Determination of crystallinity can be a fraught subject, because it is usually assumed in such measurements that the background is from amorphous material while the sharp peaks are from crystalline material. So the standard way to do this would be to have a method for extracting the background and then comparing the total area of the background with the total area under the peaks. However, the background need not arise solely from amorphous material but from several other sources, such as short range order diffuse scattering, air scattering, scattering from slits etc etc. Furthermore, determinign the total area under the background needs some care as one needs to know where it begins and where it ends.
The literature on crystallinity usually talks about 1 and 2 state models. A 2 state model is one which one has a mixture of crystals and amorphous material, and if one believes that this is what you have in your sample then the percentage crystallinity can be derived from the comparison of peaks to background, as mentioned above. A 1-state model is where one has crystalline materials with sufficient breakdown in long-range order to give a background due to diffuse scattering. Mike Glazer
