[CCP14 Home: (Frames | No Frames)]
CCP14 Mirrors: [UK] | [CA] | [US] | [AU]

(This Webpage Page in No Frames Mode)

CCP14

Methods, Problems and Solutions

Automatic Divergence Slits (ADS), Data Correction, Rietveld Analysis (and In2O3 as a Reference Material)

The CCP14 Homepage is at http://www.ccp14.ac.uk

[Back to Problems and Solutions]

Via the SDPD Mailing List (Structure Determination by Powder Diffractometry) at http://www.cristal.org/sdpd/

(Scroll down to the bottom if you just want the summary pages that get to the meat of the matter)

To: sdpd@egroups.com 
From: Armel Le Bail [armel@fluo.univ-lemans.fr] 
Mailing-List: list sdpd@egroups.com; contact sdpd-owner@egroups.com 
List-Unsubscribe: [mailto:sdpd-unsubscribe@egroups.com] 
Date: Tue, 06 Jun 2000 09:20:09 +0200 
Reply-To: sdpd@egroups.com 
Subject: [sdpd] Reference materials for calibration and indexing 


Hi,


The latest addition into PowBase is In2O3, cubic
variety (a=10.119 A; space group Ia3).


http://sdpd.univ-lemans.fr/powbase/


This compound would be a nice reference material to be mixed
with your unknown sample for indexing. No preferred
orientation occured on a sample from CERAC Inc.
The minimal FWHM is near of 0.06░ (2-theta), without
annealing. Unfortunately, 3 of the 7 first reflections are very
weak. Anyway, this material may replace NAC (Na2Ca3Al2F14)
if you need a more absorbing sample.


Other suggestions of inexpensive reference materials welcome.


Best,


Armel Le Bail
http://sdpd.univ-lemans.fr/course/


Armel Le Bail - Universite du Maine, Laboratoire des Fluorures,
CNRS ESA 6010, Av. O. Messiaen, 72085 Le Mans Cedex 9, France
http://www.cristal.org/


From: "Yokochi, Alexandre" [alex.yokochi@orst.edu] 
Mailing-List: list sdpd@egroups.com; contact sdpd-owner@egroups.com 
Delivered-To: mailing list sdpd@egroups.com 
Date: Tue, 6 Jun 2000 09:28:04 -0700 
Reply-To: sdpd@egroups.com 
Subject: [sdpd] RE: Reference materials for calibration and indexing 


Armel,


The suggestion of In2O3 is very welcome.  I too have struggled with 
finding a good calibration standard.  For reflection mode I have hit 
on ZrW2O8, cubic, P2(1)3 (at r.t.) or P a -3 (at 150 C or higher), 
with a = 9.1567 (at r.t.) and has well characterized thermal expansion 
behaviour (as studied by neutron diffraction).  Much higher linear 
absorption coefficient than NAC too, which is nice for reflection mode.

Cheers, AlexY
Dr. Alexandre F. T. Yokochi
Assistant Professor (Senior Research)
Director, X-ray Crystallographic Facilities
Department of Chemistry
Oregon State University
Corvallis, OR 97331-4003


Ph#  (541) 737-6724     Email: alex.yokochi@orst.edu
Fax# (541) 737-2062     Web Page: crystal.chem.orst.edu/~alexy (temporarily unavailable)

From: Lachlan Cranswick [L.M.D.Cranswick@dl.ac.uk] 
Mailing-List: list sdpd@egroups.com; contact sdpd-owner@egroups.com 
Delivered-To: mailing list sdpd@egroups.com 
Date: Tue, 06 Jun 2000 17:51:21 +0100 
Reply-To: sdpd@egroups.com 
Subject: Re: [sdpd] Reference materials for calibration and indexing 



>The latest addition into PowBase is In2O3, cubic
>variety (a=10.119 A; space group Ia3).
>
>http://sdpd.univ-lemans.fr/powbase/
>
>This compound would be a nice reference material to be mixed
>with your unknown sample for indexing. No preferred
>orientation occured on a sample from CERAC Inc.
>The minimal FWHM is near of 0.06░ (2-theta), without
>annealing. Unfortunately, 3 of the 7 first reflections are very
>weak. Anyway, this material may replace NAC (Na2Ca3Al2F14)
>if you need a more absorbing sample.
>
>Other suggestions of inexpensive reference materials welcome.


