Refinement of the Ferri- and Paramagnetic Phases of Magnetite from Neutron Multiple Diffraction Data

1998 ◽  
Vol 31 (5) ◽  
pp. 718-725 ◽  
Author(s):  
V. L. Mazzocchi ◽  
C. B. R. Parente
Keyword(s):  
Computer Program ◽  
Single Crystal ◽  
Diffraction Data ◽  
Room Temperature ◽  
Structural Parameters ◽  
Thermal Parameters ◽  
Multiple Diffraction ◽  
Shift Method ◽  
Step Process ◽  
Diffraction Patterns

Structural parameters for the ferrimagnetic and paramagnetic phases of magnetite have been refined from neutron multiple diffraction data. Experimental neutron multiple diffraction patterns were obtained by measuring the 111 primary reflection of a natural single crystal of this compound. Measurements were made at room temperature for the ferrimagnetic phase and at 976 K for the paramagnetic phase. The corresponding simulated patterns have been calculated byMULTI, a computer program for the simulation of neutron multiple diffraction patterns. A step-by-step process was used in the refinements according to the parameter-shift method. Both isotropic and anisotropic thermal parameters were assumed for the temperature factor. Isotropic thermal parameters were considered in two different ways: an overall parameter for all ions in the structure and three different parameters for the three special positions occupied by them in the structure. The best results were found in the refinements with anisotropic thermal parameters. In this case, the values of the profileRfactor found for these refinements were 3.00 and 3.32%, respectively, for the ferrimagnetic and paramagnetic phases.

WCEN: a computer program for initial processing of fiber diffraction patterns

2006 ◽  
Vol 39 (5) ◽  
pp. 752-756 ◽  
Author(s):  
Wen Bian ◽  
Hong Wang ◽  
Ian McCullough ◽  
Gerald Stubbs
Keyword(s):  
Computer Program ◽  
Single Crystal ◽  
Diffraction Data ◽  
Plant Viruses ◽  
Reciprocal Space ◽  
Parameter Determination ◽  
Input And Output ◽  
Fiber Diffraction ◽  
Diffraction Patterns ◽  
Initial Processing

Processing of fiber diffraction patterns is generally more difficult than for single-crystal patterns, and requires different algorithms and software. The programWCENhas been developed to determine experimental and specimen parameters and to convert diffraction data from detector to reciprocal space, and offers a variety of input and output formats, running under Mac OS X and Linux. The program is described and examples from oriented sols of filamentous plant viruses, illustrating different strategies for parameter determination and refinement, are given.

Application of the Rietveld Method for Structure Refinement with Powder Diffraction Data

1980 ◽  
Vol 24 ◽  
pp. 1-23 ◽  
Author(s):  
R.A. Young ◽  
D.B. Wiles
Keyword(s):  
Single Crystal ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Rietveld Method ◽  
Structural Parameters ◽  
Crystal Form ◽  
Atomic Scale ◽  
Human Tooth ◽  
Powder Diffraction Data ◽  
Diffraction Patterns

The object of the Rietveld method is to produce refined values of crystal structural parameters from powder diffraction data. Many materials of great interest can not be made available for study in single crystal form. This may be because it is not possible to prepare a single-crystal form at all (e.g., human tooth enamel) or because the single-crystal form differs from the polycrystalline form with the properties of interest (e.g., catalysts). Thus, our basic understanding of the atomic scale mechanisms is limited on the structural side by the information that can be deduced from powder diffraction patterns. (Only diffraction and EXAFS are direct probes of the spatial arrangements of atoms.) The Rietveld method has greatly extended the amount of structural detail that we can obtain routinely from powder diffraction patterns. In this method, structural parameters such as atom coordinate, thermal motion, and site occupancy parameters are adjusted in a least-squares refinement procedure until the best fit is obtained between entire calculated and observed powder diffraction patterns, as a whole.

scholarly journals The caesium phosphates Cs3(H1.5PO4)2(H2O)2, Cs3(H1.5PO4)2, Cs4P2O7(H2O)4, and CsPO3

2020 ◽  
Vol 151 (9) ◽  
pp. 1317-1328
Author(s):  
Matthias Weil ◽  
Berthold Stöger
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bond ◽  
Single Crystal ◽  
Diffraction Data ◽  
Room Temperature ◽  
Structure Type ◽  
Solid State Reactions ◽  
X Ray Diffraction ◽  
Hydrogen Phosphate ◽  
X Ray

