Rietveld Refienment Analysis
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Transcript of Rietveld Refienment Analysis
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ASHISH KUMAR MALLPhD
Materials Science Programme
IIT Kanpur
Crystal Structure ApproximationUsing Rietveld Refinement
Technique
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Information hidden in X-ray spectrum
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Extracting information from X-ray data
• Search and match
– ICDD or JCPDS
– High Score Plus
– Pearson crystal database
• Indexing
• Structural refinement
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Rietveld refinement
Rietveld refinement is a technique devised by Hugo Rietveldfor crystalline materials.
Uses a least squares approach to refine a theoretical line profile
until it matches the observed profile.
Very useful in case of overlapped reflection, multiple phasesand complex structures.
Function,
Where, W i is the statistical weight and c is an overall scale factor
such that
being the variance of the “observation”
=
� − 1
2
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Useful software's
X’Pert High score plus GSAS (http://www.ccp14.ac.uk/solution/gsas/ )
RIETAN
MAUD Programe
FullProf (www.ill.eu/sites/fullprof/ )
Bilbao Crystallographic Server
(http://www.cryst.ehu.es/)
Space Group Diagrams and Tables
http://img.chem.ucl.ac.uk/sgp/large/sgp.htm
Juan Rodríguez-Carvajal
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In the FullProf Suite toolbar, select ED PCR tab
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Following window pops up on clicking ED PCR tab.
Note all the tabs on the right hand side are inactive
Click new data to make a
new data file and all tabs
get activated.
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Press the General tab and fill in the sample name at
the given space for title
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Click on patterns tab to fill information related to
diffraction pattern
Click the Data file/Peak shape tab to enter the data file and peak
profile parameters
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Browse for diffraction data file which should be in .dat
format
To make a data file, copy the intensitycolumn into notepad. At the top, enter the
value of the start angle, press space, enter
the step, space and then enter the final
angle. Save the file with .dat extension.
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Click on the Refinement/simulation tab to inform
the software what you intend to do
For refinement
For simulation
Target material can be
changed as applicable
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Click the pattern calculation/peak shape tab to select
the peak shape function
It is a combination of Lorentzian and
Gaussian function and holds good for
most of the profiles
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Click on background tab to estimate the background
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Select one of the background functions from the list
Holds good only if the background is
linear. For sloppy background,
choose linear interpolation
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Click on Phases tab to enter the phase and space
group of the material
Orthorhombic
Structural model (Rietveld method)
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X Ray
Pseudo-Voigt
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Press symmetry tab and fill the space group and
press OK.
Each descriptor separated by a space
P n m a
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Press the refinement tab and the following
window appears
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Press the background tab. Insert
background parameters
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Contd….
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Press profile to input profile parameters
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Press atoms to fill atomic information
Label: IUPAC symbol of the element with a suffix if more than one
atoms are present of the same type. Ntyp: Simply IUPAC symbol or oxidation state if the same atom is
present with different oxidation states.
B: Isotropic thermal parameters
Occ: No of atoms of a particular type in the unit cell
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Save the file in the same folder containing the .dat file
Click on this to
Save the file
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Select the parameters to vary and run the program
Click on this icon to run the program. It will promptly ask for the data file.
Browse for it and select to open it. You will see the refinement taking place.
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Sequence for varying the parameters
• Scale factor
• Background and instrumental parameters
• Lattice parameters and more background parameters
• Atomic positions
• Peak shape parameters
• Atomic occupancies
• Thermal parameters
• Microstructural parameters
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Crystal structure Refinement
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Quality of the Refinement
Weighted Profile Factor:n = total number of points inthe pattern minus total
number of excluded points
Expected Weighted Profile Factor: P=number of parameters
being the variance of the “observation”
Goodness of fit indicator: Reduced chi-square:
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In the VESTA Toolbar
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