Ab initio structure determination and Rietveld refinement of a high-temperature phase of zirconium hydrogen phosphate and a new polymorph of zirconium pyrophosphate from in situ temperature-resolved powder diffraction data

2000 ◽  
Vol 56 (4) ◽  
pp. 618-625 ◽  
Author(s):  
Anne Marie Krogh Andersen ◽  
Poul Norby
Keyword(s):  
Powder Diffraction ◽  
Diffraction Data ◽  
Intermediate Phase ◽  
Temperature Phase ◽  
Powder Diffraction Data ◽  
Hydrogen Phosphate ◽  
Intermediate Phases ◽  
Zirconium Pyrophosphate ◽  
Phosphate Groups

The collected in situ temperature-resolved synchrotron powder data revealed that the transformation of the recently reported three-dimensional τ-Zr(HPO4)2 to cubic ZrP2O7 goes through two intermediate phases. The first intermediate phase, ρ-Zr(HPO4)2, is formed in a reversible phase transition at 598 K, which involves both rearrangement and disordering of the hydrogen phosphate groups of τ-Zr(HPO4)2. At 688 K condensation of the hydrogen phosphate groups leads to the formation of the second intermediate, a new polymorph of zirconium pyrophosphate (β-ZrP2O7). Heating above 973 K results in the gradual transformation of β-ZrP2O7 to cubic zirconium pyrophosphate (α-ZrP2O7). The crystal structures of the two intermediate phases were solved from the in situ powder diffraction data using direct methods and refined using the Rietveld method. Both phases are orthorhombic, space group Pnnm and Z = 2. The lattice parameters for the two phases are: ρ-Zr(HPO4)2: a = 8.1935 (2), b = 7.7090 (2), c = 5.4080 (1) Å; β-ZrP2O7: a = 8.3127 (5), b = 6.6389 (4), c = 5.3407 (3) Å. The formation mechanism for the new zirconium pyrophosphate polymorph, β-ZrP2O7, is discussed in relation to structurally restricted soft chemistry.

Structure Determination of CaH2P2O7 From In Situ Powder Diffraction Data

2000 ◽  
Vol 321-324 ◽  
pp. 374-379 ◽  
Author(s):  
J. Trommer ◽  
M. Schneider ◽  
H. Worzala ◽  
Andrew N. Fitch
Keyword(s):  
Powder Diffraction ◽  
Diffraction Data ◽  
Structure Determination ◽  
Powder Diffraction Data

Structures of three dehydration products of bischofite from in situ synchrotron powder diffraction data (MgCl2·nH2O; n = 1, 2, 4)

2007 ◽  
Vol 63 (2) ◽  
pp. 235-242 ◽  
Author(s):  
Kunihisa Sugimoto ◽  
Robert E. Dinnebier ◽  
Jonathan C. Hanson
Keyword(s):  
Crystal Structures ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Similarity Criteria ◽  
Powder Diffraction Data ◽  
Rietveld Refinements ◽  
Synchrotron Powder Diffraction ◽  
Magnesia Concrete ◽  
First Time

High-quality in situ synchrotron powder diffraction data have been used to investigate the decomposition products of bischofite in the temperature range 298 ≤ T ≤ 873 K. At least eight phases could be identified: MgCl2·nH2O (n = 1, 2, 4 and 6), MgOHCl·nH2O (0 ≤ n ≤ 1.0), MgCl2 and MgO. The crystal structures of three magnesium chloride hydrates MgCl2·nH2O (n = 1, 2, 4) were determined ab initio, replacing published Rietveld refinements from low-quality powder diffraction data based on similarity criteria. MgCl2·4H2O was found to be disordered and has been correctly determined for the first time. The crystal structures of bischofite and MgCl2·4H2O consist of discrete Mg(H2O)6 and MgCl2(H2O)4 octahedra, respectively. The crystal structure of MgCl2·2H2O is formed by single chains of edge-sharing MgCl2(H2O)4 octahedra, while in the case of MgCl2·H2O double chains of edge-sharing MgCl(H2O)5 octahedra are found. The phases in the system MgCl2–H2O are intermediates in the technologically important process of MgO and subsequently Mg production. The same phases were recently found to be of key importance in the understanding of cracks in certain magnesia concrete floors.

