Data Mining with DDView+ and the PDF-4 Databases

Solid Solution Crystal Cell Parameters

Some slides of this tutorial have sequentially-layered information that is best viewed in ‘Slide Show’ mode

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

database and it covers the following topic:

• 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 displayed in the Search Results table . . .

1. Click the ‘Preferences’ icon1. Click the ‘Preferences’ icon2. 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 in the listed order for 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

Calculated Density

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.

Save changes, but do not exit ‘Preferences’ window.

• 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 click this slide]

First click these four elements . . .

Then click ‘Only’ . . .

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

Activating the search: Cu (In, Ga) Se2

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.

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

CIGS Retrieval (Only Cu, In, Ga, Se) Results Table

• All listed entries belong to the Cu (In, Ga) Se2 solid solution series except 00-051-1222 which is Cu (Ga, In)3 Se5.

• Except for 00-051-1222, all belong to tetragonal space group I-42d (#122). (Note a ~ 5.7Å and c ~ 11.3Å for all entries.)

• PDF entries 04-005-8370 and 04-006-4510 are from the LPF database (04) and thus contain the crystal structure complete with atomic coordinates.

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

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

The resulting window gives a choice of structural views. Clicking the first one will show a rotatable 3D view that fills the window.

Structure View WindowUse a right mouse click to bring up the structure view manipulation menu.This determines the action of left mouse click-and-drag.

Through appropriate X/Y-axes rotations one can obtain the end-view perspective of the tetragonal cell shown above.

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

Add ‘Atomic %’ to CIGS Search Results Preferences

Add Atomic % to Selected Fields for Results Table

Enter New Search CriteriaBefore 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

Enter new search criteria (Page 2):

International Space Group (#122) is selected on the “Structures” page

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)

Enter new search criteria (Page 3):

• Verify chemistry criteria• Verify chemistry criteria• Click ‘Search’

Verify chemistry criteria and start search.

CIGS Search Results Including Atomic %

32 Resulting Entries4 are CuGaSe2 (2 experimental, 1 ICSD, 1 LPF)24 are CuInSe2 (1 experimental, 22 ICSD, 1 LPF)4 are Cu(In,Ga)Se2 (3 experimental, 1 LPF)

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

For the current application, we will using 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 ‘OK’ to draw Graph

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

a0

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.

Click ‘OK’ to display graph

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

c0

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 = -145.808 * a (Å) + 843.1761

* 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 = -41.6505 * c (Å) + 483.8731

* 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 = -145.808 a (Å) + 843.1761

• At % Ga = -41.6505 c (Å) + 483.8731

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

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

(www.icdd.com).