In situ Raman study of path-dependent C polymerization: Isothermal compression up to 32 GPa at 800 K

In situ Raman study of C isothermal compression at 800 K and up to 32 GPa was performed using rhombohedral or tetragonal phases as starting materials. Rhombohedral phase showed phase transition to three-dimensional polymers above 10 GPa similar to experiments where isobaric heating was used at pressures 9 to 13 GPa. Tetragonal polymer exhibited significantly stronger stability and can be followed at least up to ∼15 GPa. Heating up to 800 K of the tetragonal polymer at pressures 6 to 8 GPa confirms that due to geometrical frustrations tetragonal phase remains stable even at P–T conditions where rhombohedral polymer is usually formed from orthorhombic chain polymers. © 2003 The American Physical Society.