“Powder 3D Parametric”- A program for Automated Sequential and Parametric Rietveld Refinement Using Topas

2010 ◽  
Vol 651 ◽  
pp. 97-104 ◽  
Author(s):  
Paneerselvam Rajiv ◽  
Robert E. Dinnebier ◽  
Martin Jansen
Keyword(s):  
Powder Diffraction ◽  
Diffraction Data ◽  
Pattern Analysis ◽  
Graphical Interface ◽  
Powder Diffraction Data ◽  
Analysis Software ◽  
Software Suite ◽  
Time Resolved ◽  
Profile Refinement

A new program to perform fast sequential and parametric whole powder profile refinement of in situ time-resolved powder diffraction data is presented. The program interacts with the launch mode kernel of the total powder pattern analysis software suite Topas® for doing the refinements. The program provides a graphical interface platform, upon which the huge Topas input command files necessary to perform sequential and parametric refinements can be easily prepared and executed. This program requires the user license dongle for Topas academic version 3 or higher.

Crystal structure determination of Ga3(H3O)H8(PO4)6 · 6 H2O from X-ray powder diffraction data

2004 ◽  
Vol 219 (5) ◽  
Author(s):  
Ludmila S. Ivashkevich ◽  
Alexander S. Lyakhov ◽  
Anatoly F. Selevich ◽  
Anatoly I. Lesnikovich
Keyword(s):  
Crystal Structure ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Structure Determination ◽  
Crystal Structure Determination ◽  
Powder Diffraction Data ◽  
Hydrogen Phosphate ◽  
X Ray

AbstractThe crystal structure of the gallium hydrogen phosphate hydrate, Ga

The disordered structure of tetraferrocenyl-[3]-cumulene, (Fc)2C=C=C=C(Fc)2, by simulated annealing using synchrotron powder diffraction data

2000 ◽  
Vol 33 (5) ◽  
pp. 1199-1207 ◽  
Author(s):  
Robert E. Dinnebier ◽  
Manuela Schweiger ◽  
Benno Bildstein ◽  
Kenneth Shankland ◽  
William I. F. David ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Simulated Annealing ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Room Temperature ◽  
Rietveld Method ◽  
Rigid Bodies ◽  
Temperature Phase ◽  
Powder Diffraction Data ◽  
Synchrotron Powder Diffraction

In the molecular structure of tetraferrocenyl-[3]-cumulene, (Fc)2C=C=C=C(Fc)2, four ferrocene molecules are connectedviaa linear bridge consisting of four carbon atoms. At room temperature, the crystal structure has space groupP21/a(Z= 1) witha= 13.104 (5),b= 6.121 (2),c= 11.194 (4) Å, β = 114.922 (1)° andV= 814.3 (8) Å3. A phase transition during cooling was not observed from room temperature to 75 K. From high-resolution X-ray powder diffraction data, the structure of the room-temperature phase was solved by the method of simulated annealing and refined by the Rietveld method using rigid bodies and restraints. The crystal structure was found to be highly disordered with the molecules occupying two orientations with equal probability and a 50% occupancy of the carbon atoms in the cumulene bridge. The disorder could be modelled by stacking faults in ordered structures. In contrast to other compounds of this class, the ferrocenyl groups are in asynrather than in an up–down conformation with respect to the cumulene bridge.

scholarly journals Ab initio structure determination of the low-temperature phase of succinonitrile from laboratory X-ray powder diffraction data—Coping with potential poor powder quality using DFT ab initio methods

2008 ◽  
Vol 23 (4) ◽  
pp. 292-299 ◽  
Author(s):  
P. S. Whitfield ◽  
Y. Le Page ◽  
A. Abouimrane ◽  
I. J. Davidson
Keyword(s):  
Low Temperature ◽  
Ab Initio ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Temperature Phase ◽  
Temperature Structure ◽  
Powder Diffraction Data ◽  
Distinct Structure ◽  
Constrained Models ◽  
Cell Data

Without experimental or predicted literature crystal structures for succinonitrile at low temperature, structure solution was attempted from powder diffraction data taken at 173 and 90 K from a solid sample. Its room-temperature plastic-crystal state makes production of a sample with good particle statistics and random orientation almost impossible. Combining constrained models, simulated annealing, and careful application of second-order spherical harmonic corrections nevertheless produced viable-looking structures at 90 and 173 K, yielding two distinct structure models with the same projection down c. VASP optimization of atom coordinates in the experimental cell agreed well with the 90 K model but poorly with the model derived from the 173 K data. The refined 90 K structure changed little on optimization and fitted all datasets from 85 to 225 K. Plots of cell data, torsion angles, and isotropic displacement parameters against temperature suggest possible phase transitions around 100, 120, and 180 K. Cell data at 90 K: monoclinic P21/a, a=9.0851(5) Å, b=8.5617(5) Å, c=5.8343(3) Å, β=79.295(2)°, and Z=4. Succinonitrile has gauche conformation, in agreement with literature spectroscopy data.

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