Rietveld Refienment Analysis

8/18/2019 Rietveld Refienment Analysis

http://slidepdf.com/reader/full/rietveld-refienment-analysis 1/31

ASHISH KUMAR MALLPhD

Materials Science Programme

IIT Kanpur

Crystal Structure ApproximationUsing Rietveld Refinement

Technique



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

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



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

http://www.ccp14.ac.uk/solution/gsas/

http://www.ill.eu/sites/fullprof/

http://www.cryst.ehu.es/





http://www.ill.eu/sites/fullprof/

http://www.ccp14.ac.uk/solution/gsas/



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 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.



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 Lorentzian 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

Orthorhombic

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

P n m a



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



Crystal structure Refinement



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:



In the VESTA Toolbar







Documents

Rietveld Refienment Analysis