Abstract The caesium phosphates Cs3(H1.5PO4)2(H2O)2 and Cs3(H1.5PO4)2 were obtained from aqueous solutions, and Cs4P2O7(H2O)4 and CsPO3 from solid state reactions, respectively. Cs3(H1.5PO4)2, Cs4P2O7(H2O)4, and CsPO3 were fully structurally characterized for the first time on basis of single-crystal X-ray diffraction data recorded at − 173 °C. Monoclinic Cs3(H1.5PO4)2 (Z = 2, C2/m) represents a new structure type and comprises hydrogen phosphate groups involved in the formation of a strong non-symmetrical hydrogen bond (accompanied by a disordered H atom over a twofold rotation axis) and a very strong symmetric hydrogen bond (with the H atom situated on an inversion centre) with symmetry-related neighbouring anions. Triclinic Cs4P2O7(H2O)4 (Z = 2, P$$\bar{1}$$ 1 ¯ ) crystallizes also in a new structure type and is represented by a diphosphate group with a P–O–P bridging angle of 128.5°. Although H atoms of the water molecules were not modelled, O···O distances point to hydrogen bonds of medium strengths in the crystal structure. CsPO3 is monoclinic (Z = 4, P21/n) and belongs to the family of catena-polyphosphates (MPO3)n with a repetition period of 2. It is isotypic with the room-temperature modification of RbPO3. The crystal structure of Cs3(H1.5PO4)2(H2O)2 was re-evaluated on the basis of single-crystal X-ray diffraction data at − 173 °C, revealing that two adjacent hydrogen phosphate anions are connected by a very strong and non-symmetrical hydrogen bond, in contrast to the previously described symmetrical bonding situation derived from room temperature X-ray diffraction data. In the four title crystal structures, coordination numbers of the caesium cations range from 7 to 12. Graphic abstract

Anharmonicity of potentials of atoms in potassium hydrogensulfide (KDS) determined by neutron single-crystal diffraction

2000 ◽  
Vol 56 (6) ◽  
pp. 988-992 ◽  
Author(s):  
Frank Haarmann ◽  
Herbert Jacobs ◽  
Manfred Reehuis ◽  
Anja Loose
Keyword(s):  
Single Crystal ◽  
Room Temperature ◽  
Order Approximation ◽  
Single Crystal Diffraction ◽  
Acta Cryst ◽  
Small Deviations ◽  
Molecular Group ◽  
Diffraction Patterns ◽  
Temperature Factors ◽  
Atom Potential

Potassium hydrogensulfide (KHS) is an ionic compound with an anionic molecular group HS^-. The fast reorientational disorder of the anions was determined for the ambient temperature modification [R\bar 3m; Jeffrey (1974). Can. J. Phys. 52, 2370–2378]. Single crystals are available now as protonated or deuterated specimens. With neutron single-crystal diffraction at room temperature, a considerable anharmonicity of the atom potential of the H or D atoms was observed. Even the thermal motions of K and S atoms show small deviations from an isotropic probability density function, which can be modelled using anharmonic temperature factors. The temperature factors of the atoms were expanded into a Gram–Charlier series [Kuhs (1992). Acta Cryst. A48, 80–98] in order to evaluate the anharmonicity quantitatively. Parameters up to a fourth-order approximation are relevant for the D atoms. Results from neutron single-crystal diffraction are compared with split-atom models extracted from neutron powder diffraction patterns of fully deuterated samples.

Update in a Rietveld analysis program for x-ray powder spectro-diffractometry

2003 ◽  
Vol 18 (1) ◽  
pp. 32-35 ◽  
Author(s):  
Yanan Xiao ◽  
Fujio Izumi ◽  
Timothy Graber ◽  
P. James Viccaro ◽  
Dale E. Wittmer
Keyword(s):  
Computer Program ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Rietveld Analysis ◽  
Anomalous Scattering ◽  
Analysis Program ◽  
Powder Diffraction Data ◽  
X Ray ◽  
Synchrotron Light ◽  
Diffraction Patterns

A computer program for refining anomalous scattering factors using x-ray powder diffraction data was revised on the basis of the latest version of a versatile pattern-fitting system, RIETAN-2000. The effectiveness of the resulting program was confirmed by applying it to simulated and measured powder-diffraction patterns of Mn3O4 taken at a synchrotron light source.

scholarly journals Low-T magnetic anomaly in Ca2Fe2O5studied by single-crystal neutron diffraction

2014 ◽  
Vol 70 (a1) ◽  
pp. C1352-C1352
Author(s):  
Josie Auckett ◽  
Garry McIntyre ◽  
Maxim Avdeev ◽  
Hank De Bruyn ◽  
Chris Ling
Keyword(s):  
Magnetic Susceptibility ◽  
Single Crystal ◽  
Temperature Interval ◽  
Diffraction Data ◽  
Room Temperature ◽  
Statistical Significance ◽  
Spin Reorientation ◽  
Careful Examination ◽  
Zero Field ◽  
Zone Method

Ca2Fe2O5, which belongs to the Brownmillerite family of promising solid-oxide fuel cell membrane materials, is an antiferromagnet (AFM) below TN = 720 K. A small ferromagnetic (FM) canting perpendicular to the AFM easy axis has previously been established by physical properties measurements, but never observed crystallographically. More intriguingly, it has been known for some time to display an anomalous elevation in magnetic susceptibility for 60 K < T < 140 K. [1] Based on measurements performed with small oriented single crystals, Zhou et al. [2] proposed that this anomaly was due to a reorientation of the spins from the crystallographic a axis to the c axis below 40 K, with a region of minimal magnetocrystalline anisotropy in the anomalous temperature interval. In order to test this, we grew a very large (~1 cm3) single crystal by the floating-zone method and collected neutron Laue diffraction data, against which we refined both the atomic and magnetic structures of Ca2Fe2O5 between 10 K and 300 K. We designed and built an ad hoc sample mount to apply a small (~35 Oe) magnetic field to the sample, ensuring perfect consistency with the magnetic susceptibility data, which were collected in a comparably small field. Our refinements against both zero-field and in-field diffraction data reproduce the G-type AFM structure of Ca2Fe2O5 excellently at room temperature, including the FM canting which we have refined to statistical significance for the first time. We can also show that in the intermediate temperature interval (T = 100 K), the spins are slightly less well-ordered due to competing sublattice interactions. However, careful examination of the data reveals that the material is still best described by the room-temperature magnetic structure at all measured temperatures – i.e., the spin-reorientation hypothesis is incorrect.

