Chalcogenide materials form the basis of CD and DVD technologies. But an identity crisis looms in the wider field: what role do atomic reconfiguration, electronic processes and ionic movement play in these materials? The chalcogens — the elements ingroup VI of the periodic table, particularly sulphur (S), selenium (Se) and tellurium (Te) — react with more electropositive elements, such as silver, to form chalcogenides. These are chameleon compounds: they can be crystalline or amorphous, metallic or semiconducting, and conductors of ions or electrons. Already important in optical storage discs and fibres, they are now being proposed as the basis for solid-state memory technologies. Two recent conferences — E*PCOS 05 in Cambridge*, UK, and Euromat2005 in Prague*, Czech Republic — have demonstrated that devices using chalcogenides hinge on thermal and dynamic phenomena involving electronic, atomic and ionic processes. The links between these phenomena are not fully established, so unsuspected technological opportunities may well lie in store.
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