1. Phase diagram of solid oxygen at low temperature and high pressure
Reference F. Gorelli, M. Santoro, L. Ulivi, M. Hanfland, Phys. Rev. B 65, (2002)
SHIMIZU　Group　
MIZOBATA　Shigeki

2. Contents
Introduction ・ Character of oxygen ・ Many phases of solid oxygen ・ Phase diagram by Raman scattering
Experimental results and discussion
Summary

3. Oxygen oxygen solid oxygen liquid oxygen magnetic elementary molecule
important role
molecular arrangement in crystal,
compressibility of crystal
magnetic elementary molecule
oxygen
solid oxygen
freezing point・・・54 K superconductivity (at 120GPa Tc=0.6 K)
liquid oxygen
boiling point・・・90 K
light blue and paramagnetic liquid

4. antiferromagnetism (AFM)
Solid oxygen
at ambient pressure
23.5
43.5 54
90 K
T(K)
monoclinic
rhombohedral
cubic α β γ
liquid
short-range AFM order
antiferromagnetism (AFM)
paramagnetism
at room temperature
5.5 GPa
9.5 10 96
P(GPa)
orthorhombic
rhombohedral
monoclinic
monoclinic β δ ε ζ
molecular insulator
molecular metal

5. P-T phase diagram by Raman scattering
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 (1990)
At low temperature and high pressure the phase boundaries are uncertain.

6. Problems technical difficulty
At low temperature and high pressure the phase boundaries are uncertain.
clarify the phase transitions by x-ray diffraction experiment
extreme condition (at low temperature and high　pressure)
Oxygen is low-Z element and gas.
technical difficulty

7. Experiment 1 sample loading for oxygen cool gas liquid sample loading
gas-loading cell (membrane cell)
gasket
ruby
sample
The gas-loading cell is used to enable
the increase of pressure at low temperature.

8. Experimental process 1 ？ isothermal compression or decompression・・・・δ α
Pressure (GPa)
Temperature (K) ？
isothermal compression or
decompression・・・・
at 19, 180, 240, 277, 300 K

9. X-ray diffraction pattern
From diffraction pattern at 19 K ・・・・
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, (2001)

10. Result 1 No other phases（α´ and δ´ phases） are detected.
The α phase directly transforms to the ε phase.
α-δ boundary
・・・α phase
・・・β phase
・・・ε phase
・・・δ phase
E. Uemura et al, J. Phys. Condens. Matter 14, (2002)

11. Experimental process 2 ？
to produce a fine-grained polycrystalline powder・・・・
very rapid pressure increase
up to about 40–50 GPa
Temperature (K)
decrease pressure until the ε-δ phase transition δ ？
from δ phase・・・・
decreasing slowly temperature and pressure α
Pressure (GPa)

12. Structure of α- and δ-oxygen
α- o2 monoclinic （C2/m）
δ- o2 orthorhombic (Fmmm) β´ β´ c a b c a b
90°
monoclinic (α phase) 　　 　 orthorhombic (δ phase)
shift of the ab plane (angle β´turns exactly to 90°)

13. The α-δ phase transition
β´≠90°・・・ monoclinic (α)
β´＝90°・・・ orthorhombic (δ)
The α-δ phase transition and the anisotropy of compressibility are observed. δ
line ・・・ R.D Etters et al., Phys. Rev. B 32, 4097 (1985)
Y. Akahama et al., Phys. Rev. B 64, (2001)

14. Result 2 No other phases（α´ and δ´ phase） are detected.
・・・・α-δ transition
No other phases（α´ and δ´ phase） are detected.
The δ phase is stable at wide pressure.

15. Hysteresis δ β Result 1 ε α Result 2
Liquid
65 K δ
300
Temperature(K) β
Result 1
200 ε
100 α
Result 2 4 6 8 10 12
Pressure(GPa)
The α phase transforms again to the δ phase increasing the temperature up to 270K.

16. Summary 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.