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Rietveld Refinement

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This is a guide on rietveld refinement with FullProf and GSAS-II.

Find CIF file

Find your cif file in ICSD. Log in with your MacID.

  • Enter composition (element) + number of elements (if there is impurity)

FullProf

Change file form

  • For experimental data in XRDML:
    • Run WinPlotr -> File -> open raw data file -> 58. XRDML multiscans (Panalytical) -> counts
    • File -> save data as INSTRUM_0 file

Set up ED PCR (double click to save!!)

  • Change cif to pcr -> select cif file -> save

General

  • Change title

Pattern

  • Data file/ peak shape:
    • Data/format: free format, choose the experimental data converted before.
    • Refinement/simulation: x-ray, wavelength: Cu (note: I2/I1 = 0) or Co (note: I2/I1 = 0.5)
    • Pattern calculation/peak shape peak shape: pseudo-voigt (Gaussian + Lagrangian distribution); range
  • Background type
    • 6-coefficients polynomial function
  • Excluded region
    • Use when there is huge impurity peak

Phase

  • Change name of phase
  • Coeff to calculate the weight: Choose calculated automatically !!!
  • Contribution of Patterns:
    • Click x-ray
    • Change peak shape: pseudo-voigt
  • Symmetry:
    • Check if info imported correctly from cif

Refinement

  • This will minimize chi2.
  • Red block: fixed by symmetry.
    • Cycles of refinement: 5-10
    • Reflections ordering: Each cycle
  • First:
    • Background: d0-d3
    • Profile: set factor-scale to 0.003 (DO NOT CLICK) set to some reasonable peak height.
    • Profile: click cell parameter
    • Run Fullprof program, close, re-load PCR file (yes: save refinement, no: if it collapsed)
  • Second:
    • Profile: click factor-scale
    • Profile: click cell parameter
  • Third:
    • Background: click all
    • Instrument: zero
  • Fourth: change shape
    • Profile: FWHM Parameter UVW
    • Shape parameter: eta_0
  • Fifth: fix all refined parameter.
    • Atom: change B for each element.
    • Oxygen moves a lot, might crush the program.
  • Sixth: fix all atom refined parameter, restart first and second step.

Save file

Run WinPlotr -> File -> open rieveld data file -> 101. FullProf PRF file

Save data as multicolumn data

Two phase refinement

Easiest way: start a new PCR file do one phase refinement, and use refined parameter to do two phase refinement in the original file.

  • Second phase need to be entered manually.

  • Run vesta open cif of second phase in vesta.

  • Occupation number:
    • Occu: chemical occupancy(from chemical name, composition) × multiplicity of special position (from site) ÷ general multiplicity (from space group)

Phase:

  • Add another phase, click calculate automatically!!
  • Contribution to pattern:
    • Current phase contributes to pattern
    • Change peak shape
  • Symmetry
    • Add space group

Refinement:

  • Phase 2: Atom -> manually enter atoms
  • Under phase 2 -> profile
  • Start refinement

Info export

At the bottom of SUM file, can read out percentage of two phase.

GSAS - II

It is recommended to put powder data file, instrument file (if have any) and the cif file in one folder. Once gsas-ii runs, there will be two windows, GSAS-II project and GSAS-II plots on the screen. The following steps are mainly performed on GSAS-II project window. A short guide of plot window is provided at the end.

  • If it refuses to work right away, try entering an instrument shift of ~0.3 as a starting point for the upstairs machine, as GSAS can struggle finding a shift this large while refining the BG function.

Import data file:

For experimental data in XRDML:

  • Import -> Powder data -> from Panalytical xrdml (xml) file -> select data file -> open
  • A new window pops up -> click cancel -> Defaults for CuKa lab data -> Ok (you should see a data tree has been added)
  • instrument parameter (under PWDR data tree) -> select source type (CoKa or CuKa)
  • Sample parameter (under PWDR data tree) -> diffractometer type -> Brag-Brentano

Import cif file:

  • Import -> Phase -> from cif file -> select cif file -> open
  • A new window pops up -> Yes -> name this phase -> Ok -> tick 0) PWDR xxx. xrdml Scan 1 (connect phase info to data) -> Ok

Single phase refinement:

  • Cycle of refinements upped from 3, its under the controls tab

  • When refining each parameter, repeat the process until Max shift/sigma ~ 0.1

    • background
      • background function: chebyschev-1
      • number of coeff: 5
      • Calculate -> Refine -> select a folder to save the file -> name it -> save -> click (ok: save refinement ; cancel: if collapsed)
      • if collapsed, try different background function (a) and number of coeff (b)
      • Note: For particularily awful BGs, can set the chebyschev-1 parameter to 10, click “compute auto background” and “Set fixed points and fit”. If there are too little points, may have to turn down chebyschev-1 parameters. (this brute forces a background into fixed data points, and you can manually edit the points by going to the plot area -> fixed points dropdown at the top -> add/move/remove/delete to adjust them). The more wiggly/all over the place your BG is, the more chebyschev-1 coefficients you should use.
    • Unit cell
      • click the named phase -> tick Refine unit cell -> Calculate -> Refine
      • leave it ticked, so unit cell will be refined automatically as other parameters are refined
    • Peak shape (refine only ONE parameter at a time)
      • tick Zero -> Calculate -> Refine -> untick
      • repeat the process for U, V, W separately
      • repeat the process for X, Y respectively (click cancel: if it is negative and don’t refine that parameter)
    • Fix atomic position
      • click on the named phase -> Atoms
      • find the heaviest atom according to the periodic table
      • double click the empty box under refine -> select X -> Calculate -> Refine -> untick
      • repeat the steps from the heaviest to the lightest atoms, always leave O at the end
    • Fix thermal parameter
      • restart third and fourth step
      • double click the empty box under refine -> select U -> Calculate -> Refine -> untick
    • Refined plot has automatically saved in the folder so you can just shut down the program

Two phase refinement:

  • import the second cif file the same way like the first one
    • refine background
    • refine the second phase
    • click the second named phase
    • data -> tick phase fraction -> Calculate -> Refine (weighted fraction will show the correct percentage) -> untick
    • general -> tick refine unit cell -> Calculate -> Refine -> untick
  • refine the first phase
    • repeat steps in the single phase refinement

Refine Prefered Orientation:

  • PhaseName -> Data -> Enter Orientation and Tick “March-Dollase Ratio”
  • Under the same tab, can also refine grainsize, this shows up as peak widening

Guide to GSAS-II plot window

  • click house button -> reset to the original view
  • click four-way arrow -> drag the plot in all direction -> unclick if you don’t need it
  • click magnifier -> draw a rectangle -> zoom in the selected region -> unclick it again if you don’t need it

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