Matthew, could I please get the PDF version of the paper?
thanks, KLaus-Dieter.
[EMAIL PROTECTED] wrote:
Just to add more fat to the fire....
Have a look at Young, R. A. & Desai, P. 1989, 'Crystallite Size and
Microstrain Indicators in Rietveld Refinement', /Archiwum Nauki o
Materialach,/ vol. 10, no. 1-2, pp. 71-90. (I can send the PDF if needs be)
They talk about the Thompson, Cox and Hastings model, which explicitly
separates the gaussian and lorentzian components of a psuedo-Voight peak
shape.
FWHM(G)^2 = U tan^2(T) + V tan(T) + W
FWHM(L) = X tan(T) + Y/cos(T)
As Prof. Stephens pointed out (and is stated in Yound and Desai), the
coefficients can be broken into instrumental and sample (size, strain)
components.
U = U_inst + U_strain
V = V_inst
W = W_inst
X = X_inst + X_strain
Y = Y_inst + Y_size
You can fix the instrument components with your standard, and then
refine the difference with your sample.
If you want to stick with the straight UVW symbolism, Young and Desai
also state that you can use the size broadening term FHWM(G)^2 =
Z/cos^2(T), which yields:
FWHM(G)^2 = Z/cos^2(T) + (U_inst + U_strain) tan^2(T) + V_inst tan(T) +
W_inst
which can be re-written as
FWHM(G)^2 = (U_inst + U_strain + Z_size) tan^2(T) + V_inst tan(T) +
(W_inst + Z_size)
as long as you constrain the two Z_size's to be the same.
The last equation is what Prof Stevens alludes to in his "refinement of
U and W", all of the sample related parameters are folded up there.
Of course, your mileage may vary...
Cheers
Matthew
________________
Matthew Rowles
CSIRO Minerals - Clayton
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Dr. Klaus-Dieter Liss
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The Bragg Institute, ANSTO
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