Phase Transition and EOS of Cinnabar (α-HgS) at High Pressure and High Temperature

Phase relations and equation of state (EOS) of natural cinnabar (α-HgS) are investigated by high-pressure and high-temperature synchrotron x-ray powder diffraction. The unambiguous cinnabar-rocksalt structure phase boundaries are determined to be Plower(GPa)=15.54-0.014T°C and Pupper(GPa)=23.84-0.014T(°C) at 300-623K. With K' fixed at 4, we obtain K0= 37(4)GPa, (∂K/∂ T)P=-0.025(2)GPaK-1, and α_{0}=3.79(20)×10-5K-1 for the cinnabar phase of α-HgS. The (K/∂T)P and α0 of cinnabar phase are obtained for the first time. A nearly isotropic compression of cinnabar phase is observed by linear regressions.