1 SHIMIZU Group ONODA Suzue Metallization and molecular dissociation of SnI 4 under pressure 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 SnI 4 ・ previous work ・ pressure effect ■ Experimental results and discussion ■ Summary

3 Structure of SnI 4 at ambient pressure Sn I M. Pasternak, R. D. Taylor, Phys. Rev. B. 37, 8130 (1988) ■ tetrahedral molecule ■ crystal structure : cubic (space group Pa3) ■ insulator

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

5 Previous work ■ Pressure dependence of electrical resistivity (at room temperature) Y. Fujii et al., J. Phys. C: Solid State Phys., 18, 789(1985) SnI 4 becomes metallic above 15 GPa ・ 5 ～ 10 GPa ・・・ electrical resistivity drastic decrease ・ around 10 GPa ・・・ the change in slope appear

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

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

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

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

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

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 ). amorphous fcc ■ X-ray diffraction study (high pressure region) CP- Ⅰ＋ CP- Ⅱ

12 Discussion The phase diagram of SnI 4 electrical property pressure 0 GPa 7.2 ～ metal insulator molecular crystal non-molecular crystal structure metal fcc cubic amorphous phase Ⅱ 153

13 Summary ■ From temperature dependence of the electrical resistance, metallization occurs around 20 GPa. ■ From X-ray diffraction study ・・・ Molecular dissociation pressure is not uncertain. SnI 4 recrystallize into non-molecular (fcc) phase at 61 GPa. ■ SnI 4 show metallization in amorphous state.