Rietveld

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