vlad
At Rietveld refinement (using TOPAS v.3.0) of XRD pattern obtained from Ruthenium-containing material a strange result was obtained-in TOPAS report the value of Crystal density of Ruthenium was given as 37.933(36) g/cm3. Can this error be eliminated? Does it affect of quantitative analysis result?
Structure 1
Phase name Ruthenium
R-Bragg 1.336
Spacegroup P63/mmc
Cell Mass 606.423
Cell Volume (Å^3) 26.764(47)
Wt% - Rietveld 35.9(20)
Crystallite Size
k: 0.89 LVol-FWHM (nm) 6.37(19)
Crystal Linear Absorption Coeff. (1/cm) 6644(12)
Crystal Density (g/cm^3) 37.625(65)
Lattice parameters
a (Å) 2.6896(21)
c (Å) 4.2722(35)
Site Np x y z Atom Occ Beq
Ru1 6 0.33330 0.66670 0.25000 Ru 1 0.50(21)
johnsoevans
You need to make your fractional coordinates for Ru1 exactly 1/3 and 2/3 instead of 0.3330 and 0.66670. Use =1/3; and =2/3;. The atom will then be on the multiplicity 2 site you expect and the density will come down. The clue is in the "Np 6" entry in your post.
vlad
Thanks,John. Unfortunately my TOPAS v.3 does not accept atomic coordinates as fractions. Although the density in report is indicated correctly, the Rietveld refinement is not performed correctly. Probably this is a bug in software.
johnsoevans
v3 is a long time ago, but this should work. Did you type "=1/3;" into the relevant box (if you're using the gui) or into the site line (if you're using an input file.
What you show isn't a "bug". You've told topas in this example that x=1 and y=2 so the refinement is correct under that information.
vlad
I use GUI and I type 1/3 and 2/3. But 1/3 and 2/3 turn into 1 and 2. The same thing happens when I use .inp and .pro files.
johnsoevans
As in the previous post, type "=1/3;" not just "1/3". The = and ; indicates a topas equation.
vlad
Thank you very much for the help. In GUI mode, this did not work, but after editing the .pro file, it was wonderful!!!
rowlesmr
In GUI mode, you need to write in "=1/3;" on the codes page, not the values page.
.
And yes, it will affect quant results, as the cell mass will be wrong, and the intensities will be wrong which will bias the scale factors.
vlad
It all worked. Thanks again!