Re: Misconduct

[Kurt Leinenweber]

Hi, in our work we still sometimes encounter entirely new compounds with simple 
structures like rocksalt, spinel, etc.  in order to convince ourselves and our 
readers that the materials are real, we have to fit the powder patterns - put 
in the atoms, refine lattice parameter(s), show that thermal parameters are 
reasonable, fit the peak shapes, background etc all together.  In the case of 
spinels for example we can also refine the single atomic parameter and show 
that the bond lengths are reasonable.  The refinements are used to decide 
whether sites are fully occupied and to decide the valence of the cation when 
multiple valence states are possible.  It’s not the kind of thing that would 
get people really excited with the crystallographic methods, but it is 
necessary for convincing ourselves and others that the identification of the 
compound is reasonable.  Is that Rietveld refinement?  I don’t know so I call 
upon the list to say.

Kurt

Get Outlook for iOS

From: rietveld_l-requ...@ill.fr  on behalf of 
Matthew Rowles 
Sent: Sunday, January 14, 2024 11:04:25 PM
To: Alan W Hewat 
Cc: Le Bail Armel ; Rietveld_L 
Subject: Re: Misconduct

I see the core contribution of the Rietveld method as the point-wise 
calculation of a powder pattern. This then enables the refinement of the 
parameters.

Yes, attributing QPA to Rietveld is incorrect; that is mainly due to 
Hill/Howard and Bish/Howard - I try to make it a point to differentiate this.

calling PDF refinements Rietveld refinements is just plain wrong (afaik), 
unless you actually are moving crystallographic parameters around, in which 
case, the nomenclature gets fuzzy..

On Sat, 13 Jan 2024 at 14:39, Alan W Hewat 
mailto:alan.he...@neutronoptics.com>> wrote:
The core of Rietveld refinement is REFINING the crystallographic parameters to 
fit the pattern. That was the great innovation. Is that done here ? To 
calculate various patterns to refine phase composition you necessarily need 
models of the crystal structures. But all refinements of powder patterns are 
not Rietveld Refinement. Quantitative analysis of powder samples is an 
important technique, and to attribute that to Rietveld is wrong. Same goes for 
Pair Distribution Function analysis. Calling everything "Rietveld Refinement" 
is not helpful, and actually hides the fundamental contribution of this 
technique to crystallography.


Dr Alan Hewat, NeutronOptics
Grenoble, FRANCE (from phone)
alan.he...@neutronoptics.com
+33.476984168 VAT:FR79499450856
http://NeutronOptics.com/hewat
___


On Sat, 13 Jan 2024, 07:00 Matthew Rowles, 
mailto:rowle...@gmail.com>> wrote:
Hard disagree here.

You're using crystallographic parameters to calculate the (intensities and 
positions of the) pattern.

To me, that's the core of Rietveld refinement.

You need to apply a peak shape model. Why not apply a model from which you can 
extract crystallite parameters?

QPA can then be done on the output of a refinement, eg application of the 
internal standard method using the Hill /Howard algorithm.

Its still a Rietveld refinement, I'm not just fitting peaks willy nilly; 
they're constrained by a crystal model.


Matthew

On Sat, 13 Jan 2024, 01:48 Alan W Hewat, 
mailto:alan.he...@neutronoptics.com>> wrote:
Apart from the record number of atoms, phases, parameters, citations etc used 
to describe just 3 broad peaks, I object to this kind of refinement being 
called "Rietveld refinement". Luca called it "Rietveld-like" in MAUD, which was 
used here, but even that is wrong. The term "Rietveld refinement" should be 
restricted to the refinement of crystallographic parameters - cell dimensions, 
atom coordinates etc. and not applied to quantitative analysis of phases, 
particle size etc. Fitting peaks in powder patterns was done before Rietveld, 
who must be turning in his grave to see his name associated with this kind of 
thing.


Dr Alan Hewat, NeutronOptics
Grenoble, FRANCE (from phone)
alan.he...@neutronoptics.com
+33.476984168 VAT:FR79499450856
http://NeutronOptics.com/hewat
___


On Fri, 12 Jan 2024, 12:57 Le Bail Armel, 
mailto:le-bail.ar...@orange.fr>> wrote:

Hi,

A good candidate for the "worst Rietveld refinement of the year" award :

https://pubpeer.com/publications/12069A6AD9D5D34F26031F34705D06

Even the difference pattern is 

RE: [EXT] Re: [External] Re: Step-like basline

[Kurt Leinenweber]

Hi,  Are these things modeled in Rietveld programs, by chance?  It seems like a 
lot of baggage to put in a refinement but if it makes the results better...


  *   Kurt

From: rietveld_l-requ...@ill.fr  On Behalf Of Thomas 
Gegan
Sent: Sunday, September 3, 2023 9:16 AM
To: Bish, David L ; Shay Tirosh ; 
Fernando Igoa 
Cc: Rietveld List (rietveld_l@ill.fr) 
Subject: RE: [EXT] Re: [External] Re: Step-like basline

I agree with a Ni absorption edge, possibly with a Kβ peak around 38° 2θ.

Tom Gegan
Chemist III

Phone: +1 732 205-5111, Email: tom.ge...@basf.com
Postal Address: BASF Corporation, , 25 Middlesex Essex Turnpike, 08830 Iselin, 
United States
[cid:image001.png@01D9DE4C.79FBB4C0]

From: rietveld_l-requ...@ill.fr 
mailto:rietveld_l-requ...@ill.fr>> On Behalf Of 
Bish, David L
Sent: Sunday, September 3, 2023 7:08 AM
To: Shay Tirosh mailto:stiro...@gmail.com>>; Fernando Igoa 
mailto:fer.igoa.1...@gmail.com>>
Cc: Rietveld List (rietveld_l@ill.fr) 
mailto:rietveld_l@ill.fr>>
Subject: [EXT] Re: [External] Re: Step-like basline

Some people who received this message don't often get email from 
b...@indiana.edu. Learn why this is 
important
Hello Shay,
I think it is probably related to "tube tails". You can read about this in the 
literature (e.g., on the BGMN web site) and you can model it in some Rietveld 
software such as Topas. You don't normally notice this but it becomes apparent 
with higher-intensity peaks.

Regards,
Dave

From: rietveld_l-requ...@ill.fr 
mailto:rietveld_l-requ...@ill.fr>> on behalf of 
Fernando Igoa mailto:fer.igoa.1...@gmail.com>>
Sent: Sunday, September 3, 2023 3:06 AM
To: Shay Tirosh mailto:stiro...@gmail.com>>
Cc: Rietveld List (rietveld_l@ill.fr) 
mailto:rietveld_l@ill.fr>>
Subject: [External] Re: Step-like basline

This message was sent from a non-IU address. Please exercise caution when 
clicking links or opening attachments from external sources.

Hey Shay,

Are you using a motorized slit during the measurement? These may open up 
abruptly to compensate for the angular dependence of the footprint and thus 
generate an abrupt increase in the intensity.

Hope it helps :)

On Sun, Sep 3, 2023, 8:50 AM Shay Tirosh 
mailto:stiro...@gmail.com>> wrote:
Dear Rietvelders
I am attaching a zoom-in on a diffraction profile.
My question is what is the origin of the step-like profile next to a very large 
reflection peak?
Is it a sample preparation problem?
Is it part of the baseline?
[cid:image003.png@01D9DE4C.79FBB4C0]
Thanks
Shay
--









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Re: Rietveld website cancelled ?

[Kurt Leinenweber]

Was that Clint Eastwood?  - Kurt


From: rietveld_l-requ...@ill.fr  on behalf of Le 
Bail Armel 
Sent: Wednesday, August 29, 2018 12:01:25 PM
To: Rietveld_L@ill.fr
Subject: Re: Rietveld website cancelled ?


OK, seems that the SDPD book preface looks unclear to some.



Western movies adepts well know that sentence :

"You see, in this world there's two kinds of people, my friend: those with 
loaded guns, and those who dig. You dig. .."



Similarly, there are two kinds of people, those believing that the sense of the 
words "structure determination" and

"structure refinement" are the same, and the others. You dig.



Best



Armel









> Message du 29/08/18 18:09
> De : "Larry Finger" 
> A : "Le Bail Armel" , Rietveld_L@ill.fr
> Copie à :
> Objet : Re: Rietveld website cancelled ?
>
> On 08/29/2018 04:15 AM, Le Bail Armel wrote:
> > Hi,
> >
> > After the IUCr Monograph on Crystallography 13 (2002)
> >
> > entitled "Stucture Determination from Powder Diffraction Data"
> >
> > you may find in the preface :
> >
> > "Although the Rietveld method of structure refinement from powder
> >
> > diffraction data is often loosely considered to be synonymous with structure
> >
> > determination, it is not. The Rietveld method only comes into play in the
> >
> > final stage of the structure solution process when an approximate structural
> >
> > model has been found."
> >
> > WIF David, K Shankland, LB McCusker, C Baerlocher
> >
> > A clear distinction having my complete agreement.
> >
> > Armel
>
> Armel,
>
> Although the above statement may be generally true, I can provide a counter
> example. In Max W. Schmidt, Larry W. Finger, Ross J. Angel, and Robert E.
> Dinnabier, "Synthesis, crystal structure, and phase relations of AlSiO2OH, a
> high pressure hydrous phase", American Mineralogist, V. 83, 881-888, 1998, we
> only had a powder - no single crystals. From data measured at ESRF, we used 
> GSAS
> to isolate the peaks of interest for the unknown phase, and used program TREOR
> to autoindex the unknown and identify the impurity phases. We then extracted
> intensities using the LeBail method, and determined the structure using direct
> methods with program SIRPOW. The structure was then refined with GSAS. We were
> even able to locate the H atom from Fourier maps!
>
> Even 20 years ago, it was possible to determine the structure from X-ray 
> powder
> patterns.
>
> Larry
>
>
>
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RE: Obtaining a silicon standard wafer

[Kurt Leinenweber]

I for one, don’t blame Jim for wanting this plot to appear in an official 
publication rather than as a “freebie” on a web site.  He will get more credit 
for it this way.