While the above implies it can be used out of the bottle(?):
Does In2O3 "need" any annealing or can it be used reliably
out of the bottle?  Also, what is the general cost for 10 to
100 grams?


----


Is it possible to get a "fixed" slit data collection of this
where all the slit and geometry settings are noted?


I would be quite eager to try out a Fundamental Parameters
fit using Koalariet/XFIT.


I am quite a fan of Ian Madsen's suggestion of using annealed
cubic Y2O3.  Except you normally have to anneal it yourself.
This is 10.6 A IA3 cubic.  This has performed well in the past
using Fundamental Parameters fitting to look at diffractometer
geometry and alignment.


Lachlan.

Lachlan M. D. Cranswick


Collaborative Computational Project No 14 (CCP14)
     for Single Crystal and Powder Diffraction
Daresbury Laboratory, Warrington, WA4 4AD U.K
Tel: +44-1925-603703  Fax: +44-1925-603124
E-mail: l.cranswick@dl.ac.uk  Ext: 3703  Room C14
                            http://www.ccp14.ac.uk

From: Armel Le Bail [armel@fluo.univ-lemans.fr] 
Mailing-List: list sdpd@egroups.com; contact sdpd-owner@egroups.com 
Delivered-To: mailing list sdpd@egroups.com 
Date: Tue, 06 Jun 2000 20:08:34 +0200 
Reply-To: sdpd@egroups.com 
Subject: Re: [sdpd] Reference materials for calibration and indexing 


 >While the above implies it can be used out of the bottle(?): 
 >Does In2O3 "need" any annealing or can it be used reliably 
 >out of the bottle? Also, what is the general cost for 10 to 
 >100 grams?


Some annealing seems necessary if you compare the
FWHMs (░ 2-theta) of In2O3 and CeO2 recently distributed by
D. Balzar for his Size/strain Round Robin (recorded in "exactly"
the same conditions). There is one Y2O3 too in Powbase, not
annealed. Also is given an Y2O3-a got with the Koalariet package,
probably annealed (?) :


In2O3         CeO2        2-theta   Y2O3      Y2O3-a
0.061         0.056         30.5    0.104      0.112
0.076         0.060         51.0    0.111      0.107
0.092         0.064         69.4    0.124      0.106
0.116         0.071         89.8    0.147      0.114
0.150         0.084        110.1    0.190      0.140
0.207         0.110        130.2    0.260


About the cost, I have no catalog at home ;-).


>Is it possible to get a "fixed" slit data collection of this
>where all the slit and geometry settings are noted?


Recording conditions were : Bragg Brentano geometry, Cu-Kalpha, 
graphite monochromator in the diffracted beam, Soller 2░, variable
slits ensuring a constant 6mm illumination of the sample surface, 
Soller 2░, receiving slit 0.1mm.  The pattern in PowBase is corrected
by 1/(sin theta) and so is already equivalent to a "fixed" slit data collection.


>I would be quite eager to try out a Fundamental Parameters
>fit using Koalariet/XFIT.


Why exactly the FP approach cannot deal with that variable
slits geometry ?


Armel



Armel Le Bail - UniversitÚ du Maine, Laboratoire des Fluorures,
CNRS ESA 6010, Av. O. Messiaen, 72085 Le Mans Cedex 9, France
http://www.cristal.org/

From: L.M.D.Cranswick@dl.ac.uk 
Mailing-List: list sdpd@egroups.com; contact sdpd-owner@egroups.com 
Delivered-To: mailing list sdpd@egroups.com 
Date: Tue, 6 Jun 2000 19:26:53 +0100 (BST) 
Reply-To: sdpd@egroups.com 
Subject: Re: [sdpd] Reference materials for calibration and indexing 



> Some annealing seems necessary if you compare the
> FWHMs (░ 2-theta) of In2O3 and CeO2 recently distributed by
> D. Balzar for his Size/strain Round Robin (recorded in "exactly"
> the same conditions). There is one Y2O3 too in Powbase, not
> annealed. Also is given an Y2O3-a got with the Koalariet package,
> probably annealed (?) :
> 
>  In2O3         CeO2        2-theta   Y2O3      Y2O3-a
>  0.061         0.056         30.5    0.104      0.112
>  0.076         0.060         51.0    0.111      0.107
>  0.092         0.064         69.4    0.124      0.106
>  0.116         0.071         89.8    0.147      0.114
>  0.150         0.084        110.1    0.190      0.140
>  0.207         0.110        130.2    0.260


The Y2O3 is annealed (1200 C for around two to three days?) - 
according to the equations of XFIT/Koalariet it
has near zero strain and around 3000 Angstrom average crystallite
size.  It can refine on the common slit settings quite accurately
which is the thing that interests me.


