SPring-8, the large synchrotron radiation facility

An international joint research team examined the atomic and electronic structures of a non-glass-forming liquid and clarified, for the first time in the world, that the liquid is extremely ‘fragile’ because of its highly disordered atomic and electronic structures and hence cannot form a glass. The team consisted of researchers from JASRI, JAIST, Tampere University of Technology in Finland, JAXA, Gakushuin University, the University of Tokyo, and Yamagata University. These achievements were obtained through experiments using high-brilliance high-energy synchrotron radiation X-rays at SPring-8^*1 and large-scale simulation using supercomputers at the IT Center for Science Ltd., in Finland, Forschungszentrum Jülich in Germany, and at JAIST.

In general, glass is fabricated by melting a raw material at a high temperature and rapidly cooling the melt^*2(liquid); however, not all materials can form a glass. The existence of a difference between the atomic structure of glass-forming liquids and that of non-glass-forming liquids has long been pointed out but has been difficult to clarify at the atomistic and electronic levels. Thus, the difference has remained a major mystery in the structural science of glass even in the 21st century.

To solve the mystery, the international joint research team focused on zirconium dioxide (ZrO₂), a non-glass-forming material, and analyzed the structure of its liquid. ZrO₂ has a particularly high melting point (2715 °C) among oxides and is difficult to melt; hence, conventional structure analysis methods cannot be used for ZrO₂. In this study, the research team developed an instrument by combining the containerless gas levitation method^*3 with the SPring-8 high-energy X-ray diffraction^*4beamline and succeeded in the structural analysis of a ZrO₂ liquid at an ultrahigh temperature of 2800 °C. By conducting large-scale theoretical calculations using supercomputers, the research team found that a specific peak commonly observed for glass-forming liquids does not appear in the diffraction pattern of the ZrO₂ liquid. It was also found that the atomic configuration of structural units comprising zirconium and oxygen atoms becomes disordered in the liquid, causing electrons to move easily and that the lifetime of Zr-O bonds is only ~200 fs (1 fs = 10⁻¹⁵ s). The research team concluded that non-glass-forming liquids are disordered and so-called extremely ‘fragile’ liquids^*5; namely, ordering is required for glass-forming liquids.

The discovery in this study relates the atomic and electronic structures of liquids with their glass-forming ability and solves one of the major mysteries in the structural science of glass. In addition, the atomistic- and electronic-level understanding of the liquid obtained in this study will become a key finding leading to the development of innovative materials such as ultrahigh-refractive-index glass and novel ceramics.

The research team was led by Shinji Kohara, a senior scientist at JASRI, and the achievements of this study were published online in the British scientific journal Nature Communications on 18 December 2014.

Publication:
Article title："Atomic and electronic structures of an extremely fragile liquid"
Authors:  S. Kohara, J. Akola, L. Patrikeev, M. Ropo, K. Ohara, M. Itou, A. Fujiwara, J. Yahiro, J. T. Okada, T. Ishikawa, A. Mizuno, A. Masuno, Y. Watanabe, T. Usuki
          
Journal title：Nature Communications
Publication date: 18 December 2014 (JST)
doi: 10.1038/ncomms6892