Re: silicon

L. Cranswick ( L.M.D.Cranswick@dl.ac.uk )
Mon, 14 Sep 1998 23:54:09 +0100 (BST)

Not sure what others might think but I am not sure that Silicon is
that crash hot to refine on due to possible particle statistics
problems(?) - assuming the PCR file is correctly setup for your
diffractometer conditions.

What type of visual fit does a Le Bail extraction give you?
If LeBail fit does not do a good job - could imply something
is wrong with matching the machine settings to the PCR file.

A standard strategy for Rietveld refinement being to do a
LeBail fit - then fix the UNITCELL, width/shape, zero-offset -
then try and fit the intensities, before doing a full
refinement on all freely refining parameters.

-----

To get used to refinement with fullprof - maybe some other
standards maybe worth while running - NIST LaB6, CeO2, etc.

Data you can obtain off the internet are the pure phases
for the IUCr CPD Quant Round Robin:
http://www.fr.iucr.org/iucr-top/comm/cpd/QARR/data-kit.htm
http://www.se.iucr.org/iucr-top/comm/cpd/QARR/data-kit.htm

Corundum, Flourite, Zircon, Hematite data in Fullprof
format with structure information is provided. This is
collected on a Philips diffractometer but should give
something known to try out.

---

One option is to take a look at the shareware AXES for DOS program which can generate Fullprof PCR files based on the setup of yourXRD. Generating and validating a fullprof input file fromscratch can be a tedious experience if you don't have a handylibrary of template files already optimised for your system.Axes is available from: ftp://ftp.physic.ut.ee/pub/pc/axes/or http://www.ccp14.ac.uk/ccp/ccp14/ftp-mirror/axes/pub/pc/axes/

An article describing the software including the PCR editoris on any IUCr Commission on Powder Diffraction Newsletter site:

http://www.iucr.org/iucr-top/comm/cpd/Newsletters/no20summer1998/art21/art21.htmhttp://www.se.iucr.org/iucr-top/comm/cpd/Newsletters/no20summer1998/art21/art21.htmhttp://www.fr.iucr.org/iucr-top/comm/cpd/Newsletters/no20summer1998/art21/art21.htm

Cheers,

Lachlan.

> > I am a beginner of rietveld refinement. I try to refine silicon standart> with FullProf 3.5, but I can not obtain good R values. How can I refine> till good R values. We have rigaku diffractometer.My starting pcr file is> following:> ***************************************************************************> COMM si > ! Files => DAT-file: 1, PCR-file: 1> !Job Npr Nph Nba Nex Nsc Nor Dum Iwg Ilo Ias Res Ste Nre Cry Uni Cor> 0 7 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0> !> !Ipr Ppl Ioc Mat Pcr Ls1 Ls2 Ls3 Syo Prf Ins Rpa Sym Hkl Fou Sho Ana> 0 1 1 0 1 0 0 0 1 0 0 0 0 0 0 0 0> !> ! lambda1 Lambda2 Ratio Bkpos Wdt Cthm muR AsyLim Rpolarz> 1.540562 1.540562 1.0000 25.0000 25.0000 0.7981 0.0000 30.00 0.0000> !> !NCY Eps R_at R_an R_pr R_gl Thmin Step Thmax PSD Sent0> 11 0.03 1.00 1.00 1.00 1.00 20.0000 0.0100 90.0000 0.000 0.000> !> !> 1 !Number of refined parameters> !> ! Zero Code Sycos Code Sysin Code Lambda Code MORE> 0.0000 00.00 0.0000 0.00 0.0000 0.00 0.000000 0.00 1> !> ! Microabsorption coefficients > ! P0 Cod_P0 Cp Cod_Cp Tau Cod_Tau> 0.0000 0.00 0.0000 0.00 0.0000 0.00> ! Background coefficients/codes> 0.0000 0.0000 00.0000 0.0000 0.00000 0.00000 > 00.000 00.000 00.000 00.000 0.000 0.000> !-------------------------------------------------------------------------------> ! Data for PHASE number: 1 ==> Current R_Bragg: 94.14> !-------------------------------------------------------------------------------> Si > !> !Nat Dis Mom Pr1 Pr2 Pr3 Jbt Irf Isy Str Furth ATZ Nvk Npr More> 1 0 0 1.0 1.0 1.0 0 0 0 0 0 0.00 0 7 0> !> F d 3 m <--Space group symbol> !Atom Typ X Y Z Biso Occ In Fin N_t /Codes> Si SI 0.00000 0.00000 0.00000 0.60000 1.00000 0 0 0> 0.00 0.00 0.00 0.00 0.00> ! Scale Shape1 Bov Str1 Str2 Str3 Strain-Model> 0.000000000 0.0000 0.0000 0.0000 0.0000 0.0000 0> 11.00000 0.00 0.00 0.00 0.00 0.00> ! U V W X Y GauSiz LorSiz Size-Model> 00.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0> 00.00 00.00 000.00 000.00 0.00 0.00 0.00> ! a b c alpha beta gamma> 5.43000000 5.430000 5.43000 90.000000 90.000000 90.000000> 00.00000 00.00000 00.00000 0.00000 0.00000 0.00000> ! Pref1 Pref2 Asy1 Asy2 Asy3 Asy4> 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000> 0.00 0.00 00.00 0.00 0.00 0.00> > **************************************************************************> Thanks in Advance> > Selcuk Kevran> Ankara University> Physics Department>

-- Lachlan M. D. CranswickCollaborative Computational Project No 14 (CCP14)    for Single Crystal and Powder DiffractionDaresbury Laboratory, Warrington, WA4 4AD U.KTel: +44-1925-603703  Fax: +44-1925-603124  E-mail: l.cranswick@dl.ac.uk  Ext: 3703  Room C14NEW CCP14 Web Domain (Under heavy construction):                           http://www.ccp14.ac.uk