What is the average size/strain results determined on the In2O3 or
is this what the round robin will give?


> >Is it possible to get a "fixed" slit data collection of this
> >where all the slit and geometry settings are noted?
> 
> Recording conditions were : Bragg Brentano geometry, Cu-Kalpha, 
> graphite monochromator in the diffracted beam, Soller 2░, variable
> slits ensuring a constant 6mm illumination of the sample surface, 
> Soller 2░, receiving slit 0.1mm.  The pattern in PowBase is corrected
> by 1/(sin theta) and so is already equivalent to a "fixed" slit data collection.
> 
> >I would be quite eager to try out a Fundamental Parameters
> >fit using Koalariet/XFIT.
> 
> Why exactly the FP approach cannot deal with that variable
> slits geometry ?


Sorry - forgot that it can - matter of habit in using fixed 
slit.  XFIT can do Variable slit (not really used it) - but 
old biases against variable slits die hard.


Lachlan.


-- 
Lachlan M. D. Cranswick


Collaborative Computational Project No 14 (CCP14)
    for Single Crystal and Powder Diffraction
Daresbury Laboratory, Warrington, WA4 4AD U.K
Tel: +44-1925-603703  Fax: +44-1925-603124
E-mail: l.cranswick@dl.ac.uk  Ext: 3703  Room C14
                           http://www.ccp14.ac.uk

From: L.M.D.Cranswick@dl.ac.uk 
Mailing-List: list sdpd@egroups.com; contact sdpd-owner@egroups.com 
Delivered-To: mailing list sdpd@egroups.com 
Date: Tue, 6 Jun 2000 20:01:16 +0100 (BST) 
Reply-To: sdpd@egroups.com 
Subject: Re: [sdpd] Reference materials for calibration and indexing 



Can the raw, uncorrected for intensity data for InO3
be put on the site or Emailed to those who are
interested?  (me for starters)  The profiles of the
corrected data would still have to be modelled by
a Variable Slit profile function but not sure what
changing the intensities might be doing - even if only
a minor influence on the Fundamental Parameters fit.


On a slightly related topic.


It would be interesting to test out these new computer
controlled ADS slits vs fixed slits for Rietveld work
given the old mechanical ones used to come in for
criticism as being not as good as fixed slits for providing
reliable intensities (and used to be far more painful
to install and align compared to fixed slits).


Any comments about comparison of modern computer ADS
vs traditional fixed slit systems?  Has the above
been done?


Perhaps the major problem in the past was software not 
completely matched to handling ADS data?  
I remember having an offline (verbal)
discussion around two years ago where it was claimed the 
standard modelling/correction of ADS intensity data using
the 1/(sin theta) correction as being only approximately
correct.  An alternative was proposed based on the 
fundamentals - but unfortuntely cannot remember what that
was.


At the time this probably helped to confirm my prejudice 
for fixed slit data where the physics is known with 
respect to intensities(?)


Lachlan.


-- 
Lachlan M. D. Cranswick


Collaborative Computational Project No 14 (CCP14)
    for Single Crystal and Powder Diffraction
Daresbury Laboratory, Warrington, WA4 4AD U.K
Tel: +44-1925-603703  Fax: +44-1925-603124
E-mail: l.cranswick@dl.ac.uk  Ext: 3703  Room C14
                           http://www.ccp14.ac.uk

To: sdpd@egroups.com 
From: Armel Le Bail [armel@fluo.univ-lemans.fr] 
Mailing-List: list sdpd@egroups.com; contact sdpd-owner@egroups.com 
Delivered-To: mailing list sdpd@egroups.com 
Date: Tue, 06 Jun 2000 23:32:18 +0200 
Reply-To: sdpd@egroups.com 
Subject: Re: [sdpd] Reference materials for calibration and indexing 



>What is the average size/strain results determined on the In2O3 or
>is this what the round robin will give?


It is not determined. Moreover, CeO2 is part of this Round Robin,
but In2O3 is not yet. The Round Robin is only at its first stage :
recording patterns of selected compounds, to my knowledge.


