Table of Contents

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Figure 2. View of a Diffractogram in EVA

Removing the Background

The first step in preparing a scan for Search/Match phase identification is to subtract the background (Figure 3). There are two methods for removing the background:

• Traditional method: is recommended for all scans; it gives an arc parabola but never submerges a complete peak.
• Enhanced method: gives a smooth curve where some peaks may be under the background curve. This could be useful for crystallographic studies. See the EVA manual for greater detail.
  
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Figure 3. Background Highlighted in a Diffractogram and Background Dialog Box in inset

In Data Command Panel, select Tools > Background to open the Background dialog box (Figure 3). Default view is 'Original + Background'. If needed, use the slider on the left to adjust the curvature on background humps. When satisfied, in the drop-down box, select Background subtracted option. Close the text box . The background is removed, and the diffractogram is changed to baseline.

Search/Match

The Search/Match (scan) tool in the Data Command Panel attempts to match XRD scans with patterns found in the ICDD (International Centre for Diffraction Data) PDF database. The Search/Match process tries to identify an unknown scan based on pattern recognition techniques. EVA can also find a reference pattern by its name or ICDD number.
Note: It is at the user's discretion to identify and choose the correct pattern matches.

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In the Criterion field of the Options Tab (Figure 5), begin the search with 2: Neutral.

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In the Databases Tab, select the DB Filter. Click on the "three dots" button (Figure 6A). The Database Filter window opens (Figure 6). The default name is 'Database Filter #1', and the database used is "PDF-2 2001". The Search/Match can be enhanced using database filters such as the following (Figure 6):
–Quality Marks: Degrees of pattern quality assigned by ICDD. Recommended: *, Calculated, Indexed (a).
–Status: Recommended: Primary (b).
–Colors: Select the color of the mineral to be searched.
–Sources: Database section: select both ICDD Database (experimental) and ICSD Database (ICSD-FIZ) (c).
–Subfiles: Select the group of patterns to be searched, for example, inorganics, zeolites, minerals, etc. (d).
–Element # in Formula: Choose the minimum/maximum number of elements considered in the formula (default values are min=1 and max=24).
–Density: Enter a minimum/maximum density for the mineral being searched (default values are min=1 and max=80).

Figure 6. Database Filter.

Chemical Filter 

In the Databases Tab, select Chemical. Click on the "three dots" button . The Chemical Filter window opens (Figure 7). The default name is 'Chemical Filter #1'. A chemical filter can be set for any element in the periodic table (Figure 7).
–Green = M = Mandatory. All elements shall match.
–Red = D = Discarded. Exclude from match.
–Blue = A = At least one element shall match (must be present in the search result).
–Gray = N = Neutral. Element may match.

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Figure 8. Search List Tab in the Auto Views Panel

Residual Scan – Searching the minor phases

Minor phases are sometimes difficult to identify because the patterns of the major peaks have a better position in the list. Using the Residue tool will exclude the already matched patterns and increase the weight of the minor phases.

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Check the tick box (green square in Figure 9) to add selected peaks. To delete selected peaks, right-click on the selection and choose 'Delete'.

Figure 9. Residual Scan

Peak Search

Peak Search detects peaks automatically and is useful for phases not identified with Search/Match or to export the pattern to another program.

• Select the scan in the Data Tree Panel.
• Click Peak Search in the Tool List of the Data Command Panel (Figure 10A). The Peak Search dialog box is displayed.
• Move the slider to select the peaks you desire (Figure 10).
• Once you are satisfied, click Make DIF to create a DIF pattern (Figure 10B). The pattern list is created in the Data Tree Panel and can be Search/Matched.
• To select specific peaks click Append to List (Figure 10C) and a peak list is created in the Data Tree Panel.
• Select the DIF pattern  in the Data Tree Panel (Figure 11A) and then click Tool > Make Peaks (Figure 11B).

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Figure 12. Peak Search with Append List.

Printing in EVA

You can print any of the views in EVA.
Click Print Preview Button or click File > Print Preview. A 'Print Preview' window pops up. This allows you to enter header and footers onto your print out, in addition to editing axis and labels. You can then click on Export as Image Button and save the print preview as an image .PNG file.

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