Question regarding FullProf limits for unit cell parameters

2020-10-30 Thread Holger Putz (Crystal Impact)
Dear all,

 

I am currently trying to perform a simple refinement of Corundum in the
hexagonal setting, namely the unit cell parameters (a=b=4.7589 A, c=12.991
A, alpha=beta=90 deg., gamma=120 deg): Refining the cell parameters a and c
works without problems, and putting limits to the refinement of the
parameter c also works as expected. 

 

However, when I try to add limits to the parameter a (=b) I am running into
issues: 

 

The original value is a=4.7589 A, and I would like to add the following
limits: Min=4.7 A, Max=4.8 A. Hence, I have added the following line in the
pcr-file:

 

! Limits for selected parameters :

   1 4.7 4.8  0.   0  Cell_A_ph1_pat1

 

After running FullProf, I found the following section in the .out-file:

 

=> The following parameter limits have been read:

 

  -> Parameter no.:1 Limits: 4.70004.8000 Step for SA &
BoundaryCond: 0.0

  -> Modified internal limit for cell parameter no.:1 Limits:
0.0 0.0

  -> Modified internal limit for cell parameter no.:1 Limits:
0.0 0.0

  -> Modified internal limit for cell parameter no.:1 Limits:
0.0 0.0

 

 --

  SYMBOLIC NAMES AND INITIAL VALUES OF PARAMETERS TO BE VARIED:

 --

 

  ->  Parameter number1   -> Symbolic Name:
Cell_A_ph1_pat1 4.7589002

 

As you can see, the limits "Min=4.7 A" and "Max=4.8 A" have been read from
the pcr-file, however, FullProf then seems to calculate "modified internal
limits" for this parameter, and these are zero in this case. As you can
imagine, the refinement does not work, of course.

 

I have also tried the same for a cubic structure (in which case you also
have "coupled" unit cell vector lengths); this worked without problems.

 

I have searched the FullProf documentation as well as the tutorials and
finally the web, but I could not find anything about it.

 

Do you have any idea why this might happen? Am I doing something wrong?

 

Thank you very much in advance!

Holger Putz

 



 

Crystal Impact

Dr. H. Putz & Dr. K. Brandenburg GbR

Kreuzherrenstr. 102

53227 Bonn

Germany

 

Tel . : +49-228-9813643

Fax   : +49-228-9813644

E-mail:  <mailto:i...@crystalimpact.de> i...@crystalimpact.de

Web   :  <https://www.crystalimpact.de> https://www.crystalimpact.de

 

 

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Cell parameters

2008-10-30 Thread María Susana Conconi

Dear all

I am looking for references about cell parameters of mixed orthoferrites of 
La and Y. (Y(1-x)LaxFeO3).


I have crystal data for the end members of the serie but I can not find any 
reference about cell parameters of  intermediate compositions. Any 
information would be useful.


Many thanks,

Susana Conconi
Centro de Tecnología de Recursos Minerales y Cerámica
M.B.Gonnet
Argentina 



Le Bail vs Rietveld for crystallite size and cell parameters?

2007-11-06 Thread Sergey V. Ushakov

Dear All,

I was wondering if there are any advantages of using Rietveld vs Le Bail 
refinements when crystallite size and cell parameters are the only 
variables of interest?


Thank you,
Sergey

--
Sergey Ushakov PhD

Staff Research Associate

Peter A Rock Thermochemistry Laboratory and NEAT ORU
University of California at Davis
One Shields Avenue,
Davis, CA 95616
phone (530) 754-5863
Fax (530) 752-9307
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Re: Le Bail vs Rietveld for crystallite size and cell parameters?

2007-11-06 Thread Miguel Hesiquio-Garduño
Hi !
I have worked with both methods in ZnO, I have found that it is easier
work with Le Bail or Pawley when you are looking for size strain and
lattice parameters, because you just need some data about the crystal
structure. But this is just an specific case.
Best wishes

Miguel Hesiquio-Garduño
Profesor Titular A
Departamento de Ciencia de Materiales
Academia de Ciencias de la Ingeniería
ESFM-IPN. tel 57 29 60 00 ext. 55003, ext. 55011

 Dear All,

 I was wondering if there are any advantages of using Rietveld vs Le Bail
 refinements when crystallite size and cell parameters are the only
 variables of interest?

 Thank you,
 Sergey

 --
 Sergey Ushakov PhD

 Staff Research Associate

 Peter A Rock Thermochemistry Laboratory and NEAT ORU
 University of California at Davis
 One Shields Avenue,
 Davis, CA 95616
 phone (530) 754-5863
 Fax (530) 752-9307
 __
 This message was written entirely with recycled electrons.







