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

X-ray diffraction studies fur the alkali halide, NaI, were performed to 204 GPa at room temperature. We observed that the TLI (B33) high-pressure phase, which has been reported to succeed the B1 phase for NaI around 30 Cpa, is stable to a pressure of at least 204 Cpa. The measured relative volume, V/V-0, at 204 Cpa is 0.366. We present data for the EOS of NaI in the B33 phase between 35 and 204 Cpa. 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. Published by Elsevier Science Ltd.