Non-Ambient Diffraction Subcommittee Agenda and Minutes

ICDD Non-Ambient Diffraction Subcommittee
Wednesday, 17 March 2004

Minutes for the Non-Ambient Task Group meeting March 2004

Minutes from 2003 were accepted.

There were no comments from the Board of Directors’ liaison.

Daniel Louer gave a presentation on the importance of the zero point position in refinement of data. He illustrated his presentation with 50-0289 (potassium yttrium oxalate hydrate). He showed that on correct refinement of the data with a zero point correction that the cell dimensions changed in the third place of decimals by more than 0.005, the refinement errors dropped by a factor of two, and other indicators such as the Figure of Merit also increased. Refining the data within AIDS did not give the same improvement. Changing the optics had little effects on the improvement or lack of it. Addition of an internal standard did not improve the fits.

A motion was passed asking that AIDS be modified to add a zero point error, or that another way be found to accomplish the same result.

Scott Misture gave a presentation on the need for standards for the calibration of high temperature equipment. He gave a general idea of the requirements for these standards, which are different from those used to standardize normal diffractometers, though some may also suitable as a check on the diffractometer alignment. These standards need to be easy to use. Scott had evaluated a number of standards and the work is almost complete. His list of things to do included making more than one diffraction pattern from each sample, the need to monitor the sample atmosphere, etc., and he asked for any other suggestions from the members. Questions included: what range of temperatures are being covered; was the temperature uniform throughout the whole of the sample; and did the rate of heating change the results? The results would allow a user to get an idea of what was possible with their equipment.