rietveld
DESCRIPTION
xrdTRANSCRIPT
-
Rajesh Katoch
PhD, MSE
IIT Kanpur
Crystal structure approximation using Rietveld Refinement technique: Part 1
-
Braggs law: n= 2dsin
where n is the order of diffraction
is the wavelength of radiation
d is interplanar spacing and
is the angle of incidence
Remember: < 2d for diffraction to occur !
Interaction with matter & diffraction
-
Typical X Ray diffractograms
-
Information hidden in X-ray spectrum
-
Extracting information from X-ray data
Search and match
ICDD or JCPDS
High Score Plus
Pearson crystal database
Indexing
Structural refinement
-
Rietveld refinement
-
Useful softwares
XPert High score plus
Rietan
MAUD
FullProf
www.ill.eu/sites/fullprof/
http://www.ill.eu/sites/fullprof/
-
In the FullProf Suite toolbar, select ED PCR tab
-
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.
-
Press the General tab and fill in the sample name at the
given space for title
-
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
-
Browse for diffraction data file which should be in .dat
format
To make a data file, copy the intensity column 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.
-
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
-
Click the pattern calculation/peak shape tab to select the peak shape function
It is a combination of Lorentian and Gaussian function and holds good for most of the profiles
-
Click on background tab to estimate the background
-
Select one of the background functions from the list
Holds good only if the background is linear. For sloppy background, choose linear interpolation
-
Click on Phases tab to enter the phase and space group of
the material
Tetragonal
Structural model/ Rietveld method
-
X Ray
Pseudo-Voigt
-
Press symmetry tab and fill the space group and press OK.
Each descriptor separated by a space
-
Press the refinement tab and the following window appears
-
Press the background tab. Insert background parameters
-
Contd.
-
Press profile to input profile parameters
-
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
-
Save the file in the same folder containing the .dat file
Click on this to Save the file
-
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.
-
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
To be continued