Phase stability and EOS of orthorhombic high-pressure phase of NaI to 204 GPa

Abstract

X-ray diffraction studies for the alkali halide, NaI, were performed to 204GPa at room temperature. We observed that the TlI (B33) high-pressure phase, which has been reported to succeed the B1 phase for NaI around 30GPa, is stable to a pressure of at least 204GPa. The measured relative volume, V/V0, at 204GPa is 0.366. We present data for the EOS of NaI in the B33 phase between 35 and 204GPa. No data has been previously reported to this pressure. The EOS determined in the present study will be useful in predicting theoretically if a higher packing density B2 phase exists at still higher pressures and if an insulator–metal transition occurs in the B33 phase stability region or in some other succeeding high-pressure phase region.