1. Electrical conduction property of solid iodine in the molecular phase Shimizu Group Yu TANAKA

2. Contents ・ Introduction - pressure effect - structure of molecular crystal I 2 - previous work ・ Experiment ・ Results and Discussions ・ Summary

3. pressurization monatomic metal molecular dissociation ( 分子解離 ) Pressure effect ― diatomic molecular crystal ― Molecule Insulator covalent bond

4. Crystal structure of I 2 at ambient temperature and pressure orthorhombic crystal (space group ： Cmca) Insulator Molecules are layered to a-axis and form crystal. B. Albert, K. Schmit, Z. Anorg. Allg. Chem. 627, 809 (2001). diatomic molecule ( 二原子分子 )

5. mesophase (Phase Ⅴ ) Crystal structure Molecular (phase Ⅰ )monatomic (Phase Ⅱ ) (bct) 0 Pressure [GPa] 28 25 Measure by X-ray diffraction. molecule pressurization monatomic molecular dissociation ( 分子解離 ) Crystal structure of iodine under pressure

6. The distribution of atomic distance coordination number atomic distance ( Å ) molecular Phase Ⅰ mesophase Phase Ⅴ monatomic Phase Ⅱ Atomic distance is continuously distributed in mesophase. K. Takemura, K. Sato, H. Fujihisa and M. Onoda, Nature 423, 971 (2003).

7. Previous work (Temperature dependence of electrical resistance) K. Shimizu, N. Tamitani, N. Takeshita, M, Ishizuka, K. Amaya and S Endo, J. Phys.Soc. Jpn. 61, 3853 (1992). N. Sakai, K. Takemura and K. Tsuji, J. Phys.Soc. Jpn. 51, 1811 (1982). Under pressure, iodine becomes metal and superconductor.

8. mesophase (Phase Ⅴ ) 0 Pressure [GPa] 28 25 K. Shimizu et al., J. Phys. Soc. Jpn., 61, 3853 (1992). Crystal structure Molecular (phase Ⅰ ) monatomic (Phase Ⅱ ) (fcc) insulator metal Electrical conduction property superconductor Not clear ! Pressure phase diagram

9. Experiment for high pressure Setting Diamond Anvil Electrode Pt Deposited Electrode Ti + Pt Sample Insulator Almina Gasket SUS310 S ● [Side View] [Top View] Sample Electrical resistance measurement 4 probe method Pressure determination ruby-fluorescence Pressure cell Diamond Anvil Cell (DAC) 300 μm 50 μm 100 μm

10. Experiment for low temperature Pulse tube refrigerator Imaging plate X-ray DAC We can measure electrical resistance and X-ray diffraction at the same time under low temperature and high pressure. Little vibration Gas-pressure cable

11. In phase Ⅴ Metallization in phase Ⅴ Phase Ⅴ Metal ! 6 K 100 K 200 K 300 K Intensity (arb.units)

12. Pressure boundary of phase Ⅰ and phase Ⅴ Phase Ⅴ We can see the peaks of only phase Ⅰ from 10 GPa to 20 GPa. We can see the peaks of both of phase Ⅰ and phase Ⅴ at 28~29 GPa. XRD at room temperature Phase Ⅰ

13. 15 GPa 20 GPa At 15 GPa and 20 GPa, I 2 is metal. Temperature dependence of electrical resistance Metallization in phase Ⅰ XRD at each temperature

14. Summary Metallization in phase Ⅰ and phase Ⅴ. Molecular crystal I 2 become metal not because the structure transition. mesophase (Phase Ⅴ ) 0Pressure [GPa] 28 25 K. Shimizu et al., J. Phys. Soc. Jpn., 61, 3853 (1992). Crystal structure molecular (phase Ⅰ ) monatomic (phase Ⅱ ) (bct) Electrical conduction property insulatormetal 15 superconductor