High-pressure X-ray diffraction study on the structure of NaCl melt using synchrotron radiation

Molten NaCl was analyzed by high-pressure X-ray diffraction experiments usi ng synchrotron radiation up to 5 GPa and 1600 degrees C along the melting c urve. The interference function Qi(Q), and the correlation function g(r) we re derived from the diffraction data. The first-neighbor distance r(1) is a bout 2.7 Angstrom and the second-neighbor distance appears around 1.4r(1)-1 .5r(1). The coordination number, CN, of the nearest neighbor ions increases with pressure from 3.5 at 0.1 MPa to 4.5 at 5 GPa. This is the evidence th at the NaCl melt has a B1-like structure with large vacancies over this pre ssure range and becomes densified by an increase in CN as a result of secon d neighbor compaction.