From: "jilin_zhang_Houston" <[EMAIL PROTECTED]>
Reply-To: rietveld_l@ill.fr
To: "rietveld_l@ill.fr" <rietveld_l@ill.fr>
Subject: Re: Problems using TOPAS R (Rietveld refinement)
Date: Mon, 12 Mar 2007 10:39:41 -0600
Leandro :
here is an example of calcite I used. You can use min and max to confine
the parameters.
One way to know whether it is right is to mix a known fraction of a
compound, e.g. ZnO with a ratio of original sample/ZnO=100/15.
At the end of the refinement, you have N components with N corrected(with
volume and density) scalefactor, S(i),
Weight(i)=S(i)/S(ZnO)*15
the sum of all weight(i) should be close to 100 if the whole thing is
crystalline.
str
phase_name calcite
scale sc_calcite 0.0001813894308
space_group R-3c
r_bragg 5.769971925
Crystallite_Size(cs_calcite, 100 min =100; max =1000;)
Trigonal(a_calcite 4.995096119 min =4.95; max =5.2;,c_calcite
17.08621648 min =16.9; max =17.1;)
site Ca num_posns 6 x 0 y 0 z 0 occ Ca+2 1 beq 0.95
site C num_posns 6 x 0 y 0 z =1/4; : 0.25 occ C 1 beq 0.9
site O1 num_posns 18 x 0.257 y 0 z =1/4; : 0.25 occ O-2 1 beq 0.94
PO_Spherical_Harmonics(sh_calcite, 2 )
Cheers
J
Hi, guys,
I´m having some trouble using the Bruker software TOPAS R, right now I´m
quantifying a sinthetic sample with 50% of calcite and 50% of dolomite.
Check the following questions an help me if you can.
1) I´m using the CIF files from ICSD, but when I put it in the software it
gives me a temperature factor (beq.) of 1. Is there anyway I can check
some
good temperature factors?! When i put then to refine, sometimes they
become
negative, but the calculated - observed pattern is just good.
2) I´m using Fundamental Paramaters and for these I must have acknowledge
of
my instrument, well I have, minus sample lenght... and stuff like that...
is
there anyway I can determine these values with accuacy and use them with
sure?!
3) In TOPAS how do I know if the refinement is good?! Because each time I
refine the 50%/50% mixture I have different results and I don´t know wich
one gives me a result that I can trust.
Thank ou in advance,
Leandro Bravo Ferreira da Costa
Student, UFRJ - Universidade Federal do Rio de Janeiro - BR
CETEM - RJ
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