I would guess the trouble is coming from differences in the
scattering factor of H+, H, H- or whatever you used. But you said
that F(110) is similar in GSAS and DBWSFP?
Scattering factor, as well as SOF (as somebody proposed), could
also give an explanation for the synchrotron:conventional XRD
difference: I don't know how difficult those hydrides might be to
handle, some loss of H....
Good luck
Miguel
> Dear all,
>
> My name is Magnus H. Sorby. I'm a Norwegian inorganic solid state chemist.
> In my on-going Ph.D. study, I am doing crystal structure determination of
> metal hydrides using powder diffraction (neutron and
> synchrotron/conventional x-ray).
>
> The synchrotron diffractogram of one of my samples (measured at the
> Swiss-Norwegian Beamline at ESRF, Grenoble) has a peak at Q = 1.30 �-1 (or
> 2theta = 8,29 deg; this is the 110 peak; there are no peaks at lower Qs)
> with a realtive intensity of approx. 6% relative to the strongest peak.
> However, the same peak is barely visible with conventional PXD
> (Bragg-Brentano geometry). I'm pretty sure that this is not due to
> prefered orientation as all peaks at higher Q resemble each other closely
> in the two measurements. So my guess is that the difference has to do with
> polarization.
>
> Doing Rietveld refinement with GSAS, I get close to zero calculated
> intensity in the 110 peak. The rest of the pattern fits nicely. I have
> tried to set POLA to diffent values between 0 and 1 (usually I lock it at
> 0.98), and I have also tried the three possible settings of IPOL. None of
> this has any significant influence on the calculated intensity of 110.
>
> If I insert my refined structure model into DBWS, I immediately get
> sensible intensity in 110. The same happened when a colleague tried it in
> Fullprof. The calculated structure factor for the peak is similar in GSAS
> and DBWS.
>
> Does anybody have a idea of what I can be doing wrong? Or can it be a
> problem with GSAS? I'm currently using the Linux version, but I have also
> tried older UNIX versions.
>
> Best wishes
> Magnus H. Sorby
> (who is sorry if this message was posted twice)
>
Miguel Gregorkiewitz
Dip Scienze Terra, Universit�
via Laterina 8, I-53100 Siena, Europe
fon +39'0577'233810 fax 233938
e-mail [EMAIL PROTECTED]
