Space-group determination from powder diffraction data: a probabilistic approach

2004 ◽  
Vol 37 (6) ◽  
pp. 957-966 ◽  
Author(s):  
Angela Altomare ◽  
Rocco Caliandro ◽  
Mercedes Camalli ◽  
Corrado Cuocci ◽  
Iván da Silva ◽  
...  
Keyword(s):  
Powder Diffraction ◽  
Probabilistic Approach ◽  
Group Symmetry ◽  
Large Set ◽  
Powder Diffraction Data ◽  
Space Group ◽  
Lattice Symmetry ◽  
Quantitative Basis ◽  
Single Diffraction

Experimental powder diffraction diagrams, once indexed and decomposed into single diffraction intensities, can be submitted to statistical analysis for the determination of space-group symmetry. A new algorithm is illustrated, which is able to provide, on a quantitative basis, a probability value for each extinction symbol compatible with the previously established lattice symmetry. The algorithm has been implemented inEXPO2004[Altomare, Caliandro, Camalli, Cuocci, Giacovazzo, Moliterni & Rizzi (2004).J. Appl. Cryst.37, 1025–1028] and has been successfully tested using a large set of experimental data.

Structural characterization of anhydrous and bishydrated calcium hexafluorosilicate by powder diffraction methods

2011 ◽  
Vol 26 (4) ◽  
pp. 308-312 ◽  
Author(s):  
Simone Frisoni ◽  
Stefano Brenna ◽  
Norberto Masciocchi
Keyword(s):  
Crystal Structure ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Powder Diffraction Data ◽  
Space Group ◽  
Cell Parameters ◽  
Thermal Expansion Coefficients ◽  
Full Profile ◽  
A Minor

The synthesis and X-ray powder diffraction data for the long-known CaSiF6 and CaSiF6·2H2O species are reported. Their crystal structures have been determined from laboratory powder diffraction data by simulated annealing and full-profile Rietveld refinement methods. CaSiF6·2H2O was found to crystallize in the monoclinic P21/n space group with unit-cell parameters: a = 10.48107(9), b = 9.18272(7), c = 5.72973(5) Å, β = 98.9560(6)°, V = 544.733(8) Å3, and Z = 4. The crystal structure of CaSiF6·2H2O, eventually found to be isomorphous with SrSiF6·2H2O (but not with the Mg analogue—a hexahydrate phase), contains centrosymmetric [Ca(μ-H2O)2Ca]4+ dimers, interconnected by hexafluorosilicate anions, in a dense 3D framework. The crystal structure is completed by a further water molecule, terminally bound to the Ca2+ ion, which, consequently, attains a F5O3 octacoordination. Thermodiffractometric measurements allowed the determination of the linear and volumetric thermal expansion coefficients of CaSiF6·2H2O, which showed a minor contraction, along a, on heating. CaSiF6 is trigonal, space group R-3, a = 5.3497(3), c = 13.5831(11) Å, V = 336.66(5) Å3, and Z = 3, and isomorphous with several other species of MIIAIVF6 or MIAVF6 formulation, among which several silicates, germanates, and stannates.

Ab initiostructure determination of bethanechol chloride

2010 ◽  
Vol 25 (3) ◽  
pp. 229-234 ◽  
Author(s):  
A. Le Bail
Keyword(s):  
Powder Diffraction ◽  
Diffraction Data ◽  
Unit Cell ◽  
Powder Diffraction Data ◽  
Space Group ◽  
X Ray ◽  
Related Form ◽  
Monoclinic Unit Cell ◽  
Bethanechol Chloride

The structure of bethanechol chloride C7H17ClN2O2is solved from conventional X-ray powder diffraction data in direct space [monoclinic unit cell witha=8.8749(3) Å,b=16.4118(7) Å,c=7.1373(3) Å,β=93.803(1)°,V=1037.29(7) Å3,Z=4, and space groupP21/n]. The existence of a second orthorhombic closely related form is discussed.

Advances in space-group determination from powder diffraction data

2007 ◽  
Vol 40 (4) ◽  
pp. 743-748 ◽  
Author(s):  
Angela Altomare ◽  
Mercedes Camalli ◽  
Corrado Cuocci ◽  
Carmelo Giacovazzo ◽  
Anna Grazia Giuseppina Moliterni ◽  
...  
Keyword(s):  
Powder Diffraction ◽  
Diffraction Data ◽  
Large Set ◽  
Powder Diffraction Data ◽  
New Approach ◽  
Extinction Group ◽  
Space Group ◽  
Determination Process ◽  
New Algorithms

The space-group determination process by powder diffraction data is not straightforward. The low accuracy of the reflection intensities may invalidate the calculation of the probability associated to each extinction group that is compatible with the crystal system determined in the indexation step. Here the combination of thezstatistics with two new algorithms is reported: the first checks the quality of each 2θ interval in order to omit doubtfulzestimates from the calculations; the second creates a list of reflections with peaks that weakly overlap with any other peak, in order to check if any of them violates the extinction rules of the extinction symbol. The new approach has been applied to a large set of test structures and proved to be much more efficient than the procedure based only on thezstatistics.

Powder diffraction data for copper hexafluorides: Ba2CuF6 and Pb2CuF6

1995 ◽  
Vol 10 (3) ◽  
pp. 221-222
Author(s):  
Maurice Samouël ◽  
Patrick Gredin ◽  
Ariel de Kozak
Keyword(s):  
Crystal Structure ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Structure Determination ◽  
Crystal Structure Determination ◽  
Powder Diffraction Data ◽  
Space Group ◽  
X Ray

Based on the crystal structure determination of orthorhombic Ba2CuF6 (space group Cmca), the previous X-ray powder patterns given for Ba2CuF6 (PDF 21-809) and Pb2CuF6 (PDF 22-654) are reindexed.

FIDDLE. Simultaneous Indexing and Structure Solution from Powder Diffraction Data using a Genetic Algorithm and Correlation Functions

2019 ◽  
Author(s):  
Carmen Guguta ◽  
Jan M.M. Smits ◽  
Rene de Gelder
Keyword(s):  
Genetic Algorithm ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Correlation Functions ◽  
Cross Correlation ◽  
Simultaneous Optimization ◽  
Powder Diffraction Data ◽  
Structure Solution ◽  
Matching Technique

A method for the determination of crystal structures from powder diffraction data is presented that circumvents the difficulties associated with separate indexing. For the simultaneous optimization of the parameters that describe a crystal structure a genetic algorithm is used together with a pattern matching technique based on auto and cross correlation functions.<br>

X-ray powder diffraction data for Ba3MnSi2O8—A new phase in the system BaO–MnO–SiO2

1996 ◽  
Vol 11 (1) ◽  
pp. 26-27 ◽  
Author(s):  
Irena Georgieva ◽  
Ivan Ivanov ◽  
Ognyan Petrov
Keyword(s):  
Powder Diffraction ◽  
Diffraction Data ◽  
Data Interpretation ◽  
Powder Diffraction Data ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
New Phase

A new compound—Ba3MnSi2O8 in the system BaO–MnO–SiO2 was synthesized and studied by powder X-ray diffraction. The compound is hexagonal, space group—P6/mmm, a=5.67077 Å, c=7.30529 Å, Z=1, Dx=5.353. The obtained powder X-ray diffractometry (XRD) data were interpreted by the Powder Data Interpretation Package.

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