HIGH-PRESSURE STRUCTURAL STUDIES OF LANTHANIDES. M.I. McMahon and R.J. Nelmes. Department of Physics and Astronomy, The University of Edinburgh, Edinburgh, EH9 3JZ, U.K.

The high-pressure behaviour of the elemental lanthanides still continues to attract considerable attention. Under pressure, the regular tri-valent lanthanides exhibit a series of phase transitions to simple close-packed structures, before undergoing further transitions to the so-called 'distorted-fcc' phase, and then to still more complex structures. The two di-valent lanthanides, Eu and Yb, however, exhibit different behaviour, as does Ce. In recent years, diffraction studies utilising improved experimental techniques have re-examined many of the complex high-pressure structures observed in all these systems, and have resolved many of the outstanding structural problems. Such studies have also cast new light on the physical basis of the observed behaviour. These recent advances will be reviewed, and new structural studies of Ce, Pr and Sm made at SRS Daresbury using angle-dispersive techniques and an image-plate area detector will be presented.