High-pressure and high-temperature Raman study of cinnabar

ABSTRACT

The effects of temperature (300–600 K) and pressure (0–31.8 GPa) on the Raman spectra of natural cinnabar powder were investigated in a heatable diamond anvil cell. Raman spectral changes caused by phase transitions were observed at high pressures, which suggests a phase transformation from pure hexagonal to the coexistence of a hexagonal and rock salt structure, and finally to the rock salt structure. With increasing pressure, A₁ and modes exhibited a blueshift (0.87 cm⁻¹/GPa) and redshift (−3.64 cm⁻¹/GPa), respectively, while both modes underwent a redshift (−2.22 and −2.09 × 10⁻² cm⁻¹/K, respectively) with increasing temperature. The mode Grüneisen parameters of A₁ and at room temperature were calculated by the pressure dependences of the vibrational frequencies and the X-ray diffraction data from previous research. Simultaneous high-pressure and high-temperature results were globally fitted, and the coupling coefficients for temperature and pressure dependence of the Raman shifts were determined to be 7.28 × 10⁻⁴ and 5.12 × 10⁻⁴ cm⁻¹/K · GPa for A₁ and , respectively.

KEYWORDS:

• Cinnabar
• high pressure and high temperature
• phase transition
• Raman spectroscopy

Acknowledgments

We thank four anonymous reviewers and editor Professor R. G. Michel for their very constructive comments and suggestions in the reviewing process, which helped us greatly in improving the manuscript.