Can anyone indicate me how must I choice the 2theta step increment and the total experiment time of step scan DRX pattern for having a good rietveld refinment result.
The step increment choice depends on the instrument resolution. Determine what is your sample minimal full width at half maximum, divide it by 4 or 6. If your FWHM is close to 0.05°(2-theta), use a 0.01° step. If your minimal FWHM is close to 0.10°, a step of 0.02° will be sufficient, etc.
The total experiment time must ensure a limited noise in the background. Look at the mean amplitude of the fluctuations in your background. Having less than 1/1000 of the most intense reflections is enough maybe, better is less than 1/10000.
We have a bruker RX diffractometer, I choice a step 0.02Theta for a total time of 4Hours
for a scan of 3 to 50 theta.
The specimen is a zeolithe
Is it a good choice?
For the step, see above. For the total time, see the fluctuations in the background compared to the max intensity, but this looks really not enough with a single detector. 40 hours would be better (or even more,up to 3 to 6 days...). If the detector is of the X'celerator class, the 4 hours time could be enough, but some high resolution patterns needed up to 18 hours, see : http://sdpd.univ-lemans.fr/powdif/low_fwhm_and_rp.html
A scan from 3 to 50 theta (you mean 6 to 100 2-theta) can be enough if you do not miss any low-angle reflection - it would be better to start at 3°(2-theta), and if really the pattern shows no peaks after 100° (2-theta) - otherwise, going up to 130 or 150°(2-theta) is recommended.
Best wishes,
Armel
