David Keen

Abstract:

We describe a model-independent approach for the extraction of detailed lattice dynamics information from neutron powder diffraction data, based on a statistical analysis of atomistic configurations generated using reverse Monte Carlo structural refinement. Phonon dispersion curves for MgO extracted in this way are shown to reproduce many of the important features found in those determined independently using neutron triple-axis spectroscopy. By means of molecular dynamics simulations, we quantify the extent to which the diffraction data are sensitive to lattice dynamics in this system.

Abstract:

The newly installed, much-improved single-crystal diffractometer, SXD at ISIS, received its first neutrons in May 2001. The detector area now covers slightly more than 2π steradians in solid angle. High-pressure research using single crystals is becoming an increasingly important part of the user programme and thus, efforts are underway to provide a new sample environment as well as state-of-the-art data analysis software to open new opportunities in high-pressure single-crystal diffraction. Recently, a new gas-pressure cell with pressures up to 0.5 GPa has been successfully commissioned. First results from a series of molecular compounds containing short hydrogen bonds are presented. More recent developments at ISIS include a sapphire anvil cell for pressures up to 8GPa, which has been successfully tested on the GEM powder diffractometer. It will shortly also be tested on SXD, as well as a modified Paris-Edinburgh cell to take 5-15 mm³ single-crystal samples to pressures of more than 10GPa.