Data Mining with DDView+ and the PDF-4 Databases Solid ... Mining 2012 - Solid... · This is one of three example-based tutorials for using the data-mining capabilities of the PDF-4+

Data Mining with the PDF-4 Databases

Solid Solution

Crystal Cell Parameters

This is one of three example-based tutorials for using the data-mining capabilities of the PDF-4+ database.

• CIGS Photovoltaics – solid solution / cell parameter relationship

Two other similar tutorials for data-mining exist and cover the following topics:

• FeO Non-stoichiometric Oxides – sorting out temperature and stoichiometric effects on

cell parameters

• Carbamazepine Polymorphs – a PDF-4/Organics application investigating polymorphic

forms of an active pharmaceutical ingredient (API)

CIGS Photovoltaics

• CIGS = Cu (In, Ga) Se2 - ( 1 : 1 : 2 )

• Record-breaking light-energy conversion efficiency for film-based photovoltaics, ~20%

• Several methods of manufacture

• Efficiency depends on stoichiometry

Can stoichiometry be evaluated by XRD?

CIGS Data Mining Process Steps

1. Find the PDF-4+ entries for CIGS solid solution phases

2. Obtain chemical composition, space group, and crystal cell parameters from entries

3. Determine relationship between chemistry and crystal cell parameters, if any

Use the Preferences Window to establish what will be useful to display in the Search Results table . . .

1. Click the ‘Preferences’ icon 1. Click the ‘Preferences’ icon 2. Click the ‘Search’ tab in the

‘Preferences’ window

Selecting Fields for the Results Table

Selected Fields: Use these buttons to move a selected item up or down to obtain the desired order of data columns in the results table.

Available Fields: Use these buttons to move selected items between the ‘Available Fields’ list of categorized items and the ‘Selected Fields’ list of items that will be displayed in the results table.

Using the described arrows, set up the ‘Selected Fields’ list to match the following:

PDF File Reference #

Quality Mark

Ambient Conditions Flag

Chemical Formula

Crystal System

Space Group

Space Group # (Int. Tables)

Crystal Cell a-axis Length

Crystal Cell c-axis Length

Atomic Coordinates Included

Calculated Density

Available Fields Category (Always present) Subfiles/Database Filters Elements Structures Miscellaneous

}

Once the ‘Selected Fields’ list is set up as shown, click the ‘OK’

button to save changes and close the ‘Preferences’ window

Save changes and exit ‘Preferences’ window.

Specifying the Elemental Conditions for Cu (Ga, In) Se2 Entries

We can display just the entries in the PDF-4+ database with chemistry consisting of only Cu, Ga, In, and Se using a Periodic Table search.

• The ‘Search’ window is used to enter criteria for locating database entries of particular interest.

• There are seven different tabbed windows of search criteria available.

• Click on the ‘Periodic Table’ tab to enter elemental criteria for this search.

CIGS Photovoltaics: {Cu (In, Ga) Se2} [The sequence for specifying “Only (Cu And In And Ga And Se)” will be shown as you continue to advance the slide]


First click these four elements . . .


Then click ‘Only’ . . .


Finally click ‘Add’ to include this criterion for the search.


Verify the proper entry of the elemental criterion here . . .

Note this tab label has turned red, which denotes that search criteria now exist on this page.

Verify the proper entry of the elemental criterion here . . .

. . . and click ‘Search’ to retrieve the PDF-4+ entries that satisfy this criterion.

Activating the search: Cu (In, Ga) Se2

CIGS Retrieval: (Only Cu, In, Ga, Se)

Results Table

There are 29 entries in the 2012 PDF-4+ database that fit this chemical criterion. All entries are tetragonal - those with the proper 1:1:2 stoichiometry belong to space group I-42d (19 entries in white). Ten entries are of different stoichiometry and belong to other space groups (shaded in gray).


Results Table

Note that the ‘a’ crystal cell parameter ranges from about 5.65 Å to about 5.75 Å for the entries with the I-42d space group. The ‘c’ crystal cell parameter ranges from about 11.15 Å to about 11.55 Å


Results Table

From the ‘Coords’ column, we can see which entries include the atomic coordinates for the crystallographic structure. A black check indicates inclusion of atomic coordinates. A grey check indicates the entry is cross-referenced to another entry with atomic coordinates. For this set, four entries with the proper stoichiometry (and space group) have atomic coordinates: 00-062-0054, 00-062-0055, 04-005-8370, and 04-006-4510.


Results Table

An entry is viewed by double clicking on its row in the table. We’ll examine this one.

The PDF Card window provides access to all database information for this entry. The crystal structure is viewed by clicking the circled ‘atomic structure’ icon.

Two Views of Cu (Ga0.5 In0.5) Se2 Crystal Structure using Jmol Graphics

Note: This is the ‘Jmol’ viewer. Another viewer, the ‘ICDD’ viewer, is also available. Select the one you wish to use on the ‘PDF Card’ tab of the ‘Preferences’ screen. The last item selects the ‘3D Structure Viewer’ to be used.

A ‘right-click’ menu is available for tailoring this 3D view. See the tutorial on ‘Use 3D Structure Capabilities’ for more on using this feature.

CIGS Photovoltaics • To get a complete perspective of cell parameter relationships for

the solid solution series, it would be advantageous to include the end-members of the series, namely CuInSe2 and CuGaSe2.

• These can be included by modifying the search as follows:

– Periodic Table: • [And] Cu And Se - must have both

• [And] In Or Ga - must have at least one

• [And] Just Cu, Ga, In, Se - no other elements but these

– Space group: #122 (I-42d)

– Database filter: Primary patterns*

• Additionally, the ‘atomic %’ field should be included in the results table for examining In-Ga concentration dependencies.