-  Kurt

From: rietveld_l-requ...@ill.fr [mailto:rietveld_l-requ...@ill.fr] On Behalf Of 
Cline, James Dr.
Sent: Tuesday, July 14, 2015 9:59 AM
To: Alan Hewat
Cc: rietveld_l@ill.fr
Subject: RE: Obtaining a silicon standard wafer

Hi,
Why don't you put these plots on your sales site...
The SRM people would never do this as they would have to explain the plot in a 
technical manner to inquiring customers.
Well, the documents on the NIST site are already quite technical, and contain 
plots, just not the nice comparative plots  you might need when choosing a line 
standard eg 
https://www-s.nist.gov/srmors/certificates/view_certGIF.cfm?certificate=640E


I did, indeed, include this plot (and a discussion of it) in the Vol H paper 
and have taken measures to get it available online sooner, rather than later.

Jim


James P. Cline
Materials Measurement Science Division
National Institute of Standards and Technology
100 Bureau Dr. stop 8520 [ B113 / Bldg 217 ]
Gaithersburg, MD 20899-8523USA
jcl...@nist.govmailto:jcl...@nist.gov
(301) 975 5793
FAX (301) 975 5334

From: alan.he...@gmail.commailto:alan.he...@gmail.com 
[mailto:alan.he...@gmail.com] On Behalf Of Alan Hewat
Sent: Tuesday, July 14, 2015 12:20 PM
To: rietveld_l@ill.frmailto:rietveld_l@ill.fr
Subject: Re: Obtaining a silicon standard wafer

if you would like a preprint, send me an email.

Yes, that's the way people should offer supplementary material to list users. 
Or even better, link to your preprint.

Why don't you put these plots on your sales site...
The SRM people would never do this as they would have to explain the plot in a 
technical manner to inquiring customers.

Well, the documents on the NIST site are already quite technical, and contain 
plots, just not the nice comparative plots  you might need when choosing a line 
standard eg 
https://www-s.nist.gov/srmors/certificates/view_certGIF.cfm?certificate=640E

 What year is it ? I find it silly to discuss inclusion of a 64K image in email

OK Frank, but until someone sets up an email archive that reproduces images, 
they are lost to others if they are simply included in an email - see 
https://www.mail-archive.com/faq.html#attachments and the bit about performance.

Frankly, I am indeed a little old-fashioned. If you can't find it with 
Google... it doesn't exist.

Alan.
__
   Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE
alan.he...@neutronoptics.commailto:alan.he...@neutronoptics.com 
+33.476.98.41.68
http://www.NeutronOptics.com/hewat
__
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++

RE: What's in a name?

[Kurt Leinenweber]

Hi all,



The question could be very Rietveld-related if the person wants to know how 
well the D2 Phases diffractometer works in getting Ritveld-refinable data.  
Sometimes companies want to sell new types of focusing optics etc. and it is 
very relevant to find out whether such optics might make Rietveld refinement 
difficult.



- Kurt




From: alan.he...@gmail.com [alan.he...@gmail.com] on behalf of Alan Hewat 
[alan.he...@neutronoptics.com]
Sent: Friday, July 03, 2015 10:03 AM
To: Timothy Hyde
Cc: rietveld_l@ill.fr
Subject: Re: What's in a name?

No problem with people asking not strictly Rietveld questions Tim.
But the list is named in honour of Hugo Rietveld, and that seems right to me.
Besides, it's shorter than either of your suggested titles :-)
Alan.

On 3 July 2015 at 18:35, Timothy Hyde 
timothy.h...@matthey.commailto:timothy.h...@matthey.com wrote:
“Dear All,
Sorry not a direct Rietveld question, but I hope somebody can help……….”

Alan,

Second such question of the day! Perhaps (not wanting to go too much over old 
ground re Facebook/social media etc) all that is required to grow 
membership/usage is a simple name change of the group? I suggest “Sorry not a 
direct Rietveld question, but I hope somebody can help…”

Perhaps  “XRD and Rietveld” would be less cumbersome and inform potential new 
members that Rietveld is only a fraction of the discussion topics on the list? 
Any thoughts?

Tim Hyde


From: rietveld_l-requ...@ill.frmailto:rietveld_l-requ...@ill.fr 
[mailto:rietveld_l-requ...@ill.frmailto:rietveld_l-requ...@ill.fr] On Behalf 
Of Natale Perchiazzi
Sent: 03 July 2015 16:10
Cc: rietveld_l@ill.frmailto:rietveld_l@ill.fr
Subject: D2 phaser info





Dear All,
Sorry not a direct Rietveld question, but I hope somebody can help. We are 
evaluating to get a D2 Phaser diffractometer. If somebody has got this 
equipment and wish to share his experience with the machine, infos are warmly 
welcome .
Best regards Natale Perchiazzi
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--
__
   Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE
alan.he...@neutronoptics.com +33.476.98.41.68
http://www.NeutronOptics.com/hewat
__
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++

RE: Apologies... The No Attachment rule.

[Kurt Leinenweber]

Hi Darren,

That’s a very good point and clarification.


-  Kurt

From: Darren Broom [mailto:darrenbr...@inbox.com]
Sent: Sunday, May 10, 2015 6:54 AM
To: rietveld_l@ill.fr
Cc: Kurt Leinenweber
Subject: RE: Apologies... The No Attachment rule.

Hi Kurt

Maybe I should let others comment first but I would just like to say that I 
think a slightly harsh comment to an experienced person who has made a silly 
mistake is quite different to an abrupt and perhaps patronizing comment to a 
complete beginner who has asked a legitimate question.

I have checked back and it was definitely the latter that Bill Reese was 
commenting on previously...

Cheers,

Darren
-Original Message-
From: ku...@asu.edumailto:ku...@asu.edu
Sent: Sun, 10 May 2015 13:26:28 +
To: rietveld_l@ill.frmailto:rietveld_l@ill.fr
Subject: RE: Apologies... The No Attachment rule.

Hi,



The subject of snarky comments is a fascinating one.  I have definitely been 
the recipient of snarky comments for some of my more stupid posts on this list. 
 The good thing about them is that it lets you know that you are saying or 
doing something, crystallographically speaking, that is really unpalatable to 
someone out there, and you might need to know this for your own good.  I have 
definitely been chastised and have learned some things over the years by being 
forced to read a snarky response to one of my posts.  But on the other hand, to 
a beginner a snarky comment can be damaging.  However, these comments are not 
confined to mailing lists – they happen at conferences too and they are just 
part of the fabric of science.  As long as the whole list does not descend into 
a chaos of snarky comments, I think it’s OK to let them get through.  One 
possible remedy is for others to come to the defence of a victim of excessive 
snarkiness.  I have seen that happen on this list sometimes, and other times 
have been tempted myself to intervene, though I usually have not been brave 
enough (especially when the snark source is someone famous).



-  Kurt



From: rietveld_l-requ...@ill.frmailto:rietveld_l-requ...@ill.fr 
[mailto:rietveld_l-requ...@ill.fr] On Behalf Of Darren Broom
Sent: Sunday, May 10, 2015 3:36 AM
To: Alan Hewat; Leopoldo Suescun
Cc: rietveld_l@ill.frmailto:rietveld_l@ill.fr
Subject: RE: Apologies... The No Attachment rule.



Hi Alan

Thanks for the explanation. The point about the archive seems to me to be the 
most persuasive - I see what you mean. Providing the file sharing links stay 
active that does ensure the archive remains useful without having to host 
additional files on the archive server.

It does seem that removing any attachments automatically would be the best 
solution. Hopefully Song Zhen's suggestion will help sort that out.

Incidentally, Jon nicely illustrated one of the things about the list that I 
really appreciate, by posting an interesting link that I hadn't seen before and 
probably wouldn't have come across otherwise.

Also, I wondered if you could set up SYMPA so that it strips emails of any 
unnecessary snarkiness (above a predefined threshold)?

Best regards,

Darren



-Original Message-
From: alan.he...@neutronoptics.commailto:alan.he...@neutronoptics.com
Sent: Sat, 9 May 2015 11:39:46 +0200
To: leopo...@fq.edu.uymailto:leopo...@fq.edu.uy
Subject: Apologies... The No Attachment rule.

Dear Rietveld list.



Good to see so many people asking for the list to be continued. And even an 
example of an interesting scientific question immediately answered by an 
expert. Encouraging.



So why do I forbid sinful attachments ? (No, it's not because I'm getting old 
and snarky, though we all do eventually :-) Think of the Rietveld list as a 
kind of relaxed Twitter, except that you are not limited to 140 characters. 
And what about Google's decision this month to favour sites that can be used on 
a mobile phone ? Yes, even oldies use mobile phones for email. SMS is another 
example of beauty in brevity.



Then the Rietveld Archive is an excellent record of past discussions - without 
the attachments. Messages that rely on attachments are then often 
incomprehensible - look up that message on 
https://www.mail-archive.com/rietveld_l@ill.fr/ Frankly, if you need more than 
that, put it on a webserver with a link to it. Such links are preserved in the 
archive.



If you see my own warning about no attachments as an attachment :-) perhaps 
you should check how your email client is set up. Or tell me how I can do it 
differently with SYMPA www.sympa.orghttp://www.sympa.org I didn't design the 
mail server nor the mail archive. Clearly, it is difficult to enforce a simple 
no attachments rule, so what would it be like policing a small attachments 
rule ? Even if you personally have lots of space for email, our webserver (for 
which we don't pay) would still have to distribute ~1500 copies of your small 
attachment.



In this particular case, a figure from an unpublished paper

RE: regress in crystallographic good practices and knowledge

[Kurt Leinenweber]

Hi Alan,

I still like the Rietveld list and do read all the posts.

Is it possible to block attachments so that people can’t attach files any more?


-  Kurt

From: alan.he...@gmail.com [mailto:alan.he...@gmail.com] On Behalf Of Alan Hewat
Sent: Friday, May 08, 2015 9:07 AM
To: Leopoldo Suescun
Cc: rietveld_l@ill.fr
Subject: Re: regress in crystallographic good practices and knowledge

I apologize in advance for attaching a file but I cannot share my astonishment 
without it.
that´s why I worry more and more every day.

And I worry that people are still attaching files to the whole list when they 
are explicitly asked not too. Most papers are on-line now, so just give a link 
to the paper. Or post your file to a free file sharing service - see: 
http://en.wikipedia.org/wiki/Comparison_of_file_hosting_services

Anyone who still posts files to the whole list is automatically suspended for 1 
week.

Actually, I worry that the Rietveld list no longer serves a useful purpose. 
There are few interesting discussions, and apparently few people actually read 
the posts.

