Materials science plays a major role at the ESRF and spans a wide range of applications from chemical bonding, electronic applications, and novel synthesis to studies of grain growth and dynamic evolution of materials properties. The trend in materials science research at the ESRF is that micro focussing, time-resolved studies in situ and the application of combinations of techniques are on the rise. In order to illustrate these trends we have chosen a few examples in the categories: Materials and their Properties, Growth and Dynamics of Metals and Alloys, and Extreme Conditions.

The change of structure of molecules during chemical reactions is of fundamental importance for the understanding of reaction pathways. These often very fast processes can now be studied on the picosecond timescale by X-ray diffraction as illustrated by a study of photo dissociation of C2H2I2 using pulsed picosecond lasers and X-ray beams (100 ps) showing the dissociation of the molecules including the time evolution of metastable complexes.

Porous solids are strategic materials for catalysis, separation and storage of gases and many other applications. One example illustrates the possibility of designing new porous materials by a combination of computer design and X-ray powder analysis with an example of the production of a new material from 1,3,5-benzene tricarboxylate and chromium trimers. A second example shows a combined X-ray and spectroscopy study of the stabilisation of Ag and Cu carbonyl clusters in the zeolitic nanochannels of the well-known zeolite ZSM-5.

Thin films are important for the production of superconducting and electronic materials. The control of the deposition procedure is essential for optimal performance of these materials. In one study the in situ evaluation of the deposition of superconducting Yba2Cu3O7 films by pulsed laser deposition was followed by X-ray diffraction at high temperatures. The real-time evolution films of InO3:Sn, an n-type semiconductor, was studied by X-ray diffraction. Films of this material are used in opto-electronics, solar cells and in liquid crystal displays. Annealing is known to improve the electrical and optical properties. The study correlates the changes of the film properties with its structure during annealing in vacuum.

Powder diffraction is becoming a very useful tool for a variety of studies at synchrotron facilities due to the excellent resolution. A novel application is presented to illustrate the use of powder diffraction even for very large structures such as proteins in the temperature dependence study of the hexagonal turkey egg-white lysozyme.

The properties of metals and alloys can be improved by addition of trace elements and by mechanical processing or annealing. The mechanisms for the improvements are, however, often not known in details. Four studies of these phenomena are given. In a small-angle

X-ray scattering experiment, the dynamic precipitation in an Al-Zn-Mg-Cu alloy was studied during quenching. It was shown that the precipitation process is much faster during straining of the materials as compared to static ageing. The 3D-XRD microscope at ID11 has been used to study the individual grain growth during annealing of Al single crystals. A movie of the grain growths of several grains in three-dimensions was produced. The third example presents a novel method to study stress and strain fields in amorphous materials. Previously only crystals could be characterised by diffraction, but now, by employing high-energy X-ray correlation functions, the strain tensors in a bulk metallic glass was determined. The dynamics of amorphous materials can also be followed using the coherence of the X-ray beam. The fourth example shows how the intensity fluctuations in the speckle pattern can be analysed by autocorrelation functions. In this example, X-ray photon autocorrelation spectroscopy was used to investigate the antiphase domain dynamics in the intermetallic phase Co60Ga40.

High-pressure studies are gaining in importance for a number of areas of materials science research. The new applications of laser heating have now opened up the field for studies both at high pressures and high temperature (> 5000 K). In one study the matter of electronic topological transitions due to distortions of the electronic band structure was studied in osmium by angle-dispersive X-ray diffraction. During the study of the equation of state it was found that the Fermi surface of osmium passes through a topologic singularity at 25 GPa. A second study deals with the synthesis of nitrogen. Nitrogen usually consists of dimers with strong triple bonding. In a synthesis above 2000 K and pressures above 110 GPa, a theoretically predicted cubic phase, polymeric nitrogen, was found as evidenced by a combination of X-ray diffraction and Raman techniques. The final example deals with the boundary between the earth's mantle and the core. In this region one notices a large contrast in the properties across the region. The interaction between iron and silica (SiO2) was studied in an electrically and laser heated diamond anvil cell at pressures up to 140 GPa and temperatures over 3500°C. It was shown that iron and SiO2 do not react at high pressures and iron-silica alloys dissociate into almost pure iron and a CsCl-structured FeSi compound. The existence of the FeSi at the base of the Earth's lower mantle could explain the anomalously high electrical conductivity of this region and provide a key to the understanding why the amplitude of the Earth's nutation is out-of-phase with tidal forces.

Å. Kvick