[GSAS-II] Calculating domain size

[Viktor Zano]

Dear friends and colleagues

The size of coherently reflecting domains, also known as crystallites, is
important issue for nano structures.

I used GSAS-II to calculate the domain sizes. I used uniaxial domain size
model and got equatorial =18.6 (1) nm axial 21.7 (2) nm. These values are
higher compared to other tools: GSAS (Dv=12), STEM (12(3)) or Debye
function analysis (Da,b=13.7 (5.0) nm, Lc=14.0(5.7) nm).

Any idea what's wrong?

The procedure I used to calculate the domain size at GSAS-II was as
follows:

LaB6, NIST Standard Reference Material (SRM) 660a, was first analyzed to
define to instrumental parameters. In the phase data I used 2 micron for
domain size and 330 for microstrain. (I also tried used 5 micron for domain
size and 1 for microstrain). I used these values as in the certification of
the SRM 660a it was stated that Rietveld analysis of the XRD data gave 2
micron for domain size and no strain broadening. (SEM analysis indicated
that the particles of LaB6 consist of aggregates of crystallites; the size
of the crystallites was in the 2 to 5 micron range). The instrumental
parameters were refined.

Later I analyzed my data using the instrumental parameters I got from the
LaB6 standard, without refining that instrumental data. Instead I refined
the domain size and later microstrains of my phase.

By the way in GSAS (GSAS1) I just used parameters Lx and Gp to calculate
the size and Gu and Ly to calculate the microstrain.

Thanks

Victor
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