Alan
__
   Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE
alan.he...@neutronoptics.commailto:alan.he...@neutronoptics.com 
+33.476.98.41.68
http://www.NeutronOptics.com/hewat
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RE: regress in crystallographic good practices and knowledge

[Kurt Leinenweber]

Hi all,

In my defense, 10 of the 12 messages relating to this topic have had their 
footers attached.  I will try to figure out how to get rid of it for next time.

Here is a topic I am interested in: we are collecting a lot of data on an 
imaging plate (GSECARS and HPCAT at Advanced Photon Source).  We are interested 
in splitting of peaks in some of the samples.  The splitting is very difficult 
to see on the integrated pattern, but very easy to see on the 2-D imaging plate 
frame itself.  The rings are spotty and it's very easy to tell which spots 
are in which ring when the peak is slightly split.

My question is whether there is software I can use to take advantage of this 
and fit the spots so I can get a better resolution of the splitting.  
Something in between powder and single crystal.

Thank you,

- Kurt

-Original Message-
From: Larry Finger [mailto:larry.fin...@gmail.com] On Behalf Of Larry Finger
Sent: Friday, May 08, 2015 9:58 AM
To: Kurt Leinenweber; Alan Hewat; Leopoldo Suescun
Cc: rietveld_l@ill.fr
Subject: Re: regress in crystallographic good practices and knowledge

On 05/08/2015 11:16 AM, Kurt Leinenweber wrote:
 Hi Alan,

 I still like the Rietveld list and do read all the posts.

 Is it possible to block attachments so that people can’t attach files any 
 more?

 -Kurt

Thus writes the guy whose mailer blindly attaches a message footer rather than 
in-lining a signature. :)

Although I no longer practice crystallography, and no longer read the 
literature, I do find the discussions here of interest. At least I can follow 
how little crystallography the average solid-state researcher actually knows. 
Sad to know that bugs in a few programs could completely derail the science. 
All the greats of the early part of the 20th century must be really spinning in 
their graves!

Larry

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RE: regress in crystallographic good practices and knowledge

[Kurt Leinenweber]

P.S.  When the splitting arises from a phase transition, sometimes we see what 
we call snowmen or pairs of spots that are split between the two rings.  I 
interpret these as twins arising from the phase transition.  Has anyone seen 
these types of pairs of spots before?  I think there is a lot of information 
there that we are passing up if we don't learn to interpret it.

Hi all,

In my defense, 10 of the 12 messages relating to this topic have had their 
footers attached.  I will try to figure out how to get rid of it for next time.

Here is a topic I am interested in: we are collecting a lot of data on an 
imaging plate (GSECARS and HPCAT at Advanced Photon Source).  We are 
interested in splitting of peaks in some of the samples.  The splitting is 
very difficult to see on the integrated pattern, but very easy to see on the 
2-D imaging plate frame itself.  The rings are spotty and it's very easy to 
tell which spots are in which ring when the peak is slightly split.

My question is whether there is software I can use to take advantage of this 
and fit the spots so I can get a better resolution of the splitting.  
Something in between powder and single crystal.

Thank you,

- Kurt
++
Please do NOT attach files to the whole list alan.he...@neutronoptics.com
Send commands to lists...@ill.fr eg: HELP as the subject with no body text
The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/
++

RE: Polarization factor por Ge (111) monochromator

[Kurt Leinenweber]

Hi all,



So are all readers of the Rietveld list also supposed to search the archives 
for this information?  Tell us the answer, please!

- Kurt




From: rietveld_l-requ...@ill.fr [rietveld_l-requ...@ill.fr] on behalf of Josué 
Friedrich [josue.friedr...@gmail.com]
Sent: Sunday, April 06, 2014 12:12 PM
To: Artem Babaryk
Cc: rietveld_l@ill.fr
Subject: Re: Polarization factor por Ge (111) monochromator

Thanks Artem,

Usually I search first, but today I did not. Thanks for your help

regards, Josue

From: Artem Babarykmailto:baba...@bigmir.net
Sent: Sunday, April 06, 2014 8:56 PM
To: Josu Friedrichmailto:josue.friedr...@gmail.com
Cc: rietveld_l@ill.frmailto:rietveld_l@ill.fr
Subject: Re: Polarization factor por Ge (111) monochromator

Dear Josu,

Somethimes browsing the Rietveld list archive I'm strengthening myself that
there is nothing new under the sun...

So, look there:

http://www.mail-archive.com/rietveld_l%40ill.fr/msg05129.html

Best,
Artem

06.04.2014 20:11, Josu Friedrich josue.friedr...@gmail.com
Good afternoon,

 Does anyone know the polarization factor for an incident beam germanium (111) 
 monochromator used in a Panalytical XPert Pro diffractometer?

 Many thanks,
 Josue
++
Please do NOT attach files to the whole list alan.he...@neutronoptics.com
Send commands to lists...@ill.fr eg: HELP as the subject with no body text
The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/
++

RE: the error bars of lattice parameters using GSAS

[Kurt Leinenweber]

Dear Jin Peng,
 
The uncertainties for the lattice parameters (and all the other fitted 
parameters) are in the LST file (list file).  They are shown as separate 
numbers for the lattice parameters and the uncertainties, like so:
 
13.88843  13.88843   6.53524
0.000350.000350.00014
 
- Kurt



From: Peng, Jin [mailto:jpe...@tulane.edu]
Sent: Thu 2/18/2010 5:31 PM
To: rietveld_l@ill.fr
Subject: the error bars of lattice parameters using GSAS



Hi,

I am using the graphical interface of GSAS, EXPGUI, for the refinement, the 
problem is I can not find the error bars for the lattice constant a, b, c. I 
can find the error of band length and band angles under result - disagl. Where 
can I find the error bars for a, b and c?

Thank you!

Jin Peng
Department of Physics, Tulane University
New Orleans, LA, 70118

RE: Comparison of powder patterns recorded at different wavelengths

[Kurt Leinenweber]

Hi Mike,

If he plots in d then neither of the components will have the right d-spacing 
when he uses the average - but you're right that its standard procedure.

- Kurt

 
*
Kurt Leinenweber
Dept. of Chemistry and Biochemistry
Arizona State University
Tempe, AZ 85287-1604
 
phone (480)-965-8853
fax (480)-965-2747
 
***

-Original Message-
From: Michael Glazer [mailto:m.glaz...@physics.ox.ac.uk] 
Sent: Friday, January 15, 2010 9:49 AM
To: Kurt Leinenweber; Franz Werner; rietveld_l@ill.fr
Subject: RE: Comparison of powder patterns recorded at different wavelengths

Kurt
The standard method is to use a wavelength made from the weighted (2:1) average 
of the two components. So for CuKa the standard value is 1.5418 angstroms
Mike Glazer


-Original Message-
From: Kurt Leinenweber [mailto:ku...@asu.edu] 
Sent: 15 January 2010 16:46
To: Franz Werner; rietveld_l@ill.fr
Subject: RE: Comparison of powder patterns recorded at different wavelengths

HI Franz,

It seems to me that the best thing would be to use K alpha 1 wavelength (which 
is 66 percent of the total intensity) and then mentally ignore the K alpha 2 
contribution.  The other option is to strip the original data of K alpha 2, if 
your diffractometer's software has that option, but since stripping is a kind 
of data manipulation, I don't usually like doing it.

- Kurt

 
*
Kurt Leinenweber
Dept. of Chemistry and Biochemistry
Arizona State University
Tempe, AZ 85287-1604
 
phone (480)-965-8853
fax (480)-965-2747
 
***

-Original Message-
From: Franz Werner [mailto:franzwer...@gmx.at] 
Sent: Friday, January 15, 2010 6:27 AM
To: rietveld_l@ill.fr
Subject: Comparison of powder patterns recorded at different wavelengths

Hello Rietvelders

I want to compare graphically powder patterns of a phase which were recorded at 
different wavelengths. Therefore I'd like to overlay the patterns using 
d-values, calculated from their corresponding 2theta values. In the case of 
monochromatic X-rays it's trivial. But which wavelength should one use in the 
case of Kalpha1-Kalpha2 radiation (lab instrument)?

Thanks for your help.

Regards
Franz Werner

Tallinn University of Technology
Estonia
-- 
GRATIS für alle GMX-Mitglieder: Die maxdome Movie-FLAT!
Jetzt freischalten unter http://portal.gmx.net/de/go/maxdome01

RE: zero-background quartz plates

[Kurt Leinenweber]

Hi All,
 
What's the big deal about making these plates?  Why don't we of the community 
make our own?
 
In particular, I have found that when using one of the new wide detectors, 
you really have to worry about the angle of the cut off any crystallographic 
axes, and some of the standard plates give HUGE backgrounds when used with wide 
or area detectors.
 
- Kurt



From: Mercier, Patrick [mailto:patrick.merc...@nrc-cnrc.gc.ca]
Sent: Mon 11/16/2009 12:28 PM
To: bill.l.re...@exxonmobil.com; rietveld_l@ill.fr
Subject: RE: zero-background quartz plates



Hello,

Check out the MTI Corporation website at the following URL:

http://www.mtixtl.com/index.asp?PageAction=VIEWPRODProdID=1431

They make both silicon and quartz zero-background holders.

Regards,
-Patrick

___
|Patrick H.J. Mercier, Ph.D., P.Phys., Eng. Jr
|Competency Leader, Ceramic Materials | Chef de compétence, Matériaux céramiques
|Research Officer | Agent de recherches
|Institute for Chemical Process and Environmental Technology
|Institut de technologie des procédés chimiques et de l'environnement
|National Research Council of Canada | Conseil national de recherches du Canada
|1200 Montreal Road, Ottawa, Ontario, Canada, K1A 0R6
|Tel: 613-993-7752 Fax: 613-991-2384 patrick.merc...@nrc-cnrc.gc.ca

Internal standard

[Kurt Leinenweber]

Hi all,

 

This may be a non-issue given the high accuracy of diffraction measurements, 
and the internal checks on sample position, such as dependent peaks that lead 
to the sample shift, but there is something I've always wondered about when an 
internal standard is used in combination with refinement.

 

You can fix the lattice parameter of silicon, as Patrick says below, but the 
extent to which this fixed lattice parameter enters the refinement depends on 
how much silicon is in the sample.  If you keep adding more silicon, in effect 
you are weighting the data to have an increasing dependence on the silicon.  
So, what is the correct ratio of silicon to unknown, to be sure that you are 
making the best measurement?

 

I suppose this is only an issue if the sample shift or zero error is quite 
large, in which case you might want to work on that problem first.  But still, 
it's something I've wondered about.

