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,

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　　　 SHIMIZU 　 Group　　　　　　　　 ONODA　 Suzue

Metallization and molecular dissociation of SnI4 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)

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Contents

■ Introduction ・ structure of molecular crystal SnI4

・ previous work

・ pressure effect

■ Experimental results and discussion

■ Summary

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Structure of SnI4 at ambient pressure

SnI

M. Pasternak, R. D. Taylor, Phys. Rev. B. 37, 8130 (1988)

■ tetrahedral molecule

■ crystal structure : cubic

(space group Pa3)

■ insulator

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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

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Previous work■ Pressure dependence of electrical resistivity (at room temperature)

Y. Fujii et al., J. Phys. C: Solid State Phys., 18, 789(1985)

SnI4 becomes metallic above 15 GPa

・ 5 ～ 10 GPa ・・・ electrical resistivity drastic decrease

・ around 10 GPa ・・・ the change in slope appear

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Pressure effect

van der Waals force

covalent bond

monatomic crystal

molecular dissociation （分子解離）

pressure

pressure

molecular crystal insulator

molecular metal / insulator

― diatomic molecular crystal ―

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■ determination of the metallization pressure (by measurement of electrical resistance)

■ clarify the structure at high pressure (by X-ray diffraction experiment)

Motivation

pressure 0 10 33 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?

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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 pressuredecreasing

consistent with previous work

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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

)TkEexp(R BE: carrier activation energy

CTk

1ERln

B

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Experimental result 2■ Synchrotron X-ray diffraction study

・ (a) and (b) ・・・ typical diffraction patterns for cubic 　　　　　 (crystal phaseⅠ)

・ new peaks appeared at 7.2 GPa

CP-Ⅰ

CP-Ⅰ＋ CP-Ⅱ

・ (c) and (d) ・・・ two phases coexist

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・ 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

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DiscussionThe phase diagram of SnI4

electrical property

pressure 0

GPa7.2 ～ 20 61

metalinsulator

molecular crystal

non-molecular crystal

crystal structure metal

fcc cubic amorphousphase Ⅱ

153

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Summary

■ From temperature dependence of the electrical

　 resistance, metallization occurs around 20 GPa.

■ From X-ray diffraction study ・・・ Molecular dissociation pressure is not uncertain.　

SnI4 recrystallize into non-molecular (fcc) phase at 61 GPa. 　■ SnI4 show metallization in amorphous state.