Re: Le Bail vs Rietveld for crystallite size and cell parameters?

2007-11-06 Thread Leonid Solovyov
Le-Bail and Pawley methods give extra freedom to intensities which may
lead to adverse correlations between peak intensities and shape
especially for noisy and overlapped data. In Rietveld refinement the
intensities are restrained by the structure model and the
instrument-related parameters, so if the parameters are chosen
correctly you have a chance to reduce the correlations and obtain more
accurate results. Unfortunately, it is not always easy to choose
structural and instrumental parameters correctly enough. Anyhow, it is
better to try both variants and see the difference that might give,
besides, an estimation of the uncertainties.

Regards,
Leonid Solovyov

Dear All,

I was wondering if there are any advantages of using Rietveld vs Le
 Bail 
refinements when crystallite size and cell parameters are the only 
variables of interest?

Thank you,
Sergey

 


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Fwd: Re: [sdpd] Pt cell parameters versus temperature

2007-01-09 Thread Andy Fitch
The thermal evolution of the lattice parameters 
of Pt was discussed in 2005 on the SDPD list. One of the replies follows.


Andy



Subject:  Re: [sdpd] Pt cell parameters versus temperature
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Date: Thu, 13 Oct 2005 09:10:31 -0700 (PDT)
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Dear Guilhem,
on answer to your interest in the lattice parameters
of platinum for high temperature:
T(C)  a(A)
25  3.924
171.7  3.930
350.6  3.935
459.3  3.939
586.7  3.944
698.2  3.948
797.7  3.952
904.9  3.957
960.7  3.959
1027.5  3.962
1104.8  3.966
1154.3  3.969
1233.5  3.973
1267.1  3.975
1293.0  3.977
1300.8  3.978
1339.5  3.980

The uncertainty of values have been found ca. 0.001 A
approximately. These data were taken from preprint of
Bouchaib Manoun, Surendra K. Saxena, and Hanns-Peter
Liermann Thermal Expansion of Polycrystalline Ti3SiC2
in the 251–14001C Temperature Range J. Am. Ceram.
Soc., 00 [0] x–x (2005).
Also I can recommend to see:
1.
http://nvl.nist.gov/pub/nistpubs/jres/091/6/V91-6.pdfhttp://nvl.nist.gov/pub/nistpubs/jres/091/6/V91-6.pdf
2. James W. Edwards, Rudolph Speiser, and Herrick L.
Johnston  High Temperature Structure and Thermal
Expansion of Some Metals as Determined by X-Ray
Diffraction Data. I. Platinum, Tantalum, Niobium, and
Molybdenum Journal of Applied Physics -- April 1951 --
Volume 22, Issue 4, pp. 424-428
3. G K White Thermal expansion of platinum at low
temperatures J. Phys. F: Met. Phys. 2 L30-L31

You can calculate thermal dependence of lattice
parameters from the thermal dependence of expansion
coefficient presented in Refs. 13 via V-T equation of
state:
a(T)=a(T0)*exp(int(alpha(x),dx,T0,T)),
where a(T0) means the known lattice parameter at fixed
temperature T0, alpha(T) - thermal expansion
coefficient, int(alpha(x),dx,T0,T) - integration of
thermal expansion coefficient alpha(x) over x from T0
to temperature T.

Good luck,
Anatoliy Senyshyn

--- Guilhem DEZANNEAU [EMAIL PROTECTED]
wrote:

 Hello

 i am searching for Platinum cell parameters
 evolution
 versus temperature.

 thanks a lot

 Guilhem








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GSAS and cell parameters refinement

2001-05-22 Thread Riccardo Vivani

Dear all,
Is it possible, in GSAS, to refine only one (or two...) of the cell
parameters? If yes,
is there anyone that can explain me how to do?
Thank you very much

Riccardo Vivani
Dipartimento di Chimica
Perugia - ITALY






Re: GSAS and cell parameters refinement

2001-05-22 Thread Jonathan Burley

Dear Riccardo,
You can do this indirectly by fixing (y l o l f) the parameters
you wish to keep constant. I believe that RM11, RM22 and RM33 are likely
to correspond to you lattice parameters, and the cross terms to your
angles. However my memory is hazy, but if you have a quick play about it
should become clear.

Jonathan.

On Tue, 22 May 2001, Riccardo Vivani wrote:

 Dear all,
 Is it possible, in GSAS, to refine only one (or two...) of the cell
 parameters? If yes,
 is there anyone that can explain me how to do?
 Thank you very much
 
 Riccardo Vivani
 Dipartimento di Chimica
 Perugia - ITALY
 
 
 
 

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