Dear Alex,
Quartz is not the best standard for the instrumental asymmetry determination
since it does not have low-angle peaks. So, if you fixed the asymmetry
parameter to that determined for quartz you may have problems in the low-angle
area.
It is always better to refine the asymmetry parameter as it is not only
instrument-dependent but also sample-dependent. The asymmetry may depend on the
absorption coefficient, the powder packing density, the capillary diameter and
other parameters.
Best regards,
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 Tue, 8/11/09, Alex Sinclair <sinclaira...@hotmail.com> wrote:
> From: Alex Sinclair <sinclaira...@hotmail.com>
> Subject: Asymmetry profile
> To: rietveld_l@ill.fr
> Date: Tuesday, August 11, 2009, 12:09 PM
>
>
>
> #yiv1270810026 .hmmessage P
> {
> margin:0px;padding:0px;}
> #yiv1270810026 {
> font-size:10pt;font-family:Verdana;}
>
>
>
> Dear mailing
> list,
>
> Would anyone
> be able to help me with a problem I am having refining some
> data using TOPAS on a lab X-ray pattern?
>
> The
> diffraction patterns collected show a large amount of
> asymmetry in the first couple of (low angle)
> peaks.
>
> The
> diffractometer contribution to the profile was determined
> from refinement of a quartz standard and the sample
> dependent broadening was then modelled using the PV-II
> function within TOPAS. Axial convergence parameters were
> used to model the angle-dependent asymmetry.
>
> Unfortunately the asymmetry of the first, lowest
> angle peak is still being fitted very poorly. Are there any
> other parameters or tricks that will help to model this
> asymmetry?
>
> Many thanks
> for any help you have,
> Alex
>
>
> P.S.
> Additionally, the data was collected using a Bruker D8
> Advantix diffractometer in capillary geometry, with a Cu
> source, a Ge(111) monochromator, secondary soller slits (2.5
> degrees) and an linear PSD.
> Celebrate
> a decade of Messenger with free winks, emoticons, display
> pics, and more. Get
> Them Now
>
