Pawley & Le Bail fits

fcs30

I am trying to do a Pawley refinement on a pattern in which there are two phases present and I was wondering if there was any way of getting phase fraction (upon doing the fitting, it does not automatically appear on the Topas graph - it says there is 0% of both phases)?

Something else I am interested in getting is the total integrated intensity of the fitting. Is this possible? I did a bit of research and it seems that it is possible to do this in a Le Bail fitting in GSAS, however, I prefer working with Topas. Is there a similar tool in Topas?

I am a bit unclear as to the difference of a Le Bail and Pawley fit, is there any reading you could point me towards on this topic?

Many thanks!

mfisch

1. From scratch, you can't do quantitative phase analysis with LeBail or Pawley Method as relative intensities are not calculated from structural information.

2. See my post about the unit of the intensity of a peak from pawley refinement. I don't have an answer right now.

3. http://pd.chem.ucl.ac.uk/pdnn/solve1/pawley.htm
and http://pd.chem.ucl.ac.uk/pdnn/solve1/lebail.htm

ahhill

If some form of QPA is wanted, the PONKS (phases with partial or no known crystal structure) method may help...

http://www.bose.res.in/~xrdsnb11/QPA_PONKCS.pdf

Or am I totally misunderstanding? I am no expert in this though, however there are people on here who will know more about it.

rowlesmr

There is a bit of discussion on Pawley and Le Bail fits here: http://pd.chem.ucl.ac.uk/pdnn/solve1/solvit.htm

kunyang

I also have the problem in getting phase fraction.
I think we need to use the macro "MVW(m_v, v_v, w_v)". I have tried it, but in inp file it only showed the value of "v_v"(cell volume),the"m_v" and "w_v" still be zero, and in the TA fitting profile, it still showed each phase fraction be zero.

Hope someone can help we both :)

fcs30

I understand why we cannot get phase fractions from the Pawley refinment, but I wonder if it is possible to get the integrated intensity under the whole fit for each individual phase. I've got a series of different experiments and would be happy to compare the change in the total integrated intensity for each phase. Or, if it is possible to export the fitting for each individual phase I can then import it into another programme and calulate the area. I.e. just like you can use Out_X_Ycalc(filename) to export the total fitting, is there a command that exports the two fittings for the individual phases?

rowlesmr

In reply to kunyang:
The reason why you can't quantify on a Pawley fit, is that we don't know the unit cell contents (M). That's where the PONKCS scheme gets around it by using standards to give a value to the cell mass.

kunyang

Thank you very much to rowlesmr.

alancoelho

@fcs30

You can use the str dependent keyword crystalline_area t obtain the integrated intensity under a phase; ie.

str...
crystalline_area 0

The value returned varies with the x-axis range refined.