The liquid-$\alpha$ and $\alpha -\beta$ phase boundaries have been determined for mercury up to nearly 70 kbar with a newly developed technique of internally heated resistance measurements. The fusion curve and phase boundary diverge with pressure, thus eliminating the possibility of a triple point between the three phases. The structural distortions under pressure for Hg and some other anisotropic Group B elements are examined and an increase in coordination and packing efficiency within the given anisotropic structure is strongly suggested.

• Received 1 March 1963

DOI:https://doi.org/10.1103/PhysRev.131.1