 

- Kurt

 

 

*

Kurt Leinenweber

Dept. of Chemistry and Biochemistry

Arizona State University

Tempe, AZ 85287-1604

 

phone (480)-965-8853

fax (480)-965-2747

 

***



From: Patrick Weisbecker [mailto:weis...@yahoo.fr] 
Sent: Thursday, May 14, 2009 10:16 AM
To: leopo...@fq.edu.uy
Cc: rietveld_l@ill.fr
Subject: Re : Introduction and Unit cell parameter determination

 

It is indeed advisable to start with an internal standard to check that there 
is no instrumental error or sample position issue (sample displacement is the 
more common cause of peak shift).

Silicon powder is often used as a standard, a standard reference material (SRM) 
is sold by the NIST (SRM640) but you can also use good quality silicon powder 
(99.99%) if you don't need an accuracy better than 0.0001A (a=5.4309A).

 

Rietveld programs are indeed not necessary if you only the lattice parameters, 
standard peak fitting and lattice parameter refinement using several peaks at 
high angle should give you good results.

 

Fullprof can handle internal standard: you have to fix the lattice parameter of 
Si to its known value and refine zero error or sample displacement parameter 
(use Full profile fit prerentially as indicated by Leopoldo).

 

Patrick

 



De : Leopoldo Suescun leopo...@fq.edu.uy
À : Gumelar Pritosiwi pritos...@gmail.com; rietveld_l@ill.fr
Envoyé le : Jeudi, 14 Mai 2009, 15h45mn 16s
Objet : RE: Introduction and Unit cell parameter determination

Dear Gumelar Pritosiwi,

 

There are two independent topics in your question. If you are using a well 
calibrated conventional diffractometer to determine your cell parameters then 
you don't need an internal standard. That would be useful if you, additionally, 
need to do a quantitative phase analysis.

 

In a conventional machine with sealed tube source the cell parameters 
determination can be done easily in the case of cubic magnetite, because you 
already know the incident wavelength and d-spacings for the observed maxima are 
linearly related to a cell parameter by d(hkl)=a/sqrt(h^2+k^2+l^2).

 

Programs such as FULLPROF, GSAS, TOPAS, etc. are meant for Rietveld refinement, 
that is something a little bit more complex than cell parameters determination, 
although most of these programs have additional routines (peak search and 
indexing in Winplotr) that can help determine cell parameters of an unknown 
phase, or in your case, of the magnetite you are studying. You can also try 
full profile fit (LeBail or Pawley methods) to extract best possible cell 
parameters provided your data is of enough quality and you are willing to cope 
with profile shapes, background modeling, etc. (too complicated to start with 
in my opinion). 

 

If you use data with internal standard for lattice parameters determination you 
may choose to ignore the internal standard peaks or just collect new data on 
the raw material where you just see your magnetite peaks (be careful, if your 
sample contains other crystalline materials you will need to identify the extra 
peaks and avoid using them for the cell parameters determination).

 

Free programs like checkcell will allow you to determine your cell parameters 
by refinement of previously determined peak positions, other programs like 
Winplotr, PowderX, etc will allow you to perform a peak search and extract a 
peak list, other programs like CMPR can fit individual peaks and output a list 
of fit results. Any of these (and many more) you can then fit to obtain a 
using the abovementioned equation. There are probably many more free programs 
to do either thing more or less automatically so you should check the www or 
ccp14 site for information. 

 

If your magnetite show any kind of structural distortion this may be a bit more 
complex, but in that case you'll need to check some crystallography book to get 
a better idea of what can you do with your powder diffraction data and how can 
you do

RE: cRs

[Kurt Leinenweber]

Hi all - 
 
The way I've thought about it is that when you fit the background in Rietveld, 
that is a kind of background removal.  But, it is done in conjunction with the 
peak fit, which means that you are closer to subtracting the true background 
(a mixture of the machine background plus any scattering from the sample that 
is not part of the Bragg reflections).  And, the statistics of the background 
removal is properly included in the error analysis of the fit.
 
Still, there is cross-talk between the background and the Bragg peaks even in 
Rietveld refinement.  That cross-talk should be partly accounted for by the 
correlation matrix of errors between the different fitting parameters.  But it 
can still detract from the structure if done poorly.
 
That's how I think of it - - does it sound right, all?
 
- Kurt



From: Maxim V. Lobanov [mailto:m_loba...@huntsman-nmg.com]
Sent: Tue 3/3/2009 11:35 PM
To: rietveld_l@ill.fr
Subject: RE: cRs




As far as I understand, the major issue is that BG subtraction changes the 
error statistics (accordingly, weights applied in calculating function to 
minimize...). It is also somewhat arbitrary how you choose the BG line - so, 
you can easily subtract part of Bragg contribution from base of peak - hence, 
bias the data. Most probably there are more things I didn't mention. So, of 
course it is preferable to fit BG with some suitable empirical function (e.g. 
Chebyschev polynomials).

However, some Rietveld programs do not have good selection of BG functions, and 
it is sometimes problematic to correctly fit the BG - so, I think in this case 
careful BG removal would be the only option. I'd like to use this opportunity 
to ask Fullprof experts: is the Chebyschev option finally implemented? Or 
otherwise what is the best option to model difficult (wavy) background with 
Fullprof?

Sincerely,
Maxim.

---
Dr. Maxim Lobanov
RD Director
Huntsman-NMG
mailto: m_loba...@huntsman-nmg.com

*
If you encounter any difficulties
sending e-mails to the addresses in huntsman-nmg.com domain,
this could be due to the our spam filter malfunction.
In case of such an event please send a message to n...@fromru.com

Please note that the old domain nmg.com.ru does not exist anymore -
please update your address book accordingly


-Original Message-
From: matthew.row...@csiro.au [mailto:matthew.row...@csiro.au]
Sent: Wednesday, March 04, 2009 8:32 AM
To: olga.smirn...@hw7.ecs.kyoto-u.ac.jp
Cc: rietveld_l@ill.fr
Subject: RE: cRs


It's German... verboten == forbidden.

You should never delete the background from a diffraction pattern prior to 
(Rietveld) analysis.

It changes peak positions and shapes and generally is bad.


Cheers

Matthew


Matthew Rowles

CSIRO Minerals
Box 312
Clayton South, Victoria
AUSTRALIA 3169

Ph: +61 3 9545 8892
Fax: +61 3 9562 8919 (site)
Email: matthew.row...@csiro.au
-Original Message-
From: Olga Smirnova [mailto:olga.smirn...@hw7.ecs.kyoto-u.ac.jp]
Sent: Wednesday, 4 March 2009 16:30
To: Brian O'Connor
Cc: rietveld_l@ill.fr
Subject: Re: cRs

According to my computer, I received your response 4 minutes earlier
than forwarded the email.
What is 'verbotten' (volabulary does not find) ?
OS

Brian O'Connor wrote:
 Background removal is verbotten!
 Brian O'Connor

 

 From: Olga Smirnova [mailto:olga.smirn...@hw7.ecs.kyoto-u.ac.jp]
 Sent: Wed 4/03/2009 2:14 PM
 To: rietveld_l@ill.fr
 Subject: cRs



 Dear All,

 How is life with conventional R factors when you always have to divide
 by zero background?
 Let's have time. Considering a part of the profile without peaks one
 gets 100% cR.
 I did not give the agreement factor; I would say those cR with all
 non-excluded points is incorrect, but cR for
 points with Bragg contribution is almost the same!
 Do you decrease the Rs by adding the background or do you increase cRs
 by subtracting the background?

 OS

 PS I did not ask my supervisor before sending such a mail.




  
 

 Internal Virus Database is out-of-date.
 Checked by AVG.
 Version: 7.5.519 / Virus Database: 269.21.6/1323 - Release Date: 3/10/2008 
 11:07 AM
  

RE: Quantitative analysis

[Kurt Leinenweber]

Dear Mario,

If the quantity of FeCO3 appears to be smaller than the actual value, then it 
could be due to absorption.  If you are using a copper source (CuKalpha) then 
that excites iron fluorescence, which is radiated equally in all directions... 
this means that the beam does not penetrate the FeCO3 particles entirely, and 
results in incomplete diffraction from these particles.

There are programs that correct for this problem, but as far as I know there is 
no freeware to deal with this effect.

- Kurt

 
*
Kurt Leinenweber
Dept. of Chemistry and Biochemistry
Arizona State University
Tempe, AZ 85287-1604
 
phone (480)-965-8853
fax (480)-965-2747
 
***

-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] 
Sent: Monday, October 27, 2008 8:48 AM
To: Rietveld_l@ill.fr
Subject: Quantitative analysis

Dear all,

I have this question,

I have been refined one mixture (of well-know percentage composition) of
CaCO3, CaF2, SiO2 and Al2O3, with preferential orientation in CaCO3 (104)
and CaF2 (111) with good results. When I add to the mixture FeCO3 and I
refine with preferential orientation (104), it happens that when I don´t
apply the preferential orientation in all this phases, I have correct
values of percentage composition, but when I apply the preferential
orientation the refinement is good but with incorrect values of percentage
composition. This experiment has been taken in Bragg Brentano geometry.
How I should refine this mixture?

Thanks a lot by your help.

Mario Macías
Universidad Industrial de Santander
Colombia

RE: Beginer problems, difficulty charecterizing our diffractometer...

[Kurt Leinenweber]

Hi,
 
I am going to be in the same boat soon, especially regarding obtaining 
instrument parameters for a new instrument.  But one thing I do know, is that 
to get the polarization parameter, quartz is not a great standard.  For 
polarization factors, you need something really simple, with heavy atoms and 
all atoms on centers of symmetry, and with thermal parameters very well 
constrained, so that you can REFINE the polarization parameters for your 
machine, particularly when incindent beam monochromators are used.
 
The only problem is, I can't remember what the favorite standard is, or where 
it can be purchased.  I will need to know myself, so I will ask, on behalf of 
Blaise and myself as well, what is the best standard for refining the 
polarization of an instrument with monochromatized beam? Thank you!
 
- Kurt



From: Mibeck, Blaise [mailto:[EMAIL PROTECTED]
Sent: Wed 9/17/2008 12:22 PM
To: rietveld_l@ill.fr
Subject: Beginer problems, difficulty charecterizing our diffractometer...



 

I am re-learning GSAS to bring Rietveld to my department (for the first time). 
We have an old Phillips Xpert. 

