These templates were created by Gary Novak and Alan Colville, 1989, American Mineralogist, v. 74, p. 488-490.
These templates are a set of Excel spreadsheet programs that calculate unit cell parameters (axis lengths and angles) from X-ray powder diffraction data using a least squares fit procedure. The programs require 2θ peak positions and {hkl} indexes for each peak. There is one template for each of the six crystal systems (hexagonal and trigonal use the same template).
- The templates were developed using the Excel spreadsheet programming language.
- OPEN the template for the crystal system of interest to you (see below), then SAVE it to your computer and OPEN the saved version in Excel. It may not work properly if it is open only in your web browser.
- Copy the first yellow row (light and dark yellow) down into exactly as many rows as you have indexed peaks. Index the peaks (= find {hkl} values) using the powder diffraction file database on the XRD computer, or from the diffraction file books.
- In the Excel template, replace the 2θ and miller index {hkl} values with your own. Enter negative Miller indices (e.g., {111}) as negative numbers (e.g., {1 -1 1}).
- For hexagonal and trigonal minerals, the formal Miller indices can take the form {hkil}, as compared to {hkl} for the other crystal systems. However, because h + k + i = 0, i is not actually necessary so only h, k, and l are usually listed in the Power Diffraction File indexes.
- The best fit (refined) unit cell parameters are located in the blue area at the bottom of the spreadsheet.
- You MUST check your work. The observed and calculated d spacings should be similar, and the delta-d column values should generally be <0.01. Axial lengths should generally be within 0.02Å of the book values. If your delta-d and axial length accuracy is much worse, carefully check the 2θ angles you entered and your Miller index assignments.
Advanced notes
- If you picked the wrong crystal system, made a mistake choosing or typing in 2θ angles or {hkl} values, or use only peaks from a single zone, you may see lots of error notations where you expect numbers. This is because a physically impossible result occurred somewhere in the calculations. Carefully check your work!
- Change the Alpha and Alpha 1 X-ray wavelengths if you are using a tube other than cobalt.
- Set the 2θ Correction value if the 2θ values are systematically incorrect by a known amount.
- If you are not using Kα1-stripped 2θ values, set the Kα/Kα1 cut-over value to 50° 2θ.
Cell refinement templates: