Phase transitions in crystalline sulfur at p>8 GPa, observed by Raman spectroscopy in a diamond anvil cell

Abstract

Raman spectra of sulfur have been recorded in a diamond anvil cell, in the pressure range 0 to 40 GPa, using a 0.6 m triple spectrograph and a CCD multichannel detector.

When orthorhombic sulfur (S₈) is pressurized to 12 GPa, the appearance of either of two distinctly different phases is observed, depending on temperature. When comparatively high temperatures (high laser power. T- 380 K) are used, a phase exhibiting six prominent Raman bands is observed. To establish the identity of this phase, its pressure dependent Raman spectrum is compared with the one of chemically prepared six-ring sulfur (S₆). On the other hand, the high pressure-low temperature phase is obtained either by pressurizing S₈ at low laser powers, or by unloading S₆ after pressurizing to 40 GPa. This phase is tentatively assigned to the sulfur modification Sxii, on the basis of matching Raman spectra.

Key Words:

• High pressure
• Raman spectroscopy
• sulfur
• phase transitions