Hi, friend, Following are my opinions due to my experience, responding to your questions:
1, In principle, POLA should not be refined. To get sensible value of POLA, please just simply consult the technique support of your instrument or ask colleagues who use radiation tubes of the same type. 2, shft and trns parameters suck because they are heavily correlated. To avoid crashing, which occurs frequently when one handles both, it's better disable them and use zero instead. 3, Generally speaking, the profile asymmetry is caused by axial divergence in terms of finite sample and detector sizes. To learn more, please refer this paper: J. Appl. Cryst. (1994). 27, 892-900, by Finger et al. Faithfully Jun Lu ---------- Lst. Prof. Lijie Qiao Department of Materials Physics and Chemistry University of Science and Technology Beijing 100083 Beijing P.R. China http://www.instrument.com.cn/ilog/handsomeland/ Lst. Prof. Loidl and Lunkenheimer Experimental Physics V Center for Electronic Correlations and Magnetism (EKM) University of Augsburg Universitaetsstr. 2 86159 Augsburg Germany http://www.physik.uni-augsburg.de/exp5 ----- Original Message ----- From: <[EMAIL PROTECTED]> To: "Rietveld Method" <Rietveld_l@ill.fr> Sent: Thursday, August 07, 2008 12:59 PM Subject: confusion about some GSAS parameters > Dear all, > I am very new with GSAS and some confusions arrised to me during > refinement. I will be very much grateful if anyone helps me by giving the > explanations of the following facts.. > > 1. what the parameter POLA stands for(is it polarization > factor??)? is it necessary to refine POLA when we are refining the XRD > patterns taken by a Brag-Brenteno diffractometer with fixed source? > 2. Does 'shft' and 'trns' means sample shift and sample > transperancy? what is the difference when we are refining 'zero' in place of > refining 'shft' and 'trns'? > 3. what physical explanation is behind the asymmetry(refined > by 'asym') in the peak shape? > >
