A TRIPLE-CRYSTAL DIFFRACTOMETER FOR HIGH-ENERGY SYNCHROTRON-RADIATIONAT THE HASYLAB HIGH-FIELD WIGGLER BEAMLINE BW5

The triple-crystal diffractometer installed at HASYLAB beamline BW5 wi th a high-field wiggler of critical energy 27 keV for DORIS III, opera ted at 4.5 GeV electron energy, is described. Samples can be mounted i n large cryostats or furnaces normally used in neutron scattering expe riments. The instrument has been successfully applied to measure struc ture factors S(Q) in liquids and amorphous materials, to collect full data sets of highly accurate structure factors for charge-density work , to measure the spin component of the ground-state magnetization in t ransition-metal and rare-earth compounds, to study the diffuse scatter ing from stacking faults and dislocation loops in Si single crystals, and for the investigation of various aspects of structural phase trans itions: critical scattering in SrTiO3, oxygen order and stripe order i n high-T-c materials. A crossed-beam technique allows for local studie s of texture, internal strain and phase changes in the bulk of materia ls.