1 / 6

Rietveld Refinement

Rietveld Refinement. Why do Reitveld Refinement?. What are the limitations of Rietveld ?. Phase detection limit of 1-5% Impurity atom determination New/unknown crystal structures Determination of disorder parameter Multiple parameters can have same effect diffraction patterns

trina
Télécharger la présentation

Rietveld Refinement

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Rietveld Refinement

  2. Why do Reitveld Refinement?

  3. What are the limitations of Rietveld? • Phase detection limit of 1-5% • Impurity atom determination • New/unknown crystal structures • Determination of disorder parameter • Multiple parameters can have same effect diffraction patterns • Equipment (powder vs. single crystal, x-rays vs. neutrons) • Garbage in, garbage out! (noisy data, poor quality sample, poor sample prep)

  4. Basic refinement procedure • Refine: • Background • Lattice parameters • Peak intensities • Peak shapes • Peak positions • Phase fractions Experimental diffraction pattern Starting crystal structure (.cif, ICSD) Refinement program: GSAS, FullProf • Assess: • Goodness of fit/R factors • Impurity phases • Peak/background shapes • Difference pattern Instrument file (.inst, LaB6 standard)

  5. Some common challenges/problems • False minimas • Refinement diverges (“blows up”) • Which goodness of fit to choose? R vs. Chi sq? • Preferred orientation • Large amorphous background • Incorrect starting crystal structure or lattice parameter • Poor quality data!

  6. Resources and links • GSAS/EXPGUI: http://www.ncnr.nist.gov/programs/crystallography/software/gsas.html • GSAS tutorials: http://www.aps.anl.gov/Xray_Science_Division/Powder_Diffraction_Crystallography/ • FullProf: https://www.ill.eu/sites/fullprof/ • PowDLL (file conversion): http://users.uoi.gr/nkourkou/powdll/ • Lots of info about fitting parameters: http://www.ing.unitn.it/~luttero/laboratoriomateriali/RietveldRefinements.pdf • People: LaurynBaranowski (lbaranow@mines.edu), Lakshmi Krishna (lkrishna@mines.edu)

More Related