Degree of Crystallinity (DOC) analysis

The "degree of crystallinity" (DOC) analysis can be used to determine the amount of amorphous compounds in a sample (quantitative phase analysis). It requires that an additional "empty sample holder" diffraction pattern is available that has been recorded using the same experimental conditions as the sample's pattern. This additional pattern is used to subtract the background contribution caused by the instrument from the one of the sample.

The measurement range of both diffraction patterns (anchor pattern and "empty sample holder" pattern) should be large enough to see both the start and end of the amorphous part stack on the background.

The DOC analysis works best if the crystalline and amorphous parts have similar elemental composition. If the sample consists of crystalline fractions and an amorphous fraction of different chemical compositions, the amounts of each of the individual crystalline phases may be estimated using appropriate standard substances; the amorphous fraction is then deduced indirectly by subtraction.

If this prerequisite is met, it is neither necessary to determine the experimental peaks nor to select the matching phases (qualitative analysis) for the DOC analysis. Instead, it is sufficient to subtract the instrumental background from the sample's diffraction pattern, re-determine the background, and then calculate the area below the background curve and compare it to the area of the whole pattern.

Workflow for DOC analysis:

1. Record the sample's diffraction pattern as usual; the 2theta range should be large enough to see both the start and end of the amorphous part.
2. Record an "empty sample holder" diffraction pattern with the same experimental conditions.
3. In Match!, press the Degree of crystallinity analysis button in the toolbar, or run the menu command "Quantify / Degree of crystallinity (DOC)".
4. Select the sample's diffraction pattern file, then press "Open".
5. In the pattern graphics, check the background that has been determined automatically so that it clearly separates the diffraction peaks from the background. If you would like to modify the background, answer "No" to the corresponding question, modify the background, and finally press the "Degree of crystallinity analysis" button in the toolbar again to proceed.
6. In the window that opens after you have confirmed the background, import the "empty sample holder" diffraction pattern mentioned above, by pressing the "Select..." button in the line "Import from file:".
7. Mark the option "Full pattern" under "Subtract full 'empty sample holder' pattern or background only".
8. If you like to see the "real" diffraction pattern of the sample after subtraction of the instrument background, mark the option "Add result as a new experimental pattern".
9. Press "OK". The result of the DOC analysis will now be displayed. It will also be included/displayed in the report.

In general, the "Degree of crystallinity (DOC) analysis" window is operated as follows:

Either mark the option Import from file (in order to import the required "empty sample holder" diffraction pattern from a raw data file), or Use additional pattern if the pattern recorded for the "empty sample holder" has already been imported as an additional experimental pattern.

It is either possible to subtract the Full pattern of the empty sample holder from the anchor pattern (if the empty sample holder pattern is clear from any disturbing surplus features), or to subtract only the Background if this does not apply.

If only the background shall be subtracted, Match! will either determine it automatically (if you use the option Import from file mentioned above), or use the background defined for the additional experimental pattern.

If you mark the checkbox Add result as a new experimental pattern, the diffraction pattern calculated by subtracting the "empty sample holder" pattern from the anchor pattern will be displayed as an additional experimental pattern, so that you can visually check it.

Finally, if you mark the Save as defaults checkbox at the bottom, all current selections in the dialog will be restored when you open it for the next time.