XRD DIFFRAC.EVA:
Quick Start Guide
V371T | July 2017/ Reviewed X374/ March 2018
Introduction
This guide is a quick introduction to the DIFFRAC.EVA software and how to use the program to solve crystalline phase identification. For detailed information and an in-depth guide refer to DIFFRAC.EVALUATION User Guide & Tutorial available in hard copy in the XRD lab or online in Cumulus.
Part 1: Opening Diffractogram in DIFFRAC.EVA
To open a diffractogram for evaluation:
1. | Click File > Import Scan (Figure 1). |
2. | Select the Scan you want to open. |
3. | Click Open. |
4. | The Scan is now open and ready for evaluation. |
Figure 1. Open Scan.
Getting Acquainted
The DIFFRAC.EVA main screen has the following primary functional areas (Figure 2):
1. | Toolbar |
2. | Data Command Panel |
3. | View Command Panel |
4. | View Window |
5. | Data/View Tree Panel |
It is useful to have the Data Command Panel and Data Tree Panel open for view at all times (use the icons in the toolbar to open/close these views).
Part 2: 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: a traditional method and an enhanced method.
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.
1. | Select Data Command Panel > Tools > Background to open the Background dialog box (Figure 4). |
2. | If needed, use the slider to adjust the curvature on background humps. |
3. | In the drop-down box, select Background subtracted option. |
4. | Close text box. |
Figure 4. Background Dialog Box.
Part 3: Search Match
The Search Match tool 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.
| 1. | Select Search/Match (scan) from Data Command Panel > Tools. Notice the Search/Match dialog box has four tabs (Figure 5): –Chemical Filter –Database Filter –Candidate List –Selected Candidates |
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2. | Select desired search parameters (see suggestions below; Figures 6, 7, 8). | |
3. | Once the desired parameters are selected, click Rebuild to rebuild the database for your selections. After the database is rebuilt, click back onto Candidate List and click Match. |
Search/Match Screen
In the Criterion field of the Candidate List Tab (Figure 5), begin the search with 2: Neutral.
Figure 5. Search/Match Screen.
Chemical Filter Tab
A chemical filter can be set for any element in the periodic table (Figure 6).
–Green = element is mandatory
–Red = must be absent
–Blue = at least one of the elements in blue must be present in the search result
–Gray = not checked (absent or present)
Figure 6. Chemical Filter Tab.
Database Filter Tab
Search/Match can be enhanced using database filters such as the following (Figure 7):
–Quality Marks: degrees of pattern quality assigned by ICDD (recommended: *, Calculated, Indexed).
–Status: recommended: Primary.
–Colors: select the color of the mineral to be searched.
–Sources: database section: select both.
–Subfiles: select the group of patterns to be searched, for example, inorganics, zeolites, minerals, etc.
–Element # in Formula: choose the minimum/maximum number of elements considered in the formula.
–Density: enter a minimum/maximum density for the mineral being searched.
Figure 7. Database Filter Tab.
Candidate List Tab
Expand the table to see important information on the candidate (Figure 8), including
–Mtc: number of reference pattern lines matching the unknown
–FOM: Figure of Merit – a lower number is a better match
–Index #: rank number of the pattern
Figure 8. Candidate List Tab.
Part 4: Residual Scan – searching the minor phases
Minor phases are often difficult to identify because the patterns of the major peaks are higher on the list. Using the Residue tool will exclude the already matched patterns and increase the weight of the minor phases.
1. | In Search/Match (scan) screen, choose the Selected Candidates tab. |
2. | Select the pattern you wish to exclude in your next search. |
3. | Select the Residue tool. |
4. | Adjust the width of the zone to exclude around the pattern peaks. |
5. | Click Apply. |
6. | Click back onto Candidate List Tab and click Match. |
7. | The candidates for the residual scan are listed in Candidate List |
In addition, you can 'cut' the peaks out that you do not want included in a Search/Match.
1. | Select the Scissors tool from the View Window toolbar. |
2. | Cut the peaks that you wish to exclude from the Search/Match. |
3. | Under Search/Match (scan) box,in the Candidate List tab, select Match. |
4. | The program will search the peaks left uncut. |
5. | To undo the cuts click the Undo Arrow. |
Part 5: 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.
1. | Select the scan in the data tree. |
2. | Click Peak Search in the Tool List of the Data Command Panel. The Peak Search dialog box is displayed. |
3. | Move the slider to select the peaks you desire (Figure 9). |
4. | Once you are satisfied, click Make Dif to create a DIF pattern. The pattern list is created in the Data Tree and can be Search/Matched. |
5. | To select specific peaks click Append to List and a peak list is created in the Data Tree (Figure 10). |
6. | Highlight the peaks you want and click Search/Match (peak list) under Tool or Make DIF Pattern (which you can export to another program). |
Figure 9. Peak Search.
Figure 10. Peak Search with Append List.
Part 6: Printing in EVA
You can print any of the views in EVA.
Print Preview allows you to enter header and footers onto your print out, in addition to editing axis and labels. You can also Export the print preview as an image *.PNG file.