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Distortion-triggered loss of long-range order in solids with bonding energy hierarchy

Nature Chemistry volume 3, pages 311–316 (2011)Cite this article

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Abstract

An amorphous-to-crystal transition in phase-change materials like Ge–Sb–Te is widely used for data storage. The basic principle is to take advantage of the property contrast between the crystalline and amorphous states to encode information; amorphization is believed to be caused by melting the materials with an intense laser or electrical pulse and subsequently quenching the melt. Here, we demonstrate that distortions in the crystalline phase may trigger a collapse of long-range order, generating the amorphous phase without going through the liquid state. We further show that the principal change in optical properties occurs during the distortion of the still crystalline structure, upsetting yet another commonly held belief that attributes the change in properties to the loss of long-range order. Furthermore, our results suggest a way to lower energy consumption by condensing phase change inducing energy into shorter pulses or through the use of coherent phonon excitation.

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Figure 1: Difference in electron charge density for the simulated model of GeTe at 0 K and isolated pseudo-atoms.
Figure 2: Temperature variation of shorter Ge–Te and Sb–Te bond lengths in the metastable cubic phase of Ge2Sb2Te5 determined from an EXAFS analysis.
Figure 3: Configuration-coordinate diagram for the amorphization process of GeTe when the amorphous phase is generated by electronic excitation and subsequent lattice relaxation.

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Acknowledgements

Part of this work was supported by the New Energy and Industrial Technology Development Organization project ‘Research and Development of Nanoelectronic Device Technology’. The EXAFS measurements were performed as part of 2008B1249 proposal. M.K. acknowledges his Japan Society for the Promotion of Science Fellowship.

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Authors and Affiliations

  1. Nanodevice Innovation Research Center, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, 305-8562, Japan

    A.V. Kolobov, M. Krbal, P. Fons & J. Tominaga

  2. Japan Synchrotron Radiation Research Institute, 1-1-1 Koto, Sayo, 679-5198, Hyogo, Japan

    A.V. Kolobov, P. Fons & T. Uruga

Authors
  1. A.V. Kolobov
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Contributions

The project was conceived by A.V.K. as a result of discussions with J.T. and P.F. EXAFS measurements were done jointly by P.F., A.V.K. and T.U. The data analysis was performed by A.V.K. and P.F. DFT modelling was carried out by A.V.K., M.K. and P.F. The manuscript was written by A.V.K.; all authors commented on the manuscript.

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Correspondence to A.V. Kolobov.

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Kolobov, A., Krbal, M., Fons, P. et al. Distortion-triggered loss of long-range order in solids with bonding energy hierarchy. Nature Chem 3, 311–316 (2011). https://doi.org/10.1038/nchem.1007

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