Metallization and molecular dissociation of SnI 4 under pressure

1. Metallization and molecular dissociation of SnI4 under pressure SHIMIZUGroup ONODASuzue Ref: A.L. Chen, P.Y. Yu, M.P. Pasternak, Phys. Rev. B. 44, 2883 (1991) N. Hamaya et al., Phys. Rev. Lett. 79, 4597 (1997)

2. Contents ■ Introduction ・ structure of molecular crystal SnI4 ・ previous work ・ pressure effect ■Experimental results and discussion ■Summary

3. ■tetrahedral molecule ■ crystal structure :cubic (space group Pa3) ■ insulator Sn I Structure of SnI4 at ambient pressure M. Pasternak, R. D. Taylor, Phys. Rev. B. 37, 8130 (1988)

4. Y. Fujii et al., J. Phys. C: Solid State Phys., 18, 789(1985) Previous work ■Pressure-induced crystal-to-amorphous transition (by X-ray diffraction) amorphous gradually cubic

5. Previous work ■Pressure dependence of electrical resistivity (at room temperature) ・5～10 GPa・・・ electrical resistivity drastic decrease ・around 10 GPa・・・ the change in slope appear SnI4 becomes metallic above 15 GPa Y. Fujii et al., J. Phys. C: Solid State Phys., 18, 789(1985)

6. covalent bond pressure molecular metal / insulator van der Waals force pressure molecular crystal insulator molecular dissociation （分子解離） monatomic crystal Pressure effect ― diatomic molecular crystal ―

7. To what extent does the amorphous state exist? amorphous cubic pressure 33 GPa 0 10 What is the metallization pressure? Motivation crystal structure by X-ray diffraction electrical property metal? insulator ■ clarify the structure at high pressure (by X-ray diffraction experiment) ■ determination of the metallization pressure (by measurement of electrical resistance)

8. increasing pressure decreasing Experimental result 1 ■ Measurement of electrical resistance Pressure dependence of electrical resistance (at room temperature) ・ The resistance first decreases rapidly, with increasing pressure. ・ The change in slope occurs at 12±1 GPa. consistent with previous work

9. ・ Arrhenius' equation E: carrier activation energy E= 0 ⇒ metallization can be defined Temperature dependence of electrical resistance ・ Above 12 GPa・・・ T dependence of R is metallic 11.6GPa 12.8GPa

10. Experimental result 2 ■Synchrotron X-ray diffraction study ・(a) and (b) ・・・typical diffraction patterns for cubic (crystal phaseⅠ) CP-Ⅰ＋CP-Ⅱ ・ new peaks appeared at 7.2 GPa ・(c) and (d)・・・two phases coexist CP-Ⅰ

11. ・Diffraction peaks in (a) and (b) were slightly broadened. ・Between 24 and 55 GPa, diffraction pattern of amorphous were observed. ・At 61 GPa, the amorphous state transformed into a fcc (crystalline phase CP-Ⅲ) . ■X-ray diffraction study (high pressure region) fcc amorphous CP-Ⅰ＋CP-Ⅱ

12. Discussion The phase diagram of SnI4 non-molecular crystal molecular crystal phase Ⅱ crystal structure amorphous cubic fcc metal electrical property insulator metal 61 ～20 7.2 153 pressure 0 GPa

13. Summary ■From temperature dependence of the electrical resistance, metallization occurs around 20 GPa. ■From X-ray diffraction study・・・ Molecular dissociation pressure is notuncertain. SnI4recrystallize into non-molecular (fcc) phase at 61 GPa. ■SnI4 show metallization in amorphous state.