Abstract
Present-day multimedia strongly rely on rewritable phase-change optical memories. We demonstrate that, different from the current consensus, Ge2Sb2Te5, the material of choice in DVD-RAM, does not possess the rocksalt structure but more likely consists of well-defined rigid building blocks that are randomly oriented in space consistent with cubic symmetry. Laser-induced amorphization results in drastic shortening of covalent bonds and a decrease in the mean-square relative displacement, demonstrating a substantial increase in the degree of short-range ordering, in sharp contrast to the amorphization of typical covalently bonded solids. This novel order–disorder transition is due to an umbrella-flip of Ge atoms from an octahedral position into a tetrahedral position without rupture of strong covalent bonds. It is this unique two-state nature of the transformation that ensures fast DVD performance and repeatable switching over ten million cycles.
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Acknowledgements
The XAFS measurements were performed at beamlines 12C at the Photon Factory, Japan, and BL01B1 at SPring-8, Japan as parts of proposals 2001G332 and 2001B0099-NX, respectively. A.V.K. would like to thank A. S. Mishchenko for a useful discussion. A. I. F. acknowledges support by the US Department of Energy Grant No. DE-FG02- 03ER15477.
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Kolobov, A., Fons, P., Frenkel, A. et al. Understanding the phase-change mechanism of rewritable optical media. Nature Mater 3, 703–708 (2004). https://doi.org/10.1038/nmat1215
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DOI: https://doi.org/10.1038/nmat1215
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