>I'm working in crystal size and microstrain. I have read that
>broadening due microstrain is related to a gaussian profile and
>size broadening is related with a lorentzian profile, but i have
>not find a reason to explain these assumptions, could you help me?
The 3 reasons explaining these choices are oversimplification,
oversimplification and oversimplification. Anyway, the fact is that
a Gaussian peak shape would correspond to a size distribution
function without physical meaning (with some negative fractions
of crystallites for given sizes). A Lorentzian shape is possible
for microstrain, if the distortion varies linearly with the distance
from an arbitrary origin. Have a look at the Warren book
'X-ray diffraction', Addison-Wesley, 1969, chapter 13, or see a
recent conference online :
http://sdpd.univ-lemans.fr/egypte/conf2/content.html
You will find there the size distribution function corresponding
to a Lorentzian profile shape : it is also a Lorentzian function, which
certainly cannot match all experimental cases. However, it seems
that this kind of distribution function is rather frequent, corresponding
to a large number of crystallites with small size, with continuous
decrease of the number of crystallites as the size increases. The Gaussian
shape for microstrain means that the distortion varies as the square
of the distance from an arbitrary origin. Again, this is unlikely
to occur in all cases...
Best wishes,
Armel Le Bail
http://sdpd.univ-lemans.fr/course/