The next few slides will guide you through this process.

* There are numerous entries for the end-member compounds, this will limit the results to those determined as best by the ICDD task groups and editors.

Add ‘Atomic %’ to CIGS Search Results Preferences


Add Atomic % to Selected Fields for Results Table


‘Atomic %’ is added to the end of the ‘Selected Fields’ list

Click ‘OK’

Enter New Search Criteria Before entering new criteria, clear the previous search criterion by clicking the ‘Reset All’ button.

Enter new search criteria (Page 1):

“Primary” pattern status is selected on the “Subfiles / Database Filters” page

We are not including deleted patterns

Enter new search criteria (Page 2): International Space Group (#122) is entered on the “Structures” tab. This corresponds to the I-42d space group.

Enter new search criteria (Page 3): Enter required elements on “Periodic Table” page: (Cu And Se) . . .

Enter new search criteria (Page 3): Enter required elements: (Cu And Se)

Enter solid-solution elements: (In Or Ga) . . .

Enter new search criteria (Page 3): Enter required elements: (Cu And Se) Enter solid solution elements: (In Or Ga)

Restrict chemistry to these 4 elements: Just (Cu And Ga and In and Se) . . .


• Verify chemistry criteria

Verify chemistry criteria and start search.


• Verify chemistry criteria

Verify chemistry criteria and start search.

• Verify chemistry criteria • Click ‘Search’

CIGS Search Results Including Atomic %

49 Resulting Entries: 3 are CuGaSe2

30 are CuInSe2

16 are Cu(In,Ga)Se2


Examining the Chemical Formulas column, one observes that several of these entries are deficient in copper. Because this can also affect the cell parameter, we need to remove such entries.


One way is to ‘right-click’ on each entry to be removed to bring up the menu shown here. Clicking on ‘Remove’ will remove the entry from the list and place a message on the Results Table and any derived graphs stating “1 entry removed by user”.

A second way is to specify another search criterion to restrict the atomic percent copper to a fairly narrow range. Without resetting the ‘Search’ form, we can add this criterion on the ‘Elements’ tab. Click the ‘Atomic %’ button and specify the Element as ‘Cu’, the Value as 25.0, and the ESD as 1.25 (± 5.0%). Then perform the search.

Restricting the Stoichiometry When Searching

Restricting the Stoichiometry When Searching

The results now contain 38 entries which are stoichiometrically similar These results will now be analyzed for correllations between cell parameters and Ga/In content.

Analysis of the Resulting Database Entries Most fields in the results table can be graphically illustrated in either X-Y plot or histogram form.

For the current application, we will use an X-Y plot to illustrate cell parameters as a function of atomic % Ga.

To do this, ‘Graph Fields…’ is first selected from the ‘Results’ drop-down menu of the ‘Results’ window.

Choose X-axis field from drop-down menu: Atomic %

Choose element for Atomic % values: Ga

Choose Y-axis field from drop-down menu: XtlCell-a

Click ‘Create Graph’

1

2

3

4

Creating a Results Graph

Cu (In, Ga) Se2 - ao Cell Parameters vs. At % Ga

The data, extracted in this manner from the PDF-4+ database, clearly illustrate the linear relationship of the a-axis lattice parameter of CIGS compounds with atomic % Ga in the structure.

At 0 atomic % Ga, the a-axis is ~5.78Å, while at 25 atomic % Ga (CuGaSe2 where gallium is ¼ of the atoms in the formula), the a-axis is ~5.61Å.

Y-axis Field: XtlCell-c

Similarly, data for the c-axis cell parameter can be plotted. Using the same Ga atomic % values for the X-axis, the XtlCell-c data field can be chosen for the Y-axis.

Changing the Results Graph to Plot the c-axis Dependency

Cu (In, Ga) Se2 - Cell Parameters vs. At % Ga

Again, a linear relationship of the c-axis lattice parameter of CIGS compounds with atomic % Ga in the structure is clearly illustrated.

At 0 atomic % Ga, the c-axis is ~11.61Å, while at 25 atomic % Ga, the c-axis is ~11.02Å.

Cu (In, Ga) Se2 - Cell Parameters vs. At % Ga

Results can be exported as a comma-delimited text file for use in a spreadsheet program.

Cu (In, Ga) Se2 - a-axis Cell Parameter vs. Ga At % Linear Regression via Excel Spreadsheet*

Rearranging, At % Ga = -144.93 * a (Å) + 838.26

* Use a spreadsheet or data analysis program of your choice

Cu (In, Ga) Se2 - c-axis Cell Parameter vs. Ga At % Linear Regression via Excel Spreadsheet *

Rearranging, At % Ga = -41.667 * c (Å) + 484.29

* Use a spreadsheet or data analysis program of your choice

CIGS Summary

• Crystal cell parameters for CIGS compounds, Cu(In,Ga)Se2, can be effectively “mined” from the PDF-4+ database

• These can be plotted as a function of Ga (or In) At % to show a relationship

• Equations useful for determining At % Ga from X-ray-derived cell parameters can be generated

• At % Ga = -144.93 a (Å) + 838.26

• At % Ga = -41.667 c (Å) + 484.29

• A single, indexed powder diffraction pattern can provide two determinations of At % Ga

International Centre for Diffraction Data

12 Campus Boulevard

Newtown Square, PA 19073

Phone: 610.325.9814

Toll Free Number in US & Canada: 866.378.0331

Fax: 610.325.9823

Thank you for viewing our tutorial. Additional tutorials are available at the ICDD website.

www.icdd.com

http://www.icdd.com/

Documents

Data Mining with DDView+ and the PDF-4 Databases Solid ... Mining 2012 - Solid... · This is one of three example-based tutorials for using the data-mining capabilities of the PDF-4+