>Can the raw, uncorrected for intensity data for In2O3
>be put on the site or Emailed to those who are
>interested?  (me for starters)  


It would have been sufficient to multiply the intensities
back by sin(theta). But, yes, the original uncorrected data
set can be also found into PowBase now:
    http://sdpd.univ-lemans.fr/powbase/
Use "In2O3" as keyword (without quotes) in the search engine,
the entry number is 169b.


>It would be interesting to test out these new computer
>controlled ADS slits vs fixed slits for Rietveld work
>given the old mechanical ones used to come in for
>criticism as being not as good as fixed slits for providing
>reliable intensities (and used to be far more painful
>to install and align compared to fixed slits).


Such a comparison exists already for a NAC sample
at : http://sdpd.univ-lemans.fr/powdif/low_fwhm_and_rp.html
and the In2O3 data set adds a new convincing example that
it works sufficiently well, with the advantage of better statistics
at large angle without degrading resolution.


Let me recall that WinMProf is able to treat directly the
variable slit data without the need of any correction (the Rietveld
approach just includes the sin(theta) term, which is less
terrific than a LP correction, after all)


>I remember having an offline (verbal)
>discussion around two years ago where it was claimed the 
>standard modelling/correction of ADS intensity data using
>the 1/(sin theta) correction as being only approximately
>correct.  


This is very probably true : the correction is only approximately
correct. In my experience, the error is entirely reported on
the thermal parameters - which are knowingly the largest dustbin
in powder diffraction analysis - so that I am not sure if the B
values are degraded or improved by the process (they become
slightly smaller ;-)).


Best,



Armel Le Bail - UniversitÚ du Maine, Laboratoire des Fluorures,
CNRS ESA 6010, Av. O. Messiaen, 72085 Le Mans Cedex 9, France
http://www.cristal.org/

From: L.M.D.Cranswick@dl.ac.uk 
Mailing-List: list sdpd@egroups.com; contact sdpd-owner@egroups.com 
Delivered-To: mailing list sdpd@egroups.com 
Date: Wed, 7 Jun 2000 04:40:56 +0100 (BST) 
Reply-To: sdpd@egroups.com 
Subject: [sdpd] ADS and In2O3 data - XFIT Tutorial 



There is now a tutorial on using XFIT to profile
ADS (Automatic Divergence Slit) data in Fundamental
Parameters mode:


 http://www.ccp14.ac.uk/tutorial/xfit-95/ads_funpar.html


While not shown that well in the run-through - there might
be some problems as this is not fitting as well as
it would with fixed slits (but some of the geometry
constants may be off the optimal - plus inexperience
in what to expect with ADS data)


----


A query is: how common is it for the data collection
software to collect ADS data then convert it to
Fixed Slit data.  Would it not be better if the
data is to be stored and transmitted as "fixed
divergence slit" - then to generate it as fixed
divergence slit data?


For peak profiling (such as using Fundamental Parameters)
this could cause problems if people think the data is
fixed slit when it was really generated by Automatic
Divergence Slits?


There is at least one powder binary file format that is
"lossy" with its compression algorithm.  Shouldn't
it be the privilege of the end user to totally
abuse the data - not the programs in between?
(though the tradition in Single Crystal methods
is for both and more to occur?)


Lachlan.



-- 
Lachlan M. D. Cranswick


Collaborative Computational Project No 14 (CCP14)
    for Single Crystal and Powder Diffraction
Daresbury Laboratory, Warrington, WA4 4AD U.K
Tel: +44-1925-603703  Fax: +44-1925-603124
E-mail: l.cranswick@dl.ac.uk  Ext: 3703  Room C14
                           http://www.ccp14.ac.uk

From: "Jens Wenzel Andreasen" [aj141169@geo.geol.ku.dk] 
Mailing-List: list sdpd@egroups.com; contact sdpd-owner@egroups.com 
Delivered-To: mailing list sdpd@egroups.com 
Date: Wed, 7 Jun 2000 10:16:19 GMT+1 
Reply-To: sdpd@egroups.com 
Subject: Re: [sdpd] ADS and In2O3 data - XFIT Tutorial 


Another query which rightfully belongs in the rietveld mailing list, but 
bugs me a lot: Why is there so precious little software that models 
ADS data and none of them are any of the most well known, widely 
used packages such as GSAS and Fullprof?
If you have ADS data and want to use any of these programs, you 
have to convert your data to fixed slit data.
I wonder, because I imagine that it would take minimal effort to 
incorporate it in the software.
Jens


> A query is: how common is it for the data collection
> software to collect ADS data then convert it to
> Fixed Slit data.  Would it not be better if the
> data is to be stored and transmitted as "fixed
> divergence slit" - then to generate it as fixed
> divergence slit data?


