INTRODUCTION TO THE CIF POWDER DEFINITIONS. Brian H. Toby, Reactor Radiation Division, National Institute of Standards and Technology, Gaithersburg MD 20899 USA.

Definitions have been added to the CIF dictionary to accomodate powder diffraction measurements and results. These extensions support data from nearly all types of instruments, including energy-dispersive, multidetector and conventional x-ray and neutron diffractometers and cameras. While CIF was initially designed to document a crystallographic determination, the powder diffraction definitions allow for complete documentation of an experiment, as is required to exchange or archive raw data. In contrast to conventional single crystal CIFs, there are many circumstances where several CIF blocks will be needed for description of a single experiment or structure determination, so the powder CIF dictionary provides for pointers between CIF blocks and files.