[GSAS-II] Is it possible to apply PONKCS method (hkl fit) in GSASII?

[Toby, Brian H.]

From: Robert Von Dreele <vondreele at aps.anl.gov<mailto:vondreele at aps.anl.gov>>
Subject: Re: [GSAS-II] Is it possible to apply PONKCS method (hkl fit) in GSASII?
Date: June 19, 2015 at 1:07:07 PM CDT
To: xuerun.li <xuerun.li at epfl.ch<mailto:xuerun.li at epfl.ch>>, Brian Toby <Brian.Toby at anl.gov<mailto:Brian.Toby at anl.gov>>
Reply-To: <vondreele at anl.gov<mailto:vondreele at anl.gov>>

Hi,
After trying a little test with the old CPD 1a-h data sets in GSAS-II, one can do a PONKCS analysis. The steps are something like this:
1) Load the reference patterns into GSAS-II (corundum, fluorite & zincite in this case) into a single project.
2) Load the phases (corundum, fluorite & zincite) to get lattice parameters & space group (atom positions optional - only needed for weight fraction calcs. at end) all into the same project.
3) Setup Pawley refinements for each phase selecting just the corresponding reference pattern - you'll be doing 3 simultaneous Pawley refinements. Constrain whatever parameters across the three patterns that makes sense (usually U, V, W). Be sure no histogram scale is refined.
4) Refine until happy with the fit - The Pawley intensities you get for the three phases are your reference for the subsequent PONKCS analyses with the unknowns.
5) Unset all Pawley refinement flags - these are then fixed for the analyses.
6) Load the patterns for all the unknowns. For each phase choose all of these (& include its reference but not the other reference patterns). Be sure no histogram scale is refined.
7) Refine the phase fractions - this will give your quantitative analysis for each sample. Refine other parameters (not Pawley intensities & not histogram scales) as desired; use constraints as needed to keep parameters tied together (e.g. size & mustrain).
Give it a try..
Best,
Bob

On 6/16/2015 5:02 AM, xuerun.li wrote:
Dear GSAS II,

Is it possible to do the PONKCS[1] (Partial Or No Known Crystal Sturcture) analysis with GSAS II. With PONKCS method, we can get the amount of the amorphous phases.

In most of the softwares for PONKCS method, Pawley or LeBail fit (define the profile) were first used with consequent refinement of HKL fit (the scale factor was employed for the profile). The profile of the amorphous phase was fixed allowing just the scale to shift during the refinement. The precision is promising[1,2].

By calibrating the  (ZMV)amorphous for the amorphous content from the raw materials,we can get the amount of the amporhous content in the mixture. More details regarding this method is available in Ref [3].

Thanks for you all!
Xuerun LI

Reference:
[1] Scarlett, N. V. Y. and I. C. Madsen (2006). "Quantification of phases with partial or no known crystal structures." Powder Diffraction 21(04): 278-284.
[2] Snellings, R., et al. (2014). "Use of X-ray diffraction to quantify amorphous supplementary cementitious materials in anhydrous and hydrated blended cements." Cement And Concrete Research 64(0): 89-98.
[3] http://www.icdd.com/ppxrd/08/presentations/VanHoyland-ppxrd-8.pdf


2015-06-16
________________________________
Xuerun LI
Postdoc Researcher

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