X-ray diffraction studies and equation of state of methane at 200 GPa
Solid methane (CH{sub 4}) was compressed up to 202 GPa at 300 K in a diamond-anvil cell. The crystal structure and equation of state over this entire range were determined from angle dispersive X-ray diffraction results. CH{sub 4} undergoes phase transitions from rhombohedral to a simple cubic phase at 19 GPa and from simple cubic to a higher pressure cubic phase at approximately 94 GPa. This higher pressure cubic phase was stable to the maximum pressure investigated. Combined with previous optical measurements, it was found that at room temperature compressed CH{sub 4} remains an insulator with cubic structure to 202 GPa. X-ray images of the solid CH{sub 4} at three pressures, showing the high pressure phase with cubic structure persisting up to 202 GPa. At high pressure the XRD from the sample became increasingly weaker. To improve the quality of XRD pattern, we reduced the X-ray focus spot size and clean-up slits at 171 GPa, and increased the exposure time for each measurement.
- Research Organization:
- SLAC National Accelerator Lab., Menlo Park, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC02-76SF00515
- OSTI ID:
- 972659
- Report Number(s):
- SLAC-REPRINT-2010-032; CHPLBC; TRN: US201005%%232
- Journal Information:
- Chemical Physics Letters, Vol. 473, Issue 1-3; ISSN 0009-2614
- Country of Publication:
- United States
- Language:
- English
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