The surface roughness effect depends on both the roughness and the absorption coefficient, and for LaB6 it may be notable if the sample surface is really rough. However, this effect leads to a systematic DECREASE of the LOW-ANGLE reflections which seems to be not the case since the correction with LP=90 works conversely.
Leonid ******************************************************* Leonid A. Solovyov Institute of Chemistry and Chemical Technology 660049, K. Marx 42, Krasnoyarsk , Russia www.icct.ru/eng/content/persons/Sol_LA www.geocities.com/l_solovyov ******************************************************* --- On Thu, 7/23/09, David Lee <da...@dtlee.com> wrote: > From: David Lee <da...@dtlee.com> > Subject: Re: AW: LP factor in the Rietveld refinement > To: "Reitveld" <rietveld_l@ill.fr> > Date: Thursday, July 23, 2009, 2:19 PM > I have a question about the surface > roughness. The LaB6 powders that I have seen > are > very finely ground and produce very flat, smooth > samples. Is the roughness connected > with the absorption? I'm thinking along > the lines that a low absorbing, rough sample > might not "look" as rough to an x-ray beam as a high > absorbing, smoother sample. > > Thanks, > > David Lee, Ph.D. > DTLee Scientific, llc > http://www.dtlee.com > 614-562-6230 > > On Jul 23, 2009, at 5:23 AM, Hinrichsen, Bernd wrote: > > > One intensity correction that is perhaps more > realistic is surface roughness. This does have a vaguely > similar angular dependence to the LP correction. This > correction is generally only applied to highly absorbing > samples in Bragg-Brentano (or generally reflection) setups. > This would seem to be the case for the LaB6 measurement > mentioned by Peter. > > > > Greetings > > Bernd > > > > > > -----Ursprüngliche Nachricht----- > > Von: Peter Y. Zavalij [mailto:pzava...@umd.edu] > > Gesendet: Donnerstag, 23. Juli 2009 05:52 > > An: rietveld_l@ill.fr > > Betreff: RE: LP factor in the Rietveld refinement > > > > Well... the situation with LP is not so simple. Using > TOPAS for refinement > > data collected on D8 advance with Ni-filter and > LynxEye detector I observe > > the following: > > - For all samples LP=0 is OK and gives the best fit as > it should be by the > > book. > > - HOWEVER for LaB6 standard LP=0 yields very poor fit > for several high angle > > reflections (>120 deg. 2theta) while LP=90 gives > perfect fit. The difference > > in R factors 12% and 4% cannot be simply ignored... > > > > Can anyone explain this? > > > > > > Peter Zavalij > > > > X-ray Crystallographic Center > > University of Maryland > > College Park, MD > > > > Office: (301)405-1861 > > Lab: (301)405-3230 > > Fax: (301)314-9121 > >
