative humidity. Below the lower threshold a transformation to the monohydrate phase was observed. Dehydration and rehydration as a function of humidity is reversible. However, this process is combined with a significant loss of crystallinity of the samples.

Structural analysis of lead magnesium niobate using synchrotron powder X-ray diffraction and the Rietveld method

2016 ◽  
Vol 72 (3) ◽  
pp. 404-409 ◽  
Author(s):  
Ashok Bhakar ◽  
Adityanarayan H. Pandey ◽  
M. N. Singh ◽  
Anuj Upadhyay ◽  
A. K. Sinha ◽  
...  
Keyword(s):  
Cell Volume ◽  
Room Temperature ◽  
Unit Cell Volume ◽  
Rietveld Method ◽  
Unit Cell ◽  
Lead Magnesium Niobate ◽  
Cubic Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Lead Magnesium

The room-temperature synchrotron powder X-ray diffraction pattern of the single phase perovskite lead magnesium niobate (PMN) has shown significant broadening in theqrange ∼ 5–7 Å−1compared with standard LaB6synchrotron powder X-ray diffraction data, taken under similar conditions. This broadening/asymmetry lies mainly towards the lower 2θ side of the Bragg peaks. Attempts to fit this data with the paraelectric cubic phase (Pm\bar 3m) and the local rhombohedral phase (R3m) corresponding to polar nanoregions (PNRs) are made using the Rietveld method. Rietveld refinements show that neither cubic (Pm\bar 3m) nor rhombohedral (R3m) symmetry can fit this XRD pattern satisfactorily. The two-phase refinement fits the experimental data satisfactorily and suggests that the weight percentage of the PNRs is approximately 12–16% at room temperature. The unit-cell volume of these rhombohedral PNRs is approximately 0.15% larger than that of the unit cell volume of the paraelectric cubic phase.

Rietveld refinement X-ray powder data of Pr0.7Ba0.3MnO3

2003 ◽  
Vol 18 (1) ◽  
pp. 29-31
Author(s):  
M. Ellouze ◽  
W. Boujelben ◽  
H. Fuess
Keyword(s):  
Solid State ◽  
Rietveld Refinement ◽  
Solid State Reaction ◽  
Rietveld Method ◽  
Xrd Analysis ◽  
Orthorhombic Symmetry ◽  
X Ray Diffraction ◽  
Conventional Solid State Reaction ◽  
Space Group ◽  
X Ray

Powder X-ray diffraction (XRD) data were collected for Pr0.7Ba0.3MnO3. This sample was prepared using the conventional solid state reaction by mixing Pr6O11, Mn2O3, and BaCO3 up to 99.9% purity at 1400 °C in air for 60 h. XRD analysis using the Rietveld method was carried out and it was found that this manganite sample has orthorhombic symmetry with Pnma space group. The lattice parameters are found to be a=5.4900 Å, b=7.7578 Å, and c=5.5227 Å.

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