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Modulated structure of solid iodine during its molecular dissociation under high pressure


The application of pressure to solid iodine forces the molecules in the crystal to approach each other until intermolecular distances become comparable to the bond length of iodine; at this point, the molecules lose their identity and are essentially dissociated. According to room-temperature X-ray diffraction studies1, this process involves direct dissociation of iodine molecules at about 21 GPa, whereas spectroscopic observations2,3 have identified intermediate molecular phases at pressures ranging from 15 to 30 GPa. Here we present quasi-hydrostatic powder X-ray diffraction measurements that clearly reveal an intermediate phase during the pressure-induced dissociation of solid iodine. We find that, similar to the behaviour seen in uranium4, the structure of this intermediate phase is incommensurately modulated, with the nearest interatomic distances continuously distributed over the range 2.86–3.11 Å. The shortest of these interatomic distances falls between the bond length of iodine in the molecular crystal (2.75 Å) and the nearest interatomic distance in the fully dissociated monatomic crystal (2.89 Å), implying that the intermediate phase is a transient state during molecular dissociation. We expect that further measurements at different temperatures will help to elucidate the origin and stability of the incommensurate structure, which might lead to a better understanding of the molecular-level mechanism of the pressure-induced dissociation seen here and in the molecular crystals of hydrogen5, oxygen6 and nitrogen7.

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Figure 1: Powder X-ray diffraction pattern of the intermediate phase V of iodine.
Figure 2: Crystal structure of iodine for phases I (19.1 GPa), V (24.6 GPa) and II (30.4 GPa).
Figure 3: Variation of the interatomic distances of phase V at 24.6 GPa as a function of supplementary coordinate t′.
Figure 4: Distribution of the near interatomic distances for phases I (19.1 GPa), V (24.6 GPa) and II (30.4 GPa).


  1. Takemura, K., Minomura, S., Shimomura, O. & Fujii, Y. Observation of molecular dissociation of iodine at high pressure by x-ray diffraction. Phys. Rev. Lett. 45, 1881–1884 (1980)

    Article  ADS  CAS  Google Scholar 

  2. Pasternak, M., Farrell, J. N. & Taylor, R. D. Metallization and structural transformation of iodine under pressure: A microscopic view. Phys. Rev. Lett. 58, 575–578 (1987)

    Article  ADS  CAS  Google Scholar 

  3. Olijnyk, H., Li, W. & Wokaun, A. High-pressure studies of solid iodine by Raman spectroscopy. Phys. Rev. B 50, 712–716 (1994)

    Article  ADS  CAS  Google Scholar 

  4. van Smaalen, S. & George, T. F. Determination of the incommensurately modulated structure of α-uranium below 37 K. Phys. Rev. B 35, 7939–7951 (1987)

    Article  ADS  CAS  Google Scholar 

  5. Mao, H.-K. & Hemley, R. J. Ultrahigh-pressure transitions in solid hydrogen. Rev. Mod. Phys. 66, 671–692 (1994)

    Article  ADS  CAS  Google Scholar 

  6. Weck, G., Loubeyre, P. & LeToullec, R. Observation of structural transformations in metal oxygen. Phys. Rev. Lett. 88, 035504 (2002)

    Article  ADS  CAS  Google Scholar 

  7. Eremets, M. I., Hemley, R. J., Mao, H.-K. & Gregoryanz, E. Semiconducting non-molecular nitrogen up to 240 GPa and its low-pressure stability. Nature 411, 170–174 (2001)

    Article  ADS  CAS  Google Scholar 

  8. Shimomura, O. et al. Structure analysis of high-pressure metallic state of iodine. Phys. Rev. B 18, 715–719 (1978)

    Article  ADS  CAS  Google Scholar 

  9. Takemura, K., Minomura, S., Shimomura, O., Fujii, Y. & Axe, J. D. Structural aspects of solid iodine associated with metallization and molecular dissociation under high pressure. Phys. Rev. B 26, 998–1004 (1982)

    Article  ADS  CAS  Google Scholar 

  10. Riggleman, B. M. & Drickamer, H. G. Approach to the metallic state as obtained from optical and electrical measurements. J. Chem. Phys. 38, 2721–2724 (1963)

