Phase diagram of solid oxygen at low temperature and high pressure

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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.