Hi, Apu,
I am not a beginner of GSAS though, it seems there is no direct, GUI-based way to read
the size of grain, and basically, I dont think there is such kind of clever software,
at least for the non-commercial source. However,
We are generally taught, that Deviations from ideal crystallinity crystallinity,
crystallite size and strain (at the atomic level) lead crystallite lead to broadening
of the diffraction lines. By analyzing to broadening of the diffraction lines, and it
is possible to extract information about the microstructure of a material. we normally
have the following methods.
1.Simplified Integral Breadth Methods Simplified Integral Breadth
Methods(trenmendously popular)
2.Fourier Methods Fourier Methods
3.Double Double Voigt Voigt Methods Methods
The width of a diffraction line can be estimated by more The width of a diffraction
line can be estimated by more
than one criterion. The two most common width than one criterion. The two most common
width parameters are:
1. Full Width at Half Maximum (FWHM or Full Width at Half Maximum (FWHM or Γ)
2. Integral Breadth Integral Breadth (β)- The width of a rectangle with the The width
of a rectangle with the
same height and area as the diffraction peak same height and area as the diffraction
peak.
Most profile fitting programs gives rise to FWHM, but for accurate Most profile
fitting programs give FWHM, but for accurate size-strain broadening one should use
integral breadth as size-strain broadening one should use integral breadth as a
measure of the peak width, which can be done by normally available data analysis
software, i.e. Origin.
There is one point to mention is the integral breadth and FWHM (Γ) can be related for
) can be related for various peak shapes various peak shapes, i.e.Lorentzian
Lorentzian → β = (π/2)*Γ , Gaussian Gaussian → β = {π/(4*ln2)}^1/2 *Γ
and Pseudo-Voigt The Rietveld Rietveld ed. by R.A. Young, Oxford Science (1993).
According to Scherrer Scherrer (1918), small crystallite size (1918) first observed
that small crystallite size
could give rise to line broadeningDv = Kλ/(β cosθ), and then Stokes and Wilson
(1944) proposed that strained or
imperfect crystals containing line broadening, εstr = β/{4*tanθ}.
Noticeably, that size and strain broadening show a different θ dependence. This
provides a way to separate the two dependence, by using W-M plot.
Therefore, I personally think that relying on the simple mathematical relattion above,
you can work it out at enough accuracy.
Conclusivley, maybe the parameter in GSAS can be used, however there is still way by
using data analysis to your measured dataset to extract the info you want actually
rather then using GSAS.
Best Regards,
Lingfei Zhang
*****************************************
Neutron Scattering Physics Group
Institute for Materials Research
Maxwell Building 111
University of Salford
Salford, Greater Manchester
United Kingdom M5 4WT
Tel:0161 295 4633
Facsimile:0161 295 5147
Email:[EMAIL PROTECTED]
*****************************************
