  High-pressure powder x-ray diffraction experiments have revealed that sodium
and gold react at room temperature and form new Na-Au intermetallic compounds
under high pressure. We have identified four intermetallic phases up to 60 GPa.
The first phase (phase I) is the known Na2Au with the tetragonal CuAl2-type
structure. It changed to the second phase (phase II) at about 0.8 GPa, which
has the composition Na3Au with the trigonal Cu3As-type or hexagonal Cu3P-type
structure. Phase II further transformed to phase III at 3.6 GPa. Phase III has
the same composition Na3Au with the cubic BiF3-type structure. Finally, phase
III changed to phase IV at around 54 GPa. Phase IV gives broad diffraction
peaks, indicating large structural disorder.