 

I am trying to refine a quartz standard to acquire my profile and instrument 
parameters for this instrument and have yet to get my Chi^2 below 500. The 
instrument is not in my direct control. I have caught and asked them to correct 
a few problems already (dwell time too low, aluminum sneaking into the beam, 
etc...) and this has helped. I would like not to annoy them any more than I 
have too. 

 

At this point I think my high Chi^2s are mainly due to low angle asymmetric 
peaks that my fit is not able to copy - the asym is not terrible but may be 
messing me up. I am getting better results with peak profile functions 3 and 4, 
but unable to get Chi^2 below 500. My scans go up to 70 degrees 2theta.

 

I would like to tell the people caring for the instrument that my problem is on 
their end, but I am not confident in my own refining skills to say this. When I 
work with the tutorials or standard data from my graduate school experiment I 
am ok - I think I am proceeding in a reasonable way, although I can get stuck 
here and there. 

 

I would like to find out if I am doing something incorrectly or if the problem 
is instrument related. I hate to bug one of you but wonder if I could get 
someone to look at my work?? Is there a better forum for asking for this kind 
of help? 

 

Kindest regards to all of you,

Blaise

 

 

 

 

 

 

* * * * * * * * * * * * * 

Blaise Mibeck 

Research Scientist

Energy  Environmental Research Center

University of North Dakota

15 North 23rd Street, Stop 9018

Grand Forks, ND 58202-9018

 

Phone: (701) 777-5077

Email: [EMAIL PROTECTED]

 

 

 

RE: confusion about some GSAS parameters

[Kurt Leinenweber]

Hi all,
 
The GSAS manual is great, and so is GSAS - but in the case of IPOLA and IPOL, I 
have to admit that the GSAS manual is ambiguous, so I had to do the following 
recently when I had to set up a new diffractometer:
 
Do a Google search on the word IPOLA, and the first entry will be a wonderful 
discussion of the polarization parameters, including contributions from Bob Von 
Dreele, and I was able to set up my polarization correctly using that 
discussion.  Good luck!
 
- Kurt



From: Brian H. Toby [mailto:[EMAIL PROTECTED]
Sent: Thu 8/7/2008 10:04 AM
To: [EMAIL PROTECTED]
Cc: rietveld_l@ill.fr
Subject: Re: confusion about some GSAS parameters


On Aug 7, 2008, at 12:02 PM, [EMAIL PROTECTED] wrote:


So, for the case of a brag brenteno diffractometer without any 
monochromator, will the value for POLA should be fixed to zero??


There are two GSAS polarization models (read the manual!), but my recollection 
is that for IPOLA=0, POLA should be 0.5 when you have no monochromator or 
analyzer.


Brian

RE: RES: ADS

[Kurt Leinenweber]

Hi all,

This is an interesting discussion of quantitative phase analysis.  It sounds to 
me from what Pam is saying that we can calculate an esd for each phase if we 
know its particle size, and that the relative error would be larger for phases 
in smaller abundance.  If this is correct, then you could also repeat the 
physical experiment several times and get a variation of similar magnitude to 
the one that is calculated.  Is this what happens?  Pamela refers to the errors 
as being worse for minor phases, but they are what they are, and why not 
estimate them?

- Kurt

-Original Message-
From: Whitfield, Pamela [mailto:[EMAIL PROTECTED] 
Sent: Friday, May 30, 2008 7:30 AM
To: [EMAIL PROTECTED]
Cc: rietveld_l@ill.fr
Subject: RE: RES: ADS

Hi Rheinhard

The comments weren't aimed at you in particular!  We've been banging our heads 
against a brick wall about this stuff for some time, but not many in the cement 
community seem to be listening.

Anyway - there is a fundamental statistics problem with quantifying minor 
phases (of any symmetry) as the stats get worse with fewer diffracting 
crystallites.
The numbers that Deane Smith produced in terms of reproducibility of the quartz 
reflection dealt with a single phase system.  It doesn't take much to imagine 
(or at least I do) that things rapidly get worse in a multi-phase system where 
theoretically every phase should consist of a nice random powder, reducing the 
required average particle size even further.  It should follow then that the 
errors obtained with minor phases will be worse than major phases where the 
stats are better even without any other effects.  Maybe my logic is flawed but 
I don't think so!  Having said that it has been demonstrated that the situation 
isn't quite as bad practically as it is theoretically.

Pam 

-Original Message-
From: Reinhard Kleeberg [mailto:[EMAIL PROTECTED] 
Sent: May 30, 2008 10:10 AM
To: Whitfield, Pamela
Cc: rietveld_l@ill.fr
Subject: Re: RES: ADS


Hi Pam,
maybe a misunderstanding: I did not try to discuss the amount of 
amorphous material in cements. I'm aware of the problem, but a 
careful  Rietveld analysis with an internal standard should be able to 
determine at least the magnitude of the amorphous part. Even if not 
(e.g. if profile errors or structural uncertainties of the clinker 
phases do prohibit a reliable quantification of the amorphous), a 
systematic error of 7 instead of 5 wt% for a highly symmetric phase with 
well resolved peaks like periclase is neither acceptable nor 
unavoidable. And in my opinion a careful sample prep, measurement and 
Rietveld analysis (maybe with internal standard) should be able to 
perform better. I only tried to relativise Lubo's general denial of the 
potential of quantitative phase analysis to reach an accuracy of about 1 
wt%. Maybe I'm simply more optimistic than Lubo ;-)
Reinhard

Whitfield, Pamela schrieb:

 Hi Reinhard
  
 Saying the words amorphous content and cement in the same breath is
 heresy in many circles!  Personally I think that it's a case of 'see 
 no evil, hear no evil'!
 Anyway, many moons ago we did yet another study on the amorphous 
 content in clinkers/cements and they can vary alot - we found up to 
 20wt% in some.  The amount probably depends on the kiln conditions, 
 alkali metal content and quenching rate.
 Anyway don't take my word for it, Lerch and Brownmiller did a lovely 
 bit of work (sadly forgotten) in 1937 using quenching in mercury (?!) 
 and calorimetry yielding amorphous contents in clinker between 
 10-28%.  The Ruland method has also been used to show significant 
 amorphous contents in the various components of cement.
  
 In my opinion the cement companies are probably more interested in
 consistency rather than accuracy to track changes in their process.  
 Case in point - strictly speaking the XRF samples should be micronized 
 (or fused) as well as the XRD ones - the XRF errors from the matrix 
 effects of a 30micron cement in a pressed pellet are not exactly ideal.
  
 I would agree that it's worth trying to push the boundaries of QPA.
 All is not lost for cements though - I saw the results of a test that 
 Mati Raudsepp did with a very messy synthetic mineral mixture that 
 looked completely ridiculous with the number of phases, but the result 
 matched the weighing figures quite nicely.
  
 Pam

 --
 --
 *From:* Reinhard Kleeberg [mailto:[EMAIL PROTECTED]
 *Sent:* Fri 30/05/2008 5:36 AM
 *To:* rietveld_l@ill.fr
 *Subject:* Re: RES: ADS

 Hi Lubo,
 the difference between 6 and 7 % MgO is bigger than 15 % relatively, 
 thus the error by wrong re-scaling (e.g. if 10 % amorphous are
 missing) is smaller than the error discussed. And, if the true 
 content of periclase should be about 5 %, than a measured value of 7 % 
 is worth to be discussed to be a real systematic error. This is an 
 

RE: Preferred orientation?

[Kurt Leinenweber]

Hi all,

 

This thread  gives me a chance to ask a question I've had for a long
time.  I've heard about these large chambers where you can mix your
sample with a binder and have it fall out as small powder spheres to
avoid preferred orientation in Bragg-Brentano geometry.  But, my samples
are mostly between 10 and 50 milligrams in size. Does anyone know a way
to mount them without preferred orientation?  Thank you!

 

- Kurt

 

 



From: Whitfield, Pamela [mailto:[EMAIL PROTECTED] 
Sent: Thursday, May 08, 2008 9:16 AM
To: Kurt Leinenweber
Subject: RE: Preferred orientation?

 

It's one of the classic needle-shaped materials - it gives lovely SEM
images if you can avoid charging

 

From: Kurt Leinenweber [mailto:[EMAIL PROTECTED] 
Sent: May 8, 2008 12:12 PM
To: Whitfield, Pamela
Subject: RE: Preferred orientation?

 

HI Pamela/all,

 

This sounds intriguing.. why is wollastonite a problem in capillary
transmission?  Is it needle-like?

 

- Kurt

 



From: Whitfield, Pamela [mailto:[EMAIL PROTECTED] 
Sent: Thursday, May 08, 2008 7:55 AM
To: rietveld_l@ill.fr
Subject: RE: Preferred orientation?

 

I do that myself but it doesn't always help much if you've got something
like wollastonite! :-)

 

From: Martin [mailto:[EMAIL PROTECTED] 
Sent: May 8, 2008 10:51 AM
To: rietveld_l@ill.fr
Subject: RE: Preferred orientation?

 

Forget all that long winded stuff. Just collect the data on capillary
transmission geometry and avoid all (well, most of) the fuss.
 
Martin Vickers



Get fish-slapping on Messenger! Play Now
http://clk.atdmt.com/UKM/go/msnnkmgl001008ukm/direct/01/ 

RE: advice on new powder diffractometer

[Kurt Leinenweber]

Hi Bob,

The band of delt/sig is a little wider than that, but I think the real
problem is that they sent me the data in cps.  I am awaiting the data in
counts now.  Thanks to you and others for pointing this out.

However, in my view, having the data in cps should simply go into the
histogram scale factor and should not affect the fit.  What is wrong
with my logic?

Thanks,

- Kurt



-Original Message-
From: Von Dreele, Robert B. [mailto:[EMAIL PROTECTED] 
Sent: Friday, February 15, 2008 6:37 AM
To: rietveld_l@ill.fr
Subject: RE: advice on new powder diffractometer

Hi Kurt,
If you plot the results in POWPLOT  do the statistical analysis what
does the delt/sig vs 2-theta plot look like? If weights are right then
the band of delt/sig ought to be roughly 2-3 sig wide. Is your data in
cpm? Some instruments make that by default. That will mess up the
R-factors.
Bob

RE: advice on new powder diffractometer

[Kurt Leinenweber]

Hi all,

I never thought of background as noise - to me the noise should be
defined as the esd of the background points.  You could get that by
averaging 10 or 20 background points and getting the standard deviation.
I'm told that for typical counting statistics, that should be close to
the square root of the background, so Mike's idea of using that square
root seems reasonable.