Jens Wenzel Andreasen        "If only those geologists would let me  
Dept. of Mineralogy           alone, I could do very well, but those
Institute of Geology          dreadful hammers! I hear the clink of   
University of Copenhagen      them at the end of every cadece of the
Phone: +45 44 64 74 10        Bible verses."     - John Ruskin, 1851

To: sdpd@egroups.com 
From: "JosÚ Miguel Delgado Q."  
Mailing-List: list sdpd@egroups.com; contact sdpd-owner@egroups.com 
Delivered-To: mailing list sdpd@egroups.com 
List-Unsubscribe:  
Date: Wed, 07 Jun 2000 07:46:12 -0400 
Reply-To: sdpd@egroups.com 
Subject: Re: [sdpd] ADS and In2O3 data - XFIT Tutorial 

For the discussion... 
I have transcribed a paragraph extracted from a very good review paper 
written by McCusker, Von Dreele, Cox, Louer, Scardi: J. Appl. Cryst., 
32, 36-50 (1999) (good people!) from the Commission on Powder Diffraction, 
in which they evaluate the use of Automatic Divergence Slits in 
Rietveld refinements: 

"Many laboratory diffractometers are equipped with automatic 
divergence slits, which open as a function of 2theta. While 
there is a substantial gain in diffracted intensity at high 
angles with such slits, there is also a progressive deterioration 
of the parafocusing condition and therefore of the resolution 
as 2theta increases. In Bragg-Brentano geometry, the flat 
specimen surface is tangent to the focusing circle and, as 
2theta increases, the radius of this circle diminishes. At 
the same time, the illuminated area of the sample is reduced, 
so that the flat-sample effect on data resolution is minor, 
whatever the diffraction angle. However, if varying slits 
widths are used, a progressive angular-dependent defocusing 
occurs and the quality of the data deteriorates. Furthermore, 
if the measured intensities are to be used in a Rietveld 
refinement, the slits opening needs to have a precision of 
at least 1% or, in other words, be reproducible to a few 
microns over the entire 2theta range. For these reasons, 
the use of such slits for a Rietveld refinement is not 
recommended."
  

Miguel Delgado

To: sdpd@egroups.com 
From: Armel Le Bail  
Mailing-List: list sdpd@egroups.com; contact sdpd-owner@egroups.com 
Delivered-To: mailing list sdpd@egroups.com 
List-Unsubscribe:  
Date: Wed, 07 Jun 2000 21:59:32 +0200 
Reply-To: sdpd@egroups.com 
Subject: Re: [sdpd] ADS and In2O3 data - XFIT Tutorial 



>However, if varying slits widths are used, a progressive angular-dependent 
>defocusing occurs and the quality of the data deteriorates. Furthermore, 
>if the measured intensities are to be used in a Rietveld refinement, 
>the slits opening needs to have a precision of at least 1% or, in other 
>words, be reproducible to a few microns over the entire 2theta range. 
>For these reasons, the use of such slits for a Rietveld refinement 
>is not recommended."

Well, are all the variable slit systems identical ? Probably not.


The CeO2 pattern was also recorded with the Bruker variable slits
system (using 400 steps over the whole angular range, if I
remember well). I have now a series of patterns to which the 
Rietveld method was applied, in spite of this being not recommended.


Let me ask you to show me on these patterns, most in PowBase
  (NAC, In2O3, CeO2, NIST SRM 1976...) where is the big problem ?
The minimal FWHM  is in the range 0.045-0.060░2-theta. The Rp 
values (in the original Rietveld definition : background subtracted,
and peak-only) are in the range 5-10%. The atomic coordinates are
very close to the expected ones. The B are maybe slightly too small. 
The cell parameters are OK. This is fine for me. 


Some recommendations are made for being  transgressed ;-).


Best,


Armel Le Bail
http://sdpd.univ-lemans.fr/course/


[Back to Problems and Solutions]

[CCP14 Home: (Frames | No Frames)]
CCP14 Mirrors: [UK] | [CA] | [US] | [AU]

(This Webpage Page in No Frames Mode)

If you have any queries or comments, please feel free to contact the CCP14