High-Temperature and High-Pressure Phase Transition of Natural Barite Investigated by Raman Spectroscopy and Electrical Conductivity

Abstract

We investigated the structural, vibrational, and electrical transport properties for natural barite under the conditions of 298–873 K and 1.5–35.0 GPa using a diamond anvil cell by virtue of Raman spectroscopy and electrical conductivity measurements. Upon compression, natural barite transformed into post-barite at 18.9 GPa and atmospheric temperature, which was evidenced by the emergence of υ5 Raman peak, the discontinuities in the pressure-dependent Raman shifts, FWHM of υ1 Raman peak and electrical conductivity under non-hydrostatic condition. The phase transition is of good reversibility, whereas a considerable pressure hysteresis was detected during the process of decompression. Under quasi-hydrostatic condition, the structural transition of natural barite occurred at a higher pressure of 21.4 GPa, which is possibly related to the influence of deviatoric stress. Furthermore, our high-temperature and high-pressure Raman spectra and electrical conductivity results for natural barite revealed that the phase transformation pressures decreased as temperatures enhanced and further, the phase boundary between barite and post-barite was described as P (GPa) = 24.00–0.0166 T (K). Our obtained phase diagram of natural barite can improve the knowledge about the structural and electrical properties for other barite-group minerals MSO4 (M = Sr and Pb) under high temperature and high pressure conditions.