- Kurt

-Original Message-
From: Alan Hewat [mailto:[EMAIL PROTECTED] 
Sent: Tuesday, February 19, 2008 3:10 AM
To: rietveld_l@ill.fr
Subject: RE: advice on new powder diffractometer

 So my question remains: what is the definition of signal to noise
ratio
 that is accepted for powder diffraction?

Why does it matter? A higher Bragg/Background ratio does not necessarily
mean better data if counting statistics are poor. Exaggerating slightly
:-) consider a single peak with a ratio of 100/1 compared to a peak with
a
ratio 1/1000. The second measurement will give the lowest error, not
the first which has a much higher signal/noise. And you measure lots of
points on a slowly varying background, so you have a much better
estimate
of background than the normal error of a single point. Please don't
encourage people to simply maximise signal/noise.

Similarly, low profile R-factor's can be obtained with low resolution
data
and high background. That does not mean that low resolution data
produces
smaller errors in structural parameters.

I worry about people treating measurement and refinement as black boxes
with simplified measures of quality such as R-factors, signal-to-noise
etc. You have to look at the physical reality of the model and the
estimated errors in its parameters, while not cheating by removing data
that doesn't fit for unknown reasons, adding too much a priori
information such as constraints, or throwing in extra garbage parameters
to improve the R-factors.
__
Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE
[EMAIL PROTECTED] +33.476.98.41.68
http://www.NeutronOptics.com/
__

PS RE: advice on new powder diffractometer

[Kurt Leinenweber]

Dear Rietvelders:

P.S.  I should mention that with that background of only 2 counts, the
maximum signal was around 2000 counts.

Thanks to everyone for all the help so far.

- Kurt

-Original Message-
From: Jon Wright [mailto:[EMAIL PROTECTED] 
Sent: Friday, February 15, 2008 4:05 AM
To: rietveld_l@ill.fr
Subject: Re: advice on new powder diffractometer

Kurt Leinenweber wrote:
 ... with wRp of 25% and crystallographic R also near 25%  ..

Maybe the background is too low :-?

Jon

advice on new powder diffractometer

[Kurt Leinenweber]

Hi All,

I am attempting to assist others to choose a new powder x-ray
diffractometer.  We are currently looking at a Panalytical X'Pert Pro in
alpha-1 configuration, and I would like to know if anyone has any
experience with this for Rietveld refinements?  For other reasons we
would like to keep the sample flat, but then we could not use the
alpha-1 configuration, so instead we would consider a hybrid
monochromator - I would like to ask if this monochromator makes it
impossible to do Rietveld?  Also, any other insights and suggestions for
systems that are competitive with these would be welcome.  We are at an
early stage and have time to think about this, will be looking at other
possibilities, and I would appreciate any suggestions.

Incidentally, I received some data on quartz (supplied by me) from the
alpha-1, and refined it using GSAS.  The refined structural and thermal
parameters are fine, but I get strange r-factors, with wRp of 25% and
crystallographic R also near 25%, chi**2 of 0.5.  Does anyone know why
this might happen?  With my old Siemens D5000 I easily get down to 10%
or better in the r-factors right away, so something obvious must be
wrong.

Thank you,

- Kurt Leinenweber

RE: glass crystalline

[Kurt Leinenweber]

Hi Lubo,

Yes, one way to do this is to add a known mass X of a standard (say
alumina) to a known mass Y of the glass + crystal sample, giving a
weight ratio f = X/Y of standard to sample.  Then use x-ray diffraction
to get the weight ratio of the standard to only the crystalline part of
the sample.  This should be a larger number, call it f'.  The ratio f/f'
is then equal to the mass fraction crystal/(crystal + glass) in the
sample.

I have seen this neat trick work well for calculating the quantity of
glass in a ceramic insulator for a power line.  The fraction of glass
calculated with this method was consistent with the SEM images of the
ceramic.

Hope that helps!

- Kurt



.  
-Original Message-
From: Lubomir Smrcok [mailto:[EMAIL PROTECTED] 
Sent: Saturday, February 02, 2008 4:09 AM
To: rietveld_l@ill.fr
Subject: glass  crystalline 

Hello,
I was asked by my colleague if there is a way how to find (I'd prefer 
estimate) 
the amount of the crystalline phase in the glass matrix. Both phases
have the 
same (or very close) chemical composition.
If necessary, they can also prepare the sample totaly crystalline
without any 
glass.
My apologies for sending this problem to rietveld list, but I hardly
know any 
better address :-)
To be frank : I do not expect to solve the problem using Rietveld as
the 
structure of the crystalline phase is not very well known. They would
prefer a 
relatively simple method for daily use in their lab.
Thanks on behalf of them.
Lubo

RE: Re: Structure dissemination

[Kurt Leinenweber]

Hi all,

It's interesting to me that so many well-intentioned scientific questions are 
met with the response, why don't you check the FAQ and get back to us when you 
are a cognescenti, and yet the political question of what is legal or illegal 
to transfer always elicits a very enthusiastic discussion.

- Kurt

---

Kurt Leinenweber
Department of Chemistry
Arizona State University
Tempe, AZ  85287-1604

Phone:  (480)-965-8853
Fax: (480)-965-2747

---

Re: Structure dissemination

[Kurt Leinenweber]

Hi Rietvelders,

OK, I should have used my Webster's dictionary to begin with ... but I 
belatedly looked it up.  I meant to write cognoscente, which comes from 
Italian (originally from the Latin to know) and is used a lot here in the 
States, but to complicate matters, the Dictionary says that the modern Italian 
spelling is conoscente (can any of our Italian colleagues verify that?).

Thank you for all this fun discussion, but I will be sure to use my dictionary 
the next time I post to this list.

- Kurt


---

Kurt Leinenweber
Department of Chemistry
Arizona State University
Tempe, AZ  85287-1604

Phone:  (480)-965-8853
Fax: (480)-965-2747

---

-Original Message-
From: Dr.Ibrahim Odeh [mailto:[EMAIL PROTECTED]
Sent: Wednesday, June 07, 2006 2:43 PM
To: rietveld_l@ill.fr



  Did you mean this
  cog·no·scen·ti [ kògn? shéntee, kònny? shéntee ]
   (singular cog·no·scen·te [ kògn? shéntay ])


  plural noun

  Definition:

  connoisseurs or experts: people who have a refined and superior 
knowledge of a subject, especially the arts


Ibrahim Odeh
Physics Department
Yarmouk University
Irbid 211-63
Jordan
Tel. 962 2 721 ext.2300
E-mail:[EMAIL PROTECTED]
- Original Message - 
From: Kurt Leinenweber [EMAIL PROTECTED]
To: rietveld_l@ill.fr
Sent: Wednesday, June 07, 2006 8:57 PM


 Thanks for the correction!  - Kurt


 ---

 Kurt Leinenweber
 Department of Chemistry
 Arizona State University
 Tempe, AZ  85287-1604

 Phone:  (480)-965-8853
 Fax: (480)-965-2747

 ---

 -Original Message-
 From: Simon Billinge [mailto:[EMAIL PROTECTED]
 Sent: Wednesday, June 07, 2006 11:26 AM
 To: rietveld_l@ill.fr


 shouldn't that be a cogniscento (or cogniscenta)?

 S

 Kurt Leinenweber wrote:
 Hi all,

 It's interesting to me that so many well-intentioned scientific questions 
 are met with the response, why don't you check the FAQ and get back to 
 us when you are a cognescenti, and yet the political question of what is 
 legal or illegal to transfer always elicits a very enthusiastic 
 discussion.

 - Kurt

 ---

 Kurt Leinenweber
 Department of Chemistry
 Arizona State University
 Tempe, AZ  85287-1604

 Phone:  (480)-965-8853
 Fax: (480)-965-2747

 ---



 -- 
 Prof. Simon Billinge
 Department of Physics and Astronomy
 4268 Biomed. Phys. Sciences Building
 Michigan State University
 East Lansing, MI 48824
 tel: +1-517-355-9200 x2202
 fax: +1-517-353-4500
 email: [EMAIL PROTECTED]
 home: http://nirt.pa.msu.edu/



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Re: converting D8focus data

[Kurt Leinenweber]

Well, I was basing my information on what the company that sells Jade told
me.

- Kurt

- Original Message - 
From: A. van der Lee [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Sent: Wednesday, December 08, 2004 3:17 AM


On 7 Dec 2004 at 12:23, Kurt Leinenweber wrote:


 Bruker's data format is a binary, proprietary format.  Programs such as
Jade
 that can read it are written by clever programmers who were able to hack
 into the Bruker format.  However, the only source I have found for free
 programs is from Bruker itself.

What does this mean exactly, proprietary format? That it is secret? I
am not a very clever programmer, but with the aid of Bruker's own
manual for their data file conversion utility XCH (to which I
referred one or two days ago), Appendices A-C, in which the binary
format is explained in detail, I am able to write a conversion
utility .raw to .gsas myself in a couple of hours. I did the same
thing for the conversion of Bruker peak list files (.dif) to Crysfire
.cdt files. This utility is now distributed with the Crysfire
distribution.
And I am not the only one who did this. The LMPG suite of programs
(Jean Laugier) are all capable to read in Bruker raw files.

Arie
***
A. van der Lee
Institut Européen des Membranes (UMR 5635)
Université de Montpellier II - cc 047
Place E. Bataillon
34095 Montpellier Cedex 5
FRANCE

visiting address: 300 Av. Prof. E. Jeanbrau

tél.: 00-33-(0)4.67.14.91.35
FAX.: 00-33-(0)4.67.14.91.19
***

Re: converting D8focus data

[Kurt Leinenweber]

Bruker will send you their program raw2rawg for 
free on request. It works for converting their RAW files into GSAS files, 
at least on my D5000 system.

