Dresden 2014 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 20: Symposium SYCM: Crystallography in materials science

HL 20.1: Hauptvortrag

Montag, 31. März 2014, 15:00–15:30, HSZ 02

Complexity on Compression: The Crystallography of High-Density Matter — •Malcolm McMahon — School of Physics and Astronomy, The University of Edinburgh, Edinburgh, UK.

The crystal structure of iron was determined at *normal* conditions as long ago as 1917. But what is the structure of iron within *Super-Earth* exoplanets where core conditions approach 10 million atmospheres (1 TPa) and 10,000 K, and where carbon exists as either diamond, or as an exotic metallic form.

Until the early 1990s, the consensus was that at high pressures, all materials would become metallic, and assume high-symmetry, close-packed crystal structures. But the advent of modern crystallographic methods on synchrotron sources in the early 1990s revealed completely different behavior: even the simplest materials underwent phase transition to complex, frequently incommensurate, forms, while metals became semiconductors or insulators. This complexity is thought to arise from the constraints placed on the electronic wave functions due to the Pauli exclusion principle, the need to orthogonalise the wave functions of both core and valence electrons, and the reduction in the available interstitial space at high compression

In this talk I will present results from recent diffraction studies of elemental metallic systems showing some of the extreme complexity observed at high pressures. I will also look at the new opportunities in extreme conditions crystallography offered by x-ray lasers such as the LCLS in the Stanford, and XFEL in Hamburg.

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