It is call graininess, as Miguel said before, these are mosaic single crystals and depending on your source (divergence, spot dimension at different angles etc.) you get each mosaic crystal to create a diffraction peak that especially at low two-theta angle may be displaced a lot from its theoretical position because it is diffracting from a non center position. This is what you get also when you analyse samples with extremely large grains. If you use a 2D detector instead of scanning with a point or small psd, you will see all these individual grain or mosaic crystals diffracting around their ideal spot or if it is a sample with just large grains, distributed around the Laue circle. More the grain is on a lateral position respect to the center of the beam, more it is displaced in two-theta. At higher angle your beam size on the sample is smaller and there is less displacement for geometrical reasons. I like to work with 2D detectors (texture, stresses) because it is easy to see these “figures”. In addition you have the spectral impurities identified by Frank and you may get some small grains with different orientation and twins that will create some of the non 00l peaks. Analysing these kind of patterns would require a sophisticated simulation of the grains-crystals distribution and computing like ray-tracing for the geometrical effects. Not worth it. Single crystals and sharp textures requires a point beam to avoid these effects. And a monochromatic one.
Best regards, Luca <http://www.unitn.it/> Luca Lutterotti Dipartimento di Ingegneria Industriale Università di Trento via Sommarive, 9 - 38123 Trento (Italy) tel. +39 0461 2824-14 (Office), -34 (X-Ray lab)  Maud: http://maud.radiographema.com <http://maud.radiographema/> > On 6 Sep 2023, at 17:43, Le Bail Armel <le-bail.ar...@orange.fr> wrote: > > Dear Frank, > > Same as you. I have not a complete solution. > > Best > > Armel > >> envoyé : 6 septembre 2023 à 16:57 >> de : Frank Girgsdies <girgs...@fhi-berlin.mpg.de >> <mailto:girgs...@fhi-berlin.mpg.de>> >> à : Le Bail Armel <le-bail.ar...@orange.fr <mailto:le-bail.ar...@orange.fr>> >> Cc: Rietveld_L <Rietveld_L@ill.fr <mailto:Rietveld_L@ill.fr>> >> objet : Re: Step-like basline >> >> >> Dear Armel, >> >> Thanks for this nice quiz! >> >> However, after identifying the following spectral impurities: >> Cu K_beta, >> W L_alpha1,2 >> W L_beta1,2,3,4 and >> W L_gamma1, >> I am stuck now, leaving bout 1/2 to 1/3 of the tiny extra peaks >> unexplained. >> >> Some of them look suspiciously like Cu K_alpha1+2 doublets and might >> thus belong to an impurity phase, or differently oriented crystallites >> of the main phase, which could lie as dust on the single crystal >> surface, but I had no luck trying to identify them. >> >> Furthermore, the irregular high angle tailing of the 00l series (maybe >> stacking faults?) makes peak fitting difficult. >> >> Thus, I give up (at least for now), hoping that you might disclose the >> solution to the riddle, as far as it is known, for us after a while. >> >> Best wishes, >> Frank >> >> >> >> On 06.09.2023 10:47, Le Bail Armel wrote: >> >>> Hi, >>> >>> In the same subject. >>> >>> A special "powder pattern" to play with (try to explain all peaks) : >>> >>> http://cristal.org/muscovite.pdf <http://cristal.org/muscovite.pdf> >>> >>> Best >>> >>> Armel >>> >>> >>> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ >>> Please do NOT attach files to the whole list <alan.he...@neutronoptics.com> >>> Send commands to <lists...@ill.fr> eg: HELP as the subject with no body text >>> The Rietveld_L list archive is on >>> http://www.mail-archive.com/rietveld_l@ill.fr/ >>> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ >>> >> > >> > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > Please do NOT attach files to the whole list <alan.he...@neutronoptics.com > <mailto:alan.he...@neutronoptics.com>> > Send commands to <lists...@ill.fr <mailto:lists...@ill.fr>> eg: HELP as the > subject with no body text > The Rietveld_L list archive is on > http://www.mail-archive.com/rietveld_l@ill.fr/ > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Please do NOT attach files to the whole list <alan.he...@neutronoptics.com> Send commands to <lists...@ill.fr> eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
