Applications of high-resolution powder diffraction

A. N. Fitch

ESRF, BP220, F-38043 Grenoble Cedex, France.

Since May 1996 a dedicated high-resolution powder diffraction beam line has been in user service at the European Synchrotron Radiation Facility in Grenoble. The advantages for powder diffraction of this 6-GeV third-generation synchrotron-radiation source are the very high X-ray intensity, high angular and energy resolution, and access to a wide range of X-ray wavelengths, originally from 0.31 Å - 2.48 Å on the bending-magnet beam line BM16 [1,2], and more recently down to 0.21 Å with the beam line that has replaced BM16. This is built on insertion device ID31, and has been operational since June 2002. The new beam line is powered by three minigap undulators with a minimum magnetic gap of 11 mm which give a much enhanced X-ray flux as compared to the bending magnet.

The increase in X-ray intensity means that diffraction patterns can be measured more quickly and has opened up more opportunities for high-resolution powder diffraction measurements at ESRF, including the application of anisotropic thermal expansion to reduce the effects of peak overlap in diffraction profiles [3], thus allowing larger, more-complex crystal structures to be investigated, and also to follow the structural development of samples as a function of temperature or time, undergoing phase transitions or solid-state chemical reactions, or the evolution of microstructure. For materials-science applications, the availability of harder X-rays means that much thicker components can be investigated, such as measuring in residual strain, penetrating through 15 mm of Al or 5 mm of Ti (or their alloys).

The talk will give a brief overview of the high-resolution powder diffraction facilities available on ID31 at ESRF, and will illustrate their use with recent examples showing the solving of small-molecule crystal structures, the investigation of phase transitions, high-temperature annealing of ceramics, and the investigation of protein structures, a field pioneered by Von Dreele [4] and being taken up with enthusiasm at ESRF [5].

[1] A. N. Fitch, J. Res. Natl. Inst. Stand. Technol., 109 (2004) 133-142.

[2] J. L. Hodeau, P. Bordet, M. Anne, A. Prat, A. N. Fitch, E. Dooryhee, G. Vaughan and A. Freund, SPIE Proceedings, 3448 (1998) 353-361.

[3] K. Shankland, W. I. F. David and D. Sivia, J. Mater. Chem., 7 (1997) 569-572.

[4] R. B. Von Dreele, J. Appl. Cryst. 32 (1999) 1084-1089.

[5] I. Margiolaki and J. P Wright, to be published.