X-ray Diffraction Methods Subcommittee Minutes

X-ray Diffraction Methods Subcommittee
21 March 2007
ICDD Headquarters 
Chairman - D. Balzar

Call to Order
Attendance Sheet on record at ICDD

Appointment of Minutes Secretary
Terry Kahmer

Approval of Minutes from March 2006 Meeting
Motions at last meeting – there were no motions from the previous meeting.

  • The Board would like us to be able to construct two-dimensional diffraction pattern from a PDF. We would first need to correct for systematic errors and then create two-dimensional data.
  • We decided to run a round robin on a NIST SRM 1976 plate.

Second Task Group – look at Powder CIF and recommend to vendors to include an ability to save raw data in the Powder CIF format for publication and data visualization.

Minutes approved.

Board of Directors’ Liaison Report
P. Scardi was not at the last Board Meeting and did not have feedback

New Business
A.) Report by the Task Group “1-D and 2-D Detectors” – B. He

Bob discussed Phase ID with Linear/Area Detectors.

  • Optics and geometry
  • Defocusing and resolution
  • Preferred orientation and relative intensity

These detectors need speed, high sensitivity and angular coverage in gamma direction –
good for pharmaceutical groups. Need to develop something practical in order to build a
link to the database. PPXRD – this was a topic of discussion.

  • Soller slits can be used for 0-D an 1-D – necessary on the diffracted-beam side and the incident-beam side
  • No Soller slits can be used for 2-D detectors on the diffracted-beam side.
  • Summary – many advantages of 2-D detectors
  • Discrepancy between diffraction pattern from conventional Bragg-Brentano system and diffraction with 1-D and 2-D can be analyzed and corrected
  • Instrument parameters for system should be investigated

Please see Bob’s report (PDF) for details of this discussion.

B.) Preliminary results on the NIST SRM 1976 – D. Balzar

Davor discussed how to go from the 2-D pattern to the 1-D pattern by integrating over Chi angle.
Collapsed patterns – differences in 2 theta angles is obvious. Correct for the texture affect in Rietveld. Refine positions. When data is collapsed it is difficult to correct in Rietveld.

Should we continue with SRM 1976? It would probably be better to work with a finergrain powder.

T. Blanton - One of the next steps ICDD is going to take is the use of the PDF-3 data.

Please see Davor’s report (PDF) for details of this discussion.

C.) Report by the Task Group – Raw Data File Format - P. Zavalij

Peter will submit a list of experimental parameters that should be recommended to instrument vendors to be included in the Powder CIF format. Request CIF files from authors of articles published in Powder Diffraction.

ICDD should ask instrument vendors to allow for the minimal number of parameters to be recorded in the Powder CIF format and this capability to be included in their software.
The Task Group will create a list.

Other Matters