The Integral Breadth (B) value is more suitable for the size-strain analysis
because it is independent of the peak shape. But the FWHMs of a Gaussian and a
Lorentzian peaks with the same B are different.
The relation between IB and FWHM can be derived from the normalization factors
for the Gaussian and Lorentzian functions:
B(Gauss) = FWHM*pi^1.5/360*ln2^0.5
B(Lorentz) = FWHM*pi^2/360
(all the values are in radians)
Usually, peaks have intermediate shape between Gaussian and Lorentzian. In this
case one can use the Thompson-Cox-Hastings pseudo-Voigt function where the
FWHMs for the Gaussian and Lorentzian contributions are separated. The total
Integral Breadth can be calculated using the approximation:
B^2 = B(Lorentz)*B + B(Gauss)^2
(Halder, N. C. and Wagner, C. N. J. (1966). Acta Cryst. 20, 312)
Best Regards,
Leonid Solovyov
