And of course there is the book 'The Rietveld Method' (International Union of Crystallography Monographs on Crystallography) Edited by: R A Young

International Union of Crystallography Oxford University Press (1993)

ISBN: 0 19 855577 6

Perhaps reviewing the following page may provide useful hints in view of your question:

http://www.xrd.us/services/quantificatin.htm

http://www.xrd.us/technote/amorphous%20content%20determination.htm

In addition to the helpful advice given above, I suggest the following -

1) Ensure that the powder pattern is obtained with fine-grained sample, e.g. by micronising if it is in powdered form.

2) Use a calibration standard, with use of the external standard method being recommended rather than mixing an internal standard with your sample

3) Minimise preferred orientation in your sample through appropriate sample mounting. Where PO effects are still evident, carefully apply a PO correction to the phase(s) in question.

4) Validate the phase composition results by auditing with elemental analysis data, e.g. by XRF analysis.

Regards

Brian O'Connor