X-ray powder diffraction data for compound DyNiSn

1997 ◽  
Vol 12 (3) ◽  
pp. 134-135
Author(s):  
Liangqin Nong ◽  
Lingmin Zeng ◽  
Jianmin Hao
Keyword(s):  
Powder Diffraction ◽  
Diffraction Data ◽  
Figure Of Merit ◽  
Room Temperature ◽  
Unit Cell ◽  
Powder Diffraction Data ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Diffraction Patterns

The compound DyNiSn has been studied by X-ray powder diffraction. The X-ray diffraction patterns for this compound at room temperature are reported. DyNiSn is orthorhombic with lattice parameters a=7.1018(1) Å, b=7.6599(2) Å, c=4.4461(2) Å, space group Pna21 and 4 formula units of DyNiSn in unit cell. The Smith and Snyder Figure-of-Merit F30 for this powder pattern is 26.7(0.0178,63).

Description of Ba1 + x Ni x Rh1 − x O3 with x = 0.1170 (5) in superspace: modulated composite versus modulated-layer structure

2006 ◽  
Vol 62 (2) ◽  
pp. 197-204 ◽  
Author(s):  
Andreas Schönleber ◽  
F. Javier Zúñiga ◽  
J. Manuel Perez-Mato ◽  
Jacques Darriet ◽  
Hans-Conrad zur Loye
Keyword(s):  
Single Crystal ◽  
Diffraction Data ◽  
Room Temperature ◽  
Layer Structure ◽  
X Ray Diffraction ◽  
One Dimensional ◽  
X Ray

The structure of the compound Ba1 + x Ni x Rh1 − x O3 [x = 0.1170 (5)] has been analyzed at room temperature within the (3 + 1)-dimensional superspace approach using single-crystal X-ray diffraction data. Two different models are presented, the compound is refined as modulated composite as well as modulated-layer structure. In both models discontinuous atomic domains are applied to describe the structural modulations. While the first approach stresses the pseudo-one-dimensional constitution, the latter highlights the layered character of these structures.

X-ray powder diffraction data of anilinium trimolybdate tetrahydrate and anilinium trimolybdate dihydrate

1999 ◽  
Vol 14 (4) ◽  
pp. 280-283 ◽  
Author(s):  
A. Rafalska-Łasocha ◽  
W. Łasocha ◽  
M. Michalec
Keyword(s):  
Powder Diffraction ◽  
Diffraction Data ◽  
Room Temperature ◽  
Unit Cell ◽  
Powder Diffraction Data ◽  
Unit Cell Parameters ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters ◽  
Diffraction Patterns

The X-ray powder diffraction patterns of anilinium trimolybdate tetrahydrate, (C6H5NH3)2Mo3O10·4H2O, and anilinium trimolybdate dihyhydrate, (C6H5NH3)2Mo3O10·2H2O, have been measured in room temperature. The unit cell parameters were refined to a=11.0670(7) Å, b=7.6116(8) Å, c=25.554(3) Å, space group Pnma(62) and a=17.560(2) Å, b=7.5621(6) Å, c=16.284(2) Å, β=108.54(1)°, space group P21(4) or P21/m(11) for orthorhombic anilinium trimolybdate tetrahydrate and monoclinic anilinium trimolybdate dihydrate, respectively.

The crystal structure of a simple enol formed in a single-crystal-to-single-crystal enolene rearrangement

2004 ◽  
Vol 82 (2) ◽  
pp. 301-305 ◽  
Author(s):  
Kenneth CW Chong ◽  
Brian O Patrick ◽  
John R Scheffer
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Single Crystals ◽  
Diffraction Data ◽  
Room Temperature ◽  
Thermal Reaction ◽  
Thermal Rearrangement ◽  
X Ray Diffraction ◽  
X Ray ◽  
Phenyl Ketone

When crystals of 9-tricyclo[4.4.1.0]undecalyl-4-(carbomethoxy)phenyl ketone (1) were allowed to stand in the dark for extended periods of time at room temperature, the compound underwent a thermal reaction — the enolene rearrangement — to afford enol 2. The crystals remained transparent and appeared unchanged in shape as the reaction proceeded. X-ray diffraction data were collected on single crystals containing 17%, 25%, 66%, and 100% of the enol. The crystal structure of a simple enol was obtained via this novel single-crystal-to-single-crystal enolene rearrangement.Key words: single crystal, thermal, rearrangement, enol, enolene.

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