We combine equations of state valid for the dense, neutral fluid and the dense, fully ionized plasma to obtain an equation of state for the intermediate region where partial dissociation and ionization occur. A region of thermodynamic instability is found which is known as plasma phase transition. The corresponding coexistence region and the coexistence line are derived. As a first application of the new equation of state, Hugoniot curves are calculated and compared with experiments and other theories.

• Received 11 December 1998

DOI:https://doi.org/10.1103/PhysRevB.59.14177