The background looks suspicious "oscillating", not simply noisy. Maybe
there are some problems with the PSD or generator stability (e.g.
oscillating of cooling water temperature), or any internal or external
data treatment (e.g. smoothing, interpolation..) was applied?
Additionally, your profile fit is far from beeing acceptable. As
Professor LeBail was able to do it better without structure in Fullprof,
you should look for a better peak profile model in GSAS.
Reinhard Kleeberg
[EMAIL PROTECTED] schrieb:
Hi, All:
This morning i tried further refinement work and eventually i got a R
value of 0.0518.
As a conlusion, the critical steps are summarized:
*Step 1*--origin selection: Thanks to the suggestion from Prof.
Gottschalk, i took (1/8,1/8,1/8) origin instead of (0,0,0). It is much
improved and it shows the calibration sample has no problem, but
current match cannot be better enough. R->0.3578
*Step 2*--radiation wavelength and pola: Under the suggestion from
Prof. Gottschalk, i took the lamda=1.54056 and Pola=0.78989 instead.
R->0.2205
*Step 3*--Release Uiso refinement: after that,R->0.1563
*Step 4*--Start to refine background parameters. Diffuse scattering
was also introduced without refinement(3-type, A=1.0,
R=2.352,U=0.005), although it helped not much and neither of ARU can
be refined without divergency. R-> 0.0518
The current .exp file, as well as related pictures, can also be
downloaded via: http://www.physik.uni-augsburg.de/~lujun/
<http://www.physik.uni-augsburg.de/%7Elujun/>
The current R value of 0.0518 is acceptable in average. Our instrument
was not so bad. :)
Nevertheless, whether the device's state was suitable for refinement
analysis or not is still unclear, and i still doubt whether the
peakshapes produced by the device can be well descriped by type-3
parameters.
i am also doubting whether this rough parameters, as shown below, are
somehow reproducible for other materials when all the measurement
conditions are the same.
Moreover, the "background" looks quite bad, where the variation of
intensities is about 2000, resulting in high chi2 ~ 30! i saw normal
background oscillation is about 20-50 and good fitting gives chi2 less
than 2.
At present, to fix the remaining problem make our refinement in other
materials reliable and reasonable, what we plan to do is:
1. optimize the experimental conditions and redo the measurement for
silicon several times;
2. buy a new package of standard silicon powder;
3. ask technique supports from the manufacturer of our instrument.
Thanks for your attention! Specially thank Prof. from
GeoForschungsZentrum Potsdam.
We will be engaged to the business of careful instrument calibration
in the following weeks.
Further comments will still be quite welcomed!
By the way, Thanks to kind Prof. Le Bail, our calibration raw data has
been tried using FullProff tools.
Thoes interested FullProf experts can visit the package via this web
page, http://www.physik.uni-augsburg.de/~lujun/Si-fullprof.html
<http://www.physik.uni-augsburg.de/%7Elujun/Si-fullprof.html>. Note:
this primary trial is currently without fine structure
information(from Prof. Le Bail)
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:* Matthias Gottschalk <mailto:[EMAIL PROTECTED]>
*To:* [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>
*Sent:* Tuesday, June 10, 2008 7:39 PM
*Subject:* Re: [sdpd] calibration problems with Silicon+gsas
Ok, just as I thought.
It is the wrong atom position. 0 0 0 has in the default
origin setting a multiplicity of 16 and not 8. So put the
Si on 1/8 1/8 1/8 and then all will work. Some additional
remarks.
1. Set POLA to 0.78989 because you have probably a primary
monochromator, too.
2. Set the wavelength to 1.54056
3. Use the profile function 2
4. Write an parameter file (using EXPGUI) for your Stadi P
which also includes the GU, GV, GW, LX, and GY parameters
refied for this sample. Only use these parameters.
5. To get a meaningful Durbin-Watson factor your
intensities are to high. For a cubic phase use maximum
intensities in the order of 10000 (8000-10000) to get
reasonable statistics and esd`s.
6. Use difuse scattering for your background.
Matthias Gottschalk
On Tue, 10 Jun 2008 19:05:35 +0200
"[EMAIL PROTECTED]" <[EMAIL PROTECTED]
<mailto:jun.lu%40physik.uni-augsburg.de>> wrote:
> Hello again, everyone:
>
> i have just received a reply from Prof. Stephens,
>indicating some problems about the attachment.
> i am so sorry for this convenience, but i bet i did not
>intend to do something bad.
>
> To solve this problem, i have created a public webpage
>for my questions. If anyone still has interest please
>visit:
> http://www.physik.uni-augsburg.de/~lujun/
<http://www.physik.uni-augsburg.de/%7Elujun/>
>
> Anyway, the attention raised by Prof. Stephens should be
>heartly appreciated. :)
>
>
>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/
<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
<http://www.physik.uni-augsburg.de/exp5>
>
> ----- Original Message -----
> From: [EMAIL PROTECTED]
> To: [EMAIL PROTECTED] <mailto:sdpd%40yahoogroups.com>
> Cc: ep5
> Sent: Tuesday, June 10, 2008 5:09 PM
> Subject: [sdpd] calibration problems with Silicon+gsas
>
>
> Hello, crystallographical experts:
>
> i had never got a satisfying refinement solution for my
>interesting materials, so i began to doubt our X-ray
>device (STADI-P, STOE Company): was it capable of
>structural refining or just not well calibrated? This is
>the motivation for my calibration refining work.
> The raw data was collected and can be easily indexed. i
>was happy for a while, but when the refinement work was
>tried, i became dispointed. Whatever i tried, the match
>betrween raw data and calculation was always bad: there
>were no calculation intensities in some positions where
>should be, and in other positions also were there no
>experimental peaks where should be.
> Would anyone like to point out some reasons for such
>situation? In particular, the most important question for
>me is whether our STADI-P device suitable for refinement
>experiments or not. If so, i have no choice but to throw
>away all my previous refinement work. :(
>
> All the related files has been attached along with this
>mail (raw data with raw format, gsas format and ascii
>format; instrument data where parameters are estimated
>using CMPR programme; one well-cited published CIF file
>for silicon; and the hkl files after indexing with
>PowderX).
>
> Your reply will be quite appreciated.
>
>
>
> 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/
<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
<http://www.physik.uni-augsburg.de/exp5>
>
>
> [Non-text portions of this message have been removed]
>
>
>
>
>
> [Non-text portions of this message have been removed]
>
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