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

More Ma Zhaoyang's questions See All
Similar questions and discussions