Dear all,
I have alpha-quartz powders and I did 3 hours XRD scan for these powders both at 30 degrees Celsius and 450 degrees Celsius (there exists no phase transformation at this temperature). After refining by TOPAS-5, I wonder why my Rwp is 14% for 30 degrees and 19% for 450 degrees. Would you please check to see if the steps mentioned below are correct and Is the attached Rietveld refinement for silica done by TOPAS publishable?
I want to use TOPAS to find out the effects of temperatures on unit cell parameters (trying to calculate the thermal expansion coefficient). I calculated the thermal expansion coefficient of alpha-quartz powders according to the change of the variation in unit cell parameters, as shown in the following table and this result is in accordance with other researcher's value.
Steps:
First for 30 degrees:
1- I loaded the scan file (30 degrees). 2- load the emission file.
3- set the background order to 4
4- loaded instrument details
5- chose the correction (zero error, sample displacement, LP factor)
6- start X from 22.5 because there exists a large disagreement between the actual scan pattern and fitted scan pattern before 22.5 degree
6- load the quartz.str file (PDF Card - 00-046-1045)
7- I changed all the occ and beg from fix to refine.
8- Run and check the Rwp value
9-Save structure in str format for 450 degrees (named as fitted-30degree.str)
Then for 450 degrees:
1- I loaded the scan file (450 degrees). 2- load the emission file. 3- set the background order to 4 4- loaded instrument details 5- chose the correction (zero error, sample displacement, LP factor) 6- start X from 22.5 6- load the fitted-30degree.str file 7- I changed all the occ and beg from fix to refine. 8- Run and check the Rwp value
Regards, Zhaoyang