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Phase diagram of solid oxygen at low temperature and high pressure

ReferenceF. Gorelli, M. Santoro, L. Ulivi, M. Hanfland, Phys. Rev. B 65, 172106 (2002)

SHIMIZU 　 Group 　MIZOBATA 　

Shigeki

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Contents

Introduction・ Character of oxygen・ Many phases of solid oxygen・ Phase diagram by Raman scattering

Experimental results and discussion

Summary

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Oxygen

important role

molecular arrangement in crystal, compressibility of crystal

magnetic elementary molecule

oxygen

liquid oxygenboiling point ・・・ 90 Klight blue and paramagnetic liquid

http://www.webelements.com/

solid oxygenfreezing point ・・・ 54 Ksuperconductivity(at 120GPa Tc=0.6 K)

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Solid oxygenat ambient pressure

antiferromagnetism (AFM)

at room temperature

43.5 23.5

monoclinic cubicrhombohedral

90 K

γβα liquid

54

paramagnetismshort-range AFM order

T(K)

molecular metal

ζ

5.5 GPa 9.5 10 96

β δ εmonoclinic monoclinic

orthorhombicrhombohedral

molecular insulator

P(GPa)

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P-T phase diagram by Raman scattering

At low temperature and high pressure the phase boundaries are uncertain.

α: monoclinic

δ: orthorhombic

existence of new 　phases (α´ and δ´) ?

S. Desgreniers, Y.K. Vohra, and A.L. Ruoff, J. Phys. Chem. 94, 1117 (199

0)

?

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Problems

At low temperature and high pressure the phase boundaries are uncertain.

clarify the phase transitions by x-ray diffraction experiment

technical difficulty

Oxygen is low-Z element and gas.extreme condition (at low temperature and high 　pressure)

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The gas-loading cell is used to enablethe increase of pressure at low temperature.

http://www.diacellproducts.com/index.html

gasket

ruby sample

sample loading for oxygen

gas liquid sample loadingcool

Experiment 1

gas-loading cell (membrane cell)

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Experimental process 1

δ

α

Pressure (GPa)

Tem

pera

ture

(K

)

？

isothermal compression or decompression・・・・at 19, 180, 240, 277, 300 K

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X-ray diffraction pattern

From diffraction pattern at 19 K ・・・・ 0.96-7.2 GPa: diffraction patterns for the α phase

7.6 GPa: two phases (α phase and ε phase ） coexist

8.1 GPa: diffraction pattern for ε phase

Y. Akahama, Phy. Rev. B, 64, 054105 (2001)

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Result 1 No other phases （ α´ and δ´ phases ） are detected.

The α phase directly transforms to the ε phase.

E. Uemura et al, J. Phys. Condens. Matter 14, 10423 (2002)

・・・ α phase

・・・ β phase・・・ ε phase・・・ δ phase

α-δ boundary

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Experimental process 2

very rapid pressure increaseup to about 40–50 GPa

to produce a fine-grained polycrystalline powder ・・・・

decrease pressure until the ε-δ phase transition

decreasing slowly temperature and pressure

from δ phase・・・・

δ

α

Pressure (GPa)

Tem

pera

ture

(K

)

？

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Structure of α- and δ-oxygen

α- o2 monoclinic （ C2/m ） δ- o2 orthorhombic (Fmmm)

monoclinic (α phase) 　　 　 orthorhombic (δ phase)

shift of the ab plane (angle β´turns exactly to 90°)

β´ β´

c

ab

c

ab

90°

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The α-δ phase transition

line ・・・ R.D Etters et al., Phys. Rev. B 32, 4097 (1985)

Y. Akahama et al., Phys. Rev. B 64, 054105 (2001)

β´≠90° ・・・ monoclinic (α)

β´ ＝ 90° ・・・ orthorhombic (δ)

δ

The α-δ phase transition and the anisotropy of compressibility are observed.

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○ ・・・・ α phase

● ・・・・ δ phase

・・・・ α-δ transition

No other phases （ α´ and δ´ phase ） are detected.

The δ phase is stable at wide pressure.

Result 2

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Hysteresis

The α phase transforms again to the δ phase increasing the temperature up to 270K.

4 6 8 10 12

Pressure(GPa)

Tem

per

atur

e(K

)

100

200

300

β

ε

0

Liquid

Result 2

Result 1

65 K

δ

α

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No other phases （ α´ and δ´ phase ） are detected.

By tow X-ray diffraction studies, position of phase-transition boundaries are determined, respectively.

The hysteresis is observed at low temperature and high pressure.

Summary