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The Roles of the Ge-Te Core Network and the Sb-Te Pseudo Network During Rapid Nucleation-Dominated Crystallization of Amorphous Ge2Sb2Te5

Authors

  • Koji Ohara,

    1. Research & Utilization Division, Japan Synchrotron Radiation Research Institute (JASRI/SPring-8), 1-1-1 Kouto, Sayo, Sayo, Hyogo 679-5198, Japan
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  • László Temleitner,

    1. Research & Utilization Division, Japan Synchrotron Radiation Research Institute (JASRI/SPring-8), 1-1-1 Kouto, Sayo, Sayo, Hyogo 679-5198, Japan
    2. Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, H-1525 Budapest, P. O. Box 49, Hungary
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  • Kunihisa Sugimoto,

    1. Research & Utilization Division, Japan Synchrotron Radiation Research Institute (JASRI/SPring-8), 1-1-1 Kouto, Sayo, Sayo, Hyogo 679-5198, Japan
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  • Shinji Kohara,

    1. Research & Utilization Division, Japan Synchrotron Radiation Research Institute (JASRI/SPring-8), 1-1-1 Kouto, Sayo, Sayo, Hyogo 679-5198, Japan
    2. JST, CREST, 5 Sanbancho, Chiyoda-ku, Tokyo 102-0075, Japan
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  • Toshiyuki Matsunaga,

    1. JST, CREST, 5 Sanbancho, Chiyoda-ku, Tokyo 102-0075, Japan
    2. Materials Science and Analysis Technology Centre, Panasonic Corporation, 3-1-1 Yagumo-Nakamachi, Moriguchi, Osaka 570-8501, Japan
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  • László Pusztai,

    1. Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, H-1525 Budapest, P. O. Box 49, Hungary
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  • Masayoshi Itou,

    1. Research & Utilization Division, Japan Synchrotron Radiation Research Institute (JASRI/SPring-8), 1-1-1 Kouto, Sayo, Sayo, Hyogo 679-5198, Japan
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  • Hiroyuki Ohsumi,

    1. RIKEN/SPring-8, 1-1-1 Kouto, Sayo, Sayo, Hyogo 679-5148, Japan
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  • Rie Kojima,

    1. Digital & Network Technology Development Centre, Panasonic Corporation, Osaka, Japan
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  • Noboru Yamada,

    1. JST, CREST, 5 Sanbancho, Chiyoda-ku, Tokyo 102-0075, Japan
    2. Digital & Network Technology Development Centre, Panasonic Corporation, Osaka, Japan
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  • Takeshi Usuki,

    1. Department of Material and Biological Chemistry, Faculty of Science, Yamagata University, 1-4-12 Koshirakawa, Yamagata 990-8560, Japan
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  • Akihiko Fujiwara,

    1. Research & Utilization Division, Japan Synchrotron Radiation Research Institute (JASRI/SPring-8), 1-1-1 Kouto, Sayo, Sayo, Hyogo 679-5198, Japan
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  • Masaki Takata

    Corresponding author
    1. Research & Utilization Division, Japan Synchrotron Radiation Research Institute (JASRI/SPring-8), 1-1-1 Kouto, Sayo, Sayo, Hyogo 679-5198, Japan
    2. JST, CREST, 5 Sanbancho, Chiyoda-ku, Tokyo 102-0075, Japan
    3. RIKEN/SPring-8, 1-1-1 Kouto, Sayo, Sayo, Hyogo 679-5148, Japan
    4. Department of Advanced Materials Science, School of Frontier Science, The University of Tokyo, 5-1-5 Kashiwanoha, Chiba 277-8561, Japan
    • Research & Utilization Division, Japan Synchrotron Radiation Research Institute (JASRI/SPring-8), 1-1-1 Kouto, Sayo, Sayo, Hyogo 679-5198, Japan.
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Abstract

Ge2Sb2Te5 (GST) has demonstrated its outstanding importance among rapid phase-change (PC) materials, being applied for optical and electrical data storage for over three decades. The mechanism of nanosecond phase change in GST, which is vital for its application, has long been disputed: various, quite diverse scenarios have been proposed on the basis of various experimental and theoretical approaches. Nevertheless, one central question still remains unanswered: why is amorphous GST stable at room temperature for long time while it can rapidly transform to the crystalline phase at high temperature? Here it is revealed for the first time, by modelling the amorphous structure based on synchrotron radiation anomalous X-ray scattering data, that germanium and tellurium atoms form a “core” Ge-Te network with ring formation. It is also suggested that the Ge-Te network can stabilize the amorphous phase at room temperature and can persist in the crystalline phase. On the other hand, antimony does not contribute to ring formation but constitutes a “pseudo” network with tellurium, in which the characteristic Sb–Te distance is somewhat longer than the covalent Sb–Te bond distance. This suggests that the Sb-Te pseudo network may act as a precursor to forming critical nuclei during the crystallization process. The findings conclude that the Ge-Te core network is responsible for the outstanding stability and rapid phase change of the amorphous phase while the Sb-Te pseudo network is responsible for triggering critical nucleation.

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