  


 - Kurt c

  - Original Message - 
  From: 
  Liliana 
  Viciu 
  To: [EMAIL PROTECTED] 
  Sent: Monday, December 06, 2004 6:10 
  PM
  Subject: converting D8focus data
  
  
  Dear 
  all,
  I am collecting data with a Bruker D8focus diffractometer 
  (.raw file) and would like to use GSAS for Rietveld 
  refinement. However, I was not able to have the data converted in GSAS format. 
  Is there any software able to convert such a file to a gsas format file? 
  Any hint will be highly 
  appreciated.
  Thank you in 
  advance,
  Liliana
  
  
  Liliana Viciu, 
  PhD
  Chemistry 
  Department
  Princeton 
  University
  Princeton, 
  NJ, 
  08544 

Re: converting D8focus data

[Kurt Leinenweber]

Dear All,

Unfortunately, I can't supply the program myself.  It came from Bruker (In
the US: 1-800-234-XRAY).  As I said, they sent it to me for free and I don't
see why they wouldn't give it to anyone who wants it.  Better yet, it might
be a newer version.  I think it will work for D500 data too.

Bruker's data format is a binary, proprietary format.  Programs such as Jade
that can read it are written by clever programmers who were able to hack
into the Bruker format.  However, the only source I have found for free
programs is from Bruker itself.

- Kurt

- Original Message - 
From: William Bisson [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Sent: Tuesday, December 07, 2004 9:58 AM


 Dear Kurt,

 Please may have a copy too? Will that work for D500 data?

 Regards
 William

 On Tue, 7 Dec 2004, Kurt Leinenweber wrote:

  Bruker will send you their program raw2rawg for free on request.  It
works for converting their RAW files into GSAS files, at least on my D5000
system.
 
 - Kurt c
   - Original Message -
   From: Liliana Viciu
   To: [EMAIL PROTECTED]
   Sent: Monday, December 06, 2004 6:10 PM
   Subject: converting D8focus data
 
 
   Dear all,
 
   I am collecting data with a Bruker D8focus diffractometer (.raw file)
and would like to use GSAS for Rietveld refinement. However, I was not able
to have the data converted in GSAS format. Is there any software able to
convert such a file to a gsas format file?
 
   Any hint will be highly appreciated.
 
   Thank you in advance,
 
   Liliana
 
 
 
   
 
   Liliana Viciu, PhD
 
   Chemistry Department
 
   Princeton University
 
   Princeton, NJ, 08544
 

Re: Next Endeavour version without Hofmann potential

[Kurt Leinenweber]

Thank you for this interesting discussion.  Does this also apply to the ICSD
database?  I have made tables from data taken from ICSD - am I going to go
to jail?

- Kurt


- Original Message - 
From: Brian H. Toby [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Sent: Thursday, July 08, 2004 9:00 AM


 I have to agree with Vincent that I find aspects of CCDC's apparent
 actions troubling and warrant discussion even if all parties reach a
 happy agreement behind closed doors. If the CCDC claims partial
 ownership of everything derived from their database then how far does
 that go? Can they prevent someone from publishing an average bond
 distance mined from 10,000 structures? Do they require that the entire
 staff of the CCDC be included as coauthors?

 Alan is correct that there is much that we do not know: What information
 has Dr. Hoffmann has supplied only to Crystal Impact and what
 information is in the public domain?

 Since much is unclear, I will offer one possible argument on the CCDC's
 behalf. Academic researchers are given access to the CSD (and other)
 databases for academic (public) research at rates considerably reduced
 from that of commercial research. If someone makes a discovery from
 these academic facilities but rather than disclose it in the open
 literature, instead decides to use that information for private gain
 (either for the researcher or the employer's institution) then from my
 perspective this academic researcher/institution is cheating by paying
 academic rates, but performing commercial research. (I am not suggesting
 that I know this to be the case here).

 The CCDC is a valuable resource to our scientific community. The CCDC
 should take all steps needed to protect their intellectual property -- 
 which is their compilation of data (note anyone can compile their own
 data collection from the literature by simply typing in all the
 coordinates again), plus the wealth of tools they have built over the
 decades, as well as the comments and corrections they have created and
 include in their data collection. I think it reasonable that the CCDC
 forge agreements with organizations that would mine their data
 collection for profit.

 If on the other hand, the CCDC works to prevent the open publication of
 research results that derive from their data collection, or uses their
 size to prevent companies from producing software that competes with
 their own products, then I think they can no longer claim to be a
 non-profit organization dedicated to the advancement of chemistry and
 crystallography for the public benefit... (I am also not suggesting
 that I know this to be the case here).

 What exactly is the case here? I don't claim to know. I would hope that
 Dr. Hoffmann will publish all of his results from use of the CSD. At
 that point I would hope that the CCDC would not feel that algorithms or
 software that implements this public information is their intellectual
 property, unless developed within the CCDC. I will wait quietly and see
 what we learn over the months to come.

 Brian

Re: Defining the origin of P2/n

[Kurt Leinenweber]

Yes, but the atom doesn't have to sit there, unlike in the case of 2/m.  So,
GSAS has to fix z for one atom...

I don't have my International Tables with me, please correct me if I'm wrong
(there should be no sites with a fixed z parameter in P2/n).

- Kurt


---

Kurt Leinenweber
Department of Chemistry
Arizona State University
Tempe, AZ  85287-1604

Phone:  (480)-965-8853
Fax: (480)-965-2747

---

-Original Message-
From: Magnus H. Sørby [mailto:[EMAIL PROTECTED]
Sent: Wednesday, March 31, 2004 12:24 AM
To: [EMAIL PROTECTED]


Stephen and Kurt,

P2/n has a 2-fold axis perpendicular to a glide plane, so it does have fixed
points (unlike e.g. R3c).

Best regards,
Magnus H. Sørby


 -Opprinnelig melding-
 Fra: Kurt Leinenweber [mailto:[EMAIL PROTECTED]
 Sendt: 31. mars 2004 08:55
 Til: [EMAIL PROTECTED]
 Emne: Defining the origin of P2/n


 Stephen,

 I think that P2/n has no fixed points, and in order to keep the whole
 structure from shifting along the c-axis, one of the atoms has to be
 arbitrarily fixed.  GSAS automatically fixes the first atom
 z-parameter (was
 your atom on the 2-fold symmetry axis?).  I remember this from
 refining the
 structure of high pressure FeTiO3 which had space group R3c.

   - Kurt


 ---

 Kurt Leinenweber
 Department of Chemistry
 Arizona State University
 Tempe, AZ  85287-1604

 Phone:  (480)-965-8853
 Fax: (480)-965-2747

 ---

 -Original Message-
 From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
 Sent: Tuesday, March 30, 2004 11:03 PM
 To: [EMAIL PROTECTED]


 Dear Rietvelders,

 I used GSAS to refine my structure in P2/n, however the program
 automatically
 fixed the the XYZ positions of the first atom during refinement. To my
 surprise, this atom is not seen in the fixed atom list in the atom
 parameters
 menu of GSAS.

 Please advise and many thanks,

 stephen

Re: Defining the origin of P2/n

[Kurt Leinenweber]

Sorry Allen - I guess this new generation of crystallographers really is as
bad as you think!

- Kurt


---

Kurt Leinenweber
Department of Chemistry
Arizona State University
Tempe, AZ  85287-1604

Phone:  (480)-965-8853
Fax: (480)-965-2747

---

-Original Message-
From: Allen Larson [mailto:[EMAIL PROTECTED]
Sent: Wednesday, March 31, 2004 9:33 AM
To: [EMAIL PROTECTED]


[EMAIL PROTECTED] wrote:

 Dear Rietvelders,

 I used GSAS to refine my structure in P2/n, however the program
automatically
 fixed the the XYZ positions of the first atom during refinement. To my
 surprise, this atom is not seen in the fixed atom list in the atom
parameters
 menu of GSAS.

 Please advise and many thanks,

 stephen

I am amazed by the flow of miss information that flows on this list whenever
an
apparent problem with a space group comes up. I am forced to wonder if the
correspondents in these exchanges have ever looked at 'The International
Tables,
Volume A(1983)' or Volume 1(1969) or the earlier volume which dates in the
1930's. Or any of the several other treatises that can also serve as a
source
for this information.

The GSAS package contains a program, SpcGroup, that can be used to list the
symmetry operations of any possible string defining a possible space group.
In
general the space group symbol consists of 2 or more groups of characters
delimited by spaces. Please note that the spaces separating axial operations
are
required in the GSAS interpretation of the space group symbol. Thus 'R3c'
must
be written as 'R 3 c' or taking advantage of the fact that the lattice type
can
only occupy one character, 'R3 c', is accepted, but not recommended.

I might also note that all of this is based on the use of keyboards in
general
use in English speaking countries. And I did have no information concerning
what
you might get using other keyboards.

Now for P2/n is a centric space group for which there, in my mind, there
exists
no reasonable origin choice that the 1bar site. Therefore the software would
always choose that for the origin of the unit cell.

Allen C. Larson

Re: Defining the origin of P2/n

[Kurt Leinenweber]

Thanks 
Andreas. I realized I was wrong when I drew a picture of how the glide 
plane and the 2-fold axis interact with the translational symmetry. They 
make 4 points at +x +y +z, -x -y +z, +x +y -z, -x -y -z (2 pairs definitely 
related by a center of symmetry). I should have done that before I posted 
tothe list!

I am 
at home with newborn twins and have not had my hands on the blue book for 
several days.

 
- Kurt
---Kurt LeinenweberDepartment of 
ChemistryArizona State UniversityTempe, AZ 
85287-1604Phone: (480)-965-8853Fax: 
(480)-965-2747--- 
-Original Message-From: Andreas Leineweber 
[mailto:[EMAIL PROTECTED]Sent: Wednesday, March 31, 2004 11:09 
AMTo: [EMAIL PROTECTED]Subject: Re: Defining the origin of 
P2/nThis problem can actually quite simply be solved 
without tables:There is the old rule (which crystrallographers a definitely 
able to prove) to obtain the crystal class:1.delete the Bravais type symbol 
(delete P in case of P2/n)2.substitute screw axes by the correspondingly 
oriented simple rotations (we already have a rotation, 2(1) becomes 
2)3.substitute glide planes by mirror planes with the same 
orientation. (2/n becomes 2/m)This gives you the symbol of the crystal 
class/crystallographic point group.Thus you can see that P2/n belongs to the 
crystal class 2/m, which has a centre of inversion. All space group types 
belonging to a centrosymmetric crystal class have one or several Wyckoff 
sites with centre of inversion. Therefore, there must be a position (there are 
several ones) with fixed z coordinate.Andreas LeineweberKurt 
Leinenweber wrote:
Yes, but the atom doesn't have to sit there, unlike in the case of 2/m.  So,
GSAS has to fix z for one atom...

I don't have my International Tables with me, please correct me if I'm wrong
(there should be no sites with a fixed z parameter in P2/n).

