Peak type : Amending peak type (pv) to add a Lorentzian function

o1ivier

Hello,

I have been trying - without success - to add a lorentzian function on top of the peak type pv.
I realised that this may be a odd thing to do, but I am not able to reach the desired gof/rwp (currenlty 0.214/4.287) of my standard (CeO2) with a standard pv function (the data originates from a synchrotron radiation - in transmission - with subsequently performing a radial integration - which may be the origin of such a (abnormal) peak shape).

Given that I would like to evaluate strain in some phases part of the mixture I have, I need to obtained a better fit for the instrumental broadening (I realised that the values I obtained changed quite significantly while trying a TCHZ peak).

Do any of you know how I would be able to either add a(another) lorentzian function to a Pseudo-Voight or create a new peak function for scratch ?

Thank you for your help.

alancoelho

>Do any of you know how I would be able to either add a(another)
>lorentzian function to a Pseudo-Voight or create a new peak
>function for scratch ?

I'm not sure what you mean "from scratch". A Lorentzain can be convoluted to any peak type by using lor_fwhm; ie.

lor_fwhm = SOME_EQUATION;

johnsoevans

There are some simple examples of what Alan mentioned in his reply at:

http://community.dur.ac.uk/john.evans/topas_workshop/tutorial_joyofconv.htm

There are some other tutorials on other aspects of peak shapes that might be useful:

http://community.dur.ac.uk/john.evans/topas_workshop/tutorial_fundamentalparams.htm
http://community.dur.ac.uk/john.evans/topas_workshop/tutorial_ceo2_sizestrain.htm

o1ivier

Thank you very much.

I normally does not have such issues and the pseudo voight peak function has always worked well.
I had read about it, but I had not grasp how peak type was working exactly.

But with both your reply and information, I managed to get a better handle on it, although I still need to find the appropriate peak fitting parameters/equation that can fully account for the one I observed in the experiment data that have been gathered.

Thank again for your help and quick reply.

Ramon13

I've seen a lot of different peak types fitted with JEdit (e.g. TCHZ, LVol_FWHM_CS_G_L and e0_from_Strain, CS_L (etc.)); is there any guide on when to use these different peak types so that the user can select the most appropriate peak for the specific phase?

johnsoevans

There's the Rietveld text that has a chapter on peak shapes. It's really up to the user to describe what's needed for their specific problem.