Neutron Powder Diffraction with High-Flux Isotope Reactor

Recent developments in instrumentation at the High-Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory, Oak Ridge, TN, USA have brought on-line a high resolution neutron powder diffractometer, which has been operating since 1991. The technical and scientific team have brought this instrumentation from the conceptual design to a user-friendly and routinely operating research tool. Upgrades to hardware and software are ongoing; however, this instrument has already demonstrated itself as an important addition to the expanding repertoire of experimental tools available at the HFIR.

Presently, the monochromator is a (115) Ge crystal, which can be oriented to select incident wavelengths of 1.0, 1.4, 2.2, and 4.2 Å. The diffractometer control program is user-friendly and operates presently on a VAX computer which is part of a network. A variety of special environment devices are available to provide sample temperatures between 4.5 and 1900 K. A clamp-type high-pressure cell can provide pressures up to 3 GPa.

Local utility programs provide for instrumental calibration corrections, statistical check for noisy data points, individual detector displays, peak fitting, pattern addition, pattern archiving, and retrieval. A full range of software for Rietveld structure analysis (GSAS, RIETAN, LHPM), unit-cell refinement and various crystallographic computations are also available.

Recent experiments performed on this instrument have included studies of the structures of the cuprate superconductors both under high pressure and ambient pressure, phase transformations, crystal structure-property relationships in oxides, and structure refinements of other interesting oxides.

The HFIR is a user-facility and available for qualified experiments at no cost. Proprietary work can be done, but on a fee basis. As the new custodian of the HB4 powder diffractometer, I invite you to consider the use of neutron powder diffraction at the HFIR. Contact me with your questions and proposals: B. C. Chakoumakos, Solid State Div., Oak Ridge National Lab., Oak Ridge, TN 37831-6393, USA. Tel: 615-574-5235, FAX: 615-574-6286, e-mail: (Bitnet) kou@ornlstc, (Telnet) kou@solid.ssd.ornl.gov.