I try to calculate crystal size and strains in Al powder using Topas. After I add strain L to calculation, Topas shows increased crystal size from 100 nm to 150 nm.
It is best to use LVol-IB for crystallite size (not crystal size) rather than Cry-L. Switch on the calculate errors and watch for good low error values, reject settings with high error values. Try both L and G (Lorentzian and Gaussian) in turn to see which gives the lowest errors and best fits. Remember to reset the starting values each time you try a different parameter.
I usually consider the L component to estimate LVol-IB and the G component to estimate the microstrain (e0). If the diffractogram has been measured in a wide 2theta range and good enough statistics, you should diferentiate both phenomena (Crystallite size and microstrain) if they are present in the sample. For TOPAS 4, the e0 must be multiplyed by Pi/360 in order to get the microstrain (e0) in Angstroms. I agree with Ian J. Slipper that the errors determine the the final contributions L or G that you can use for a given diffractogram. It is obvious that prior to these analysis you must consider the instrumental effects by using the FPA option or analyzing an standard (LaB6 SRM 660a). I prefer the last option.
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