    Article  ADS  CAS  Google Scholar 

  11. Sakai, N., Takemura, K. & Tsuji, K. Electrical properties of high-pressure metallic modification of iodine. J. Phys. Soc. Jpn 51, 1811–1816 (1982)

    Article  ADS  CAS  Google Scholar 

  12. Fujii, Y., Hase, K., Ohishi, Y., Hamaya, N. & Onodera, A. Pressure-induced monatomic tetragonal phase of metallic iodine. Solid State Commun. 59, 85–89 (1986)

    Article  ADS  CAS  Google Scholar 

  13. Fujii, Y. et al. Pressure-induced face-centered-cubic phase of monatomic metallic iodine. Phys. Rev. Lett. 58, 796–799 (1987)

    Article  ADS  CAS  Google Scholar 

  14. Reichlin, R. et al. Optical, x-ray, and band-structure studies of iodine at pressures of several megabars. Phys. Rev. B 49, 3725–3733 (1994)

    Article  ADS  CAS  Google Scholar 

  15. Takemura, K. Evaluation of the hydrostaticity of a helium-pressure medium with powder x-ray diffraction techniques. J. Appl. Phys. 89, 662–668 (2001)

    Article  ADS  CAS  Google Scholar 

  16. Yamamoto, A. et al. Rietveld analysis of the modulated structure in the superconducting oxide Bi2(Sr,Ca)3Cu2O8+x. Phys. Rev. B 42, 4228–4239 (1990)

    Article  ADS  CAS  Google Scholar 

  17. Wilson, A. J. C. & Prince, E. (eds) International Tables for Crystallography Vol. C, 2nd edn, 914–926 (Kluwer Academic, Dordrecht, 1999)

  18. Luty, T. & Raich, J. C. Molecular to atomic transformation in solid iodine under high pressure. Can. J. Chem. 66, 812–818 (1988)

    Article  CAS  Google Scholar 

  19. Nelmes, R. J., Allan, D. R., McMahon, M. I. & Belmonte, S. A. Self-hosting incommensurate structure of barium IV. Phys. Rev. Lett. 83, 4081–4084 (1999)

    Article  ADS  CAS  Google Scholar 

  20. Fujihisa, H., Fujii, Y., Takemura, K. & Shimomura, O. Structural aspects of dense solid halogens under high pressure studied by x-ray diffraction—molecular dissociation and metallization. J. Phys. Chem. Solids 56, 1439–1444 (1995)

    Article  ADS  CAS  Google Scholar 

  21. Fujii, Y. et al. Evidence for molecular dissociation in bromine near 80 GPa. Phys. Rev. Lett. 63, 536–539 (1989)

    Article  ADS  CAS  Google Scholar 

  22. Takemura, K., Sahu, P. Ch, Kunii, Y. & Toma, Y. Versatile gas-loading system for diamond-anvil cells. Rev. Sci. Instrum. 72, 3873–3876 (2001)

    Article  Google Scholar 

  23. Zha, C.-S., Mao, H.-K. & Hemley, R. J. Elasticity of MgO and a primary pressure scale to 55 GPa. Proc. Natl Acad. Sci. USA 97, 13494–13499 (2000)

    Article  ADS  CAS  Google Scholar 

  24. Shimomura, O. et al. Application of an imaging plate to high-pressure X-ray study with a diamond anvil cell. Rev. Sci. Instrum. 63, 967–973 (1992)

    Article  ADS  Google Scholar 

  25. Takemura, K. & Nakano, S. Performance of a synthetic diamond-backing plate for the diamond-anvil cell at ultrahigh pressures. Rev. Sci. Instrum. 74, 3017–3020 (2003)

    Article  Google Scholar 

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We thank A. Yamamoto for the use of his programs for the analysis of the modulated structure, and O. Mishima for comments. The synchrotron radiation experiments were performed with the approval of the Photon Factory.

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Correspondence to Takemura Kenichi.

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Kenichi, T., Kyoko, S., Hiroshi, F. et al. Modulated structure of solid iodine during its molecular dissociation under high pressure. Nature 423, 971–974 (2003).

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