			- Kurt


---

Kurt Leinenweber
Department of Chemistry
Arizona State University
Tempe, AZ  85287-1604

Phone:  (480)-965-8853
Fax: (480)-965-2747

---

-Original Message-
From: Magnus H. Sørby [mailto:[EMAIL PROTECTED]]
Sent: Wednesday, March 31, 2004 12:24 AM
To: [EMAIL PROTECTED]


Stephen and Kurt,

P2/n has a 2-fold axis perpendicular to a glide plane, so it does have fixed
points (unlike e.g. R3c).

Best regards,
Magnus H. Sørby


  
  -Opprinnelig melding-
Fra: Kurt Leinenweber [mailto:[EMAIL PROTECTED]]
Sendt: 31. mars 2004 08:55
Til: [EMAIL PROTECTED]
Emne: Defining the origin of P2/n


Stephen,

I think that P2/n has no fixed points, and in order to keep the whole
structure from shifting along the c-axis, one of the atoms has to be
arbitrarily fixed.  GSAS automatically fixes the first atom
z-parameter (was
your atom on the 2-fold symmetry axis?).  I remember this from
refining the
structure of high pressure FeTiO3 which had space group R3c.

- Kurt


---

Kurt Leinenweber
Department of Chemistry
Arizona State University
Tempe, AZ  85287-1604

Phone:  (480)-965-8853
Fax: (480)-965-2747

---

-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, March 30, 2004 11:03 PM
To: [EMAIL PROTECTED]


Dear Rietvelders,

I used GSAS to refine my structure in P2/n, however the program
automatically
fixed the the XYZ positions of the first atom during refinement. To my
surprise, this atom is not seen in the "fixed atom list" in the atom
parameters
menu of GSAS.

Please advise and many thanks,

stephen











  

Re: Bragg R and GSAS

[Kurt Leinenweber]

I tend to use bond lengths to check refinements.  If bond lengths - and
thermal parameters too - aren't physically reasonable, it can mean that the
structure is correct but the refinement is bad, that the structure is
somehow wrong, or the atom assignments are wrong.

Bond-valence sums are great for this purpose.  I use Eutax by Mike O'Keeffe
for this, but there are many other programs for bond-valence sums as well.

Philosophically, though, I sometimes get disturbed by the fact that the
structure has to agree with what we already know in order to be published.
It might be better not to think about this too much when doing
crystallography.

- Kurt


---

Kurt Leinenweber
Department of Chemistry
Arizona State University
Tempe, AZ  85287-1604

Phone:  (480)-965-8853
Fax: (480)-965-2747

---

-Original Message-
From: Jon Wright [mailto:[EMAIL PROTECTED]
Sent: Thursday, February 26, 2004 8:28 AM
To: [EMAIL PROTECTED]


In comparing refinements with different powder datasets there is no
number of observations in common usage and no 10:1 rule of thumb.
Broadly, this means crappy data with a chemically unreasonable model
can sometimes give much better figures of merit than a good structure
with good data.

Sad, isn't it?

Jon


Von Dreele, Robert B. wrote:

Nandini,
I suggest you look at the paper Rietveld refinement guidelines, J. Appl.
Cryst. (1999) 32, 36-50.
Bob Von Dreele


-Original Message-
From: Nandini Devi Radhamonyamma [mailto:[EMAIL PROTECTED]
Sent: Thu 2/26/2004 8:38 AM
To: [EMAIL PROTECTED]

Thank you.
In parallel with single crystal analysis, is there an
accepted limit for R(F2) or any other parameter like
Rexp to follow? I'm using synchrotron data.
nandini

RE: Re: thermal parameters at low temperature

[Kurt Leinenweber]

Wait!  I have to mention - the heaviness of atoms (atomic number Z) is
important in x-ray diffraction, but is uncorrelated with the neutron
scattering factor for the nuclei.  When you say heavy, do you mean the
highly scattering ones for neutrons, or the high-Z ones?

- Kurt


---

Kurt Leinenweber
Department of Chemistry
Arizona State University
Tempe, AZ  85287-1604

Phone:  (480)-965-8853
Fax: (480)-965-2747

---

-Original Message-
From: Maxim V. Lobanov [mailto:[EMAIL PROTECTED]
Sent: Thursday, February 26, 2004 12:59 PM
To: [EMAIL PROTECTED]



Sorry for the ambiguous information I gave previously. The data at
room temperature were taken with a variable wavelength (TOF) whether
at low temperature the data were recorded with constant wavelength.
There is no magnetic contribution on the pattern. The negative thermal
parameters are for the heaviest atoms in the crystal.

Then it seems that you really overlooked some instrumental issue that can
affect thermal factors. As pointed out by Andreas, indeed it would be most
critical for heavy atoms, with intrinsically low thermal factors at low T.
For example, absorprion. It is typically not very significant for neutrons,
but anyway I would calculate it (for example, using
http://www.ncnr.nist.gov/instruments/bt1/neutron.html), then fix in the
refinement and look if it would cure the thermal factors.

According to GSAS manual,
For constant wavelength data the absorption coefficient, Ah, is related to
the value for 1 neutrons; the correction is indistinguishable from thermal
motion effects and should not be refined. 

By the way, I would be grateful if one could share the knowledge about some
other important instrumental factors, relevant for thermal factors in
neutrons, and ways to estimate reasonable correction values.
Sincerely,  Maxim.
__
Maxim V. Lobanov
Department of Chemistry
Rutgers University
610 Taylor Rd
Piscataway, NJ 08854
Phone: (732) 445-3811

RE: diamond powder source

[Kurt Leinenweber]

About the crystallinity of amorphous Boron, even if it is a glass you
might get some strong and sharp x-ray peaks from the B-B bonds in the
icosahedra of boron atoms.  Does anyone know if this is the reason for
seeing strong peaks in the x-ray pattern of amorphous boron?

- Kurt Leinenweber

-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]]
Sent: Tuesday, July 31, 2001 3:53 AM
To: [EMAIL PROTECTED]
Subject: RE: diamond powder source


Actually, I checked out a reference for amorphous boron, namely the CERAC
catalog. They apparently have a somewhat dubious definition of
crystallinity:

typ. 5 microns aver. or less (essentially amorphous)

Jens

-Original Message-
From: Madsen, Ian (Minerals, Clayton)
[mailto:[EMAIL PROTECTED]]
Sent: 30. juli 2001 01:17
To: '[EMAIL PROTECTED]'
Subject: RE: diamond powder source

Re: amorphous boron - at the time that we were looking for appropriate
diluents, we tried several different sources of boron, including some
specifically listed as amorphous boron. At no time during these tests did
we find any boron that was remotely amorphous. All materials has strong
crystalline peaks and some had very complex XRD patterns, rendering them
unsuitable for use as a diluent.

Cheers

o--oo0oo---o
 Ian Madsen

Re: GSAS on Virtual PC?

[Kurt Leinenweber]

Kaye (and others)

Did you get memory access violation errors when you tried to run expedt?
The same thing happened to me when I tried GSAS on the virtual PC.  It runs
fine on a regular PC.

- Kurt Leinenweber  

At 09:17 AM 3/21/00 -0800, you wrote:
Has anyone successfully run GSAS using virtual PC (on Macintosh)? The
program appears to be installed, i.e. launches and allows me to create a
new experiment file, but will not run expedt (even though the extended
menus appear after creating an experiment file).

Any suggestions?

Thanks, -Kaye

Kaye Savage
Dept. of Geological and Environmental Sciences
Stanford University
Stanford CA 94305-2115
650-723-8017 ph
650-725-0979 fax
[EMAIL PROTECTED]



-

Kurt Leinenweber
Dept. of Chemistry
Arizona State University
Tempe, AZ 85287-1604

Ph. (480)-965-8853
Fax (480)-965-0474

-

Advice on a new diffractometer

[Kurt Leinenweber]

Hi everyone,

There is a diffractometer here for rapid data collection (Siemens D5000,
7.5 degree position-sensitive detector, no monochromator and can't be
retrofitted for one).

My question is, what would be a good choice for a second diffractometer in
this situation (ie what brand, what kind of monochromators and detectors,
etc)?  I am hoping to be able to collect data that can be used to find unit
cells and do refinements, perform Monte Carlo solutions for complex phases,
etc.  The PSD system is not very good for this (it even has K-beta bumps
that come through the nickel filter!) Thanks!

- Kurt Leinenweber

*
Kurt Leinenweber
Dept. of Chemistry
Arizona State University
Tempe, AZ  85287-1604

Phone (480)-965-8853
Fax   (480)-965-0474

CIF format

[Kurt Leinenweber]

Rietvelders,

I notice that the new beta version of GSAS has a conversion to CIF format
under the Utilities heading (GSAS2cif).  Are other programs being made CIF
friendly as well?  Can I dump the extracted structure factors from GSAS
into ESPOIR, for example?  It would be nice if this was really happening...

- Kurt Leinenweber

*
Kurt Leinenweber
Dept. of Chemistry
Arizona State University
Tempe, AZ  85287-1604

Phone (480)-965-8853
Fax   (480)-965-0474

Thin samples in Bragg-Brentano geometry

[Kurt Leinenweber]

Rietvelders,

For a lot of small powder samples (say 10 milligrams) in Bragg-Brentano
geometry, the sample has to be spread very thin over the diffracting
surface of a slide in the diffractometer.  I notice that a lot of the
textbook formulas are for "infinitely thick" samples.  Is there a special
way to deal with the thin samples?  It seems like the absorption part of
the formula for peak intensities (for example, for phase fractions in
multiphase mixtures) will be changed.

    - Kurt Leinenweber

*
Kurt Leinenweber
Dept. of Chemistry
Arizona State University
Tempe, AZ  85287-1604

Phone (480)-965-8853
Fax   (480)-965-0474

Re: weight fractions in GSAS .LST file

[Kurt Leinenweber]

Hello all,

In my experience GSAS always reports the weght fractions - and their
uncertainties - in the .LST file, as long as you have 
atoms in all the phases, and are refining all but one of the phase
fractions under the selection L O S.

Has anyone else ever had the problem that Roger is asking about?

- Kurt Leinenweber


How do I get GSAS to report weight fractions  their uncertainties in a
.LST file? 
Thanks,

Roger Mason



*
Kurt Leinenweber
Dept. of Chemistry
Arizona State University
Tempe, AZ  85287-1604

Phone (480)-965-8853
Fax   (480)-965-0474